Quantum and Classical Two-photon Interference of Single Photons with Ultralong Coherence Time
arxiv(2024)
摘要
Two-photon interference (TPI) is a fundamental phenomenon in quantum optics
and plays a crucial role in quantum information science and technology. TPI is
commonly considered as quantum interference with an upper bound of 100% for
both the TPI visibility and the beat visibility in contrast to its classical
counterpart with a maximum visibility of 50%. However, this is not always
the case. Here we report a simultaneous observation of quantum and classical
TPI of single photons with ultralong coherence time which is longer than the
photon correlation time by five orders of magnitude. We observe a TPI
visibility of 94.3%± 0.2% but a beat visibility of 50%. Besides an
anti-bunching central dip due to single-photon statistics, we observe two
bunching side peaks in cross-correlation curves for indistinguishable photons.
Using either classical wave superposition theory or quantum field approach, we
derive the same expressions for the cross-correlation functions which reproduce
and explain the experiments well. We conclude that quantum TPI with a stream of
single photons is equivalent to classical TPI, both of which are the
fourth-order interference arising from the second-order interference occurring
on the time scale of photon coherence time.
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