The Hanbury Brown-Twiss (HBT) effect marked a significant milestone in quantum optics by illustrating that intensity correlations can reveal inherently quantum features of light. Motivated by the structure of the original 8-mode HBT interferometer, we develop a simplified 4-mode toy-model that captures its essential physical ingredients while significantly reducing analytical complexity. Our toy-model provides an intuitive and well-structured framework for examining the desired correlation functions. We investigate whether our toy-model can exhibit genuinely non-classical behaviour by formulating and applying a Bell-type inequality tailored to its specific measurement configuration. Our analysis shows that the correlations generated by the toy-model violate the inequality, indicating the presence of non-local features that are incompatible with any classical hidden-variable description. The results highlight the power of simplified models in uncovering fundamental aspects of non-classicality in optical systems.
The Hanbury Brown-Twiss (HBT) effect marked a significant milestone in quantum optics by illustrating that intensity correlations can reveal inherently quantum features of light. Motivated by the structure of the original 8-mode HBT interferometer, we develop a simplified 4-mode toy-model that captures its essential physical ingredients while significantly reducing analytical complexity. Our toy-model provides an intuitive and well-structured framework for examining the desired correlation functions. We investigate whether our toy-model can exhibit genuinely non-classical behaviour by formulating and applying a Bell-type inequality tailored to its specific measurement configuration. Our analysis shows that the correlations generated by the toy-model violate the inequality, indicating the presence of non-local features that are incompatible with any classical hidden-variable description. The results highlight the power of simplified models in uncovering fundamental aspects of non-classicality in optical systems.
The Hanbury Brown–Twiss (HBT) effect, at the quantum level, is essentially an interference of one particle with another, as opposed to interference of a particle with itself. Conventional treatments of identical particles encounter difficulties while dealing with entanglement. A recently introduced label-free approach to indistinguishable particles is described, and is used to analyze the HBT effect. Quantum wave-packets have been used to provide a better understanding of the quantum interpretation of the HBT effect. The effect is demonstrated for two independent particles governed by Bose–Einstein or Fermi–Dirac statistics. The HBT effect is also analyzed for pairs of entangled particles. Surprisingly, entanglement has almost no effect on the interference seen in the HBT effect. In the light of the results, an old quantum optics experiment is reanalyzed, and it is argued that the interference seen in that experiment is not a consequence of non-local correlations between the photons, as is commonly believed. Quanta 2017; 6: 61–69.
Quantum opticians usually employ and exploit genuine or modified HBT setups as standard tools for characterizing non-classical states of light. One the one hand, HBT measurements permit to characterize the emission statistics of photonic modes that are, depending on the emitter and on the spatial and spectral features, thermal, poissonnian, sub-poissonnian, or deterministic. On the other hand, auto-correlation and cross-correlation functions, recorded in the single photon counting regime, permit to infer the unique properties of single photon and two photons sources, that are further utilized in quantum communication applications. For instance, when applied to a single photon source, a genuine HBT setup helps qualifying the uniqueness emission feature. Moreover, when applied to a two photon source, a modified HBT setup permits measuring simultaneous emission time correlations, as well as single photon coherence time. During this talk, I will review some situations in which HBT type setups and related measurements are exploited in and for quantum optics or communication experiments.
Violations of Bell inequalities are commonly interpreted as evidence for either nonlocal dynamics or the failure of classical realism. In this work, we show that Bell-type correlations can arise without invoking superluminal influences, retrocausality, or local hidden variables, provided that the mapping between underlying configurations and observable outcomes is non-injective. We study a class of effective models in which multiple underlying states correspond to the same observable description. Such non-injective projections generically induce non-factorizable joint probability structures at the level of observables, even when the underlying description itself is fully local and deterministic. As a result, the statistical assumptions required to derive Bell inequalities are violated at the effective level, while locality is preserved at the underlying level. Within this framework, quantum correlations emerge as structural features of projected descriptions rather than as signatures of nonlocal causation. We clarify the precise assumption of Bell’s theorem that fails in this setting and show how classical behavior is recovered in regimes where the effective projection becomes approximately injective, suppressing nonlocal correlations through decoherence and environmental coarse-graining. Our results suggest that Bell inequality violations need not reflect a fundamental nonlocality of nature, but may instead indicate intrinsic information loss induced by non-injective mappings between underlying configurations and observable descriptions.
In spite of the predilections of the authors, the work of Hanbury Brown and Twiss on intensity interferometry may have had a more powerful impact on quantum optics than on astronomy. That it could have such an impact on quantum optics is even more surprising when one considers that the their results are more easily explained in the context of classical optics than quantum optics. Nevertheless for more than 50 years, quantum optics has been inspired by intensity interferometry and continues to add new variations and insights. I will discuss experiments using cold atoms, both bosons and fermions, and from sources both coherent and incoherent. The observations yield useful information concerning what happens in atomic systems both when they interact with each other and when they interact with light.
The Hanbury Brown-Twiss effect is one of the celebrated phenomenologies of modern physics that accommodates equally well classical (interferences of waves) and quantum (correlations between indistinguishable particles) interpretations. The effect was discovered in the late thirties with a basic observation of Hanbury Brown that radio-pulses from two distinct antennas generate signals on the oscilloscope that wiggle similarly to the naked eye. When Hanbury Brown and his mathematician colleague Twiss took the obvious step to propose bringing the effect in the optical range, they met with considerable opposition as single-photon interferences were deemed impossible. The Hanbury Brown-Twiss effect is nowadays universally accepted and, being so fundamental, embodies many subtleties of our understanding of the wave/particle dual nature of light. Thanks to a novel experimental technique, we report here a generalized version of the Hanbury Brown-Twiss effect to include the frequency of the detected light, or, from the particle point of view, the energy of the detected photons. Our source of light is a polariton condensate, that allows high-resolution filtering of a spectrally broad source with a high degree of coherence. In addition to the known tendencies of indistinguishable photons to arrive together on the detector, we find that photons of different colors present the opposite characteristic of avoiding each others. We postulate that fermions can be similarly brought to exhibit positive (boson-like) correlations by frequency filtering.
The Hanbury Brown-Twiss effect is one of the celebrated phenomenologies of modern physics that accommodates equally well classical (interferences of waves) and quantum (correlations between indistinguishable particles) interpretations.The effect was discovered in the late thirties with a basic observation of Hanbury Brown that radio-pulses from two distinct antennas generate signals on the oscilloscope that wiggle similarly to the naked eye.When Hanbury Brown and his mathematician colleague Twiss took the obvious step to propose bringing the effect in the optical range, they met with considerable opposition as single-photon interferences were deemed impossible.The Hanbury Brown-Twiss effect is nowadays universally accepted and, being so fundamental, embodies many subtleties of our understanding of the wave/particle dual nature of light.Thanks to a novel experimental technique, we report here a generalized version of the Hanbury Brown-Twiss effect to include the frequency of the detected light, or, from the particle point of view, the energy of the detected photons.Our source of light is a polariton condensate, that allows high-resolution filtering of a spectrally broad source with a high degree of coherence.In addition to the known tendencies of indistinguishable photons to arrive together on the detector, we find that photons of different colors present the opposite characteristic of avoiding each others.We postulate that fermions can be similarly brought to exhibit positive (bosonlike) correlations by frequency filtering.