The use of a Kerr nonlinearity to generate squeezed light is a well-known way to surpass the quantum noise limit along a given field quadrature. Nevertheless, in the most common regime of weak nonlinearity, a single Kerr resonator is unable to provide the proper interrelation between the field amplitude and squeezing required to induce a sizable deviation from Poissonian statistics. We demonstrate experimentally that weakly coupled bosonic modes allow exploration of the interplay between squeezing and displacement, which can give rise to strong deviations from the Poissonian statistics. In particular, we report on the periodic bunching in a Josephson junction formed by two coupled exciton-polariton modes. Quantum modeling traces the bunching back to the presence of quadrature squeezing. Our results, linking the light statistics to squeezing, are a precursor to the study of nonclassical features in semiconductor microcavities and other weakly nonlinear bosonic systems.

Polariton condensates have proved to be model systems to investigate topological defects, as they allow for direct and nondestructive imaging of the condensate complex order parameter. The fundamental topological excitations of such systems are quantized vortices. In specific configurations, further ordering can bring the formation of vortex lattices. In this work we demonstrate the spontaneous formation of ordered vortical states, consisting in geometrically self-arranged vortex-antivortex pairs. A mean-field generalized Gross-Pitaevskii model reproduces and supports the physics of the observed phenomenology. Quantized vortices are fundamental and ubiquitous entities across physics, playing a central role in mechanisms ranging from galaxy formation to phase conformation in microscopic quantum systems. They represent topological excitations of quantum degenerate Bose gases, such as Bose-Einstein condensates (BEC), superfluids, and superconductors.1 Throughout the past decades, these systems have offered the unprecedented opportunity of studying such topological defects and their phenomenology in a direct and controlled way. Under peculiar conditions, quantized vortices have the unique property of arranging themselves in geometrically ordered structures, such as the Abrikosov lattices.2,3 Vortex lattices were first observed in type-II superconductors under magnetic fields, 4 then in both superfluids 5 and atom BEC, [6][7][8][9] by setting the system into rotation, and also in optical nonlinear systems. 10-12 Ultimately, in the limit of high vortex density, these lattices are predicted to undergo a quantum phase transition to strongly correlated states, similar to quantum Hall states, that still represent an open experimental challenge. 1 Recently, exciton polaritons have established themselves as a model two-dimensional Bose gas.13 Such quasiparticles arise as the eigenmodes of the strong-coupling regime between light and matter, which was demonstrated in planar semiconductor microcavities.14 The polariton system being dissipative in nature, due to the finite lifetime of the quasiparticles, has phenomenology intrinsically and strongly out of equilibrium. Thus, continuous optical pumping is required to replenish the polariton population. Shaping of the excitation conditions allows manipulation of the condensate phenomenology in a simple way, unveiling striking physical effects. Moreover, thanks to the mixed light-matter components of polaritons, the emitted photons inherit all the properties of the quantum fluid that can, thus, be fully characterized by optical measurement of the extracavity field. 15After the recent demonstration of polariton condensation 16 and superfluidity 17 in semiconductor microcavities, much effort has been devoted to the study of quantum turbulence and vorticity, under different excitation conditions, in such outof-equilibrium quantum fluids. [18][19][20] In particular, quantized vortices were demonstrated to spontaneously occur in the system as topological defects pinned by the disorder ...

Planar nanostructures allow near-ideal extraction of emission from a quantum emitter embedded within, thereby realizing deterministic single-photon sources. Such a source can be transformed into M single-photon sources by implementing active temporal-to-spatial mode demultiplexing. We report on the realization of such a demultiplexed source based on a quantum dot embedded in a nanophotonic waveguide. Efficient outcoupling (> 60%) from the waveguide into a single mode optical fiber is obtained with high-efficiency grating couplers. As a proof-of-concept, active demultiplexing into M = 4 spatial channels is demonstrated by the use of electro-optic modulators with an end-to-end efficiency of > 81% into single-mode fibers. Overall we demonstrate four-photon coincidence rates of > 1 Hz even under nonresonant excitation of the quantum dot. The main limitation of the current source is the residual population of other exciton transitions that corresponds to a finite preparation efficiency of the desired transition. We quantitatively extract a preparation efficiency of 15% using the second-order correlation function measurements. The experiment highlights the applicability of planar nanostructures as efficient multiphoton sources through temporal-to-spatial demultiplexing and lays out a clear path way of how to scale up towards demonstrating quantum advantages with the quantum dot sources.The recent advances in experimental quantum-information processing 1-5 and cryptography 6-8 highlight the necessity for efficient single-photon sources. Photons are robust carriers of quantum information and enable scalable quantum simulations. 9-11 These applications require efficient deterministic sources of multiple indistinguishable single photons. [12][13][14] The traditional approach to multiphoton generation is based on probabilistic parametric downconversion or four wave mixing sources. [15][16][17] The scaling up of the number of generated photons using such sources is limited by the low generation efficiency and the large amount of resources (detectors and optical switches) needed for heralding the photons. Over the last decade, fundamental and technological progress in the growth and control of semiconductor quantum dots has resulted in their applicability as near-ideal single-photon emitters. [18][19][20] Crucially, enhancing light-matter interaction through the fabrication of on-chip nanophotonic structures containing quantum dots has resulted in efficient deterministic and coherent single-photon sources. 21-25 However, the inhomogeneous broadening of the quantum dots poses a challenge in creating multiple identical sources.An alternative route towards high-brightness multi-photon generation is by implementing active temporal-to-spatial mode demultiplexing of the emitted single-photon train from a single quantum dot. 26,27 Recent experiments achieved high degree of indistinguishability (> 90%) over long timescales, 28 which enabled the temporal demultiplexing of a quantum dot in a micropillar cavity. 26 Planar nanostructures...

International audienceWe demonstrate that the singular binding mechanism characterizing isoelectronic centers formed from two isoelectronic traps can also bind, in addition to the well-studied excitons, various number of charges. Using the emission fine structure of Te dyads in ZnSe and N dyads in GaAs, we establish that these pseudodonors and pseudoacceptors can bind positively and negatively charged excitons, respectively, and that both can bind biexcitons. This ability to bind various charge configurations, in addition to their very low inhomogeneous broadenings and perfectly defined symmetries, further establishes isoelectronic centers as an interesting alternative to epitaxial quantum dots for a number of applications