Bose-Einstein Condensate Research Articles

Quantum-enhanced sensing by echoing spin-nematic squeezing in atomic Bose–Einstein condensate

Quantum-enhanced sensing by echoing spin-nematic squeezing in atomic Bose–Einstein condensate

Photon Bose–Einstein Condensation and Lasing in Semiconductor Cavities

AbstractPhoton Bose–Einstein condensation and photon thermalisation have been largely studied with molecular gain media in optical cavities. However, their observation with semiconductors has remained elusive despite a large body of experimental results and very well established theoretical models. In this work, these models are used to build a new theoretical framework that enables revisiting lasing to compare with photon Bose–Einstein condensation in the driven‐dissipative regime. The thermalisation figures of merit and the different experimental procedures to asses thermalization are discussed. Finally, the fluctuations of the system and their relation to the different regimes are explored.

Retrieval of optical solitons: Complex cubic–quintic Ginzburg–Landau equation augmented with the anti-cubic law

This article presents an investigation of soliton solutions for the complex cubic–quintic Ginzburg–Landau equation having anti-cubic law nonlinearity which arises in wave propagation through optical fibers using the enhanced Kudryashov method for the first time. The used method generates all the solutions extracted by classical Kudryashov and new Kudryashov methods at once. This simple yet powerful technique can be applied to a broad range of nonlinear partial differential equations. Applying the method to the Ginzburg–Landau equation, dark, bright, and kink solitons were successfully obtained. Moreover, the effect of the anti-cubic law form, which is the nonlinearity form of the model, on the dynamics of the soliton was examined and it was observed that this form caused a deterioration from a dark soliton to a W-like soliton. Both types of solitons are important in nonlinear systems and are monitored in a variety of physical systems such as optical fibers, Bose–Einstein condensates, and superconductors. This study may have valuable insights into the behavior of soliton solutions of the complex cubic–quintic Ginzburg–Landau equation having anti-cubic law nonlinearity and can contribute to the development of new technologies in nonlinear optics.

Phase Diagram of High-Temperature Electron-Hole Quantum Droplet in Two-Dimensional Semiconductors.

Quantum liquids, systems exhibiting effects of quantum mechanics and quantum statistics at macroscopic levels, represent one of the most exciting research frontiers of modern physical science and engineering. Notable examples include Bose-Einstein condensation (BEC), superconductivity, quantum entanglement, and a quantum liquid. However, quantum liquids are usually only stable at cryogenic temperatures, significantly limiting fundamental studies and device development. Here we demonstrate the formation of stable electron-hole liquid (EHL) with the quantum statistic nature at temperatures as high as 700 K in monolayer MoS2 and elucidate that the high-temperature EHL exists as droplets in sizes of around 100-160 nm. We also develop a thermodynamic model of high-temperature EHL and, based on the model, compile an exciton phase diagram, revealing that the ionized photocarrier drives the gas-liquid transition, which is subsequently validated with experimental results. The high-temperature EHL provides a model system to enable opportunities for studies in the pursuit of other high-temperature quantum liquids. The results can also allow for the development of quantum liquid devices with practical applications in quantum information processing, optoelectronics, and optical interconnections.

Dual Control of Enhanced Quasi-Bound States in the Continuum Emission from Resonant c-Si Metasurfaces.

Optical bound states in the continuum (BICs) offer strong interactions with quantum emitters and have been extensively studied for manipulating spontaneous emission, lasing, and polariton Bose-Einstein condensation. However, the out-coupling efficiency of quasi-BIC emission, crucial for practical light-emitting devices, has received less attention. Here, we report an adaptable approach for enhancing quasi-BIC emission from a resonant monocrystalline silicon (c-Si) metasurface through lattice and multipolar engineering. We identify dual-BICs originating from electric quadrupoles (EQ) and out-of-plane magnetic dipoles, with EQ quasi-BICs exhibiting concentrated near-fields near the c-Si nanodisks. The enhanced fractional radiative local density of states of EQ quasi-BICs overlaps spatially with the emitters, promoting efficient out-coupling. Furthermore, coupling the EQ quasi-BICs with Rayleigh anomalies enhances directional emission intensity, and we observe inherent opposite topological charges in the multipolarly controlled dual-BICs. These findings provide valuable insights for developing efficient nanophotonic devices based on quasi-BICs.

Efficient atom-molecule conversion in Bose–Einstein condensates based on nonlinear dressed-state scheme

We investigate the dynamics of atomic and molecular Bose–Einstein condensates via nonlinearly dressed states. Under the resonance-locking condition, we add a correction for an initial Hamiltonian to construct the dressed states with only second-order nonlinearity. Compared to the nonlinear stimulated Raman adiabatic passage, atomic-molecular conversion in our protocol is realized by following the dressed states instead of the dark state, thus it can produce a fast conversion passage. Furthermore, we introduce a control parameter to reduce the occupancy of the excited molecule state, and the conversion efficiency can be improved significantly by increasing the value of this parameter.

Matter-wave gap solitons and vortices of dense Bose–Einstein condensates in Moiré optical lattices

Optical lattices provide a key enabling and controllable platform for exploring new physical phenomena and implications of degenerate quantum gases both in the quantum and nonlinear regimes. Based on the Gross–Pitaevskii/nonlinear Schrödinger equation with competing cubic–quintic nonlinearity, we show, numerically and theoretically, the nonlinear localization of dense Bose–Einstein condensates (BECs) in a novel two-dimensional twisted periodic potential called Moiré optical lattices which, in essence, build a bridge between the perfect optical lattices and aperiodic ones. Our theory reveals that the Moiré optical lattices display a wider second gap and flat-band feature, and support two kinds of localized matter-wave structures like gap solitons and topological states (gap vortices) with vortex charge s=1, all populated inside the finite gaps of the linear Bloch-wave spectrum. We demonstrate, by means of linear-stability analysis and direct perturbed evolutions, that these localized structures have wide stability regions, paving the way for studying flat-band and Moiré physics in shallow optical lattices and for finding robust coherent matter waves therein. The twisted periodic structures can be readily implemented with currently available optical-lattice technique in BECs and nonlinear optics experiments where the results predicted here are observable.

Relative dynamics of quantum vortices and massive cores in binary BECs

We study the motion of superfluid vortices with filled massive cores. Previous point-vortex models already pointed out the impact of the core mass on the vortex dynamical properties, but relied on an assumption that is questionable in many physical systems where the immiscibility condition is barely satisfied: the fact that the massive core always lays at the very bottom of the effective confining potential constituted by the hosting vortex. Here, we relax this assumption and present a new point-vortex model where quantum vortices are harmonically coupled to their massive cores. We thoroughly explore the new dynamical regimes offered by this improved model; we then show that the functional dependence of the system normal modes on the microscopic parameters can be correctly interpreted only within this new generalized framework. Our predictions are benchmarked against the numerical simulations of coupled Gross–Pitaevskii equations for a realistic mixture of atomic Bose–Einstein condensates.

One-dimensional Townes solitons in dual-core systems with localized coupling.

The recent creation of Townes solitons (TSs) in binary Bose-Einstein condensates and experimental demonstration of spontaneous symmetry breaking (SSB) in solitons propagating in dual-core optical fibers has drawn renewed interest in the TS and SSB phenomenology in these and other settings. In particular, stabilization of TSs, which are always unstable in free space, is a relevant problem with various ramifications. We introduce a system which admits exact solutions for both TSs and SSB of solitons. It is based on a dual-core waveguide with quintic self-focusing and fused (localized) coupling between the cores. The respective system of coupled nonlinear Schrödinger equationsgives rise to exact solutions for full families of symmetric and asymmetric solitons, which are produced by the supercritical SSB bifurcation (i.e., the symmetry-breaking phase transition of the second kind). Stability boundaries of asymmetric solitons are identified by dint of numerical methods. Unstable solitons spontaneously transform into robust moderately asymmetric breathers or strongly asymmetric states with small intrinsic oscillations. The setup can be used in the design of photonic devices operating in coupling and switching regimes.

Hyper-entangling mesoscopic bound states

We predict hyper-entanglement generation by binary scattering of mesoscopic bound states, considering solitary waves in Bose–Einstein condensates containing thousands of identical Bosons. For it to occur, the underlying many-body Hamiltonian must not be integrable, and the pre-collision quantum state of the solitons needs to be fragmented. Under these conditions, we show that the post-collision state will be hyper-entangled in spatial degrees of freedom and atom number within solitons, for realistic parameters. The effect links aspects of non-linear systems and quantum-coherence and the entangled post-collision state challenges present entanglement criteria for identical particles. Our results are based on simulations of colliding quantum solitons in a quintic interaction model beyond the mean-field, using the truncated Wigner approximation.

The condensation of ideal Bose gas in a gravitational field in the framework of Dunkl-statistic

In the framework of the theory of Dunkl-deformed bosons, Bose-Einstein condensation of two and three-dimensional Dunkl-boson gases confined in the one-dimensional gravitational field is investigated. Using the semi-classical approximation method, we calculate the expressions of the Dunkl-critical temperature $T_{c}^{D}$, the ground state population $\frac{N_{0}^{D}}{N}$ and the Dunkl-mean energy and Dunkl-specific heat functions. Further numerical calculation shows that the condensation temperature ratio $\frac{T_{c}^{D}}{T_{c}^{B}}$ increases with the increasing Wigner parameter.

Emergence of tunable periodic density correlations in a Floquet–Bloch system

In quantum gases, two-body interactions are responsible for a variety of instabilities that depend on the characteristics of both trapping and interactions. These instabilities can lead to the appearance of new structures or patterns. We report on the Floquet engineering of such a parametric instability, on a Bose-Einstein condensate held in a time-modulated optical lattice. The modulation triggers a destabilization of the condensate into a state exhibiting a density modulation with a new spatial periodicity. This new crystal-like order, which shares characteristic correlation properties with a supersolid, directly depends on the modulation parameters: The interplay between the Floquet spectrum and interactions generates narrow and adjustable instability regions, leading to the growth, from quantum or thermal fluctuations, of modes with a density modulation noncommensurate with the lattice spacing. This study demonstrates the production of metastable exotic states of matter through Floquet engineering and paves the way for further studies of dissipation in the resulting phase and of similar phenomena in other geometries.

BCS–BEC crossover in a quasi-two-dimensional Fermi superfluid

We study the crossover from the Bardeen–Cooper–Shrieffer regime to the Bose–Einstein-condensation regime in an anisotropic trapped quantum gas of ultracold fermionic atoms. Using an effective two-dimensional Hamiltonian with renormalized interactions between atoms and dressed molecules, we extend the Gaussian pair fluctuation theory to quasi-two-dimensional systems. The equation of state, pair size and sound velocity as well as the convexity parameters of the Goldstone mode are investigated to show how Fermi superfluidity is affected by reduced dimensionality and Gaussian fluctuations at zero temperature in a wide range of crossover. We compare our results with the recent experiment of atomic gases and find good agreements.

Dynamics of polaron formation in 1D Bose gases in the strong-coupling regime

We discuss the dynamics of the formation of a Bose polaron when an impurity is injected into a weakly interacting one-dimensional Bose condensate. While for small impurity-boson couplings this process can be described within the Froehlich model as generation, emission and binding of Bogoliubov phonons, this is no longer adequate if the coupling becomes strong. To treat this regime we consider a mean-field approach beyond the Froehlich model which accounts for the backaction to the condensate, complemented with Truncated Wigner simulations to include quantum fluctuation. For the stationary polaron we find a periodic energy-momentum relation and non-monotonous relation between impurity velocity and polaron momentum including regions of negative impurity velocity. Studying the polaron formation after turning on the impurity-boson coupling quasi-adiabatically and in a sudden quench, we find a very rich scenario of dynamical regimes. Due to the build-up of an effective mass, the impurity is slowed down even if its initial velocity is below the Landau critical value. For larger initial velocities we find deceleration and even backscattering caused by emission of density waves or grey solitons and subsequent formation of stationary polaron states in different momentum sectors. In order to analyze the effect of quantum fluctuations we consider a trapped condensate to avoid 1D infrared divergencies. Using Truncated Wigner simulations in this case we show under what conditions the influence of quantum fluctuations is small.

Dipolar Bose–Einstein condensation of 168Er and anisotropic expansion dynamics

We report on the realization of Bose–Einstein condensation (BEC) of 168Er atoms in a crossed optical dipole trap. A magneto-optical trap is realized with just one laser driving the narrow-line transition which increases the phase space density and facilitates the evaporative cooling. A pure BEC with 3 ×104 atoms is achieved by forced evaporative cooling. The complex Feshbach resonance and anisotropic expansion of 168Er are investigated by the loss spectroscopy and controlling the rotating dipoles.

Well-posedness of space fractional Ginzburg–Landau equations involving the fractional Laplacian arising in a Bose–Einstein condensation and its kernel based approximation

This study aims to investigate some theoretical results, numerical study and a real-word application of the SFGLE, involving the fractional Laplacian. First, we describe the application of SFGLE in the Bose–Einstein condensate, where the energy of bosons is transported over long distances. Then, the existence, uniqueness and regularity of the local weak solutions are briefly analyzed. These theoretical results are presented for the first time. Next, the new Green reproducing kernels are introduced for utilization in the numerical solution of SFGLE. The finite difference scheme, introduced by Meerschaer in 2004, is employed to estimate the fractional derivative. For the temporal discretization, an implicit midpoint difference method is applied. The stability, well-posedness of the numerical solution, and the doubled L2–convergence order are attended in details. Our numerical method has the ability to handle high dimensions for numerically solve the equations defined in the hypercube domain. The accuracy and efficiency of our method are evaluated by presenting various 2D and 3D examples and the results will be validated with the previous related works. Ultimately, the utilization of an artificial neural network and empirical outcomes is employed to anticipate the BEC dynamics of Strontium by SFGLE at a specific instance. Subsequently, a comparison between the obtained consequences and experimental data is carried out to demonstrate the authentic applicability of FGLE in precisely describing several physical phenomena.

Bound states in Bose-Einstein condensates with radially-periodic spin-orbit coupling

We consider Bose-Einstein condensate (BEC) subject to the action of spin-orbit-coupling (SOC) periodically modulated in the radial direction. In contrast to the commonly known principle that periodic potentials do not create bound states, the binary BEC maintains multiple localized modes in the linear limit, with their chemical potential falling into spectral gaps of the (numerically found) radial band structure induced by the spatial modulation of the SOC. In the presence of the repulsive nonlinearity, the SOC modulation supports fundamental gap solitons of the semi-vortex types, as well as higher-order vortex gap solitons. The localization degree and stability of the gap solitons strongly depend on the location of their chemical potential in the gap. Stability intervals for vortex gap solitons in a broad range of the intrinsic vorticity, from −2 to 3, are identified. Thus, the analysis reveals the previously unexplored mechanism of linear and nonlinear localization provided by the spatially periodic modulation of SOC, which may be extended to other settings, such as those for optical beams and polaritons. Unlike the commonly known quartets of eigenvalues for small perturbations, in the present system the instability is accounted for by shifted complex eigenvalue pairs.

Exploring the role of beyond mean-field interaction in the structure and dynamics of one-dimensional quantum droplets

We present simulation results of the ground state structure and dynamics of quantum droplets (QDs) in one-dimensional spin–orbit coupled binary Bose–Einstein condensates. We have considered two cases for this analysis, such as (i) the mean-field term has a vanishingly small contribution utilizing the equal and opposite inter- and intraspecies interactions and (ii) unequal inter- and intraspecies interactions. The QD exhibits remarkably different natures in each case. In the former case, it exhibits a bright sech-like droplet nature, while in the latter case, we find the flattened sech-like shape of the droplet. Further, we analyze the effect of velocity perturbation on the dynamics in both cases. For the first case, we find a systematic change from the solitonic droplet nature to the breathing droplet, which finally has a moving droplet feature upon increasing the velocity. However, the second case shows similar dynamics except having more dynamically stable features than the first. Finally, we present various dynamics that ensued in the QD due to the quenching of the interaction parameters, coupling parameters or allowing the droplet to undergo collisions.

Rayleigh-Taylor instability in a phase-separated three-component Bose-Einstein condensate

Rayleigh-Taylor instability in a phase-separated three-component Bose-Einstein condensate

Matter-wave solitons in an array of spin-orbit-coupled Bose-Einstein condensates.

We investigate matter-wave solitons in a binary Bose-Einstein condensate (BEC) with spin-orbit (SO) coupling, loaded in a one-dimensional (1D) deep optical lattice and a three-dimensional anisotropic magnetic trap, which creates an array of elongated sub-BECs with transverse tunneling. We show that the system supports 1D continuous and discrete solitons localized in the longitudinal (along the array) and the transverse (across the array) directions, respectively. In addition, such solitons are always unpolarized in the zero-momentum state but polarized in finite-momentum states. We also show that the system supports stable two-dimensional semidiscrete solitons, including single- and multiple-peaked ones, localized in both the longitudinal and transverse directions. Stability diagrams for single-peaked semidiscrete solitons in different parameter spaces are identified. The results reported here are beneficial not only for understanding the physical property of SO-coupled BECs but also for generating new types of matter-wave solitons.