We report the experimental observation and control of space and time-resolved light-matter Rabi oscillations in a microcavity. Our setup precision and the system coherence are so high that coherent control can be implemented with amplification or switching off of the oscillations and even erasing of the polariton density by optical pulses. The data are reproduced by a quantum optical model with excellent accuracy, providing new insights on the key components that rule the polariton dynamics. DOI: 10.1103/PhysRevLett.113.226401 PACS numbers: 71.36.+c, 78.47.JRabi oscillations [1] are the embodiment of quantum interactions: when a mode a is excited and is coupled to a second mode b, the excitation is transferred from a to b and when the symmetric situation is established, the excitation comes back in a cyclical unitary flow. When this occurs at the single particle level between two-level systems, it provides the ground for qubits [2], which, if they can be further manipulated, opens the possibility to perform quantum information processing [3]. Such an oscillation is of probability amplitudes and therefore is a strongly quantum mechanical phenomenon, that involves maximally entangled statesThe same physics also holds, not at the quantum level, but with coherent states of the fields, a situation known in the literature as implementing an "optical atom" [4] or a "classical two-level system" [5]. The oscillation is then more properly qualified as "normal mode coupling" [6,7] as it is now between the fields themselves,rather than their probability amplitudes. The denomination of Rabi oscillations remains, however, popular also in this case [8,9]. While of limited value for hardcore implementation of quantum information processing, it is desirable for fundamental purposes and semiclassical applications to have access to such classical qubits, or "cebits" [10]. In particular, they can help to explore the origin and mechanism of nonlocality and parallelization in genuinely quantum systems . While Rabi oscillations are at the heart of polariton physics, they are so fast in a typical microcavity-in the subpicosecond time range-that they are typically glossed over and the macroscopic physics of polaritons investigated in their coarse graining. Pioneering attempts to observe them showed the inherent difficulty and reported hardly two oscillations with 3 orders of magnitude loss of contrast each time [29], attributed to the inhomogeneous broadening of excitons by the theory [30], which could provide a qualitative agreement only. Later reports through pump-probe techniques [31][32][33], in particular, in conjunction with an applied magnetic field [34], increased their visibility but remained tightly constrained to their bare observation. Since polaritons are increasingly addressed at the single particle level [35,36], it becomes capital to harness their Rabi dynamics [37]. In this Letter, thanks to significant progress in both the quality of the structures (the sample description is given in the Supplemental Material [38]) ...

Microcavity polaritons are two-dimensional bosonic fluids with strong nonlinearities, composed of coupled photonic and electronic excitations. In their condensed form, they display quantum hydrodynamic features similar to atomic Bose–Einstein condensates, such as long-range coherence, superfluidity and quantized vorticity. Here we report the unique phenomenology that is observed when a pulse of light impacts the polariton vacuum: the fluid which is suddenly created does not splash but instead coheres into a very bright spot. The real-space collapse into a sharp peak is at odd with the repulsive interactions of polaritons and their positive mass, suggesting that an unconventional mechanism is at play. Our modelling devises a possible explanation in the self-trapping due to a local heating of the crystal lattice, that can be described as a collective polaron formed by a polariton condensate. These observations hint at the polariton fluid dynamics in conditions of extreme intensities and ultrafast times.

We study the propagation of non-interacting polariton wavepackets. We show how two qualitatively different concepts of mass that arise from the peculiar polariton dispersion lead to a new type of particle-like object from non-interacting fields-much like self-accelerating beams-shaped by the Rabi coupling out of Gaussian initial states. A divergence and change of sign of the diffusive mass results in a "mass wall" on which polariton wavepackets bounce back. Together with the Rabi dynamics, this yield propagation of ultrafast subpackets and ordering of a spacetime crystal.Field theory unifies the concepts of waves and particles [1]. In quantum physics, this brought at rest the dispute of the pre-second-quantization era, on the nature of the wavefunction. As one highlight of this conundrum, the coherent state emerged as an attempt by Schrödinger to prove Heisenberg that his equation is suitable to describe particles since some solutions exist that remain localized [2]. However, the reliance on an external potential and the lack of other particle properties-like resilience to collisions-makes this qualification a moot point and quantum particles are now understood as excitations of the field. The deep connection between fields and particles is not exclusively quantum and classical fields also provide a robust notion of particles, most famously with solitons [3]. The particle cohesion is here assured selfconsistently by the interactions, allowing free propagation and surviving collisions with other solitons (possibly with a phase shift). For a long time, this has been the major example of how to define a particle out of a classical field, until Berry and Balazs discovered the first case of a similar behaviour in a non-interacting context: the Airy beams [4]. These solutions to Schrödinger equation (or equivalently through the Eikonal approximation, to Maxwell equations) retain their shape as they propagate as a train of peaks (or sub-packets) and also exhibit self-healing after passing through an obstacle [5]. The ingredient powering these particle behaviours is phaseshaping, assuring the cohesion by the acceleration of the sub-packets inside the mother packet. The solution was first regarded as a mathematical curiosity as it is not normalizable, till a truncated version was experimentally realized and shown to exhibit this dramatic phenomenology but for a finite time [6]. The Airy beam is now a recognized particle-like object, in some cases emerging from fields that quantize elementary particles [7], thus behaving like a meta-particle. It is in fact but one example of a full family of so-called "accelerating beams" [8], that all similarly endow linear fields with particle properties: shape-preservation and resilience to collisions.In this Letter, we add another member to the family of mechanisms that provide non-interacting fields with particle properties. Namely, we show that two coupled fields of different masses can support self-interfering wavepack- Effective masses for the LPB as a function of momentum: in pur...

We propose theoretically and demonstrate experimentally the generation of light pulses whose polarization varies temporally to cover selected areas of the Poincaré sphere with both tunable swirling speed and total duration (1 ps and 10 ps, respectively, in our implementation). The effect relies on the Rabi oscillations of two polariton polarized fields excited by two counter-polarized and delayed pulses. The superposition of the oscillating fields result in the precession of the Stokes vector of the emitted light while polariton lifetime imbalance results in its drift from a circle of controllable radius on the Poincaré sphere to a single point at long times. The positioning of the initial circle and final point allows to engineer the type of polarization spanning, including a full sweeping of the Poincaré sphere. The universality and simplicity of the scheme should allow for the deployment of time-varying full-Poincaré polarization fields in a variety of platforms, timescales, and regimes.

Shock waves are examples of the far-from-equilibrium behavior of matter; they are ubiquitous in nature, yet the underlying microscopic mechanisms behind their formation are not well understood. Here, we study the dynamics of dispersive quantum shock waves in a one-dimensional Bose gas, and show that the oscillatory train forming from a local density bump expanding into a uniform background is a result of quantum mechanical self-interference. The amplitude of oscillations, i.e., the interference contrast, decreases with the increase of both the temperature of the gas and the interaction strength due to the reduced phase coherence length. Furthermore, we show that vacuum and thermal fluctuations can significantly wash out the interference contrast, seen in the mean-field approaches, due to shot-to-shot fluctuations in the position of interference fringes around the mean.