Abstract
Interference lies at the heart of the behavior of classical and quantum light. It is thus crucial to understand the boundaries between which interference patterns can be explained by a classical electromagnetic description of light and which, on the other hand, can only be understood with a proper quantum mechanical approach. While the case of two-mode interference has received a lot of attention, the multimode case has not yet been fully explored. Here we study a general scenario of intensity interferometry: we derive a bound on the average correlations between pairs of output intensities for the classical wavelike model of light, and we show how it can be violated in a quantum framework. As a consequence, this violation acts as a nonclassicality witness, able to detect the presence of sources with sub-Poissonian photon-number statistics. We also develop a criterion that can certify the impossibility of dividing a given interferometer into two independent subblocks.
Highlights
Interference lies at the heart of the behavior of classical and quantum light
Ou, and Mandel (HOM) discovered that if two independent and indistinguishable photons, in pure quantum states, impinge on the two input ports of a balanced beam splitter, they always bunch together and exit the apparatus from the same output port [1]. This simple effect has many consequences, e.g., in distinguishability testing [2], linear-optical quantum computing [3], entanglement detection [4] or swapping [5], and metrology [6,7,8,9]. The nonclassicality of this phenomenon can be well understood by repeating the experiment many times, and by recording the intensities I1, I2 at the two output ports: labeling the average over many runs by h·i, the correlation function, G12
G12 has a well-defined classical limit, which makes it a suitable candidate to use in distinguishing quantum light beams from classical ones
Summary
Ou, and Mandel (HOM) discovered that if two independent and indistinguishable photons, in pure quantum states, impinge on the two input ports of a balanced beam splitter, they always bunch together and exit the apparatus from the same output port [1] This simple effect has many consequences, e.g., in distinguishability testing [2], linear-optical quantum computing [3], entanglement detection [4] or swapping [5], and metrology [6,7,8,9]. We can either consider completely distinguishable photons, i.e., single excitations occupying orthogonal space-time modes, or pulses of classical light, described by electromagnetic fields In both cases, if they are emitted by statistically independent sources and injected into the beam splitter, G12 is constrained to be greater than or equal to 1=2 [10,11].
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