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arXiv:1902.02566 · Journal of Physics B Atomic Molecular and Optical Physics

Generating strong anti-bunching by interfering nonclassical and classical states of light

Rajiv Boddeda, Quentin C. Glorieux, Alberto Bramati, Simon Pigeon

Published Aug 30, 2019• 9 citations
arXivHTMLPDF

Abstract

Abstract In quantum optics, the second-order correlation function g (2)(τ) characterizes the photon statistics of a state of light and can be used to distinguish between its classical or quantum nature. In this article, we study a simple setup which offers the possibility to generate quantum states of light with very small g (2)(0), a signature of strong anti-bunched light. This can be achieved by mixing on a beamsplitter a coherent state with a nonclassical state, such as a squeezed state, and even with a bunched state (g (2)(0) > 1) such as a Schrödinger cat state. We elucidate the interference mechanism generating such strong anti-bunching and relate it to the unconventional photon blockade. We also detail how this effect can be applied to detect weakly squeezed states of light.

DOI
10.1088/1361-6455/ab3e98

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Abstract In quantum optics, the second-order correlation function g (2)(τ) characterizes the photon statistics of a state of light and can be used to distinguish between its classical or quantum nature. In this article, we study a simple setup which offers the possibility to generate quantum states of light with very small g (2)(0), a signature of strong anti-bunched light. This can be achieved by mixing on a beamsplitter a coherent state with a nonclassical state, such as a squeezed state, and even with a bunched state (g (2)(0) > 1) such as a Schrödinger cat state. We elucidate the interference mechanism generating such strong anti-bunching and relate it to the unconventional photon blockade. We also detail how this effect can be applied to detect weakly squeezed states of light.
The antibunching effect generated in a cavity containing first a single two-level atomic system and then two identical atoms is explored for off-resonant interactions, in strong- and weak-coupling regimes. The cavity is driven by coherent and squeezed sources. Using the second-order correlation function analytically derived in the weak-excitation regime, we show that squeezed light achieves and improves strong antibunching, leading to a photon blockade. This enhancement is due to a destructive quantum interference mechanism induced by the nonclassical light, creating a supplementary transition pathway. The best effect is obtained for equal frequency detunings in the strong-coupling regime. More interestingly, our investigation reveals that the two-atom-cavity system can further improve the antibunching effect compared to the single-atom cavity. It turns out that the additional couplings appearing in the cavity due to the implementation of the two atoms, combined with the squeezed light, could substantially enhance the photon-blockade effect.
Spatial anti-bunching, in contrast to the well-known bunching behavior observed in classical light sources, describes a situation where photons tend to avoid each other in space, resulting in a reduced probability of detecting two or more photons in proximity. This anti-bunching effect, a hallmark of nonclassical light, signifies a deviation from classical intensity fluctuations and has been observed not only in free electrons and entangled photon pairs but also in chaotic-thermal light. This work investigates the generation mechanism of spatial anti-bunching correlation in random light fields, leveraging the wandering of light centers to induce a second-order coherence degree below unity. Unlike traditional Gaussian Schell-model partially coherent light, this work predicts the emergence of two fundamentally distinct orbital angular momentum states, arising from the inherent differences between rigid body rotation and fluid-like rotation in the wandering light. These predictions are supported by experimental evidence. Based on these findings, we propose a resolution-enhanced lensless ghost imaging system as an application example. Experimental results indicate that the adoption of the anti-bunching correlated light field as the illumination source enables the imaging system to attain super-resolution imaging capabilities. Our findings provide new insights into the utilization of anti-correlated light fields for precision imaging and detection applications.
Similar to interferences in classical optics that can combine two waves to produce no output or more output than input, multiphoton interferences can produce, for instance, anti-bunched light by admixing squeezed (bunched) and laser (uncorrelated) light. The general case of quantum-field interferences, that can be self- or externally realized in coherently driven quantum sources, leads to a classification of conventional and unconventional photon statistics, as discussed by Elena del Valle and co-workers in article number 1900279.
Photon antibunching is a quantum phenomenon typically observed in strongly nonlinear systems where photon blockade suppresses the probability of detecting two photons at the same time. Antibunching has also been reported with Gaussian states, where optimized amplitude squeezing yields classically forbidden values of the intensity correlation, g(2)(0)<1{g}^{(2)}(0)<1g(2)(0)<1. As a consequence, observation of antibunching is not necessarily a signature of photon-photon interactions. To clarify the significance of the intensity correlations, we derive a sufficient condition for deducing whether a field is non-Gaussian based on a g(2)(0){g}^{(2)}(0)g(2)(0) measurement. We then show that the Gaussian antibunching obtained with a degenerate parametric amplifier is close to the ideal case reached using dissipative squeezing protocols. We finally shed light on the so-called unconventional photon blockade effect predicted in a driven two-cavity setup with surprisingly weak Kerr nonlinearities, stressing that it is a particular realization of optimized Gaussian amplitude squeezing.
Photon anti-bunching is the direct evidence for the existence of photons without having a classical counterpart. Unlike bunching of photons, which can have a semi-classical description, the effect of photon anti-bunching can only be understood with quantized electromagnetic fields. However, for the process of high harmonic generation (HHG), where many photons of the driving field are upconverted to a single photon of higher energy, there is yet no clear evidence for the presence of individual photon emission. The key result of this work is the prediction of photon anti-bunching in the process of HHG, marking it the first theoretical discovery of non-classicality in the temporal correlations of HHG photons. While other non-classical signatures in HHG, such as sub-Poissonian statistics or squeezing, have been discussed for an ensemble of photons, the anti-bunching signature reported here is a signature of a single photon. This is achieved by using the recently developed Heisenberg picture approach for quantum optical HHG, revealing clear anti-bunching signatures in the intensity correlation function across the entire harmonic spectrum.
Abstract The photon statistics emitted by a large variety of light‐matter systems under weak coherent driving can be understood, to lowest order in the driving, in the framework of an admixture of (or interference between) a squeezed state and a coherent state, with the resulting state accounting for all bunching and antibunching features. One can further identify two mechanisms that produce resonances for the photon correlations: i) conventional photon blockade describes cases that involve a particular quantum level or set of levels in the excitation/emission processes with interferences occurring to all orders in the photon numbers, while ii) unconventional photon blockade describes cases where the driving laser is far from resonance with any level and the interference occurs for a particular number of photons only, yielding stronger correlations but only for a definite number of photons. Such an understanding and classification allows for a comprehensive and transparent description of the photon statistics from a wide range of disparate systems, where optimum conditions for various types of photon correlations can be found and realized.