Tag / Hanbury Brown Twiss

by David D. Nolte

Timelines in the History of Light and Interference

Light is one of the most powerful manifestations of the forces of physics because it tells us about our reality. The interference of light, in particular, has led to the detection of exoplanets orbiting distant stars, discovery of the first gravitational waves, capture of images of black holes and much more. The stories behind the history of light and interference go to the heart of how scientists do what they do and what they often have to overcome to do it. These time-lines are organized along the chapter titles of the book Interference. They follow the path of theories of light from the first wave-particle debate, through the personal firestorms of Albert Michelson, to the discoveries of the present day in quantum information sciences.

  1. Thomas Young Polymath: The Law of Interference
  2. The Fresnel Connection: Particles versus Waves
  3. At Light Speed: The Birth of Interferometry
  4. After the Gold Rush: The Trials of Albert Michelson
  5. Stellar Interference: Measuring the Stars
  6. Across the Universe: Exoplanets, Black Holes and Gravitational Waves
  7. Two Faces of Microscopy: Diffraction and Interference
  8. Holographic Dreams of Princess Leia: Crossing Beams
  9. Photon Interference: The Foundations of Quantum Communication
  10. The Quantum Advantage: Interferometric Computing

1. Thomas Young Polymath: The Law of Interference

Thomas Young was the ultimate dabbler, his interests and explorations ranged far and wide, from ancient egyptology to naval engineering, from physiology of perception to the physics of sound and light. Yet unlike most dabblers who accomplish little, he made original and seminal contributions to all these fields. Some have called him the “Last Man Who Knew Everything“.

Thomas Young. The Law of Interference.

Topics: The Law of Interference. The Rosetta Stone. Benjamin Thompson, Count Rumford. Royal Society. Christiaan Huygens. Pendulum Clocks. Icelandic Spar. Huygens’ Principle. Stellar Aberration. Speed of Light. Double-slit Experiment.

1629 – Huygens born (1629 – 1695)

1642 – Galileo dies, Newton born (1642 – 1727)

1655 – Huygens ring of Saturn

1657 – Huygens patents the pendulum clock

1666 – Newton prismatic colors

1666 – Huygens moves to Paris

1669 – Bartholin double refraction in Icelandic spar

1670 – Bartholinus polarization of light by crystals

1671 – Expedition to Hven by Picard and Rømer

1673 – James Gregory bird-feather diffraction grating

1673 – Huygens publishes Horologium Oscillatorium

1675 – Rømer finite speed of light

1678 – Huygens and two crystals of Icelandic spar

1681 – Huygens returns to the Hague

1689 – Huyens meets Newton

1690 – Huygens Traite de la Lumiere

1695 – Huygens dies

1704 – Newton’s Opticks

1727 – Bradley abberation of starlight

1746 – Euler Nova theoria lucis et colorum

1773 – Thomas Young born

1786 – François Arago born (1786 – 1853)

1787 – Joseph Fraunhofer born (1787 – 1826)

1788 – Fresnel born in Broglie, Normandy (1788 – 1827)

1794 – École Polytechnique founded in Paris by Lazar Carnot and Gaspard Monge, Malus enters the Ecole

1794 – Young elected member of the Royal Society

1794 – Young enters Edinburg (cannot attend British schools because he was Quaker)

1795 – Young enters Göttingen

1796 – Young receives doctor of medicine, grand tour of Germany

1797 – Young returns to England, enters Emmanual College (converted to Church of England)

1798 – The Directory approves Napoleon’s Egyptian campaign, Battle of the Pyramids, Battle of the Nile

1799 – Young graduates from Cambridge

1799 – Royal Institution founded

1799 – Young Outlines

1800 – Young Sound and Light read to Royal Society,

1800 – Young Mechanisms of the Eye (Bakerian Lecture of the Royal Society)

1801 – Young Theory of Light and Colours, three color mechanism (Bakerian Lecture), Young considers interference to cause the colored films, first estimates of the wavelengths of different colors

1802 – Young begins series of lecturs at the Royal Institution (Jan. 1802 – July 1803)

1802 – Young names the principle (Law) of interference

1803 – Young’s 3rd Bakerian Lecture, November.  Experiments and Calculations Relative Physical to Optics, The Law of Interference

1807 – Young publishes A course of lectures on Natural Philosophy and the Mechanical Arts, based on Royal Institution lectures, two-slit experiment described

1808 – Malus polarization

1811 – Young appointed to St. Georges hospital

1813 – Young begins work on Rosetta stone

1814 – Young translates the demotic script on the stone

1816 – Arago visits Young

1818 – Young’s Encyclopedia article on Egypt

1822 – Champollion publishes translation of hieroglyphics

1827 – Young elected foreign member of the Institute of Paris

1829 – Young dies

2. The Fresnel Connection: Particles versus Waves

Augustin Fresnel was an intuitive genius whose talents were almost squandered on his job building roads and bridges in the backwaters of France until he was discovered and rescued by Francois Arago.

Augustin Fresnel. Image Credit.

Topics: Particles versus Waves. Malus and Polarization. Agustin Fresnel. Francois Arago. Diffraction. Daniel Bernoulli. The Principle of Superposition. Joseph Fourier. Transverse Light Waves.

1665 – Grimaldi diffraction bands outside shadow

1673 – James Gregory bird-feather diffraction grating

1675 – Römer finite speed of light

1704 – Newton’s Optics

1727 – Bradley abberation of starlight

1774 – Jean-Baptiste Biot born

1786 – David Rittenhouse hairs-on-screws diffraction grating

1786 – François Arago born (1786 – 1853)

1787 – Fraunhofer born (1787 – 1826)

1788 – Fresnel born in Broglie, Normandy (1788 – 1827)

1790 – Fresnel moved to Cherbourg

1794 – École Polytechnique founded in Paris by Lazar Carnot and Gaspard Monge

1804 – Fresnel attends Ecole polytechnique in Paris at age 16

1806 – Fresnel graduated and attended the national school of bridges and highways

1808 – Malus polarization

1809 – Fresnel graduated from Les Ponts

1809 – Arago returns from captivity in Algiers

1811 – Arago publishes paper on particle theory of light

1811 – Arago optical ratotory activity (rotation)

1814 – Fraunhofer spectroscope (solar absorption lines)

1815 – Fresnel meets Arago in Paris on way home to Mathieu (for house arrest)

1815 – Fresnel first paper on wave properties of diffraction

1816 – Fresnel returns to Paris to demonstrate his experiments

1816 – Arago visits Young

1816 – Fresnel paper on interference as origin of diffraction

1817 – French Academy announces its annual prize competition: topic of diffraction

1817 – Fresnel invents and uses his “Fresnel Integrals”

1819 – Fresnel awarded French Academy prize for wave theory of diffraction

1819 – Arago and Fresnel transverse and circular (?) polarization

1821 – Fraunhofer diffraction grating

1821 – Fresnel light is ONLY transverse

1821 – Fresnel double refraction explanation

1823 – Fraunhofer 3200 lines per Paris inch

1826 – Publication of Fresnel’s award memoire

1827 – Death of Fresnel by tuberculosis

1840 – Ernst Abbe born (1840 – 1905)

1849 – Stokes distribution of secondary waves

1850 – Fizeau and Foucault speed of light experiments

3. At Light Speed

There is no question that Francois Arago was a swashbuckler. His life’s story reads like an adventure novel as he went from being marooned in hostile lands early in his career to becoming prime minister of France after the 1848 revolutions swept across Europe.

Francois Arago. Image Credit.

Topics: The Birth of Interferometry. Snell’s Law. Fresnel and Arago. The First Interferometer. Fizeau and Foucault. The Speed of Light. Ether Drag. Jamin Interferometer.

1671 – Expedition to Hven by Picard and Rømer

1704 – Newton’s Opticks

1729 – James Bradley observation of stellar aberration

1784 – John Michel dark stars

1804 – Young wave theory of light and ether

1808 – Malus discovery of polarization of reflected light

1810 – Arago search for ether drag

1813 – Fraunhofer dark lines in Sun spectrum

1819 – Fresnel’s double mirror

1820 – Oersted discovers electromagnetism

1821 – Faraday electromagnetic phenomena

1821 – Fresnel light purely transverse

1823 – Fresnel reflection and refraction based on boundary conditions of ether

1827 – Green mathematical analysis of electricity and magnetism

GreenEssayGoogleDownload

1830 – Cauchy ether as elastic solid

1831 – Faraday electromagnetic induction

1831 – Cauchy ether drag

1831 – Maxwell born

1831 – Faraday electromagnetic induction

1834 – Lloyd’s mirror

1836 – Cauchy’s second theory of the ether

1838 – Green theory of the ether

1839 – Hamilton group velocity

1839 – MacCullagh properties of rotational ether

1839 – Cauchy ether with negative compressibility

1841 – Maxwell entered Edinburgh Academy (age 10) met P. G. Tait

1842 – Doppler effect

DopplerFarbigeLicht-3Download

1845 – Faraday effect (magneto-optic rotation)

1846 – Haidinger fringes

1846 – Stokes’ viscoelastic theory of the ether

1847 – Maxwell entered Edinburgh University

1848 – Fizeau proposal of the Fizeau-Doppler effect

1849 – Fizeau speed of light

1850 – Maxwell at Cambridge, studied under Hopkins, also knew Stokes and Whewell

1852 – Michelson born Strelno, Prussia

1854 – Maxwell wins the Smith’s Prize (Stokes’ theorem was one of the problems)

1855 – Michelson’s immigrate to San Francisco through Panama Canal

1855 – Maxwell “On Faraday’s Line of Force”

1856 – Jamin interferometer

1856 – Thomson magneto-optics effects (of Faraday)

1857 – Clausius constructs kinetic theory, Mean molecular speeds

Clausius (1857)_Nature motion we call heatDownload

1859 – Fizeau light in moving medium

1862 – Fizeau fringes

1865 – Maxwell “A Dynamical Theory of the Electromagnetic Field”

1867 – Thomson and Tait “Treatise on Natural Philosophy”

1867 – Thomson hydrodynamic vortex atom

1868 – Fizeau proposal for stellar interferometry

1870 – Maxwell introduced “curl”, “convergence” and “gradient”

1871 – Maxwell appointed to Cambridge

1873 – Maxwell “A Treatise on Electricity and Magnetism”

4. After the Gold Rush

No name is more closely connected to interferometry than that of Albert Michelson. He succeeded, sometimes at great personal cost, in launching interferometric metrology as one of the most important tools used by scientists today.

Albert A. Michelson, 1907 Nobel Prize. Image Credit.

Topics: The Trials of Albert Michelson. Hermann von Helmholtz. Michelson and Morley. Fabry and Perot.

1810 – Arago search for ether drag

1813 – Fraunhofer dark lines in Sun spectrum

1813 – Faraday begins at Royal Institution

1820 – Oersted discovers electromagnetism

1821 – Faraday electromagnetic phenomena

1827 – Green mathematical analysis of electricity and magnetism

1830 – Cauchy ether as elastic solid

1831 – Faraday electromagnetic induction

1831 – Cauchy ether drag

1831 – Maxwell born

1831 – Faraday electromagnetic induction

1836 – Cauchy’s second theory of the ether

1838 – Green theory of the ether

1839 – Hamilton group velocity

1839 – MacCullagh properties of rotational ether

1839 – Cauchy ether with negative compressibility

1841 – Maxwell entered Edinburgh Academy (age 10) met P. G. Tait

1842 – Doppler effect

1845 – Faraday effect (magneto-optic rotation)

1846 – Stokes’ viscoelastic theory of the ether

1847 – Maxwell entered Edinburgh University

1850 – Maxwell at Cambridge, studied under Hopkins, also knew Stokes and Whewell

1852 – Michelson born Strelno, Prussia

1854 – Maxwell wins the Smith’s Prize (Stokes’ theorem was one of the problems)

1855 – Michelson’s immigrate to San Francisco through Panama Canal

1855 – Maxwell “On Faraday’s Line of Force”

1856 – Jamin interferometer

1856 – Thomson magneto-optics effects (of Faraday)

1859 – Fizeau light in moving medium

1859 – Discovery of the Comstock Lode

1860 – Maxwell publishes first paper on kinetic theory.

1861 – Maxwell “On Physical Lines of Force” speed of EM waves and molecular vortices, molecular vortex model

1862 – Michelson at boarding school in SF

1865 – Maxwell “A Dynamical Theory of the Electromagnetic Field”

1867 – Thomson and Tait “Treatise on Natural Philosophy”

1867 – Thomson hydrodynamic vortex atom

1868 – Fizeau proposal for stellar interferometry

1869 – Michelson meets US Grant and obtained appointment to Annapolis

1870 – Maxwell introduced “curl”, “convergence” and “gradient”

1871 – Maxwell appointed to Cambridge

1873 – Big Bonanza at the Consolidated Virginia mine

1873 – Maxwell “A Treatise on Electricity and Magnetism”

1873 – Michelson graduates from Annapolis

1875 – Michelson instructor at Annapolis

1877 – Michelson married Margaret Hemingway

1878 – Michelson First measurement of the speed of light with funds from father in law

1879 – Michelson Begin collaborating with Newcomb

1879 – Maxwell proposes second-order effect for ether drift experiments

1879 – Maxwell dies

1880 – Michelson Idea for second-order measurement of relative motion against ether

1880 – Michelson studies in Europe with Helmholtz in Berlin

1881 – Michelson Measurement at Potsdam with funds from Alexander Graham Bell

1882 – Michelson in Paris, Cornu, Mascart and Lippman

1882 – Michelson Joined Case School of Applied Science

1884 – Poynting energy flux vector

1885 – Michelson Began collaboration with Edward Morley of Western Reserve

1885 – Lorentz points out inconsistency of Stokes’ ether model

1885 – Fitzgerald wheel and band model, vortex sponge

1886 – Michelson and Morley repeat the Fizeau moving water experiment

Michelson1886Download

1887 – Michelson Five days in July experiment on motion relative to ether

1887 – Michelson-Morley experiment published

MichelsonMorley1887Download

1887 – Voigt derivation of relativistic Doppler (with coordinate transformations)

Voigt1887Download

1888 – Hertz generation and detection of radio waves

1889 – Michelson moved to Clark University at Worcester

1889 – Fitzgerald contraction

1889 – Lodge cogwheel model of electromagnetism

1890 – Michelson Proposed use of interferometry in astronomy

1890 – Thomson devises a mechanical model of MacCullagh’s rotational ether

1890 – Hertz Galileo relativity and ether drag

1891 – Mach-Zehnder

1891 – Michelson measures diameter of Jupiter’s moons with interferometry

1891 – Thomson vortex electromagnetism

1892 – 1893    Michelson measurement of the Paris meter

1893 – Sirks interferometer

1893 – Michelson moved to University of Chicago to head Physics Dept.

1893 – Lorentz contraction

1894 – Lodge primitive radio demonstration

1895 – Marconi radio

1896 – Rayleigh’s interferometer

1897 – Lodge no ether drag on laboratory scale

1898 – Pringsheim interferometer

1899 – Fabry-Perot interferometer

1899 – Michelson remarried

1901 – 1903    Michelson President of the APS

1905 – Poincaré names the Lorentz transformations

1905 – Einstein’s special theory of Relativity

1907 – Michelson Nobel Prize

1913 – Sagnac interferometer

1916 – Twyman-Green interferometer

1920 – Stellar interferometer on the Hooker 100-inch telescope (Betelgeuse)

1923 – 1927 Michelson presided over the National Academy of Sciences

1931 – Michelson dies

5. Stellar Interference

Learning from his attempts to measure the speed of light through the ether, Michelson realized that the partial coherence of light from astronomical sources could be used to measure their sizes. His first measurements using the Michelson Stellar Interferometer launched a major subfield of astronomy that is one of the most active today.

R Hanbury Brown

Topics: Measuring the Stars. Astrometry. Moons of Jupiter. Schwarzschild. Betelgeuse. Michelson Stellar Interferometer. Banbury Brown Twiss. Sirius. Adaptive Optics.

1838 – Bessel stellar parallax measurement with Fraunhofer telescope

1868 – Fizeau proposes stellar interferometry

1873 – Stephan implements Fizeau’s stellar interferometer on Sirius, sees fringes

1880 – Michelson Idea for second-order measurement of relative motion against ether

1880 – 1882    Michelson Studies in Europe (Helmholtz in Berlin, Quincke in Heidelberg, Cornu, Mascart and Lippman in Paris)

1881 – Michelson Measurement at Potsdam with funds from Alexander Graham Bell

1881 – Michelson Resigned from active duty in the Navy

1883 – Michelson Joined Case School of Applied Science

1889 – Michelson moved to Clark University at Worcester

1890 – Michelson develops mathematics of stellar interferometry

1891 – Michelson measures diameters of Jupiter’s moons

Michelson1891Download

1893 – Michelson moves to University of Chicago to head Physics Dept.

1896 – Schwarzschild double star interferometry

1907 – Michelson Nobel Prize

1908 – Hale uses Zeeman effect to measure sunspot magnetism

1910 – Taylor single-photon double slit experiment

1915 – Proxima Centauri discovered by Robert Innes

1916 – Einstein predicts gravitational waves

1920 – Stellar interferometer on the Hooker 100-inch telescope (Betelgeuse)

Michelson1921Download

1947 – McCready sea interferometer observes rising sun (first fringes in radio astronomy

1952 – Ryle radio astronomy long baseline

1954 – Hanbury-Brown and Twiss radio intensity interferometry

1956 – Hanbury-Brown and Twiss optical intensity correlation, Sirius (optical)

1958 – Jennison closure phase

1970 – Labeyrie speckle interferometry

1974 – Long-baseline radio interferometry in practice using closure phase

1974 – Johnson, Betz and Townes: IR long baseline

1975 – Labeyrie optical long-baseline

1982 – Fringe measurements at 2.2 microns Di Benedetto

1985 – Baldwin closure phase at optical wavelengths

1991 – Coude du Foresto single-mode fibers with separated telescopes

1993 – Nobel prize to Hulse and Taylor for binary pulsar

1995 – Baldwin optical synthesis imaging with separated telescopes

1991 – Mayor and Queloz Doppler pull of 51 Pegasi

1999 – Upsilon Andromedae multiple planets

2009 – Kepler space telescope launched

2014 – Kepler announces 715 planets

2015 – Kepler-452b Earthlike planet in habitable zone

2015 – First detection of gravitational waves

2016 – Proxima Centauri b exoplanet confirmed

2017 – Nobel prize for gravitational waves

2018 – TESS (Transiting Exoplanet Survey Satellite)

2019 – Mayor and Queloz win Nobel prize for first exoplanet

2019 – First direct observation of exoplanet using interferometry

2019 – First image of a black hole obtained by very-long-baseline interferometry

6. Across the Universe

Stellar interferometry is opening new vistas of astronomy, exploring the wildest occupants of our universe, from colliding black holes half-way across the universe (LIGO) to images of neighboring black holes (EHT) to exoplanets near Earth that may harbor life.

Image of the supermassive black hole in M87 from Event Horizon Telescope.

Topics: Gravitational Waves, Black Holes and the Search for Exoplanets. Nulling Interferometer. Event Horizon Telescope. M87 Black Hole. Long Baseline Interferometry. LIGO.

1947 – Virgo A radio source identified as M87

1953 – Horace W. Babcock proposes adaptive optics (AO)

Babcock1953Download

1958 – Jennison closure phase

1967 – First very long baseline radio interferometers (from meters to hundreds of km to thousands of km within a single year)

1967 – Ranier Weiss begins first prototype gravitational wave interferometer

1967 – Virgo X-1 x-ray source (M87 galaxy)

1970 – Poul Anderson’s Tau Zero alludes to AO in science fiction novel

1973 – DARPA launches adaptive optics research with contract to Itek, Inc.

1974 – Wyant (Itek) white-light shearing interferometer

1974 – Long-baseline radio interferometry in practice using closure phase

1975 – Hardy (Itek) patent for adaptive optical system

1975 – Weiss funded by NSF to develop interferometer for GW detection

1977 – Demonstration of AO on Sirius (Bell Labs and Berkeley)

1980 – Very Large Array (VLA) 6 mm to 4 meter wavelengths

1981 – Feinleib proposes atmospheric laser backscatter

1982 – Will Happer at Princeton proposes sodium guide star

1982 – Fringe measurements at 2.2 microns (Di Benedetto)

1983 – Sandia Optical Range demonstrates artificial guide star (Rayleigh)

1983 – Strategic Defense Initiative (Star Wars)

1984 – Lincoln labs sodium guide star demo

1984 – ESO plans AO for Very Large Telescope (VLT)

1985 – Laser guide star (Labeyrie)

1985 – Closure phase at optical wavelengths (Baldwin)

1988 – AFWL names Starfire Optical Range, Kirtland AFB outside Albuquerque

1988 – Air Force Maui Optical Site Schack-Hartmann and 241 actuators (Itek)

1988 – First funding for LIGO feasibility

1989 – 19-element-mirror Double star on 1.5m telescope in France

1989 – VLT approved for construction

1990 – Launch of the Hubble Space Telescope

1991 – Single-mode fibers with separated telescopes (Coude du Foresto)

1992 – ADONIS

1992 – NSF requests declassification of AO

1993 – VLBA (Very Long Baseline Array) 8,611 km baseline 3 mm to 90 cm

1994 – Declassification completed

1994 – Curvature sensor 3.6m Canada-France-Hawaii

1994 – LIGO funded by NSF, Barish becomes project director

1995 – Optical synthesis imaging with separated telescopes (Baldwin)

1995 – Doppler pull of 51 Pegasi (Mayor and Queloz)

1998 – ESO VLT first light

1998 – Keck installed with Schack-Hartmann

1999 – Upsilon Andromedae multiple planets

2000 – Hale 5m Palomar Schack-Hartmann

2001 – NAOS-VLT  adaptive optics

2001 – VLTI first light (MIDI two units)

2002 – LIGO operation begins

2007 – VLT laser guide star

2007 – VLTI AMBER first scientific results (3 units)

2009 – Kepler space telescope launched

2009 – Event Horizon Telescope (EHT) project starts

2010 – Large Binocular Telescope (LBT) 672 actuators on secondary mirror

2010 – End of first LIGO run.  No events detected.  Begin Enhanced LIGO upgrade.

2011 – SPHERE-VLT 41×41 actuators (1681)

2012 – Extremely Large Telescope (ELT) approved for construction

2014 – Kepler announces 715 planets

2015 – Kepler-452b Earthlike planet in habitable zone

2015 – First detection of gravitational waves (LIGO)

2015 – LISA Pathfinder launched

2016 – Second detection at LIGO

2016 – Proxima Centauri b exoplanet confirmed

2016 – GRAVITY VLTI  (4 units)

2017 – Nobel prize for gravitational waves

2018 – TESS (Transiting Exoplanet Survey Satellite) launched

2018 – MATTISE VLTI first light (combining all units)

2019 – Mayor and Queloz win Nobel prize

2019 – First direct observation of exoplanet using interferometry at LVTI

2019 – First image of a black hole obtained by very-long-baseline interferometry (EHT)

2020 – First neutron-star black-hole merger detected

2020 – KAGRA (Japan) online

2024 – LIGO India to go online

2025 – First light for ELT

2034 – Launch date for LISA

7. Two Faces of Microscopy

From the astronomically large dimensions of outer space to the microscopically small dimensions of inner space, optical interference pushes the resolution limits of imaging.

Ernst Abbe. Image Credit.

Topics: Diffraction and Interference. Joseph Fraunhofer. Diffraction Gratings. Henry Rowland. Carl Zeiss. Ernst Abbe. Phase-contrast Microscopy. Super-resolution Micrscopes. Structured Illumination.

1021 – Al Hazeni manuscript on Optics

1284 – First eye glasses by Salvino D’Armate

1590 – Janssen first microscope

1609 – Galileo first compound microscope

1625 – Giovanni Faber coins phrase “microscope”

1665 – Hook’s Micrographia

1676 – Antonie van Leeuwenhoek microscope

1787 – Fraunhofer born

1811 – Fraunhofer enters business partnership with Utzschneider

1816 – Carl Zeiss born

1821 – Fraunhofer first diffraction publication

1823 – Fraunhofer second diffraction publication 3200 lines per Paris inch

1830 – Spherical aberration compensated by Joseph Jackson Lister

1840 – Ernst Abbe born

1846 – Zeiss workshop in Jena, Germany

1850 – Fizeau and Foucault speed of light

1851 – Otto Schott born

1859 – Kirchhoff and Bunsen theory of emission and absorption spectra

1866 – Abbe becomes research director at Zeiss

1874 – Ernst Abbe equation on microscope resolution

1874 – Helmholtz image resolution equation

1880 – Rayleigh resolution

1888 – Hertz waves

1888 – Frits Zernike born

1925 – Zsigmondy Nobel Prize for light-sheet microscopy

1931 – Transmission electron microscope by Ruske and Knoll

1932 – Phase contrast microscope by Zernicke

1942 – Scanning electron microscope by Ruska

1949 – Mirau interferometric objective

1952 – Nomarski differential phase contrast microscope

1953 – Zernicke Nobel prize

1955 – First discussion of superresolution by Toraldo di Francia

1957 – Marvin Minsky patents confocal principle

1962 – Green flurescence protein (GFP) Shimomura, Johnson and Saiga

1966 – Structured illumination microscopy by Lukosz

1972 – CAT scan

1978 – Cremer confocal laser scanning microscope

1978 – Lohman interference microscopy

1981 – Binnig and Rohrer scanning tunneling microscope (STM)

1986 – Microscopy Nobel Prize: Ruska, Binnig and Rohrer

1990 – 4PI microscopy by Stefan Hell

1992 – GFP cloned

1993 – STED by Stefan Hell

1993 – Light sheet fluorescence microscopy by Spelman

1995 – Structured illumination microscopy by Guerra

1995 – Gustafsson image interference microscopy

1999 – Gustafsson I5M

2004 – Selective plane illumination microscopy (SPIM)

2006 – PALM and STORM (Betzig and Zhuang)

2014 – Nobel Prize (Hell, Betzig and Moerner)

8. Holographic Dreams of Princess Leia

The coherence of laser light is like a brilliant jewel that sparkles in the darkness, illuminating life, probing science and projecting holograms in virtual worlds.

Ted Maiman

Topics: Crossing Beams. Denis Gabor. Wavefront Reconstruction. Holography. Emmett Leith. Lasers. Ted Maiman. Charles Townes. Optical Maser. Dynamic Holography. Light-field Imaging.

1900 – Dennis Gabor born

1926 – Hans Busch magnetic electron lens

1927 – Gabor doctorate

1931 – Ruska and Knoll first two-stage electron microscope

1942 – Lawrence Bragg x-ray microscope

1948 – Gabor holography paper in Nature

1949 – Gabor moves to Imperial College

1950 – Lamb possibility of population inversion

1951 – Purcell and Pound demonstration of population inversion

1952 – Leith joins Willow Run Labs

1953 – Townes first MASER

1957 – SAR field trials

1957 – Gould coins LASER

1958 – Schawlow and Townes proposal for optical maser

1959 – Shawanga Lodge conference

1960 – Maiman first laser: pink ruby

1960 – Javan first gas laser: HeNe at 1.15 microns

1961 – Leith and Upatnieks wavefront reconstruction

1962 – HeNe laser in the visible at 632.8 nm

1962 – First laser holograms (Leith and Upatnieks)

1963 – van Heerden optical information storage

1963 – Leith and Upatnieks 3D holography

1966 – Ashkin optically-induced refractive index changes

1966 – Leith holographic information storage in 3D

1968 – Bell Labs holographic storage in Lithium Niobate and Tantalate

1969 – Kogelnik coupled wave theory for thick holograms

1969 – Electrical control of holograms in SBN

1970 – Optically induced refractive index changes in Barium Titanate

1971 – Amodei transport models of photorefractive effect

1971 – Gabor Nobel prize

1972 – Staebler multiple holograms

1974 – Glass and von der Linde photovoltaic and photorefractive effects, UV erase

1977 – Star Wars movie

1981 – Huignard two-wave mixing energy transfer

2012 – Coachella Music Festival

9. Photon Interference

What is the image of one photon interfering? Better yet, what is the image of two photons interfering? The answer to this crucial question laid the foundation for quantum communication.

Leonard Mandel. Image Credit.

Topics: The Beginnings of Quantum Communication. EPR paradox. Entanglement. David Bohm. John Bell. The Bell Inequalities. Leonard Mandel. Single-photon Interferometry. HOM Interferometer. Two-photon Fringes. Quantum cryptography. Quantum Teleportation.

1900 – Planck (1901). “Law of energy distribution in normal spectra.” [1]

Planck-1901-Annalen_der_PhysikDownload

1905 – A. Einstein (1905). “Generation and conversion of light wrt a heuristic point of view.” [2]

1909 – A. Einstein (1909). “On the current state of radiation problems.” [3]

1909 – Single photon double-slit experiment, G.I. Taylor [4]

1915 – Milliken photoelectric effect

1916 – Einstein predicts stimulated emission

1923 –Compton, Arthur H. (May 1923). Quantum Theory of the Scattering of X-Rays.[5]

1926 – Gilbert Lewis names “photon”

1926 – Dirac: photons interfere only with themselves

1927 – D. Dirac, P. A. M. (1927). Emission and absorption of radiation [6]

1932 – von Neumann textbook on quantum physics

1932 – E. P. Wigner: Phys. Rev. 40, 749 (1932)

1935 – EPR paper, A. Einstein, B. Podolsky, N. Rosen: Phys. Rev. 47 , 777 (1935)

1935 – Reply to EPR, N. Bohr: Phys. Rev. 48 , 696 (1935) 

1935 – Schrödinger (1935 and 1936) on entanglement (cat?)  “Present situation in QM”

1948 – Gabor holography

1950 – Wu correlated spin generation from particle decay

1951 – Bohm alternative form of EPR gedankenexperiment (quantum textbook)

1952 – Bohm nonlocal hidden variable theory[7]

1953 – Schwinger: Coherent states

1956 – Photon bunching,  R. Hanbury-Brown, R.W. Twiss: Nature 177 , 27 (1956)

1957 – Bohm and Ahronov proof of entanglement in 1950 Wu experiment

1959 – Ahronov-Bohm effect of magnetic vector potential

1960 – Klauder: Coherent states

1963 – Coherent states, R. J. Glauber: Phys. Rev. 130 , 2529 (1963)

1963 – Coherent states, E. C. G. Sudarshan: Phys. Rev. Lett. 10, 277 (1963)

1964 – J. S. Bell: Bell inequalities [8]

1964 – Mandel professorship at Rochester

1967 – Interference at single photon level, R. F. Pfleegor, L. Mandel: [9]

1967 – M. O. Scully, W.E. Lamb: Phys. Rev. 159 , 208 (1967)  Quantum theory of laser

1967 – Parametric converter (Mollow and Glauber)   [10]

1967 – Kocher and Commins calcium 2-photon cascade

1969 – Quantum theory of laser, M. Lax, W.H. Louisell: Phys. Rev. 185 , 568 (1969) 

1969 – CHSH inequality [11]

1972 – First test of Bell’s inequalities (Freedman and Clauser)

1975 – Carmichel and Walls predicted light in resonance fluorescence from a two-level atom would display photon anti-bunching (1976)

1977 – Photon antibunching in resonance fluorescence.  H. J. Kimble, M. Dagenais and L. Mandel [12]

1978 – Kip Thorne quantum non-demolition (QND)

1979 – Hollenhorst squeezing for gravitational wave detection: names squeezing

1982 – Apect Experimental Bell experiments,  [13]

1985 – Dick Slusher experimental squeezing

1985 – Deutsch quantum algorithm

1986 – Photon anti-bunching at a beamsplitter, P. Grangier, G. Roger, A. Aspect: [14]

1986 – Kimble squeezing in parametric down-conversion

1986 – C. K. Hong, L. Mandel: Phys. Rev. Lett. 56 , 58 (1986) one-photon localization

1987 – Two-photon interference (Ghosh and Mandel) [15]

1987 – HOM effect [16]

1987 – Photon squeezing, P. Grangier, R. E. Slusher, B. Yurke, A. La Porta: [17]

1987 – Grangier and Slusher, squeezed light interferometer

1988 – 2-photon Bell violation:  Z. Y. Ou, L. Mandel: Phys. Rev. Lett. 61 , 50 (1988)

1988 – Brassard Quantum cryptography

1989 – Franson proposes two-photon interference in k-number (?)

1990 – Two-photon interference in k-number (Kwiat and Chiao)

1990 – Two-photon interference (Ou, Zhou, Wang and Mandel)

1993 – Quantum teleportation proposal (Bennett)

1994 – Teleportation of quantum states (Vaidman)

1994 – Shor factoring algorithm

1995 – Down-conversion for polarization: Kwiat and Zeilinger (1995)

1997 – Experimental quantum teleportation (Bouwmeester)

1997 – Experimental quantum teleportation (Bosci)

1998 – Unconditional quantum teleportation (every state) (Furusawa)

2001 – Quantum computing with linear optics (Knill, Laflamme, Milburn)

2013 – LIGO design proposal with squeezed light (Aasi)

2019 – Squeezing upgrade on LIGO (Tse)

2020 – Quantum computational advantage (Zhong)

10. The Quantum Advantage

There is almost no technical advantage better than having exponential resources at hand. The exponential resources of quantum interference provide that advantage to quantum computing which is poised to usher in a new era of quantum information science and technology.

David Deutsch.

Topics: Interferometric Computing. David Deutsch. Quantum Algorithm. Peter Shor. Prime Factorization. Quantum Logic Gates. Linear Optical Quantum Computing. Boson Sampling. Quantum Computational Advantage.

1980 – Paul Benioff describes possibility of quantum computer

1981 – Feynman simulating physics with computers

1985 – Deutsch quantum Turing machine [18]

1987 – Quantum properties of beam splitters

1992 – Deutsch Josza algorithm is exponential faster than classical

1993 – Quantum teleportation described

1994 – Shor factoring algorithm [19]

1994 – First quantum computing conference

1995 – Shor error correction

1995 – Universal gates

1996 – Grover search algorithm

1998 – First demonstration of quantum error correction

1999 – Nakamura and Tsai superconducting qubits

2001 – Superconducting nanowire photon detectors

2001 – Linear optics quantum computing (KLM)

2001 – One-way quantum computer

2003 – All-optical quantum gate in a quantum dot (Li)

2003 – All-optical quantum CNOT gate (O’Brien)

2003 – Decoherence and einselection (Zurek)

2004 – Teleportation across the Danube

2005 – Experimental quantum one-way computing (Walther)

2007 – Teleportation across 114 km (Canary Islands)

2008 – Quantum discord computing

2011 – D-Wave Systems offers commercial quantum computer

2011 – Aaronson boson sampling

2012 – 1QB Information Technnologies, first quantum software company

2013 – Experimental demonstrations of boson sampling

2014 – Teleportation on a chip

2015 – Universal linear optical quantum computing (Carolan)

2017 – Teleportation to a satellite

2019 – Generation of a 2D cluster state (Larsen)

2019 – Quantum supremacy [20]

2020 – Quantum optical advantage [21]

2021 – Programmable quantum photonic chip

References:

[1] Annalen Der Physik 4(3): 553-563.

[2] Annalen Der Physik 17(6): 132-148.

[3] Physikalische Zeitschrift 10: 185-193.

[4] Proc. Cam. Phil. Soc. Math. Phys. Sci. 15 , 114 (1909)

[5] Physical Review. 21 (5): 483–502.

[6] Proceedings of the Royal Society of London Series a-Containing Papers of a Mathematical and Physical Character 114(767): 243-265.

[7] D. Bohm, “A suggested interpretation of the quantum theory in terms of hidden variables .1,” Physical Review, vol. 85, no. 2, pp. 166-179, (1952)

[8] Physics 1 , 195 (1964); Rev. Mod. Phys. 38 , 447 (1966)

[9] Phys. Rev. 159 , 1084 (1967)

[10] B. R. Mollow, R. J. Glauber: Phys. Rev. 160, 1097 (1967); 162, 1256 (1967)

[11] J. F. Clauser, M. A. Horne, A. Shimony, and R. A. Holt, ” Proposed experiment to test local hidden-variable theories,” Physical Review Letters, vol. 23, no. 15, pp. 880-&, (1969)

[12] (1977) Phys. Rev. Lett. 39, 691-5

[13] A. Aspect, P. Grangier, G. Roger: Phys. Rev. Lett. 49 , 91 (1982). A. Aspect, J. Dalibard, G. Roger: Phys. Rev. Lett. 49 , 1804 (1982)

[14] Europhys. Lett. 1 , 173 (1986)

[15] R. Ghosh and L. Mandel, “Observation of nonclassical effects in the interference of 2 photons,” Physical Review Letters, vol. 59, no. 17, pp. 1903-1905, Oct (1987)

[16] C. K. Hong, Z. Y. Ou, and L. Mandel, “Measurement of subpicosecond time intervals between 2 photons by interference,” Physical Review Letters, vol. 59, no. 18, pp. 2044-2046, Nov (1987)

[17] Phys. Rev. Lett 59, 2153 (1987)

[18] D. Deutsch, “QUANTUM-THEORY, THE CHURCH-TURING PRINCIPLE AND THE UNIVERSAL QUANTUM COMPUTER,” Proceedings of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences, vol. 400, no. 1818, pp. 97-117, (1985)

[19] P. W. Shor, “ALGORITHMS FOR QUANTUM COMPUTATION – DISCRETE LOGARITHMS AND FACTORING,” in 35th Annual Symposium on Foundations of Computer Science, Proceedings, S. Goldwasser Ed., (Annual Symposium on Foundations of Computer Science, 1994, pp. 124-134.

[20] F. Arute et al., “Quantum supremacy using a programmable superconducting processor,” Nature, vol. 574, no. 7779, pp. 505-+, Oct 24 (2019)

[21] H.-S. Zhong et al., “Quantum computational advantage using photons,” Science, vol. 370, no. 6523, p. 1460, (2020)

Further Reading: The History of Light and Interference (2023)

Available at Amazon.

by David D. Nolte

Orion’s Dog: The Serious Science of Sirius

The constellation Orion strides high across the heavens on cold crisp winter nights in the North, followed at his heel by his constant companion, Canis Major, the Great Dog.  Blazing blue from the Dog’s proud chest is the star Sirius, the Dog Star, the brightest star in the night sky.  Although it is only the seventh closest star system to our sun, the other six systems host dimmer dwarf stars. Sirius, on the other hand, is a young bright star burning blue in the night.  It is an infant star, really, only as old as 5% the age of our sun, coming into being when Dinosaurs walked our planet.

The Sirius star system is a microcosm of mankind’s struggle to understand the Universe.  Because it is close and bright, it has become the de facto bench-test for new theories of astrophysics as well as for new astronomical imaging technologies.  It has played this role from the earliest days of history, when it was an element of religion rather than of science, down to the modern age as it continues to test and challenge new ideas about quantum matter and extreme physics.

Sirius Through the Ages

To the ancient Egyptians, Sirius was the star Sopdet, the welcome herald of the flooding of the Nile when it rose in the early morning sky of autumn.  The star was associated with Isis of the cow constellation Hathor (Canis Major) following closely behind Osiris (Orion).  The importance of the annual floods for the well-being of the ancient culture cannot be underestimated, and entire religions full of symbolic significance revolved around the heliacal rising of Sirius.

Fig. Canis Major.

To the Greeks, Sirius was always Sirius, although no one even as far back as Hesiod in the 7th century BC could recall where it got its name.  It was the dog star, as it was also to the Persians and the Hindus who called it Tishtrya and Tishya, respectively.  The loss of the initial “T” of these related Indo-European languages is a historical sound shift in relation to “S”, indicating that the name of the star dates back at least as far as the divergence of the Indo-European languages around the fourth millennium BC.  (Even more intriguing is the same association of Sirius with  dogs and wolves by the ancient Chinese and by Alaskan Innuits, as well as by many American Indian tribes, suggesting that the cultural significance of the star, if not its name, may have propagated across Asia and the Bering Strait as far back as the end of the last Ice Age.)  As the brightest star of the sky, this speaks to an enduring significance for Sirius, dating back to the beginning of human awareness of our place in nature.  No culture was unaware of this astronomical companion to the Sun and Moon and Planets.

The Greeks, too, saw Sirius as a harbinger, not for life-giving floods, but rather of the sweltering heat of late summer.  Homer, in the Iliad, famously wrote:

And aging Priam was the first to see him

sparkling on the plain, bright as that star

in autumn rising, whose unclouded rays

shine out amid a throng of stars at dusk—

the one they call Orion's dog, most brilliant,

yes, but baleful as a sign: it brings

great fever to frail men. So pure and bright

the bronze gear blazed upon him as he ran.

The Romans expanded on this view, describing “the dog days of summer”, which is a phrase that echoes till today as we wait for the coming coolness of autumn days.

The Heavens Move

The irony of the Copernican system of the universe, when it was proposed in 1543 by Nicolaus Copernicus, is that it took stars that moved persistently through the heavens and fixed them in the sky, unmovable.  The “fixed stars” became the accepted norm for several centuries, until the peripatetic Edmund Halley (1656 – 1742) wondered if the stars really did not move.  From Newton’s new work on celestial dynamics (the famous Principia, which Halley generously paid out of his own pocket to have published not only because of his friendship with Newton, but because Halley believed it to be a monumental work that needed to be widely known), it was understood that gravitational effects would act on the stars and should cause them to move.

Fig. Halley’s Comet

In 1710 Halley began studying the accurate star-location records of Ptolemy from one and a half millennia earlier and compared  them with what he could see in the night sky.  He realized that the star Sirius had shifted in the sky by an angular distance equivalent to the diameter of the moon.  Other bright stars, like Arcturus and Procyon, also showed discrepancies from Ptolemy.  On the other hand, dimmer stars, that Halley reasoned were farther away, showed no discernible shifts in 1500 years.  At a time when stellar parallax, the apparent shift in star locations caused by the movement of the Earth, had not yet been detected, Halley had found an alternative way to get at least some ranked distances to the stars based on their proper motion through the universe.  Closer stars to the Earth would show larger angular displacements over 1500 years than stars farther away.  By being the closest bright star to Earth, Sirius had become a testbed for observations and theories of the motions of stars.  With the confidence of the confirmation of the nearness of Sirius to the Earth, Jacques Cassini claimed in 1714 to have measured the parallax of Sirius, but Halley refuted this claim in 1720.  Parallax would remain elusive for another hundred years to come.

The Sound of Sirius

Of all the discoveries that emerged from nineteenth century physics—Young’s fringes, Biot-Savart law, Fresnel lens, Carnot cycle, Faraday effect, Maxwell’s equations, Michelson interferometer—only one is heard daily—the Doppler effect [1].  Doppler’s name is invoked every time you turn on the evening news to watch Doppler weather radar.  Doppler’s effect is experienced as you wait by the side of the road for a car to pass by or a jet to fly overhead.  Einstein may have the most famous name in physics, but Doppler’s is certainly the most commonly used.   

Although experimental support for the acoustic Doppler effect accumulated quickly, corresponding demonstrations of the optical Doppler effect were slow to emerge.  The breakthrough in the optical Doppler effect was made by William Huggins (1824-1910).  Huggins was an early pioneer in astronomical spectroscopy and was famous for having discovered that some bright nebulae consist of atomic gases (planetary nebula in our own galaxy) while others (later recognized as distant galaxies) consist of unresolved emitting stars.  Huggins was intrigued by the possibility of using the optical Doppler effect to measure the speed of stars, and he corresponded with James Clerk Maxwell (1831-1879) to confirm the soundness of Doppler’s arguments, which Maxwell corroborated using his new electromagnetic theory.  With the resulting confidence, Huggins turned his attention to the brightest star in the heavens, Sirius, and on May 14, 1868, he read a paper to the Royal Society of London claiming an observation of Doppler shifts in the spectral lines of the star Sirius consistent with a speed of about 50 km/sec [2].

Fig. Doppler spectroscopy of stellar absorption lines caused by the relative motion of the star (in this illustration the orbiting exoplanet is causing the star to wobble.)

The importance of Huggins’ report on the Doppler effect from Sirius was more psychological than scientifically accurate, because it convinced the scientific community that the optical Doppler effect existed.  Around this time the German astronomer Hermann Carl Vogel (1841 – 1907) of the Potsdam Observatory began working with a new spectrograph designed by Johann Zöllner from Leipzig [3] to improve the measurements of the radial velocity of stars (the speed along the line of sight).  He was aware that the many values quoted by Huggins and others for stellar velocities were nearly the same as the uncertainties in their measurements.  Vogel installed photographic capabilities in the telescope and spectrograph at the Potsdam Observatory [4] in 1887 and began making observations of Doppler line shifts in stars through 1890.  He published an initial progress report in 1891, and then a definitive paper in 1892 that provided the first accurate stellar radial velocities [5].  Fifty years after Doppler read his paper to the Royal Bohemian Society of Science (in 1842 to a paltry crowd of only a few scientists), the Doppler effect had become an established workhorse of quantitative astrophysics. A laboratory demonstration of the optical Doppler effect was finally achieved in 1901 by Aristarkh Belopolsky (1854-1934), a Russian astronomer, by constructing a device with a narrow-linewidth light source and rapidly rotating mirrors [6].

White Dwarf

While measuring the position of Sirius to unprecedented precision, the German astronomer Friedrich Wilhelm Bessel (1784 – 1846) noticed a slow shift in its position.  (This is the same Bessel as “Bessel function” fame, although the functions were originally developed by Daniel Bernoulli and Bessel later generalized them.)  Bessel deduced that Sirius must have an unseen companion with an orbital of around 50 years.  This companion was discovered by accident in 1862 during a test run of a new lens manufactured by the Clark&Sons glass manufacturing company prior to delivery to Northwestern University in Chicago.  (The lens was originally ordered by the University of Mississippi in 1860, but after the Civil War broke out, the Massachusetts-based Clark company put it up for bid.  Harvard wanted it, but Northwestern got it.)  Sirius itself was redesignated Sirius A, while this new star was designated Sirius B (and sometimes called “The Pup”). 

Fig. White dwarf and planet.

The Pup’s spectrum was measured in 1915 by Walter Adams (1876 – 1956) which put it in the newly-formed class of “white dwarf” stars that were very small but, unlike other types of dwarf stars, they had very hot (white) spectra.  The deflection of the orbit of Sirius A allowed its mass to be estimated at about one solar mass, which was normal for a dwarf star.  Furthermore, its brightness and surface temperature allowed its density to be estimated, but here an incredible number came out: the density of Sirius B was about 30,000 times greater than the density of the sun!  Astronomers at the time thought that this was impossible, and Arthur Eddington, who was the expert in star formation, called it “nonsense”.  This nonsense withstood all attempts to explain it for over a decade.

In 1926, R. H. Fowler (1889 – 1944) at Cambridge University in England applied the newly-developed theory of quantum mechanics and the Pauli exclusion principle to the problem of such ultra-dense matter.  He found that the Fermi sea of electrons provided a type of pressure, called degeneracy pressure, that counteracted the gravitational pressure that threatened to collapse the star under its own weight.  Several years later, Subrahmanyan Chandrasekhar calculated the upper limit for white dwarfs using relativistic effects and accurate density profiles and found that a white dwarf with a mass greater than about 1.5 times the mass of the sun would no longer be supported by the electron degeneracy pressure and would suffer gravitational collapse.  At the time, the question of what it would collapse to was unknown, although it was later understood that it would collapse to a neutron star.  Sirius B, at about one solar mass, is well within the stable range of white dwarfs.

But this was not the end of the story for Sirius B [7].  At around the time that Adams was measuring the spectrum of the white dwarf, Einstein was predicting that light emerging from a dense star would have its wavelengths gravitationally redshifted relative to its usual wavelength.  This was one of the three classic tests he proposed for his new theory of General Relativity.  (1 – The precession of the perihelion of Mercury. 2 – The deflection of light by gravity.  3 – The gravitational redshift of photons rising out of a gravity well.)  Adams announced in 1925 (after the deflection of light by gravity had been confirmed by Eddington in 1919) that he had measured the gravitational redshift.  Unfortunately, it was later surmised that he had not measured the gravitational effect but had actually measured Doppler-shifted spectra because of the rotational motion of the star.  The true gravitational redshift of Sirius B was finally measured in 1971, although the redshift of another white dwarf, 40 Eridani B, had already been measured in 1954.

Static Interference

The quantum nature of light is an elusive quality that requires second-order experiments of intensity fluctuations to elucidate them, rather than using average values of intensity.  But even in second-order experiments, the manifestations of quantum phenomenon are still subtle, as evidenced by an intense controversy that was launched by optical experiments performed in the 1950’s by a radio astronomer, Robert Hanbury Brown (1916 – 2002).  (For the full story, see Chapter 4 in my book Interference from Oxford (2023) [8]).

Hanbury Brown (he never went by his first name) was born in Aruvankandu, India, the son of a British army officer.  He never seemed destined for great things, receiving an unremarkable education that led to a degree in radio engineering from a technical college in 1935.  He hoped to get a PhD in radio technology, and he even received a scholarship to study at Imperial College in London, when he was urged by the rector of the university, Sir Henry Tizard, to give up his plans and join an effort to develop defensive radar against a growing threat from Nazi Germany as it aggressively rearmed after abandoning the punitive Versailles Treaty.  Hanbury Brown began the most exciting and unnerving five years of his life, right in the middle of the early development of radar defense, leading up to the crucial role it played in the Battle of Britain in 1940 and the Blitz from 1940 to 1941.  Partly due to the success of radar, Hitler halted night-time raids in the Spring of 1941, and England escaped invasion.

In 1949, fourteen years after he had originally planned to start his PhD, Hanbury Brown enrolled at the relatively ripe age of 33 at the University of Manchester.  Because of his background in radar, his faculty advisor told him to look into the new field of radio astronomy that was just getting started, and Manchester was a major player because it administrated the Jodrell Bank Observatory, which was one of the first and largest radio astronomy observatories in the World.  Hanbury Brown was soon applying all he had learned about radar transmitters and receivers to the new field, focusing particularly on aspects of radio interferometry after Martin Ryle (1918 – 1984) at Cambridge with Derek Vonberg (1921 – 2015) developed the first radio interferometer to measure the angular size of the sun [9] and of radio sources on the Sun’s surface that were related to sunspots [10].  Despite the success of their measurements, their small interferometer was unable to measure the size of other astronomical sources.  From Michelson’s formula for stellar interferometry, longer baselines between two separated receivers would be required to measure smaller angular sizes.  For his PhD project, Hanbury Brown was given the task of designing a radio interferometer to resolve the two strongest radio sources in the sky, Cygnus A and Cassiopeia A, whose angular sizes were unknown.  As he started the project, he was confronted with the problem of distributing a stable reference signal to receivers that might be very far apart, maybe even thousands of kilometers, a problem that had no easy solution. 

After grappling with this technical problem for months without success, late one night in 1949 Hanbury Brown had an epiphany [11], wondering what would happen if the two separate radio antennas measured only intensities rather than fields.  The intensity in a radio telescope fluctuates in time like random noise.  If that random noise were measured at two separated receivers while trained on a common source, would those noise patterns look the same?  After a few days considering this question, he convinced himself that the noise would indeed share common features, and the degree to which the two noise traces were similar should depend on the size of the source and the distance between the two receivers, just like Michelson’s fringe visibility.  But his arguments were back-of-the-envelope, so he set out to find someone with the mathematical skills to do it more rigorously.  He found Richard Twiss.

Richard Quentin Twiss (1920 – 2005), like Hanbury Brown, was born in India to British parents but had followed a more prestigious educational path, taking the Mathematical Tripos exam at Cambridge in 1941 and receiving his PhD from MIT in the United States in 1949.  He had just returned to England, joining the research division of the armed services located north of London, when he received a call from Hanbury Brown at the Jodrell Bank radio astronomy laboratory in Manchester.  Twiss travelled to meet Hanbury Brown in Manchester, who put him up in his flat in the neighboring town of Wilmslow.  The two set up the mathematical assumptions behind the new “intensity interferometer” and worked late into the night. When Hanbury Brown finally went to bed, Twiss was still figuring the numbers.  The next morning, the tall and lanky Twiss appeared in his silk dressing gown in the kitchen and told Hanbury Brown, “This idea of yours is no good, it doesn’t work”[12]—it would never be strong enough to detect the intensity from stars.  However, after haggling over the details of some of the integrals, Hanbury Brown, and then finally Twiss, became convinced that the effect was real.  Rather than fringe visibility, it was the correlation coefficient between two noise signals that would depend on the joint sizes of the source and receiver in a way that captured the same information as Michelson’s first-order fringe visibility.  But because no coherent reference wave was needed for interferometric mixing, this new approach could be carried out across very large baseline distances.

After demonstrating the effect on astronomical radio sources, Hanbury Brown and Twiss took the next obvious step: optical stellar intensity interferometry.  Their work had shown that photon noise correlations were analogous to Michelson fringe visibility, so the stellar intensity interferometer was expected to work similarly to the Michelson stellar interferometer—but with better stability over much longer baselines because it did not need a reference.  An additional advantage was the simple light collecting requirements.  Rather than needing a pair of massively expensive telescopes for high-resolution imaging, the intensity interferometer only needed to point two simple light collectors in a common direction.  For this purpose, and to save money, Hanbury Brown selected two of the largest army-surplus anti-aircraft searchlights that he could find left over from the London Blitz.  The lamps were removed and replaced with high-performance photomultipliers, and the units were installed on two train cars that could run along a railroad siding that crossed the Jodrell Bank grounds.

Fig. Stellar Interferometers: (Left) Michelson Stellar Field Interferometer. (Right) Hanbury Brown Twiss Stellar Intensity Interferometer.

The target of the first test of the intensity interferometer was Sirius, the Dog Star.  Sirius was chosen because it is the brightest star in the night sky and was close to Earth at 8.6 light years and hence would be expected to have a relatively large angular size.  The observations began at the start of winter in 1955, but the legendary English weather proved an obstacle.  In addition to endless weeks of cloud cover, on many nights dew formed on the reflecting mirrors, making it necessary to install heaters.  It took more than three months to make 60 operational attempts to accumulate a mere 18 hours of observations [13].  But it worked!  The angular size of Sirius was measured for the first time. It subtended an angle of approximately 6 milliarcseconds (mas), which was well within the expected range for such a main sequence blue star.  This angle is equivalent to observing a house on the Moon from the Earth.  No single non-interferometric telescope on Earth, or in Earth orbit, has that kind of resolution, even today.  Once again, Sirus was the testbed of a new observational technology.  Hanbury Brown and Twiss went on the measure the diameters of dozens of stars.

Adaptive Optics

Any undergraduate optics student can tell you that bigger telescopes have higher spatial resolution.  But this is only true up to a point.  When telescope diameters become not much bigger than about 10 inches, the images they form start to dance, caused by thermal fluctuations in the atmosphere.  Large telescopes can still get “lucky” at moments when the atmosphere is quiet, but this usually only happens for a fraction of a second before the fluctuation set in again.  This is the primary reason that the Hubble Space Telescope was placed in Earth orbit above the atmosphere, and why the James Webb Space Telescope is flying a million miles away from the Earth.  But that is not the end of Earth-based large telescoped.  The Very Large Telescope (VLT) has a primary diameter of 8 meters, and the Extremely Large Telescope (ELT), coming online soon, has an even bigger diameter of 40 meters.  How do these work under the atmospheric blanket?  The answer is adaptive optics.

Adaptive optics uses active feedback to measure the dancing images caused by the atmosphere and uses the information to control a flexible array of mirror elements to exactly cancel out the effects of the atmospheric fluctuations.  In the early days of adaptive-optics development, the applications were more military than astronomic, but advances made in imaging enemy satellites soon was released to the astronomers.  The first civilian demonstrations of adaptive optics were performed in 1977 when researchers at Bell Labs [14] and at the Space Sciences Lab at UC Berkeley [15] each made astronomical demonstrations of improved seeing of the star Sirius using adaptive optics.  The field developed rapidly after that, but once again Sirius had led the way.

Star Travel

The day is fast approaching when humans will begin thinking seriously of visiting nearby stars—not in person at first, but with unmanned spacecraft that can telemeter information back to Earth.  Although Sirius is not the closest star to Earth—it is 8.6 lightyears away while Alpha Centauri is almost twice as close at only 4.2 lightyears away—it may be the best target for an unmanned spacecraft.  The reason is its brightness. 

Stardrive technology is still in its infancy—most of it is still on drawing boards.  Therefore, the only “mature” technology we have today is light pressure on solar sails.  Within the next 50 years or so we will have the technical ability to launch a solar sail towards a nearby star and accelerate it to a good fraction of the speed of light.  The problem is decelerating the spaceship when it arrives at its destination, otherwise it will go zipping by with only a few seconds to make measurements after its long trek there.

Fig. NASA’s solar sail demonstrator unit (artist’s rendering).

A better idea is to let the star light push against the solar sail to decelerate it to orbital speed by the time it arrives.  That way, the spaceship can orbit the target star for years.  This is a possibility with Sirius.  Because it is so bright, its light can decelerate the spaceship even when it is originally moving at relativistic speeds. By one calculation, the trip to Sirius, including the deceleration and orbital insertion, should only take about 69 years [16].  That’s just one lifetime.  Signals could be beaming back from Sirius by as early as 2100—within the lifetimes of today’s children.

Footnotes

[1] The section is excerpted from D. D. Nolte, The Fall and Rise of the Doppler Effect, Physics Today (2020)

[2] W. Huggins, “Further observations on the spectra of some of the stars and nebulae, with an attempt to determine therefrom whether these bodies are moving towards or from the earth, also observations on the spectra of the sun and of comet II,” Philos. Trans. R. Soc. London vol. 158, pp. 529-564, 1868. The correct value is -5.5 km/sec approaching Earth.  Huggins got the magnitude and even the sign wrong.

[3] in Hearnshaw, The Analysis of Starlight (Cambridge University Press, 2014), pg. 89

[4] The Potsdam Observatory was where the American Albert Michelson built his first interferometer while studying with Helmholtz in Berlin.

[5] Vogel, H. C. Publik. der astrophysik. Observ. Potsdam 1: 1. (1892)

[6] A. Belopolsky, “On an apparatus for the laboratory demonstration of the Doppler-Fizeau principle,” Astrophysical Journal, vol. 13, pp. 15-24, Jan 1901.

[7] https://adsabs.harvard.edu/full/1980QJRAS..21..246H

[8] D. D. Nolte, Interference: The History of Optical Interferometry and the Scientists who Tamed Light (Oxford University Press, 2023)

[9] M. Ryle and D. D. Vonberg, “Solar Radiation on 175 Mc/sec,” Nature, vol. 158 (1946): pp. 339-340.; K. I. Kellermann and J. M. Moran, “The development of high-resolution imaging in radio astronomy,” Annual Review of Astronomy and Astrophysics, vol. 39, (2001): pp. 457-509.

[10] M. Ryle, ” Solar radio emissions and sunspots,” Nature, vol. 161, no. 4082 (1948): pp. 136-136.

[11] R. H. Brown, The intensity interferometer; its application to astronomy (London, New York, Taylor & Francis; Halsted Press, 1974).

[12] R. H. Brown, Boffin : A personal story of the early days of radar and radio astronomy (Adam Hilger, 1991), p. 106.

[13] R. H. Brown and R. Q. Twiss. ” Test of a new type of stellar interferometer on Sirius.” Nature 178, no. 4541 (1956): pp. 1046-1048.

[14] S. L. McCall, T. R. Brown, and A. Passner, “IMPROVED OPTICAL STELLAR IMAGE USING A REAL-TIME PHASE-CORRECTION SYSTEM – INITIAL RESULTS,” Astrophysical Journal, vol. 211, no. 2, pp. 463-468, (1977)

[15] A. Buffington, F. S. Crawford, R. A. Muller, and C. D. Orth, “1ST OBSERVATORY RESULTS WITH AN IMAGE-SHARPENING TELESCOPE,” Journal of the Optical Society of America, vol. 67, no. 3, pp. 304-305, 1977 (1977)

[16] https://www.newscientist.com/article/2128443-quickest-we-could-visit-another-star-is-69-years-heres-how/

by David D. Nolte

A Short History of the Photon

The quantum of light—the photon—is a little over 100 years old.  It was born in 1905 when Einstein merged Planck’s blackbody quantum hypothesis with statistical mechanics and concluded that light itself must be quantized.  No one believed him!  Fast forward to today, and the photon is a modern workhorse of modern quantum technology.  Quantum encryption and communication are performed almost exclusively with photons, and many prototype quantum computers are optics based.  Quantum optics also underpins atomic and molecular optics (AMO), which is one of the hottest and most rapidly advancing  frontiers of physics today.

Only after the availability of “quantum” light sources … could photon numbers be manipulated at will, launching the modern era of quantum optics.

This blog tells the story of the early days of the photon and of quantum optics.  It begins with Einstein in 1905 and ends with the demonstration of photon anti-bunching that was the first fundamentally quantum optical phenomenon observed seventy years later in 1977.  Across that stretch of time, the photon went from a nascent idea in Einstein’s fertile brain to the most thoroughly investigated quantum particle in the realm of physics.

The Photon: Albert Einstein (1905)

When Planck presented his quantum hypothesis in 1900 to the German Physical Society [1], his model of black body radiation retained all its classical properties but one—the quantized interaction of light with matter.  He did not think yet in terms of quanta, only in terms of steps in a continuous interaction.

The quantum break came from Einstein when he published his 1905 paper proposing the existence of the photon—an actual quantum of light that carried with it energy and momentum [2].  His reasoning was simple and iron-clad, resting on Planck’s own blackbody relation that Einstein combined with simple reasoning from statistical mechanics.  He was led inexorably to the existence of the photon.  Unfortunately, almost no one believed him (see my blog on Einstein and Planck). 

This was before wave-particle duality in quantum thinking, so the notion that light—so clearly a wave phenomenon—could be a particle was unthinkable.  It had taken half of the 19th century to rid physics of Newton’s corpuscules and emmisionist theories of light, so to bring it back at the beginning of the 20th century seemed like a great blunder.  However, Einstein persisted.

In 1909 he published a paper on the fluctuation properties of light [3] in which he proposed that the fluctuations observed in light intensity had two contributions: one from the discreteness of the photons (what we call “shot noise” today) and one from the fluctuations in the wave properties.  Einstein was proposing that both particle and wave properties contributed to intensity fluctuations, exhibiting simultaneous particle-like and wave-like properties.  This was one of the first expressions of wave-particle duality in modern physics.

In 1916 and 1917 Einstein took another bold step and proposed the existence of stimulated emission [4].  Once again, his arguments were based on simple physics—this time the principle of detailed balance—and he was led to the audacious conclusion that one photon can stimulated the emission of another.  This would become the basis of the laser forty-five years later.

While Einstein was confident in the reality of the photon, others sincerely doubted its existence.  Robert Milliken (1868 – 1953) decided to put Einstein’s theory of photoelectron emission to the most stringent test ever performed.  In 1915 he painstakingly acquired the definitive dataset with the goal to refute Einstein’s hypothesis, only to confirm it in spectacular fashion [5].  Partly based on Milliken’s confirmation of Einstein’s theory of the photon, Einstein was awarded the Nobel Prize in Physics in 1921.

Einstein at a blackboard.

From that point onward, the physical existence of the photon was accepted and was incorporated routinely into other physical theories.  Compton used the energy and the momentum of the photon in 1922 to predict and measure Compton scattering of x-rays off of electrons [6].  The photon was given its modern name by Gilbert Lewis in 1926 [7].

Single-Photon Interference: Geoffry Taylor (1909)

If a light beam is made up of a group of individual light quanta, then in the limit of very dim light, there should just be one photon passing through an optical system at a time.  Therefore, to do optical experiments on single photons, one just needs to reach the ultimate dim limit.  As simple and clear as this argument sounds, it has problems that only were sorted out after the Hanbury Brown and Twiss experiments in the 1950’s and the controversy they launched (see below).  However, in 1909, this thinking seemed like a clear approach for looking for deviations in optical processes in the single-photon limit.

In 1909, Geoffry Ingram Taylor (1886 – 1975) was an undergraduate student at Cambridge University and performed a low-intensity Young’s double-slit experiment (encouraged by J. J. Thomson).  At that time the idea of Einstein’s photon was only 4 years old, and Bohr’s theory of the hydrogen atom was still a year away.  But Thomson believed that if photons were real, then their existence could possibly show up as deviations in experiments involving single photons.  Young’s double-slit experiment is the classic demonstration of the classical wave nature of light, so performing it under conditions when (on average) only a single photon was in transit between a light source and a photographic plate seemed like the best place to look.

G. I. Taylor

The experiment was performed by finding an optimum exposure of photographic plates in a double slit experiment, then reducing the flux while increasing the exposure time, until the single-photon limit was achieved while retaining the same net exposure of the photographic plate.  Under the lowest intensity, when only a single photon was in transit at a time (on average), Taylor performed the exposure for three months.  To his disappointment, when he developed the film, there was no significant difference between high intensity and low intensity interference fringes [8].  If photons existed, then their quantized nature was not showing up in the low-intensity interference experiment.

The reason that there is no single-photon-limit deviation in the behavior of the Young double-slit experiment is because Young’s experiment only measures first-order coherence properties.  The average over many single-photon detection events is described equally well either by classical waves or by quantum mechanics.  Quantized effects in the Young experiment could only appear in fluctuations in the arrivals of photons, but in Taylor’s day there was no way to detect the arrival of single photons. 

Quantum Theory of Radiation : Paul Dirac (1927)

After Paul Dirac (1902 – 1984) was awarded his doctorate from Cambridge in 1926, he received a stipend that sent him to work with Niels Bohr (1885 – 1962) in Copenhagen. His attention focused on the electromagnetic field and how it interacted with the quantized states of atoms.  Although the electromagnetic field was the classical field of light, it was also the quantum field of Einstein’s photon, and he wondered how the quantized harmonic oscillators of the electromagnetic field could be generated by quantum wavefunctions acting as operators.  He decided that, to generate a photon, the wavefunction must operate on a state that had no photons—the ground state of the electromagnetic field known as the vacuum state.

Dirac put these thoughts into their appropriate mathematical form and began work on two manuscripts.  The first manuscript contained the theoretical details of the non-commuting electromagnetic field operators.  He called the process of generating photons out of the vacuum “second quantization”.  In second quantization, the classical field of electromagnetism is converted to an operator that generates quanta of the associated quantum field out of the vacuum (and also annihilates photons back into the vacuum).  The creation operators can be applied again and again to build up an N-photon state containing N photons that obey Bose-Einstein statistics, as they must, as required by their integer spin, and agreeing with Planck’s blackbody radiation. 

Dirac then showed how an interaction of the quantized electromagnetic field with quantized energy levels involved the annihilation and creation of photons as they promoted electrons to higher atomic energy levels, or demoted them through stimulated emission.  Very significantly, Dirac’s new theory explained the spontaneous emission of light from an excited electron level as a direct physical process that creates a photon carrying away the energy as the electron falls to a lower energy level.  Spontaneous emission had been explained first by Einstein more than ten years earlier when he derived the famous A and B coefficients [4], but the physical mechanism for these processes was inferred rather than derived. Dirac, in late 1926, had produced the first direct theory of photon exchange with matter [9]. 

Paul Dirac in his early days.

Einstein-Podolsky-Rosen (EPR) and Bohr (1935)

The famous dialog between Einstein and Bohr at the Solvay Conferences culminated in the now famous “EPR” paradox of 1935 when Einstein published (together with B. Podolsky and N. Rosen) a paper that contained a particularly simple and cunning thought experiment. In this paper, not only was quantum mechanics under attack, but so was the concept of reality itself, as reflected in the paper’s title “Can Quantum Mechanical Description of Physical Reality Be Considered Complete?” [10].

Bohr and Einstein at Paul Ehrenfest’s house in 1925.

Einstein considered an experiment on two quantum particles that had become “entangled” (meaning they interacted) at some time in the past, and then had flown off in opposite directions. By the time their properties are measured, the two particles are widely separated. Two observers each make measurements of certain properties of the particles. For instance, the first observer could choose to measure either the position or the momentum of one particle. The other observer likewise can choose to make either measurement on the second particle. Each measurement is made with perfect accuracy. The two observers then travel back to meet and compare their measurements.   When the two experimentalists compare their data, they find perfect agreement in their values every time that they had chosen (unbeknownst to each other) to make the same measurement. This agreement occurred either when they both chose to measure position or both chose to measure momentum.

It would seem that the state of the particle prior to the second measurement was completely defined by the results of the first measurement. In other words, the state of the second particle is set into a definite state (using quantum-mechanical jargon, the state is said to “collapse”) the instant that the first measurement is made. This implies that there is instantaneous action at a distance −− violating everything that Einstein believed about reality (and violating the law that nothing can travel faster than the speed of light). He therefore had no choice but to consider this conclusion of instantaneous action to be false.  Therefore quantum mechanics could not be a complete theory of physical reality −− some deeper theory, yet undiscovered, was needed to resolve the paradox.

Bohr, on the other hand, did not hold “reality” so sacred. In his rebuttal to the EPR paper, which he published six months later under the identical title [11], he rejected Einstein’s criterion for reality. He had no problem with the two observers making the same measurements and finding identical answers. Although one measurement may affect the conditions of the second despite their great distance, no information could be transmitted by this dual measurement process, and hence there was no violation of causality. Bohr’s mind-boggling viewpoint was that reality was nonlocal, meaning that in the quantum world the measurement at one location does influence what is measured somewhere else, even at great distance. Einstein, on the other hand, could not accept a nonlocal reality.

Entangled versus separable states. When the states are separable, no measurement on photon A has any relation to measurements on photon B. However, in the entangled case, all measurements on A are related to measurements on B (and vice versa) regardless of what decision is made to make what measurement on either photon, or whether the photons are separated by great distance. The entangled wave-function is “nonlocal” in the sense that it encompasses both particles at the same time, no matter how far apart they are.

The Intensity Interferometer:  Hanbury Brown and Twiss (1956)

Optical physics was surprisingly dormant from the 1930’s through the 1940’s. Most of the research during this time was either on physical optics, like lenses and imaging systems, or on spectroscopy, which was more interested in the physical properties of the materials than in light itself. This hiatus from the photon was about to change dramatically, not driven by physicists, but driven by astronomers.

The development of radar technology during World War II enabled the new field of radio astronomy both with high-tech receivers and with a large cohort of scientists and engineers trained in radio technology. In the late 1940’s and early 1950’s radio astronomy was starting to work with long baselines to better resolve radio sources in the sky using interferometery. The first attempts used coherent references between two separated receivers to provide a common mixing signal to perform field-based detection. However, the stability of the reference was limiting, especially for longer baselines.

In 1950, a doctoral student in the radio astronomy department of the University of Manchester, R. Hanbury Brown, was given the task to design baselines that could work at longer distances to resolve smaller radio sources. After struggling with the technical difficulties of providing a coherent “local” oscillator for distant receivers, Hanbury Brown had a sudden epiphany one evening. Instead of trying to reference the field of one receiver to the field of another, what if, instead, one were to reference the intensity of one receiver to the intensity of the other, specifically correlating the noise on the intensity? To measure intensity requires no local oscillator or reference field. The size of an astronomical source would then show up in how well the intensity fluctuations correlated with each other as the distance between the receivers was changed. He did a back of the envelope calculation that gave him hope that his idea might work, but he needed more rigorous proof if he was to ask for money to try out his idea. He tracked down Richard Twiss at a defense research lab and the two working out the theory of intensity correlations for long-baseline radio interferometry. Using facilities at the famous Jodrell Bank Radio Observatory at Manchester, they demonstrated the principle of their intensity interferometer and measured the angular size of Cygnus A and Cassiopeia A, two of the strongest radio sources in the Northern sky.

R. Hanbury Brown

One of the surprising side benefits of the intensity interferometer over field-based interferometry was insensitivity to environmental phase fluctuations. For radio astronomy the biggest source of phase fluctuations was the ionosphere, and the new intensity interferometer was immune to its fluctuations. Phase fluctuations had also been the limiting factor for the Michelson stellar interferometer which had limited its use to only about half a dozen stars, so Hanbury Brown and Twiss decided to revisit visible stellar interferometry using their new concept of intensity interferometry.

To illustrate the principle for visible wavelengths, Hanbury Brown and Twiss performed a laboratory experiment to correlate intensity fluctuations in two receivers illuminated by a common source through a beam splitter. The intensity correlations were detected and measured as a function of path length change, illustrating an excess correlation in noise for short path lengths that decayed as the path length increased. They published their results in Nature magazine in 1956 that immediately ignited a firestorm of protest from physicists [12].

In the 1950’s, many physicists had embraced the discrete properties of the photon and had developed a misleading mental picture of photons as individual and indivisible particles that could only go one way or another from a beam splitter, but not both. Therefore, the argument went, if the photon in an attenuated beam was detected in one detector at the output of a beam splitter, then it cannot be detected at the other. This would produce an anticorrelation in coincidence counts at the two detectors. However, the Hanbury Brown Twiss (HBT) data showed a correlation from the two detectors. This launched an intense controversy in which some of those who accepted the results called for a radical new theory of the photon, while most others dismissed the HBT results as due to systematics in the light source. The heart of this controversy was quickly understood by the Nobel laureate E. M Purcell. He correctly pointed out that photons are bosons and are indistinguishable discrete particles and hence are likely to “bunch” together, according to quantum statistics, even under low light conditions [13]. Therefore, attenuated “chaotic” light would indeed show photodetector correlations, even if the average photon number was less than a single photon at a time, the photons would still bunch.

The bunching of photons in light is a second order effect that moves beyond the first-order interference effects of Young’s double slit, but even here the quantum nature of light is not required. A semiclassical theory of light emission from a spectral line with a natural bandwidth also predicts intensity correlations, and the correlations are precisely what would be observed for photon bunching. Therefore, even the second-order HBT results, when performed with natural light sources, do not distinguish between classical and quantum effects in the experimental results. But this reliance on natural light sources was about to change fundmaentally with the invention of the laser.

Invention of the Laser : Ted Maiman (1959)

One of the great scientific breakthroughs of the 20th century was the nearly simultaneous yet independent realization by several researchers around 1951 (by Charles H. Townes of Columbia University, by Joseph Weber of the University of Maryland, and by Alexander M. Prokhorov and Nikolai G. Basov at the Lebedev Institute in Moscow) that clever techniques and novel apparati could be used to produce collections of atoms that had more electrons in excited states than in ground states. Such a situation is called a population inversion. If this situation could be attained, then according to Einstein’s 1917 theory of photon emission, a single photon would stimulate a second photon, which in turn would stimulate two additional electrons to emit two identical photons to give a total of four photons −− and so on. Clearly this process turns a single photon into a host of photons, all with identical energy and phase.

Theodore Maiman

Charles Townes and his research group were the first to succeed in 1953 in producing a device based on ammonia molecules that could work as an intense source of coherent photons. The initial device did not amplify visible light, but amplified microwave photons that had wavelengths of about 3 centimeters. They called the process microwave amplification by stimulated emission of radiation, hence the acronym “MASER”. Despite the significant breakthrough that this invention represented, the devices were very expensive and difficult to operate. The maser did not revolutionize technology, and some even quipped that the acronym stood for “Means of Acquiring Support for Expensive Research”. The maser did, however, launch a new field of study, called quantum electronics, that was the direct descendant of Einstein’s 1917 paper. Most importantly, the existence and development of the maser became the starting point for a device that could do the same thing for light.

The race to develop an optical maser (later to be called laser, for light amplification by stimulated emission of radiation) was intense. Many groups actively pursued this holy grail of quantum electronics. Most believed that it was possible, which made its invention merely a matter of time and effort. This race was won by Theodore H. Maiman at Hughes Research Laboratory in Malibu California in 1960 [14]. He used a ruby crystal that was excited into a population inversion by an intense flash tube (like a flash bulb) that had originally been invented for flash photography. His approach was amazingly simple −− blast the ruby with a high-intensity pulse of light and see what comes out −− which explains why he was the first. Most other groups had been pursuing much more difficult routes because they believed that laser action would be difficult to achieve.

Perhaps the most important aspect of Maiman’s discovery was that it demonstrated that laser action was actually much simpler than people anticipated, and that laser action is a fairly common phenomenon. His discovery was quickly repeated by other groups, and then additional laser media were discovered such as helium-neon gas mixtures, argon gas, carbon dioxide gas, garnet lasers and others. Within several years, over a dozen different material and gas systems were made to lase, opening up wide new areas of research and development that continues unabated to this day. It also called for new theories of optical coherence to explain how coherent laser light interacted with matter.

Coherent States : Glauber (1963)

The HBT experiment had been performed with attenuated chaotic light that had residual coherence caused by the finite linewidth of the filtered light source. The theory of intensity correlations for this type of light was developed in the 1950’s by Emil Wolf and Leonard Mandel using a semiclassical theory in which the statistical properties of the light was based on electromagnetics without a direct need for quantized photons. The HBT results were fully consistent with this semiclassical theory. However, after the invention of the laser, new “coherent” light sources became available that required a fundamentally quantum depiction.

Roy Glauber was a theoretical physicist who received his PhD working with Julian Schwinger at Harvard. He spent several years as a post-doc at Princeton’s Institute for Advanced Study starting in 1949 at the time when quantum field theory was being developed by Schwinger, Feynman and Dyson. While Feynman was off in Brazil for a year learning to play the bongo drums, Glauber filled in for his lectures at Cal Tech. He returned to Harvard in 1952 in the position of an assistant professor. He was already thinking about the quantum aspects of photons in 1956 when news of the photon correlations in the HBT experiment were published, and when the laser was invented three years later, he began developing a theory of photon correlations in laser light that he suspected would be fundamentally different than in natural chaotic light.

Roy Glauber

Because of his background in quantum field theory, and especially quantum electrodynamics, it was a fairly easy task to couch the quantum optical properties of coherent light in terms of Dirac’s creation and annihilation operators of the electromagnetic field. Related to the minimum-uncertainty wave functions derived initially by Schrödinger in the late 1920’s, Glauber developed a “coherent state” operator that was a minimum uncertainty state of the quantized electromagnetic field [15]. This coherent state represents a laser operating well above the lasing threshold and predicted that the HBT correlations would vanish. Glauber was awarded the Nobel Prize in Physics in 2005 for his work on such “Glauber” states in quantum optics.

Single-Photon Optics: Kimble and Mandel (1977)

Beyond introducing coherent states, Glauber’s new theoretical approach, and parallel work by George Sudarshan around the same time [16], provided a new formalism for exploring quantum optical properties in which fundamentally quantum processes could be explored that could not be predicted using only semiclassical theory. For instance, one could envision producing photon states in which the photon arrivals at a detector could display the kind of anti-bunching that had originally been assumed (in error) by the critics of the HBT experiment. A truly one-photon state, also known as a Fock state or a number state, would be the extreme limit in which the quantum field possessed a single quantum that could be directed at a beam splitter and would emerge either from one side or the other with complete anti-correlation. However, generating such a state in the laboratory remained a challenge.

In 1975 by Carmichel and Walls predicted that resonance fluorescence could produce quantized fields that had lower correlations than coherent states [17]. In 1977 H. J. Kimble, M. Dagenais and L. Mandel demonstrated, for the first time, photon antibunching between two photodetectors at the two ports of a beam splitter [18]. They used a beam of sodium atoms pumped by a dye laser.

This first demonstration of photon antibunching represents a major milestone in the history of quantum optics. Taylor’s first-order experiments in 1909 showed no difference between classical electromagnetic waves and a flux of photons. Similarly the second-order HBT experiment of 1956 using chaotic light could be explained equally well using classical or quantum approaches to explain the observed photon correlations. Even laser light (when the laser is operated far above threshold) produced classic “classical” wave effects with only the shot noise demonstrating the discreteness of photon arrivals. Only after the availability of “quantum” light sources, beginning with the work of Kimble and Mandel, could photon numbers be manipulated at will, launching the modern era of quantum optics. Later experiments by them and others have continually improved the control of photon states.

By David D. Nolte, Jan. 18, 2021

TimeLine:

  • 1900 – Planck (1901). “Law of energy distribution in normal spectra.” Annalen Der Physik 4(3): 553-563.
  • 1905 – A. Einstein (1905). “Generation and conversion of light with regard to a heuristic point of view.” Annalen Der Physik 17(6): 132-148.
  • 1909 – A. Einstein (1909). “On the current state of radiation problems.” Physikalische Zeitschrift 10: 185-193.
  • 1909 – G.I. Taylor: Proc. Cam. Phil. Soc. Math. Phys. Sci. 15 , 114 (1909) Single photon double-slit experiment
  • 1915 – Millikan, R. A. (1916). “A direct photoelectric determination of planck’s “h.”.” Physical Review 7(3): 0355-0388. Photoelectric effect.
  • 1916 – Einstein, A. (1916). “Strahlungs-Emission un -Absorption nach der Quantentheorie.” Verh. Deutsch. Phys. Ges. 18: 318.. Einstein predicts stimulated emission
  • 1923 –Compton, Arthur H. (May 1923). “A Quantum Theory of the Scattering of X-Rays by Light Elements”. Physical Review. 21 (5): 483–502.
  • 1926 – Lewis, G. N. (1926). “The conservation of photons.” Nature 118: 874-875.. Gilbert Lewis named “photon”
  • 1927 – D. Dirac, P. A. M. (1927). “The quantum theory of the emission and absorption of radiation.” Proceedings of the Royal Society of London Series a-Containing Papers of a Mathematical and Physical Character 114(767): 243-265.
  • 1932 – E. P. Wigner: Phys. Rev. 40, 749 (1932)
  • 1935 – A. Einstein, B. Podolsky, N. Rosen: Phys. Rev. 47 , 777 (1935). EPR paradox.
  • 1935 – N. Bohr: Phys. Rev. 48 , 696 (1935). Bohr’s response to the EPR paradox.
  • 1956 – R. Hanbury-Brown, R.W. Twiss: Nature 177 , 27 (1956) Photon bunching
  • 1963 – R. J. Glauber: Phys. Rev. 130 , 2529 (1963) Coherent states
  • 1963 – E. C. G. Sudarshan: Phys. Rev. Lett. 10, 277 (1963) Coherent states
  • 1964 – P. L. Kelley, W.H. Kleiner: Phys. Rev. 136 , 316 (1964)
  • 1966 – F. T. Arecchi, E. Gatti, A. Sona: Phys. Rev. Lett. 20 , 27 (1966); F.T. Arecchi, Phys. Lett. 16 , 32 (1966)
  • 1966 – J. S. Bell: Physics 1 , 105 (1964); Rev. Mod. Phys. 38 , 447 (1966) Bell inequalities
  • 1967 – R. F. Pfleegor, L. Mandel: Phys. Rev. 159 , 1084 (1967) Interference at single photon level
  • 1967 – M. O. Scully, W.E. Lamb: Phys. Rev. 159 , 208 (1967).  Quantum theory of laser
  • 1967 – B. R. Mollow, R. J. Glauber: Phys. Rev. 160, 1097 (1967); 162, 1256 (1967) Parametric converter
  • 1969 – M. O. Scully, W.E. Lamb: Phys. Rev. 179 , 368 (1969).  Quantum theory of laser
  • 1969 – M. Lax, W.H. Louisell: Phys. Rev. 185 , 568 (1969).  Quantum theory of laser
  • 1975 – Carmichael, H. J. and D. F. Walls (1975). Journal of Physics B-Atomic Molecular and Optical Physics 8(6): L77-L81. Photon anti-bunching predicted in resonance fluorescence
  • 1977 – H. J. Kimble, M. Dagenais and L. Mandel (1977) Photon antibunching in resonance fluorescence. Phys. Rev. Lett. 39, 691-5:  Kimble, Dagenais and Mandel demonstrate the effect of antibunching

References

• Parts of this blog are excerpted from Mind at Light Speed, D. Nolte (Free Press, 2001) that tells the story of light’s central role in telecommunications and in the future of optical and quantum computers. Further information can be found in Interference: The History of Optical Interferometry and the Scientists who Tamed Light (Oxford, 2023).

[1] Planck (1901). “Law of energy distribution in normal spectra.” Annalen Der Physik 4(3): 553-563.

[2] A. Einstein (1905). “Generation and conversion of light with regard to a heuristic point of view.” Annalen Der Physik 17(6): 132-148

[3] A. Einstein (1909). “On the current state of radiation problems.” Physikalische Zeitschrift 10: 185-193.

[4] Einstein, A. (1916). “Strahlungs-Emission un -Absorption nach der Quantentheorie.” Verh. Deutsch. Phys. Ges. 18: 318; Einstein, A. (1917). “Quantum theory of radiation.” Physikalische Zeitschrift 18: 121-128.

[5] Millikan, R. A. (1916). “A direct photoelectric determination of planck‘s “h.”.” Physical Review 7(3): 0355-0388.

[6] Compton, A. H. (1923). “A quantum theory of the scattering of x-rays by light elements.” Physical Review 21(5): 0483-0502.

[7] Lewis, G. N. (1926). “The conservation of photons.” Nature 118: 874-875.

[8] Taylor, G. I. (1910). “Interference fringes with feeble light.” Proceedings of the Cambridge Philosophical Society 15: 114-115.

[9] Dirac, P. A. M. (1927). “The quantum theory of the emission and absorption of radiation.” Proceedings of the Royal Society of London Series a-Containing Papers of a Mathematical and Physical Character 114(767): 243-265.

EinsteinPR35Download

[10] Einstein, A., B. Podolsky and N. Rosen (1935). “Can quantum-mechanical description of physical reality be considered complete?” Physical Review 47(10): 0777-0780.

BohrPR35Download

[11] Bohr, N. (1935). “Can quantum-mechanical description of physical reality be considered complete?” Physical Review 48(8): 696-702.

• Hanbury Brown 1956Download

[12] Brown, R. H. and R. Q. Twiss (1956). “Correlation Between Photons in 2 Coherent Beams of Light.” Nature 177(4497): 27-29; [1] R. H. Brown and R. Q. Twiss, “Test of a new type of stellar interferometer on Sirius,” Nature, vol. 178, no. 4541, pp. 1046-1048, (1956).

• Purcell 1956Download

[13] Purcell, E. M. (1956). “Question of Correlation Between Photons in Coherent Light Rays.” Nature 178(4548): 1448-1450.

[14] Maimen, T. H. (1960). “Stimulated optical radiation in ruby.” Nature 187: 493.

• Glauber 1963Download

[15] Glauber, R. J. (1963). “Photon Correlations.” Physical Review Letters 10(3): 84.

[16] Sudarshan, E. C. G. (1963). “Equivalence of semiclassical and quantum mechanical descriptions of statistical light beams.” Physical Review Letters 10(7): 277-&.; Mehta, C. L. and E. C. Sudarshan (1965). “Relation between quantum and semiclassical description of optical coherence.” Physical Review 138(1B): B274.

• Carmichel 1975Download

[17] Carmichael, H. J. and D. F. Walls (1975). “Quantum treatment of spontaneous emission from a strongly driven 2-level atom.” Journal of Physics B-Atomic Molecular and Optical Physics 8(6): L77-L81.

[18] Kimble, H. J., M. Dagenais and L. Mandel (1977). “Photon anti bunching in resonance fluorescence.” Physical Review Letters 39(11): 691-695.

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