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Direct observation of photon pairs at a single output port of a beam-splitter interferometer



Matthew Shaw, Giovanni Di Giuseppe, A. Sergeinko, Bahaa E. A. Saleh, Malvin C. Teich, Aaron J. Miller, Sae Woo Nam


The seminal experiment carried out by Hong, Ou, and Mandel some fifteen years ago is one of the most important in the annals of quantum optics. This experiment demonstrated that two indistinguishable photons incident on a simple beam splitter interfere in such a way as to always emerge from the device as a pair. The photons stuck together, so to speak, exiting randomly from one port or the other. They could only observe this phenomenon indirectly, however, since traditional single-photon-counting detectors cannot register more than one photon within the dead-time period of the device. Hong, Ou, and Mandel circumvented this technical limitation by designing an experiment in which they measured the complement of what they sought to observe. They used two single-photon-counting detectors, placing one at each output port of the beam splitter, and then searched for cross-coincidences between the two detectors. Finding none, they inferred that the two photons do not exit from different ports of the beam splitter. Based on this "test of exclusion," and energy conservation, they deduced that both photons must exit via the same port of the device. There have been many variations on this original theme of Hong--Ou--Mandel, but all rely on the same "test of exclusion." We have carried out a polarization version of the Hong--Ou--Mandel experiment and report the first direct observation of photon coincidences at a single output port of the interferometer. What makes this possible is a unique energy detector, called a transition-edge detector, that has the capability of registering the number of photons impinging on it. Our experimental results provide the first full confirmation of the quantum theory of photon interference at a beam splitter.
Physical Review A


Hong-Ou-Mandel, quantum interference, single photon


Shaw, M. , Di Giuseppe, G. , Sergeinko, A. , Saleh, B. , Teich, M. , Miller, A. and Nam, S. (2003), Direct observation of photon pairs at a single output port of a beam-splitter interferometer, Physical Review A, [online], (Accessed July 22, 2024)


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Created December 15, 2003, Updated October 12, 2021