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SUMMARY: To show the double slit experiment with single photons and to demonstrate wave-particle duality at the microscopic level of individual photons.






Single photon set up


SETUP NOTES: Call at least 24 hours ahead. The low light imaging system consists of a Hamamatsu C2400 ICCD camera pictured below.  It is used without a lens and is connected to a power supply and an ARGUS image processor.

A light tight box originally designed to develop film is modified to hold a tiny light source. A small tungsten filament is the light source.  The tungsten filament acts as a warm blackbody that spontaneously emits photons. The intensity of the light source is adjustable with a potentiometer knob that controls the DC current from a pair of D cell batteries. The spontaneously emitted photons pass through a small pinhole which acts as a spatial filter. After passing through the pinhole the photons are filtered with a 400 nm monochromatic filter. This filter attenuates and filters the photons. Only photons and groups of photons with a particular energy level can pass.

 The mean distance between photons can be adjusted by changing the intensity. It is typically adjusted so that there is 2 km between each photon. Each photon that has passed through the pinhole and the filter then go through one of the double slits.  The slit widths are 0.06mm and the slit separation is 0.25mm. After passing through one or the other of the double slits each photon then enters the aperture of a PMT detector for amplification and detection.  The PMT detector the output is sent to a photon counting camera.

 The PMT is a device that has two successive stages of micro-channel plates followed by a high gain CCD. The camera has a 768 by 420 pixel array. It is read out at video rates of 60 fps. At maximum sensitivity in the 400 nm bandwidth, the PMT Quantum Efficiency is about 0.3.  At  680 nm the QE is 0.001. After each photon passes through the double slits and strikes PMT the photon is absorbed and then emits photoelectrons via the photoelectric effect. The PMT then amplifies the photoelectrons by a factor of more than a million. The amplified signal from the photoelectron will then produce a flash of light. The flash of light is acquired by a video camera and sent to a custom photon counting computer. The photon counting computer can be set to average many photon events and display the integrated data on a video screen.


The demonstration of single photon interference was done by G. Reynolds in 1938. 

A 1909 paper entitled ``Interference Fringes with Feeble Light,'' by G. I. Taylor shows that a 2000 hour exposure of highly attenuated X-rays (Rontgen rays) produced a diffraction pattern. This paper is reprinted in ``The Pleasures of Counting'' by T. Koerner.

The Feynman Lectures on Physics. Vol. 3, R. P. Feynman, R. B. Leighton, & M. Sands, Addison-Wesley, 1965

The Feynman Messenger Lecture series Video #6, The Quantum Mechanical View of Nature discusses this experiment. 

This web page is comprised of some excerpts taken from Robert Austin and Lyman Page at Princeton University 

Am. J. Phys. Vol. 64, No. 2, Feb 1996, Pages 184-188 A lecture demonstration of single photon interference Wolfgang Rueckner and Paul Titcomb

Roy H. Biser, Undergraduate Research Project, Photon Diffraction, AJP 31, 29-31, (1963).

Sherwood Parker, A Single-Photon Double-Slit Interference Experiment, AJP 39, 420-424, (1971).

Sherwood Parker, Single-Photon Double-Slit Interence - A Demonstration, AJP 40, 310-314, (1972).

Greenberger, et al, Multiparticle Interferometry and The Superposition Principle, Physics Today, (Aug 1993).

Wolfgang Rueckner and Paul Titcomb, A lecture demonstration of single photon interference, AJP 64, 184-188 (1996).

P. Koczyk, P. Wiewior, and C. Radziwicz, Photon counting statistics - Undergraduat experiment, AJP 64, 240-245 (1996).

Jose L. Cereceda, An apparent paradox at the heart of quantum mechanics, AJP 64, 459-466 (1996).Lecture Demonstrations Formulas for Calculations and Graphs.Lecture Demonstrations Circuit Diagram: Laser Diode Driver ( handwritten).

Data Sheet, Laser Diode NDL3200, NEC.Hamamatsu, Photomultiplier Tube Final Test Sheet.

John H. Marburger, III, What is a Photon?, TPT 34, 482-486 (1996).

Kurt Gottfried, Two-particle interference, AJP 68, 143-147 (2000).

Stephan Dürr and Gerhard Rempe, Can wave-particle duality be based on the uncertainty relation?, AJP 68, 1021-1024 (2000).

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