Coherent States—From Single Photons to Beams of Light

Thomas P. Pearsall

Sibel Başkal, Young S Kim, Marilyn E. Noz

Richard J. Birrittella, Jihane Mimih, Christopher C. Gerry

We study multiphoton quantum-interference effects at a beam splitter and its connection to the prospect of attaining interferometric phase-shift measurements with noise levels below the standard quantum limit. Specifically, we consider the mixing of the most classical states of light coherent states with the most nonclassical states of light number states at a 50 : 50 beam splitter. Multiphoton quantum-interference effects from mixing photon-number states of small photon numbers with coherent states of arbitrary amplitudes are dramatic even at the level of a single photon. For input vacuum and coherent states, the joint photon-number distribution after the beam splitter is unimodal, a product of Poisson distributions for each of the output modes but with the input of a single photon, the original distribution is symmetrically bifurcated into a bimodal distribution. With a two-photon-number state mixed with a coherent state, a trimodal distribution is obtained, etc. The obtained distributions are shown to be structured so as to be conducive for approaching Heisenberg-limited sensitivities in photon-number parity-based interferometry. We show that mixing a coherent state with even a single photon results in a significant reduction in noise over that of the shot-noise limit. Finally, based on the results of mixing coherent light with single photons, we consider the mixing coherent light with the squeezed vacuum and the squeezed one-photon states and find the latter yields higher sensitivity in phase-shift measurements for the same squeeze parameter owing to the absence of the vacuum state.

Lukas Oberreiter, Ilja Gerhardt

Abstract One of the most fundamental quantum random number generators is implemented with light impinging onto a beam splitter, and two single photon detectors at its output. Often, this generator is described as “a photon which takes one or other path towards a detector”. The input state of light in conjunction with the detector response is relevant for the amount, the pattern, and the correlation of the generated clicks. Only a fraction of all generator outcomes, the min‐entropy, can be used as a further resource for true randomness. This paper addresses the difference in the common description with incoming single photons and the often implemented scheme with a weak coherent light source, such as an attenuated laser. For this very fundamental and widely used configuration the amount of usable entropy is compared. If single photons from an anti‐bunched light source are supplied, the amount of entropy is higher than for the case of a supplied coherent state – although the latter can be arbitrarily bright unlike the single photon source. image

Luca Salasnich

Petr Steindl, Henk Snijders, G. Westra +9 more