Abstract
Squeezed-vacuum twin beams, commonly generated through parametric down-conversion, are known to have perfect photon-number correlations. According to the Heisenberg principle, this is accompanied by a huge uncertainty in their relative phase. By overlapping bright twin beams on a beam splitter, we convert phase fluctuations into photon-number fluctuations and observe this uncertainty as a typical ‘U-shape’ of the output photon-number distribution. This effect, although reported for atomic ensembles and giving hope for phase super-resolution, has never been observed for light beams. The shape of the normalized photon-number difference distribution is similar to the one that would be observed for high-order Fock states. It can be also mimicked by classical beams with artificially mixed phase, but without any perspective for phase super-resolution. The probability distribution at the beam splitter output can be used for filtering macroscopic superpositions at the input.
Highlights
Interference of non-classical light [1] is a fascinating phenomenon, playing the central role in quantum optics and quantum information research
To observe the interference of the two beams, the state is 45◦ polarization rotated by a half-wave plate (HWP) and sent to a polarizing beam splitter (PBS)
In order to obtain higher parametric downconversion (PDC) signal we focused the pump radiation using a telescopic system, which consisted of a convex lens (F = 50 cm) and a concave lens (F = −7.5 cm) at a distance of 42.5 cm
Summary
Interference of non-classical light [1] is a fascinating phenomenon, playing the central role in quantum optics and quantum information research. The reason why the U-shape is observed in the output photon-number distribution is that for the input identical Fock states, the photon-number difference has zero uncertainty. Since the phase difference between the input fields is Heisenberg conjugate to the amplitude difference [11], it is completely uncertain This feature is transformed by the beam splitter into the uncertainty of the photon-number difference at the output [3]. In its turn, the huge photon-number uncertainty can mean, for a sufficiently pure state, reduced phase uncertainty after the beam splitter, the U-shape was considered in the literature as an indication for possible phase superresolution [3, 11, 13, 14] It has been never observed for light twin beams.
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