Exact states and spectra of vibrationally dressed polaritons

Strong coupling between light and matter is possible with a variety of organic materials. In contrast to the simpler inorganic case, organic materials often have a complicated spectrum, with vibrationally dressed electronic transitions. Strong coupling to light competes with this vibrational dressing and, if strong enough, can suppress the entanglement between electronic and vibrational degrees of freedom. By exploiting symmetries, we can perform exact numerical diagonalization to find the polaritonic states for intermediate numbers of molecules and use these to define and validate accurate expressions for the lower polariton states and strong-coupling spectrum in the thermodynamic limit. Using this approach, we find that vibrational decoupling occurs as a sharp transition above a critical matter-light coupling strength. We also demonstrate how the polariton spectrum evolves with the number of molecules, recovering classical linear optics results only at large N

Hydrodynamics of local excitations after an interaction quench in 1D cold atomic gases

We discuss the hydrodynamic approach to the study of the time evolution -induced by a quench- of local excitations in one dimension. We focus on interaction quenches: the considered protocol consists in creating a stable localized excitation propagating through the system, and then operating a sudden change of the interaction between the particles. To highlight the effect of the quench, we take the initial excitation to be a soliton. The quench splits the excitation into two packets moving in opposite directions, whose characteristics can be expressed in a universal way. Our treatment allows to describe the internal dynamics of these two packets in terms of the different velocities of their components. We confirm our analytical predictions through numerical simulations performed with the Gross-Pitaevskii equation and with the Calogero model (as an example of long range interactions and solvable with a parabolic confinement). Through the Calogero model we also discuss the effect of an external trapping on the protocol. The hydrodynamic approach shows that there is a difference between the bulk velocities of the propagating packets and the velocities of their peaks: it is possible to discriminate the two quantities, as we show through the comparison between numerical simulations and analytical estimates. In the realizations of the discussed quench protocol in a cold atom experiment, these different velocities are accessible through different measurement procedures. ArXI

Topological order and thermal equilibrium in polariton condensates

We report the observation of the Berezinskii-Kosterlitz-Thouless transition for a 2D gas of exciton-polaritons, and through the joint measurement of the first-order coherence both in space and time we bring compelling evidence of a thermodynamic equilibrium phase transition in an otherwise open driven/dissipative system. This is made possible thanks to long polariton lifetimes in high-quality samples with small disorder and in a reservoir-free region far away from the excitation spot, that allow topological ordering to prevail. The observed quasi-ordered phase, characteristic for an equilibrium 2D bosonic gas, with a decay of coherence in both spatial and temporal domains with the same algebraic exponent, is reproduced with numerical solutions of stochastic dynamics, proving that the mechanism of pairing of the topological defects (vortices) is responsible for the transition to the algebraic order. Finally, measurements in the weak-coupling regime confirm that polariton condensates are fundamentally different from photon lasers and constitute genuine quantum degenerate macroscopic states

Laser Operation and Bose-Einstein Condensation: Analogies and Differences

After reviewing the interpretation of laser operation as a non-equilibrium Bose-Einstein condensation phase transition, we illustrate the novel features arising from the non-equilibrium nature of photon and polariton Bose-Einstein condensates recently observed in experiments. We then proposea quantitative criterion to experimentally assess the equilibrium vs. non-equilibrium nature of a specific condensation process, based on fluctuation-dissipation relations. The power of this criterion is illustrated on two models which shows very different behaviours

Thermalization and Bose-Einstein condensation of quantum light in bulk nonlinear media

We study the thermalization and the Bose-Einstein condensation of a paraxial, spectrally narrow beam of quantum light propagating in a lossless bulk Kerr medium. The spatiotemporal evolution of the quantum optical field is ruled by a Heisenberg equation analogous to the quantum nonlinear Schrödinger equation of dilute atomic Bose gases. Correspondingly, in the weak-nonlinearity regime, the phase-space density evolves according to the Boltzmann equation. Expressions for the thermalization time and for the temperature and the chemical potential of the eventual Bose-Einstein distribution are found. After discussing experimental issues, we introduce an optical setup allowing the evaporative cooling of a guided beam of light towards Bose-Einstein condensation. This might serve as a novel source of coherent light

Surgical treatment of parasagittal and falcine meningiomas of the posterior third.

BACKGROUND: To the authors' knowledge, meningiomas of the posterior third of the falx and the parasagittal sinus have never been specifically described to date and correlated visual outcome remains unclear. With this retrospective study we describe the clinical characteristics of these tumours, their surgical management, and the improvement in visual disturbances after surgery. METHODS: Twenty-six consecutive patients (22 females, 4 males; mean age, 54\ua0years) operated on for parasagittal (n\u2009=\u200922) and falcine (n\u2009=\u20094) meningioma between 1990 and 2010 were analysed retrospectively. Preoperative planning included magnetic resonance imaging (MRI) and magnetic resonance venography (MRV) or angiography. Sinus invasion was classified as normal, stenotic or occluded from the imaging findings and according to the Sindou classification from the intraoperative notes. RESULTS: Visual disturbances and headache (in 21 and 14 cases, respectively) were the most commonly referred symptoms; visual field deficit was present in 19 patients. Simpson grade I was obtained in four patients, grade II in 15, grade III in three, and grade IV in four. The main limiting factor for total removal was sinus involvement. No perioperative deaths or relevant postoperative complications occurred. The mean follow-up was 107\ua0months. Visual field deficit improved or resolved in almost half of the patients during the follow-up period. Three (12\%) patients relapsed, two were treated with Gamma Knife surgery (stable at current writing) and the third died of disease progression. CONCLUSIONS: Outcome after surgery compares favourably with other parasagittal meningioma localisations and overall morbidity is negligible. Visual function is crucial for clinical outcome. Since an improvement of the deficit might still be possible, every effort should be undertaken to preserve the visual cortex

Universal late-time dynamics in isolated one-dimensional statistical systems with topological excitations

We investigate the nonequilibrium dynamics of a class of isolated one-dimensional systems possessing two degenerate ground states, initialized in a low-energy symmetric phase. We report the emergence of a timescale separation between fast (radiation) and slow (kink or domain wall) degrees of freedom. We find a universal long-time dynamics, largely independent of the microscopic details of the system, in which the kinks control the relaxation of relevant observables and correlations. The resulting late-time dynamics can be described by a set of phenomenological equations, which yield results in excellent agreement with the numerical tests