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arXiv:quant-ph/9903048 · Physical Review A

Quantum interference by two temporally distinguishable pulses

Yoon-Ho Kim, Maria V. Chekhova, S. P. Kulik, Yanhua H. Shih

Published Jul 1, 1999• 20 citations
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Abstract

We report a two-photon interference effect, in which the entangled photon pairs are generated from two laser pulses well separated in time. In a single pump pulse case, interference effects did not occur in our experimental scheme. However, by introducing a second pump pulse delayed in time, quantum interference was then observed. The visibility of the interference fringes shows a dependence on the delay time between two laser pulses. The results are explained in terms of indistinguishability of biphoton amplitudes that originates from two temporally separated laser pulses.

DOI
10.1103/physreva.60.r37

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We report a two-photon interference effect, in which the entangled photon pairs are generated from two laser pulses well separated in time. In a single pump pulse case, interference effects did not occur in our experimental scheme. However, by introducing a second pump pulse delayed in time, quantum interference was then observed. The visibility of the interference fringes shows a dependence on the delay time between two laser pulses. The results are explained in terms of indistinguishability of biphoton amplitudes that originates from two temporally separated laser pulses.
We report a two-photon interference effect, in which the entangled photon pairs are generated from two laser pulses well-separated in time. In a single pump pulse case, interference effects did not occur in our experimental scheme. However, by introducing a second pump pulse delayed in time, quantum interference was then observed. The visibility of the interference fringes shows a dependence on the delay time between two laser pulses. The results are explained in terms of indistinguishability of biphoton amplitudes which originates from two temporally separated laser pulses.
We report a two-photon interference effect, in which the entangled photon pairs are generated from two laser pulses well-separated in time. In a single pump pulse case, interference effects did not occur in our experimental scheme. However, by introducing a second pump pulse delayed in time, quantum interference was then observed. The visibility of the interference fringes shows a dependence on the delay time between two laser pulses. The results are explained in terms of indistinguishability of biphoton amplitudes which originates from two temporally separated laser pulses.
We have experimentally demonstrated two-photon interference between biphoton amplitudes arising from two well-separated pump pulses. It is important to note the following. 1) The pump pulse intensity was low enough so that single counting rates of the detectors were kept much smaller than pulse repetition rates: the probability of having one spontaneous parametric down conversion (SPDC) photon pair per pulse in our experiment is negligible. Hence the interference cannot be explained as two SPDC photons from two pump pulses (one SPDC photon pair from each pulse) interfering at the detectors. The two pump pulses simply provide two biphoton amplitudes which could result in coincidence counts, and interference occurs between these two biphoton amplitudes only when they are indistinguishable. 2) The BBO crystal in our experiment was only 100 /spl mu/m thick, so the two-pulse did not exist in BBO at the same time at any moment. 3) Due to the delays in the interferometer (/spl tau/ /spl tau//sub 1/), the signal-idler never met at the beamsplitter. Therefore, the existence of two-photon interference cannot be viewed as the interference between the signal and idler photons. These three points again emphasize the fact that it is the indistinguishability of the two-photon Feynman alternatives for the biphoton amplitudes which is responsible for the two-photon quantum interference effects.
A ${\ensuremath{\chi}}^{(2)}$ nonlinear optical crystal is pumped by two temporally well-distinguishable femtosecond laser pulses to generate entangled photon pairs in the process of spontaneous parametric down-conversion. We have observed first- and second-order interference between amplitudes generated from the first and the second pump pulse as a function of the time delay between the two pump pulses. The criteria for first- and second-order interference are found to be very different, which reflect the quantum entanglement nature of the state of spontaneous parametric down-conversion.
We present experimental demonstrations of two-photon interference involving temporally separated photons within two types of interferometers: a Mach-Zehnder interferometer and a polarization-based Michelson interferometer. The two-photon states are probabilistically prepared in a symmetrically superposed state within the two interferometer arms by introducing a large time delay between two input photons; this state is composed of two temporally separated photons, which are in two different or the same spatial modes. We then observe two-photon interference fringes involving both the Hong-Ou-Mandel interference effect and the interference of path-entangled two-photon states simultaneously in a single interferometric setup. The observed two-photon interference fringes provide simultaneous observation of the interferometric properties of the single-photon and two-photon wavepackets. The observations can also facilitate a more comprehensive understanding of the origins of the interference phenomena arising from spatially bunched/anti-bunched two-photon states comprised of two temporally separated photons within the interferometer arms.
We report an interference experiment in which the two-photon entangled state interference cannot be pictured in terms of the overlap and bunching of two individual photons on a beamsplitter. We also demonstrate that two-photon interference, or photon bunching effect on a beamsplitter, does not occur if the two-photon Feynman amplitudes are distinguishable, even though individual photons do overlap on a beamsplitter. Therefore, two-photon interference cannot be viewed as interference of two individual photons, rather it should be viewed as two-photon or biphoton interfering with itself. The results may also be useful for studying decoherence management in entangled two-qubit systems as we observe near complete restoration of quantum interference after the qubit pairs, generated by a femtosecond laser pulse, went through certain birefringent elements.