The Hong-Ou-Mandel effect is considered a signature of the quantumness of light, as the dip in coincidence probability using semiclassical theories has an upper bound of 50%. Here we show, theoretically and experimentally, that, with proper phase control of the signals, classical pulses can mimic a Hong-Ou-Mandel-like dip. We demonstrate a dip of (99.635 ± 0.002)% with classical microwave fields. Quantumness manifests in wave-particle complementarity of the two-photon state. We construct quantum and classical interferometers for the complementarity test and show that while the two-photon state shows wave-particle complementarity the classical pulses do not. * usinha@rri.res.in arXiv:1810.01297v3 [quant-ph]

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We show unambiguous violations of the different macrorealist inequalities, like the Leggett-Garg inequality (LGI) and its variant called the Wigner form of Leggett-Garg inequality (WLGI) using a heralded, single-photon based experimental setup comprising one Mach-Zehnder interferometer followed by a displaced Sagnac interferometer. In our experiment, the negative result measurements are implemented in order to validate the presumption of non-invasive measurability used in defining the notion of macrorealism. Among all the experiments to date testing macrorealism, the present experiment stands out in comprehensively addressing the relevant loopholes. The clumsiness loophole is addressed through the precision testing of any classical invasiveness involved in the implementation of negative result measurements. This is done by suitably choosing the experimental parameters so that the quantum mechanically predicted validity of all the relevant two-time no-signalling in time (NSIT) conditions is maintained in all the three pairwise experiments performed to show the violation of LGI/WLGI. Further, importantly, the detection efficiency loophole is addressed in our experimental scheme by adopting suitable modifications in the measurement strategy enabling the demonstration of the violation of LGI/WLGI for any non-zero detection efficiency. We also show how other relevant loopholes like the multiphoton emission loophole, coincidence loophole, and the preparation state loophole are all closed in the present experiment. We report the LGI violation of 1.32 ± 0.04 and the WLGI violation of 0.10 ± 0.02 in our setup, where the magnitudes of violation are respectively eight times and five times the corresponding error values, while agreeing perfectly with the ranges of the quantum mechanically predicted values of the LGI, WLGI expressions that we estimate by taking into account the non-idealities of the actual experiment. At the same time, the experimentally observed probabilities satisfy all the two-time NSIT conditions up to the order of 10 −2 , which ensures non-invasiveness in the implemented negative result measurements.

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