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Turbulent radiation flow is commonplace in systems with strong, incoherent, light-matter interactions. In astrophysical contexts, photon bubble turbulence is considered a key mechanism behind enhanced radiation transport, and its importance has been widely asserted for a variety of high energy objects such as accretion disks and massive stars. Here, we show that analogous conditions to those of dense astrophysical objects can be obtained in large clouds of cold atoms, prepared in a laser-cooling experiment, driven close to a sharp electronic resonance. By accessing the spatially-resolved atom density, we are able to identify a photon bubble instability and the resulting regime of photon bubble turbulence. We also develop a theoretical model describing the coupled dynamics of both photon and atom gases, which accurately describes the statistical properties of the turbulent regime. This study thus opens the possibility of simulating radiation-dominated astrophysical systems in cold atom experiments., Photon bubble turbulence is an astrophysical phenomenon involving radiation transport. Here, the authors report analogous behavior in ultracold gas by observing signatures of photon bubble instabilities in Rb atoms trapped in a MOT.

Superradiance is the anomalous radiance describing coherent photon emission from a gas. It plays a crucial role in atomic physics, quantum mechanics and astrophysics. Because the intensity of superradiant light beams is proportional to the number of particles squared, superradiance is also at the core of today’s most powerful light sources. Superradiant emission is intuitively expected when the distance between light-emitting particles is much smaller than the photon wavelength. Here, we break this assumption by predicting a never considered superradiance effect that holds even when the particle number per wavelength vanishes. We discover that a bunch of relativistic charged particles arranged in certain ways can generate an optical shock along the Vavilov–Cherenkov angle in vacuum, thereby concentrating broadband radiation in any spectral region into single light bullets. The process leaves clear experimental signatures, and we illustrate it in the form of a previously unrecognized nonlinear superradiant Thomson scattering. This concept may enable new forms of superradiant emission in advanced light sources, atomic physics systems, and unlock coherent emission in plasma accelerators. A new form of superradiance is predicted that ‘in contrast to the standard effect’ arises even for vanishing numbers of particles per wavelength. This finding may enable coherent emission in plasma accelerators.

Axions, the hypothetical particles restoring the charge-parity symmetry in the strong sector of the Standard Model and one of the most prone candidates for dark matter, are well known to interact with plasmas. In a recent publication [Phys. Rev. Lett. 120, 181803 (2018)PRLTAO0031-900710.1103/PhysRevLett.120.181803], we show that if the plasma dynamically responds to the presence of axions, then a new quasiparticle (the axion-plasmon polariton) can be formed, being at the basis of a new generation of plasma-based detection techniques. In this work, we exploit the axion-plasmon hybridization to actively produce axions in streaming magnetized plasmas. The produced axions can then be detected by reconversion into photons in a scheme that is similar to the light-shining-through-a-wall experiments.

Starting from a three-wave interaction system of equations for free-electron lasers in the framework of a quantum fluid model, the full spatio-temporal solution of this set of equations is numerically obtained. Although this quantum fluid model does not take into account the electron recoil, it is accurate enough to model free-electron lasers down to soft X-ray range using a counter propagating optical wiggler and a moderately relativistic electron beam for a table-top compact device. We have shown that the scattered radiation is amplified and divided into sub-pulses while it absorbs energy from the optical wiggler through the negative energy beam plasma mode. Furthermore, the leading pulse gets more energy than the others while the longitudinal waist is reduced and has a shape similar to a “π-pulse” solution from the sine-Gordon equation.

In this paper, we discuss a variety of temporal optical phenomena in a gas of Rydberg atoms, which can take place in the presence of varying quasi-static electric fields and control laser beams. This includes the discussion of temporal spectral changes of probe laser beams, associated with purely temporal processes created by Stark and ac-Stark shifts of the atomic susceptibility. Such changes include phase and group velocity perturbations, time delays, frequency shifts, and other temporal changes of the transmitted and reflected probe signals. We mainly focus on ultrafast temporal transitions, known as time-refraction, and their specific signatures, which envolve the occurrence of a temporally induced reflection coefficient. Our model assumes that the temporal variations of the applied Stark shifts are much shorter than the Rydberg life-times. We also discuss the Rydberg atom response to ultrashort laser pulses, in the attosecond time domain, and derive the corresponding atomic susceptibilities. Finally, the optical properties of a temporally perturbed Rydberg-EIT configuration, and the expected influence of dipole blockade are considered. This could eventually lead to new experimental studies in Rydberg optics.

Dark matter is a key ingredient to physical cosmology, and one of the mysteries of modern science. Among a variety of possible candidates which have been explored in recent decades (such as WIMPs and WISPs), the axions are the most promising constituents of dark matter. These hypothetical particles have been proposed to solve fundamental problems of charge- parity (CP) invariance and their discovery could therefore solve two important problems in cosmology and in particle physics. The axions, and axion-like particles, have been actively searched without success since the 80’s of the last century, using both laboratory experiments and astrophysical observations. In recent years, it became clear that the axions, if they exist, could be actively produced by intense laser pulses in magnetised and unmagnetised vacuum, and that the axion field could become unstable under the action of intense laser beams. Alternatively, the signature of axions could possibly be found in the dispersion relation of electrostatic waves in strongly magnetised plasmas, due to the formation of the axion-plasmon mode. This new mode could be excited by intense laser pulses in a plasma. In the present work, we consider different configurations leading to the excitation of axions by intense laser pulses, and consider propagation both in vacuum and in plasmas. A discussion of possible experimental arrangements, using the available laser technology is included.

The modulatonal instability theory for the generation of large-scale (zonal) modes by drift modes has been extended to the second order including the effects of finite amplitude zonal flows, ϕq. The nonlinear (second-order) sidebands are included in the perturbative expansion to derive the nonlinear equation for the evolution of ϕq. It is shown that effects of finite ϕq reduce the growth rate of zonal flow with a possibility of oscillatory regimes at a later stage.

We study the modulational instability of an intense photon beam in a relativistic pair plasma. We use the wave-kinetic description of the photon field and relativistic fluid equations for electrons and positrons. This allows us to consider the influence of the photon spectral distribution and photon recoil effects on the instability threshold and growth rates. The case of very low frequencies modulations, well below plasma frequency, is compared to that of high-frequency modulations corresponding to the plasmon decay instability.

We consider the excitation of polariton wakefields due to a propagating light pulse in a semiconductor microcavity. We show that two kinds of wakes are possible, depending on the constituents fraction (either exciton or photon) of the polariton wavefunction. The nature of the wakefields (pure excitonic or polaritonic) can be controlled by changing the speed of propagation of the external pump. This process could be used as a diagnostic for the internal parameters of the microcavity.

We have studied collective recoil lasing by a cold atomic gas, scattering photons from an incident laser into many radiation modes in free space. The model consists of a system of classical equations for the atomic motion of N atoms, where the radiation field has been adiabatically eliminated. We performed numerical simulations using a molecular dynamics code, Pretty Efficient Parallel Coulomb Solver or PEPC, to track the trajectories of the atoms. These simulations show the formation of an atomic density grating and collective enhancement of scattered light, both of which are sensitive to the shape and orientation of the atomic cloud. In the case of an initially circular cloud, the dynamical evolution of the cloud shape plays an important role in the development of the density grating and collective scattering. The ability to use efficient molecular dynamics codes will be a useful tool for the study of the multimode interaction between light and cold gases.

We provide an explicit model for a spin-1/2 quasi-particle, based on the superposition of plasmon excitations in a quantum plasmas with intrinsic orbital angular momentum. Such quasi-particle solutions can show remarkable similarities with single electrons moving in vacuum: they have spin-1/2, a finite rest mass, and a quantum dispersion. We also show that these quasi-particle solutions satisfy a criterium of energy minimum.

Axions are hypothetical particles related to the violation of the charge-parity symmetry, being the most prone candidates for dark matter. Multiple attempts to prove their existence are currently performed in different physical systems. Here, we anticipate the possibility of the axions coupling to the electrostatic (Langmuir) modes of a strongly magnetized plasma, by showing that a new quasi-particle can be defined, the axion-plasmon polariton. The excitation of axions can be inferred from the pronounced modification of the dispersion relation of the Langmuir waves, a feature that we estimate to be accessible in state-of-the-art plasma-based experiments. We further show that, under extreme density and magnetic field conditions (e.g. at the interior of dense neutron stars), the axion-plasmon polariton becomes dynamically unstable, similarly to the case of the Jeans instability occurring in self-gravitating fluids. This latter result anticipates a plausible mechanism to the creation of axion-like particles in the universe., Comment: Axions, polaritons, avoided crossing, dynamical instability, axion-like particles, magnetized plasmas

We report on the self-induced electron trapping occurring in an ultracold neutral plasma that is set to expand freely. At the early stages of the plasma, the ions are not thermalized which follow a Gaussian spatial profile, providing the trapping to the coldest electrons. In the present work, we provide a theoretical model describing the electrostatic potential and perform molecular dynamics simulations to validate our findings. We show that in the strong confinement regime, the plasma potential is of a Thomas-Fermi type, similar to the case of heavy atomic species. The numerically simulated spatial profiles of the particles corroborate this claim. We also extract the electron temperature and coupling parameter from the simulation, so the duration of the transient Thomas-Fermi is obtained.We report on the self-induced electron trapping occurring in an ultracold neutral plasma that is set to expand freely. At the early stages of the plasma, the ions are not thermalized which follow a Gaussian spatial profile, providing the trapping to the coldest electrons. In the present work, we provide a theoretical model describing the electrostatic potential and perform molecular dynamics simulations to validate our findings. We show that in the strong confinement regime, the plasma potential is of a Thomas-Fermi type, similar to the case of heavy atomic species. The numerically simulated spatial profiles of the particles corroborate this claim. We also extract the electron temperature and coupling parameter from the simulation, so the duration of the transient Thomas-Fermi is obtained.

New features of the twisted dusty plasma modes and associated instabilities are investigated in permeating plasmas. Using the Vlasov–Poisson model equations, a generalized dispersion relation is obtained for a Maxwellian distributed plasma to analyse the dust-acoustic and dust-ion-acoustic waves with finite orbital angular momentum (OAM) states. Existence conditions for damping/growth rates are discussed and showed significant modifications in twisted dusty modes as compared to straight propagating dusty modes. Numerically, the instability growth rate, which depends on particle streaming and twist effects in the wave potential, is significantly modified due to the Laguerre–Gaussian profiles. Relevance of the study to wave excitations due to penetration of solar wind into cometary clouds or interstellar dusty plasmas is discussed.

Turbulence in the quantum (superfluid) regime, similarly to its classical counterpart, continues to attract a great deal of scientific inquiry, due to the yet high number of unresolved problems. While turbulent states can be routinely created in degenerate atomic gases, there is no generic scheme to produce turbulence in fluids of light. Under paraxial propagation, light in bulk nonlinear media behaves as a two-dimensional superfluid, described by a nonlinear Schr\"{o}dinger equation formally equivalent to the Gross-Pitaevskii model of a weakly interacting Bose gas, where photon-photon interactions are mediated by a third order (Kerr) nonlinearity. Here, we develop the theory describing the onset of a kinetic instability when two paraxial optical fluids with different streaming velocities interact via the optical nonlinearity. From numerical simulations of the nonlinear Schr\"{o}dinger equation, we further characterize the onset of the instability and describe its saturation in the form of vortex nucleation and excitation of turbulence. The experimental observation of such effects is also discussed. The class of instabilities described here thus provide a natural route towards the investigation of quantum (superfluid) turbulence, structure formation and out-of-equilibrium dynamics in superfluids of light., Comment: Accepted for publication in Physical Review A

Twisted Laguerre-Gaussian lasers, with orbital angular momentum and characterised by doughnut shaped intensity profiles, provide a transformative set of tools and research directions in a growing range of fields and applications, from super-resolution microcopy and ultra-fast optical communications to quantum computing and astrophysics. The impact of twisted light is widening as recent numerical calculations provided solutions to long-standing challenges in plasma-based acceleration by allowing for high gradient positron acceleration. The production of ultrahigh intensity twisted laser pulses could then also have a broad influence on relativistic laser-matter interactions. Here we show theoretically and with ab-initio three-dimensional particle-in-cell simulations, that stimulated Raman backscattering can generate and amplify twisted lasers to Petawatt intensities in plasmas. This work may open new research directions in non-linear optics and high energy density science, compact plasma based accelerators and light sources., Comment: 18 pages, 4 figures, 1 table

We consider Landau damping of elementary excitations in Bose-Einstein condensates (BECs) with dipolar interactions. We discuss quantum and quasi-classical regimes of Landau damping. We use a generalized wave-kinetic description of BECs which, apart from the long range dipolar interactions, also takes into account the quantum fluctuations and the finite energy corrections to short-range interactions. Such a description is therefore more general than the usual mean field approximation. The present wave-kinetic approach is well suited for the study of kinetic effects in BECs, such as those associated with Landau damping, atom trapping and turbulent diffusion. The inclusion of quantum fluctuations and energy corrections change the dispersion relation and the damping rates, leading to possible experimental signatures of these effects. Quantum Landau damping is described with generality, and particular examples of dipole condensates in two and three dimensions are studied. The occurrence of roton-maxon configurations, and their relevance to Landau damping is also considered in detail, as well as the changes introduced by the three different processes, associated with dipolar interactions, quantum fluctuations and finite energy range collisions. The present approach is mainly based on a linear perturbative procedure, but the nonlinear regime of Landau damping, which includes atom trapping and atom diffusion, is also briefly discussed., Quantum fluctuations, LHY correction, Landau damping, roton minimum, dipolar Bose gases

Atoms excited into high-lying Rydberg states and under strong dipole-dipole interactions exhibit phenomena associated with highly correlated and complex systems. We perform first principles numerical simulations on the dynamics of such systems. The emergence of a roton minimum in the excitation spectrum, as expected in strongly correlated gases and accurately described by Feynman's theory of liquid helium, is shown to significantly inhibit particle transport, with a strong suppression of the diffusion coefficient, due to the emerging spatial order. We also demonstrate how the ability to temporally tune the interaction strength among Rydberg atoms can be used in order to overcome the effects of disorder induced heating, allowing the study of unprecedented highly coupled regimes.

We describe the emergence of strong spatial correlations, akin to liquid-like behavior and crystallization effects, in low (one and two) dimensional gases of cold Rydberg atoms. The presence of an external electric field permanently polarizes the atoms, which became highly correlated due to the long-range dipole-dipole interaction. We describe a theoretical approach particularly suited for strongly coupled systems and numerically obtain both the two-particle distribution function and the static structure factor. The experimental implementation of such highly interacting systems is discussed, including detailed calculations of the interaction strength for different Rydberg states. The results provide new insights into many-body effects associated with strongly interacting Rydberg atoms, including the possibility of observing novel highly ordered phases.

We analyze the role of collisional effects on the coupling between ion-acoustic waves and neutrino flavor oscillations, discussing its relevance for plasma instabilities in extreme plasma environments like in type II supernovae, where intense neutrino bursts exist. Electrons (leptons) are coupled to the electron-neutrino fluid through the weak Fermi force, but the electron-neutrinos are allowed to convert to other neutrino flavors and vice versa. Due to the typically slow frequency of neutrino flavor oscillations, many orders smaller than, e.g., the plasma frequency, an effective energy transfer between plasma waves and neutrino flavor oscillations takes place at the low-frequency electrostatic branch, viz., the ion-acoustic mode. We show the destabilization of ion-acoustic waves in dense astrophysical scenarios, with a focus on the collisional effects mediated by electron-ion scattering. The maximal instability growth-rate is evaluated and compared to the characteristic inverse times of type II supernova explosions. The results can be used for independent experimental verification of the non-zero neutrino mass, in a plasma physics context. Published by AIP Publishing.

We study the Bose-Einstein condensation of photons in a plasma, where we include the cases of both transverse photons and plasmons. We consider four-wave mixing processes of photon and plasmon modes in a relativistic isotropic plasma to determine the coupling constant to lowest order. We further show that photon condensation is possible in an unbounded plasma because, in contrast with other optical media, plasmas introduce an effective photon mass. This guarantees the existence of a finite chemical potential and a critical temperature, which is calculated for both transverse photons and plasmons. By considering four-wave mixing processes, we derive the interactions between the photons in the condensate. We also study the elementary excitations (or Bogoliubov modes) of the condensed photon and plasmon gases, and determine the respective dispersion relations. Finally, we discuss the kinetics of photon condensation via inverse Compton scattering between the photons and the electrons in the plasma., Photon BEC, four-wave mixing, kinetic equations, quantisation, Bogoliubov spectrum

Vortex light beams are structures of the electromagnetic field with a spiral phase ramp around a point-phase singularity. These vortices have many applications in the optical regime, ranging from optical trapping and quantum information to spectroscopy and microscopy. The extension of vortices into the extreme-ultraviolet (XUV)/X-ray regime constitutes a significant step forward to bring those applications to the nanometer or even atomic scale. The recent development of a new generation of X-ray sources, and the refinement of other techniques, such as harmonic generation, have boosted the interest of producing vortex beams at short wavelengths. In this manuscript, we review the recent studies in the subject, and we collect the major prospects of this emerging field. We also focus on the unique and promising applications of ultrashort XUV/X-ray vortex pulses, A.P. acknowledges support from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 702565. C.H.-G. acknowledges support from the Marie Curie International Outgoing Fellowship within the EU Seventh Framework Programme for Research and Technological Development (2007-2013), under REA grant Agreement No 328334. We acknowledge support and from Junta de Castilla y León (Project SA046U16) and MINECO (FIS2013-44174-P, FIS2015-71933-REDT, FIS2016-75652-P).

We propose a wave kinetic description of super- fluidity in Bose Einstein condensates. This is based on the traditional two-fluid model, where in contrast with current analysis, the two fluids are treated on similar grounds. Each of the fluids (the condensed gas and the phonon gas) is described by a similar wave kinetic equation. These two equations are coupled. Perturbations of the coupled fluids lead to the formation of excitons which, in the appropriate limits, tend to the first and second sound waves.

This work considers quantum electron states in the field of twisted waves in a plasma. We consider electromagnetic and electrostatic waves. They can be associated with intense laser pulses carrying orbital angular momentum, and to the resulting twisted wakefields. Klein-Gordon and Dirac equations are considered. We show that twisted Volkov states of electrons in electromagnetic and electrostatic waves in a plasma can be excited, and discuss their main properties. These results support the idea that acceleration of helical electron beams in plasmas is possible.

We consider broadband radiation interacting with a gas of self-gravitating dust grains. We show that photon-bubble formation can occur, due to a modified Jeans instability, which will imply the formation of two different kinds of dust density perturbations. This could be useful for understanding the B-mode signal observed in the CMB polarization survey, and other astrophysical processes, such as the formation of protoplanets and voids in dust clouds.

We consider the formation of time crystals in a gas of laser-cooled atoms. We show that the phonon frequency is shifted inside a time crystal, and the phonon backscattering resulting from a temporal Bragg diffraction can be observed. A quantum-field description allows us to demonstrate that these effects are accompanied by emission of the phonon pairs from vacuum. The same description can be used for the dynamical Casimir effect, which, in some sense, is as a special case of the time crystal with similar quantum vacuum properties. Due to its low temperature and low noise level, a gas of ultracold atoms seems promising for experimental studies in quantum vacuum phenomena, such as those associated with time crystals.

We show that the second sound can exist in the ultra-cold gas of atoms confined and cooled in a magneto-optical trap. Our approach is based on a two-fluids model, similar to that used for superfluidity. Each of the fluids (the atomic gas and the phonon gas) is described by similar kinetic and fluid equation, which are coupled. The second sound modes are elementary excitations of these two coupled fluids. The ultra-cold gas could be used as an experimental test bed for detailed studies of the dispersion properties of the first and second sound.

The work investigates the coupling between ion-acoustic waves and neutrino flavor oscillations in a non-relativistic electron-ion plasma under the influence of a mixed neutrino beam. Neutrino oscillations are mediated by the flavor polarization vector dynamics in a material medium. The linear dispersion relation around homogeneous static equilibria is developed. When resonant with the ion-acoustic mode, the neutrino flavor oscillations can transfer energy to the plasma exciting a new fast unstable mode in extreme astrophysical scenarios. The growth rate and the unstable wavelengths are determined in typical type II supernovae parameters. The predictions can be useful for a new indirect probe on neutrino oscillations in nature.

The destabilizing role of neutrino beams on the Trivelpiece-Gould modes is considered, assuming electrostatic perturbations in a magnetized plasma composed by electrons in a neutralizing ionic background, coupled to a neutrino species by means of an effective neutrino force arising from the electroweak interaction. The magnetic field is found to significantly improve the linear instability growth rate, as calculated for supernova type II environments. On the formal level, for wave vectors parallel or perpendicular to the magnetic field, the instability growth rate is found from the unmagnetized case replacing the plasma frequency by the appropriated Trivelpiece-Gould frequency. The growth rate associated with oblique propagation is also obtained.

We establish the spectrum of Tonks-Dattner mode resonances in a quantum plasma bubble and consider the spectral changes associated with plasma quenching and plasma expansion. The quantum corrections associated with the mode spectrum are specified, which can be used as a diagnostic tool to identify the quantum regime. The frequency shifts associated with time-varying plasma bubbles correspond to time refraction and can also be used as a plasma diagnostic. We also study the energy mode coupling, in the presence of a low-frequency perturbation. It will be shown that the mode coupling equations take the form of generalized Bloch equations, where a nonlinear Rabi frequency can also be identified.

A possible new mechanism for anomalous ion heating in ultra-intense laser plasmas is considered here. This mechanism is based on the excitation of an electron two-stream instability that is driven by the fast electron beam and resonantly decays into ion-acoustic waves. These low frequency waves are then strongly damped by the ion collisions in the dense plasma. The model gives a simple explanation for the preferential heating of the bulk ion population observed in recent laser experiments in the petawatt (PW) regime. © 2005 IOP Publishing Ltd.

We introduce an hydrodynamic description of a laser cooled gas. In large traps, with as much as \(10^{10}\) atoms, multiple scattering of light leads to a collective interaction field which can be described by a Poisson-like equation, included in our formulation. A behaviour similar to a one-component trapped plasma should then be observed. By considering equilibrium conditions we extract the theoretical atomic density profiles and, in particular, its dependence on the effective plasma frequency of the system. The model is compared with experimentally measured profiles with an extraordinary agreement, thus corroborating both the plasma nature of the dynamics in the gas as well as the validity of the hydrodynamic formulation introduced here.

We propose to amplify and compress an ultrashort Light Spring laser seed with a long Gaussian-shaped laser pump through Raman amplification. This Light Spring, which has a helical spatio-temporal intensity profile, can be built on the superposition of three distinct laser frequency components. In order to get an independent frequency amplification, two criteria are established. Besides these criteria, a non equal frequency separation is necessary to avoid resonance overlapping when three or more frequencies are involved. The independent set of equations, which describes the wave-wave interaction in a plasma, is solved numerically for two different Light Spring configurations. In both cases, the amplification and transversal compression of the seed laser pulse have been observed, with a final profile similar to that of the usual Gaussian-shaped seed pulses. In addition, two different kinds of helical plasma waves are excited., Comment: Submitted to Physics of Plasma, 10 pages, 5 figures