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A laser pulse composed of a fundamental and properly phased second harmonic exhibits an asymmetric electric field that can drive a time-dependent current of photoionized electrons. The current produces an ultrashort burst of terahertz (THz) radiation. When driven by a conventional laser pulse, the THz radiation is emitted into a cone with an angle determined by the dispersion of the medium. Here we demonstrate that the programmable-velocity intensity peak of a spatiotemporally structured, two-color laser pulse can be used to control the emission angle, focal spot, and spectrum of the THz radiation. Of particular interest for applications, a structured pulse with a subluminal intensity peak can drive highly focusable, on-axis THz radiation.

Paraxial fluids of light represent an alternative platform to atomic Bose-Einstein condensates and superfluid liquids for the study of the quantum behavior of collective excitations. A key step in this direction is the precise characterization of the Bogoliubov dispersion relation, as recently shown in two experiments. However, the predicted interferences between the phonon excitations that would be a clear signature of the collective superfluid behavior have not been observed to date. Here, by analytically, numerically, and experimentally exploring the phonon phase velocity, we observe the presence of interferences between counterpropagating Bogoliubov excitations and demonstrate their critical impact on the measurement of the dispersion relation. These results are evidence of a key signature of light superfluidity and provide a characterization tool for quantum simulations with photons.

Collective excitations, such as vortex-antivortex and dark solitons, are among the most fascinating effects of macroscopic quantum states. However, two-dimensional (2D) dark solitons are unstable and collapse into vortices due to snake instabilities. Making use of the optical bistability in exciton-polariton microcavities, we demonstrate that a pair of dark solitons can be formed in the wake of an obstacle in a polariton flow resonantly supported by a homogeneous laser beam. Unlike the purely dissipative case where the solitons are gray and spatially separate, here the two solitons are fully dark, rapidly align at a specific separation distance, and propagate parallel as long as the flow is in the bistable regime. Remarkably, the use of this regime allows us to relax the phase fixing constraints imposed by the resonant pumping and to circumvent the polariton decay. Our work opens very wide possibilities for studying new classes of phase-density defects which can form in driven-dissipative quantum fluids of light.

The general theory of dark solitons relies on repulsive interactions and, therefore, predicts the impossibility to form dark-soliton bound states. One important exception to this prediction is the observation of bound solitons in nonlocal nonlinear media. Here, we report that exciton-polariton superfluids can also sustain dark-soliton molecules, although the interactions are fully local. With a novel all-optical technique, we create two dark solitons that bind together to form an unconventional dark-soliton molecule. We demonstrate that the stability of this structure and the separation distance between two dark solitons is tightly connected to the driven-dissipative nature of the polariton fluid.

Ultrafast laser irradiation of silicon can significantly modify charge densities and optical indices, impacting the formation and the development of nanoscale-arranged periodic structures. Photoexcitation degree as well as thermodynamic, hydrodynamic, and structural aspects are reported for crossed orientation of laser-induced periodic surface structures generated on single-crystal silicon after multiple-pulse femtosecond laser irradiation. The periodic topography and microstructure generated by light scattering on surface nanoroughness were characterized to gain insights into the regime of photoexcitation, subsequent thermodynamic conditions, and inhomogeneous energy deposition related to periodic nanostructure formation and growth. A generated free-carrier density around (3±2)×10^{21}cm^{−3} is estimated from time-resolved ellipsometry and supported by time-dependent density-functional theory calculations. A finite-difference time-domain solution of the far-field interference of the surface scattered light and the refracted laser wave confirms the periodically crossed energy deposition for this excitation degree. The interference process does not necessarily involve surface plasmon polaritons, and quasicylindrical evanescent waves are identified as plausible scattered waves requiring less restrictive conditions of photoexcitation. Ab initio calculations are also performed to evaluate the transient state of silicon under strong electron-phonon nonequilibrium upon fs laser irradiation. For the reached excitation degree, an electron temperature up to 8000 K is deduced, supporting local amorphization processes observed as a result of high mechanical stress and quenching rates. Ab initio combined with electromagnetic calculations agree well with the results of topography and structural characterization.

In this work we implement an experimental configuration which exploits the specific properties of the optical bistability exhibited by the polariton system and we demonstrate the generation of a superfluid turbulent flow in the wake of a potential barrier. The propagation and direction of the turbulent flow are sustained by a support beam on distances an order of magnitude longer than previously reported. This technique is a powerful tool for the controlled generation and propagation of quantum turbulence and paves the way for the study of the hydrodynamics of quantum turbulence in driven-dissipative two-dimensional polariton systems.

We show that weakly incoherent optical beams propagating in a Kerr medium exhibit a universal algebraic coherence after a short propagation time, mimicking the quasi-long-range order of ultracold quantum Bose gases in two dimensions. If two plates are inserted in the medium, this optical quasi-condensate gives rise to a long-range Casimir-like force, attractive at large distances and repulsive at short distances.

Some actions intended to adapt to climate change may do more harm than good, especially when they consume energy, making it more difficult to shift to decarbonized energy, or when, in meeting the needs of one group of people, they increase the vulnerability of others. Heat wave risk provides a typical example: air conditioning (AC) equipment may trigger large energy consumption and worsen outdoor heat stress. Alternative adaptation strategies exist, but it is not clear whether they can prevent the massive use of AC. Here, with an interdisciplinary modeling platform, taking Paris as a case study, we provide a first quantified analysis of the efficiency of adaptation strategies (large scale urban greening, building insulation policy, and generalized behavioral changes in AC use) in reducing future potential AC need. We find that even ambitious strategies do not appear sufficient to totally replace AC and ensure thermal comfort, under a median climate change scenario. They can, however, reduce AC energy use by half during heat waves and compensate for the heat released to the outdoor environment. Our results show that adaptation actions, implemented early, may play a key role if we are to remain on a low-carbon pathway.

High resolution simulation of complex aerosol particle evolution and gaseous chemistry over an atmospheric urban area is of great interest for understanding air quality and processes. In this context, the CAPITOUL (Canopy and Aerosol Particle Interactions in the Toulouse Urban Layer) field experiment aims at a better understanding of the interactions between the urban dynamics and the aerosol plumes. During a two-day Intensive Observational Period, a numerical model experiment was set up to reproduce the spatial distribution of specific particle pollutants, from the regional scales and the interactions between different cities, to the local scales with specific turbulent structures. Observations show that local dynamics depends on the day-regime, and may lead to different mesoscale dynamical structures. This study focuses on reproducing these fine scale dynamical structures, and investigate the impact on the aerosol plume dispersion. The 500-m resolution simulation manages to reproduce convective rolls at local scale, which concentrate most of the aerosol particles and can locally affect the pollutant dispersion and air quality.

We report the fabrication and characterization of photonic structures using tapered optical nanofibers. Thanks to the extension of the evanescent electromagnetic field outside of the nanofiber two types of devices can be built: a ring interferometer and a knot resonator. We propose a general approach to predict the properties of these structures using the linear coupling theory. In addition, we describe a new source of birefringence due to the ovalization of a nanofiber under strong bending, known in mechanical engineering as the Brazier effect.

We develop the full counting statistics of dissipated heat to explore the relation with Landauer’s principle. Combining the two-time measurement protocol for the reconstruction of the statistics of heat with the minimal set of assumptions for Landauer’s principle to hold, we derive a general one-parameter family of upper and lower bounds on the mean dissipated heat from a system to its environment. Furthermore, we establish a connection with the degree of non-unitality of the system’s dynamics and show that, if a large deviation function exists as stationary limit of the above cumulant generating function, then our family of lower and upper bounds can be used to witness and understand first-order dynamical phase transitions. For the purpose of demonstration, we apply these bounds to an externally pumped three level system coupled to a finite sized thermal environment.

We present a simple method to compensate for losses in a polariton superfluid. Based on a weak support field, it allows for the extended propagation of a resonantly driven polariton superfluid with minimal energetic cost. Moreover, this setup is based on optical bistability and leads to the significant release of the phase constraint imposed by resonant driving. This release, together with macroscopic polariton propagation, offers a unique opportunity to study the hydrodynamics of the topological excitations of polariton superfluids such as quantized vortices and dark solitons. We numerically study how the coherent field supporting the superfluid flow interacts with the vortices and how it can be used to control them. Interestingly, we show that standard hydrodynamics does not apply for this driven-dissipative fluid and new types of behaviour are identified.

We consider the non-equilibrium dynamics of a simple system consisting of interacting spin-1/2 particles subjected to a collective damping. The model is close to situations that can be engineered in hybrid electro/opto-mechanical settings. Making use of large-deviation theory, we find a Gallavotti–Cohen symmetry in the dynamics of the system as well as evidence for the coexistence of two dynamical phases with different activity levels. We show that additional damping processes smooth out this behavior. Our analytical results are backed up by Monte Carlo simulations that reveal the nature of the trajectories contributing to the different dynamical phases.

We present a general method to undertake a thorough analysis of the thermodynamics of the quantum jump trajectories followed by an arbitrary quantum harmonic network undergoing linear and bilinear dynamics. The approach is based on the phase-space representation of the state of a harmonic network. The large deviation function associated with this system encodes the full counting statistics of exchange and also allows one to deduce fluctuation theorems (FTs) obeyed by the dynamics. We illustrate the method showing the validity of a local FT about the exchange of excitations between a restricted part of the environment (i.e., a local bath) and a harmonic network coupled with different schemes.

We analyze the nature of the statistics of the work done on or by a quantum many-body system brought out of equilibrium. We show that, for the sudden quench and for an initial state that commutes with the initial Hamiltonian, it is possible to retrieve the whole nonequilibrium thermodynamics via single projective measurements of observables. We highlight, in a physically clear way, the qualitative implications for the statistics of work coming from considering processes described by operators that either commute or do not commute with the unperturbed Hamiltonian of a given system. We consider a quantum many-body system and derive an expression that allows us to give a physical interpretation, for a thermal initial state, to all of the cumulants of the work in the case of quenched operators commuting with the unperturbed Hamiltonian. In the commuting case, the observables that we need to measure have an intuitive physical meaning. Conversely, in the noncommuting case, we show that, although it is possible to operate fully within the single-measurement framework irrespectively of the size of the quench, some difficulties are faced in providing a clear-cut physical interpretation to the cumulants. This circumstance makes the study of the physics of the system nontrivial and highlights the nonintuitive phenomenology of the emergence of thermodynamics from the fully quantum microscopic description. We illustrate our ideas with the example of the Ising model in a transverse field showing the interesting behavior of the high-order statistical moments of the work distribution for a generic thermal state and linking them to the critical nature of the model itself.