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The investigation of atom number fluctuations in quantum gases at finite temperatures showcases the ongoing challenges in understanding complex quantum systems. Recently, the microcanonical nature of atom number fluctuations in weakly interacting Bose–Einstein condensates was observed. This motivates an investigation of the thermal component of partially condensed Bose gases, due to the conservation of the total atom number. Here, we present a combined analysis of both components, including a comprehensive analysis of the uncertainties in the preparation and parameter extraction of partially condensed quantum gases. This enables a complementary observation of the thermal atom number fluctuations and yields and improved value of the peak BEC atom number fluctuations Δ N p , 0 2 = (3.7 ± 7) × 10 5 close to the critical temperature. This corresponds to a reduction by 41% with respect to previous analysis and corroborates the microcanonical nature of the fluctuations. The analysis of noise contributions due to the preparation and evaluation of partially condensed Bose gases is based on Monte Carlo simulations of optical density profiles. Importantly, this allows for an estimation of the technical noise contributions to the atom number and temperature, which is generally applicable in the field of ultracold atoms. [ABSTRACT FROM AUTHOR]

We consider semiclassically scaled, weakly nonlinear Schrödinger equations with external confining potentials and additional angular-momentum rotation term. This type of model arises in the Gross–Pitaevskii theory of trapped, rotating quantum gases. We construct asymptotic solutions in the form of semiclassical wave packets, which are concentrated in both space and in frequency around an classical Hamiltonian phase-space flow. The rotation term is thereby seen to alter this flow, but not the corresponding classical action. [ABSTRACT FROM AUTHOR]

Toxic gases emitted by industries and vehicles cause environmental pollution and pose significant health risks which are becoming increasingly dangerous. Therefore, the detection of the toxic gases is crucial. The development of gas sensors with high sensitivity and fast response based on nanomaterials has garnered significant interest. In this work, we studied the adsorption behavior of B 9 − wheel structures of pristine and nitrogen functionalized borophene quantum dots for major hazardous environmental gases, such as NO2, CO2, CO, and NH3. The self-consistent-charge density-functional tight-binding method (SCC-DFTB) method was performed to investigate structural geometries, the most favorable adsorption sites, charge transfer, total densities of states, and electronic properties of the structures before and after adsorption of the gas molecules. Based on calculated results, it was found that the interaction between the borophene quantum dots and the gas molecules was chemisorption. The functionalized nitrogen atom contributed to impurity states, leading to higher adsorption energies of the functionalized borophene quantum dots compared to the pristine ones. Total densities of states revealed insights into electronic properties of gas molecules adsorbed on borophene quantum dots. The nitrogen-doped borophene quantum dots demonstrated excellent performance as a sensing material for hazardous environmental gases, especially CO2. [ABSTRACT FROM AUTHOR]

Deployment of ultracold atom interferometers (AI) into space will capitalize on quantum advantages and the extended freefall of persistent microgravity to provide high-precision measurement capabilities for gravitational, Earth, and planetary sciences, and to enable searches for subtle forces signifying physics beyond General Relativity and the Standard Model. NASA's Cold Atom Lab (CAL) operates onboard the International Space Station as a multi-user facility for fundamental studies of ultracold atoms and to mature space-based quantum technologies. We report on pathfinding experiments utilizing ultracold 87Rb atoms in the CAL AI. A three-pulse Mach–Zehnder interferometer was studied to understand the influence of ISS vibrations. Additionally, Ramsey shear-wave interferometry was used to manifest interference patterns in a single run that were observable for over 150 ms free-expansion time. Finally, the CAL AI was used to remotely measure the Bragg laser photon recoil as a demonstration of the first quantum sensor using matter-wave interferometry in space. NASA's Cold Atom Lab has operated on the International Space Station since 2018 to study quantum gases and mature quantum technologies in Earth's orbit. Here, Williams et al., report on a series of pathfinding experiments exploring the first quantum sensor using atom interferometry in space. [ABSTRACT FROM AUTHOR]

Ultracold quantum gases are usually prepared in conservative traps for quantum simulation experiments. The atomic density inhomogeneity, together with the consequent position-dependent energy and time scales of cold atoms in traditional harmonic traps, makes it difficult to manipulate and detect the sample at a higher level. These problems are partially solved by optical box traps made of blue-detuned hollow beams. However, generating a high-quality hollow beam with high light efficiency for the box trap is challenging. Here, we present a scheme that combines the fixed optics, including axicons and prisms, to pre-shape a Gaussian beam into a hollow beam with a digital micromirror device (DMD) to improve the quality of the hollow beam further, providing a nearly ideal optical potential of various shapes for preparing highly homogeneous cold atoms. The highest power-law exponent of potential walls can reach a value over 100, and the light efficiency from a Gaussian to a hollow beam is also improved compared to direct optical shaping by a mask or a DMD. Combined with a one-dimensional optical lattice, a nearly ideal two-dimensional uniform quantum gas with different geometrical boundaries can be prepared for exploring quantum many-body physics to an unprecedented level. [ABSTRACT FROM AUTHOR]

Quantum thermal engines have received much attention in recent years due to their potential applications. For a candidate group, harmonically trapped gases under Bose–Einstein condensation (BEC), we see little investigation on the energy transference around that transition. Therefore, we present an empirical study with rubidium-87 gas samples in a magnetic harmonic trap. We developed an empirical equation of state model to fit to our experimental dataset, expressing the pressure parameter in terms of temperature, and six technical coefficients, functions of the volume parameter and the number of atoms. By using standard thermodynamic relations, we determine the system's entropy, shown to be constant at the BEC transition, as expected. Being isentropic makes the BEC transition an energy source for non-mechanical work. Hence, we observed that the enthalpy at the BEC transition, at fixed values of the volume parameter, grows fairly linearly with the number of atoms. We fitted a linear function to that data, finding the specific enthalpy of the BEC transformation and the intrinsic enthalpic loss for BEC. We deem this study to be a step closer to practical quantum-based engines. [ABSTRACT FROM AUTHOR]

Recent progress in out-of-equilibrium closed quantum systems has significantly advanced the understanding of mechanisms behind their evolution toward thermalization. Notably, the concept of nonthermal fixed points (NTFPs)--responsible for the emergence of spatiotemporal universal scaling in far-from-equilibrium systems--has played a crucial role in both theoretical and experimental investigations. In this work, we introduce a differential equation that has the universal scaling associated with NTFPs as a solution. The advantage of working with a differential equation, rather than only with its solution, is that we can extract several insightful properties not necessarily present in the solution alone. How the differential equation is derived allows physical interpretation of the universal exponents in terms of the time dependence of the amplitude of the distributions and their momentum scaling. Employing two limiting cases of the equation, we determined the universal exponents related to the scaling using the distributions near just two momentum values. We established a solid agreement with previous investigations by validating this approach with three distinct physical systems. This consistency highlights the universal nature of scaling due to NTFPs and emphasizes the predictive capabilities ofthe proposed differential equation. Moreover, under specific conditions, the equation predicts a power-law related to the ratio of the two universal exponents, leading to implications concerning particle and energy transport. This suggests that the observed power-laws in far-from-equilibrium turbulent fluids could be related to the universal scaling due to NTFPs, potentially offering insights into the study of turbulence. [ABSTRACT FROM AUTHOR]

Recent advances in automated algebra for dilute Fermi gases in the virial expansion, where coarse temporal lattices were found advantageous, motivate the study of more general computational schemes that could be applied to arbitrary densities, beyond the dilute limit where the virial expansion is physically reasonable. We propose here such an approach by developing what we call the Quantum Thermodynamics Computational Engine (QTCE). In QTCE, the imaginary-time direction is discretized and the interaction is accounted for via a quantum cumulant expansion, where the coefficients are expressed in terms of non-interacting expectation values. The aim of QTCE is to enable the systematic resolution of interaction effects at fixed temporal discretization, as in lattice Monte Carlo calculations, but here in an algebraic rather than numerical fashion. Using this approach, in combination with numerical integration techniques (both known and alternative ones proposed here), we explore the thermodynamics of spin-1/2 fermions across spatial dimensions, focusing on the unitary limit. We find that, remarkably, extremely coarse temporal lattices, when suitably renormalized using known results from the virial expansion, yield stable partial sums for QTCE's cumulant expansion that are qualitatively and quantitatively correct in wide regions (when compared with known experimental results). This article is part of the theme issue 'The liminal position of Nuclear Physics: from hadrons to neutron stars'. [ABSTRACT FROM AUTHOR]

Superfluid and dissipative regimes in the dynamics of a two-component quasi-one-dimensional Bose–Einstein condensate (BEC) with unequal atom numbers in the two components have been explored. The system supports localized waves of the symbiotic type owing to the same-species repulsion and cross-species attraction. The minority BEC component moves through the majority component and creates excitations. To quantify the emerging excitations, we introduce a time-dependent function called disturbance. Through numerical simulations of the coupled Gross–Pitaevskii equations with periodic boundary conditions, we have identified a critical velocity of the localized wave, above which a transition from the superfluid to dissipative regime occurs, as evidenced by a sharp increase in the disturbance function. The factors responsible for the discrepancy between the actual critical velocity and the speed of sound, expected from theoretical arguments, have been discussed. [ABSTRACT FROM AUTHOR]

The 25th European Conference on Few-Body Problems in Physics (EFB25) was held in Mainz, Germany, in 2023, bringing together international physicists to discuss problems with only a few degrees of freedom in various areas of physics. The conference featured diverse participation, with 22% female attendees and 19% junior researchers without a doctoral degree. The event included plenary talks, special prize sessions, poster presentations, and a popular lecture on nuclear fusion as a CO2-free energy source. The next conference in the series will take place in Prague, Czech Republic, in 2026. [Extracted from the article]

Starting from a degenerate Bose gas in a hybrid trap combining a magnetic quadrupole trap and an attractive optical trap resulting from a focused laser beam, we demonstrate the efficient loading of this quantum gas into a shell-shaped trap. The shell trap is purely magnetic and relies on adiabatic potentials for atoms in an inhomogeneous magnetic field dressed by a radiofrequency (rf) field. We show that direct rf evaporation in the hybrid trap enables an efficient and simple preparation of the cold sample, well adapted to the subsequent loading procedure. The transfer into the shell trap is adiabatic and limits the final excitation of the center-of-mass motion to below 2 μ m. [ABSTRACT FROM AUTHOR]

We review the quantum statistical properties of two-dimensional shell-shaped gases, produced by cooling and confining atomic ensembles in thin hollow shells. We consider both spherical and ellipsoidal shapes, discussing at zero and at finite temperature the phenomena of Bose–Einstein condensation and of superfluidity, the physics of vortices, and the crossover from the Bardeen–Cooper–Schrieffer regime to a Bose–Einstein condensate. The novel aspects associated to the curved geometry are elucidated in comparison with flat two-dimensional superfluids. We also describe the hydrodynamic excitations and their relation with the Berezinskii–Kosterlitz–Thouless transition for two-dimensional flat and curved superfluids. In the next years, shell-shaped atomic gases will be the leading experimental platform for investigations of quantum many-body physics in curved spatial domains. [ABSTRACT FROM AUTHOR]

In this paper, we study-induced spin–orbit coupling (SOC) in one-dimensional ultracold quantum gases composed of atoms of different species. One species is subjected to an equal combination of Rashba and Dresselhaus SOC generated by Raman transition. The two species interact with each other through spin-independent and spin-exchange contact interactions. The spin-exchange interaction introduces a locking pattern of the momentum and spin degrees of freedom for the species without direct SOC. For small spin-independent interactions, the two species overlap and the induced SOC is effective. For large spin-independent interactions, however, the two species keep separate from each other and the induced SOC is negligible. We propose to generate inhomogeneous SOC by exploiting density engineering technique applied to the directly spin–orbit coupled Bose–Einstein condensate. When the effective potential is of Gaussian type, the single-particle eigenenergies and eigenstates are calculated by exact diagonalization method. For general cases, mean-field ground states are obtained by numerically searching for the minimum of energy functional. With the density engineering technique, it is possible to produce hybrid structures of plane wave, stripe and/or zero-momentum phases. [ABSTRACT FROM AUTHOR]

When a system undergoes a rapid quench from a disordered to an ordered phase, it does not order instantly but instead relaxes towards equilibrium over time. During this relaxation, the dynamical scaling hypothesis predicts that the length scale of ordered regions increases, with later patterns statistically similar to earlier ones except for a change in global scale. Quantum gases are one of many systems in which such out of equilibrium behaviour is predicted to occur. Here, we present a method for systematically testing when dynamical scaling is taking place, by quantifying the similarity of the rescaled two-point correlation function over time using the Mahalanobis distance. Data on the velocity field of a two-dimensional quantum fluid, generated from point vortex simulations, are used to illustrate the application of this method. [ABSTRACT FROM AUTHOR]

The quantum regression theorem states that the correlations of a system at two different times are governed by the same equations of motion as the single-time averages. This provides a powerful framework for the investigation of the intrinsic microscopic behaviour of physical systems by studying their macroscopic response to a controlled external perturbation. Here we experimentally demonstrate that the two-time particle number correlations in a photon Bose-Einstein condensate inside a dye-filled microcavity exhibit the same dynamics as the response of the condensate to a sudden perturbation of the dye molecule bath. This confirms the regression theorem for a quantum gas, and, moreover, demonstrates it in an unconventional form where the perturbation acts on the bath and only the condensate response is monitored. For strong perturbations, we observe nonlinear relaxation dynamics which our microscopic theory relates to the equilibrium fluctuations, thereby extending the regression theorem beyond the regime of linear response. Perturbing a physical system, for example, picking a guitar string to make it vibrate, tells a lot about its intrinsic properties. Here the authors show that such concepts hold even for quantum gases of light, which respond to a perturbation with the same dynamics as they fluctuate on their own. [ABSTRACT FROM AUTHOR]

Quantum-clock interferometry has been suggested as a quantum probe to test the universality of free fall and the universality of gravitational redshift. In typical experimental schemes, it seems advantageous to employ Doppler-free E1–M1 transitions which have so far been investigated in quantum gases at rest. Here, we consider the fully quantized atomic degrees of freedom and study the interplay of the quantum center-of-mass (COM)—that can become delocalized—together with the internal clock transitions. In particular, we derive a model for finite-time E1–M1 transitions with atomic intern–extern coupling and arbitrary position-dependent laser intensities. We further provide generalizations to the ideal expressions for perturbed recoilless clock pulses. Finally, we show, at the example of a Gaussian laser beam, that the proposed quantum-clock interferometers are stable against perturbations from varying optical fields for a sufficiently small quantum delocalization of the atomic COM. [ABSTRACT FROM AUTHOR]

Solvation, the result of the complicated interplay between solvent–solute and solvent–internal interactions, is one of the most important chemical processes. Consequently, a complete theoretical understanding of solvation seems like a heroic task. However, it is possible to elucidate fundamental solvation mechanisms by looking into simpler systems, such as ion solvation in atomic baths. In this work, we study ion solvation by calculating the ground state properties of a single ion in a neutral bath from the high‐density to the low‐density regimes, finding common ground for these two, in principle, disparate regimes. Our results indicate that a single 174Yb+ ion in a bath of 7Li atoms forms a coordination complex at high densities with a coordination number of 8, with strong electrostriction characteristic of the snowball effect. On the contrary, treating the atomic bath as a dilute quantum gas at low densities, we find that the ion‐atom interaction's short‐range plays a significant role in the physics of many‐body‐bound states and polarons. Furthermore, in this regime, we explore the role of an ion trap necessary to experimentally realize this system, which drastically affects the binding mechanism of the ion and atoms from a quantum gas. Therefore, our results give a novel insight into the universality of ion‐neutral systems in the ultracold regime and the possibilities of observing exotic many‐body effects. Keypoints: A global study of ion solvation in atomic baths from the high‐ to the low‐density regimes.The ion–atom short‐range interaction is critical to understanding the presence of many‐body‐bound states and polarons.The ion‐trapping potential drastically impacts many‐body‐bound states and polaron formation. [ABSTRACT FROM AUTHOR]

Palatini-like theories of gravity have a remarkable connection to models incorporating linear generalized uncertainty principles. Considering this, we delve into the thermodynamics of systems comprising both Bose and Fermi gases. Our analysis encompasses the equations of state for various systems, including general Fermi gases, degenerate Fermi gases, Boltzmann gases, and Bose gases such as phonons and photons, as well as Bose–Einstein condensates and liquid helium. [ABSTRACT FROM AUTHOR]

We present an all-optical method to measure and compensate for residual magnetic fields present in a cloud of ultracold atoms trapped in an optical dipole trap. Our approach leverages the increased loss from the trapped atomic sample through electromagnetically induced absorption. Modulating the excitation laser provides coherent sidebands, resulting in a Λ-type pump–probe scheme. Scanning an additional magnetic offset field leads to pairs of sub-natural linewidth resonances, whose positions encode the magnetic field in all three spatial directions. Our measurement scheme is readily implemented in typical quantum gas experiments and has no particular hardware requirements. [ABSTRACT FROM AUTHOR]

Recently universal dynamic scaling is observed in several systems, which exhibit a spatiotemporal self-similar scaling behavior, analogous to the spatial scaling near phase transition. The latter one arises from the emergent continuous scaling symmetry. Motivated by this, we investigate the possible relation between the scaling dynamics and the continuous scaling symmetry in this paper. We derive a theorem that the scaling invariance of the quenched Hamiltonian and the initial density matrix can lead to the universal dynamic scaling. It is further demonstrated both in a two-body system analytically and in a many-body system numerically. For the latter one, we calculate the dynamics of quantum gases quenched from the zero interaction to a finite interaction via the non-equilibrium high-temperature virial expansion. A dynamic scaling of the momentum distribution appears in certain momentum-time windows at unitarity as well as in the weak interacting limit. Remarkably, this universal scaling dynamics persists approximately with smaller scaling exponents even if the scaling symmetry is fairly broken. Our findings may offer a new perspective to interpret the related experiments. We also study the Contact dynamics in the BEC–BCS crossover. Surprisingly, the half-way time displays a maximum near unitarity while some damping oscillations occur on the BEC side due to the dimer state, which can be used to detect possible two-body bound states in experiments. [ABSTRACT FROM AUTHOR]

The electron tunneling rates between a two-dimensional electron gas (2DEG) and self-assembled InAs quantum dots are studied by applying a magnetic field perpendicular to the tunneling direction. For both the ground and the first excited states, the tunneling rate can be modified by a magnetic field. The field dependence of both the s and p state tunneling rates can be explained with a model, based on momentum matching between the Fermi surface of the 2DEG and the wave function of the quantum dots in momentum space. The results, together with the comparison between charging and discharging rates, provide insight into the filling sequence of the p-state electrons. [ABSTRACT FROM AUTHOR]

The recently developed concept of optical skyrmions has introduced an exciting dimension to the emerging field of Poincaré engineering in optical lattices. There remains an unexplored territory in investigating system geometries to enhance the versatility of manipulating the topological landscape within optical lattices. Here, we present both experimental and theoretical evidence showcasing the periodic vectorial characteristics of field- and spin-based skyrmion lattices, generated by plasmonic vortices with varying topological charges. Our findings reveal that the geometric symmetry of the system plays a pivotal role in governing the periodic arrangement of these vortex patterns. Building upon this arrangement, the orbital–orbital coupling of plasmonic vortices gives rise to densely packed energy flow distributions, intricately bonded to topological charges. Consequently, this results in the formation of sublattices within the momentum space, each characterized by distinct k-vectors. Skyrmion and meron topologies, driven by the intrinsic spin–orbital coupling, are presented in these lattices. This proposed framework illuminates how symmetry serves as a fundamental tool in the manipulation of optical lattice topologies, opening up new avenues in fields ranging from optical trapping, laser writing, quantum gas microscopy, to electron quantum state control, each of which is poised to benefit from these nontrivial advances. [ABSTRACT FROM AUTHOR]

Cold atomic gases provide a remarkable testbed to study the physics of interacting many-body quantum systems. Temperatures are necessarily nonzero, but cooling to the ultralow temperatures needed for quantum simulation purposes or even simply measuring the temperatures directly on the system can prove to be very challenging tasks. Here, we implement thermometry on strongly interacting two-and one-dimensional Bose gases with high sensitivity in the nanokelvin temperature range. Our method is aided by the fact that the decay of the first-order correlation function is very sensitive to the temperature when interactions are strong. We find that there may be a substantial temperature variation when the three-dimensional quantum gas is cut into two-dimensional slices or into one-dimensional tubes. Notably, the temperature for the one-dimensional case can be much lower than the initial temperature. Our findings show that this decrease results from the interplay of dimensional reduction and strong interactions. [ABSTRACT FROM AUTHOR]

In past years, optical lattices have been demonstrated as an excellent platform for making, understanding, and controlling quantum matters at nonlinear and fundamental quantum levels. Shrinking experimental observations include matter-wave gap solitons created in ultracold quantum degenerate gases, such as Bose–Einstein condensates with repulsive interaction. In this paper, we theoretically and numerically study the formation of one-dimensional gap soliton molecules and clusters in ultracold coherent atom ensembles under electromagnetically induced transparency conditions and trapped by an optical lattice. In numerics, both linear stability analysis and direct perturbed simulations are combined to identify the stability and instability of the localized gap modes, stressing the wide stability region within the first finite gap. The results predicted here may be confirmed in ultracold atom experiments, providing detailed insight into the higher-order localized gap modes of ultracold bosonic atoms under the quantum coherent effect called electromagnetically induced transparency. [ABSTRACT FROM AUTHOR]

Quantum thermal engines have received much attention in recent years due to their potential applications. For a candidate group, harmonically trapped gases under Bose–Einstein condensation (BEC), we see little investigation on the energy transference around that transition. Therefore, we present an empirical study with rubidium-87 gas samples in a magnetic harmonic trap. We developed an empirical equation of state model to fit to our experimental dataset, expressing the pressure parameter in terms of temperature, and six technical coefficients, functions of the volume parameter and the number of atoms. By using standard thermodynamic relations, we determine the system’s entropy, shown to be constant at the BEC transition, as expected. Being isentropic makes the BEC transition an energy source for non-mechanical work. Hence, we observed that the enthalpy at the BEC transition, at fixed values of the volume parameter, grows fairly linearly with the number of atoms. We fitted a linear function to that data, finding the specific enthalpy of the BEC transformation and the intrinsic enthalpic loss for BEC. We deem this study to be a step closer to practical quantum-based engines.

Quantum optical theory of absorption properties of interacting atoms is developed. The concept of local absorptance is introduced as a derivative of the logarithm of intensity with respect to the distance in the vicinity of a given spatial point and a moment of time. The intensity is represented by the quantum and statistically averaged normal product of creation and annihilation operators of the electromagnetic field. The development of an analytical method of the estimation for the kinetic and optical parameters for the system is proposed here. The calculation method of the absorption coefficient includes thermal atomic motion, Doppler effect, and the short-range interaction between atoms. The absorption coefficient explicitly takes into account the quantum nature of the optical field. The ability of the system to absorb or emit quanta is quantitatively expressed through the special form of interaction integrals. The specific form of integrals results from the structure of the quantum brackets. The interplay between the collective (virtual photon exchange) and binary (optically induced inter-particle bonding) processes determines the system behavior. The spectral profile of the local absorption coefficient for different atomic densities and time intervals is simulated for realistic parameters. [ABSTRACT FROM AUTHOR]

We consider a two-component Bose–Bose mixture at infinitely strong repulsive interactions in a tightly confining, one-dimensional ring trap and subjected to an artificial gauge field. By employing the Bethe Ansatz exact solution for the many-body wavefunction, we obtain the ground state energy and the persistent currents up to four particles. For each value of the applied flux, we then determine the symmetry of the state under particles exchange. We find that the ground-state energy and the persistent currents display a reduced periodicity with respect to the case of non-interacting particles, corresponding to reaching states with fractional angular momentum per particle. We relate this effect to the change of symmetry of the ground state under the effect of the artificial gauge field. Our results generalize the ones previously reported for fermionic mixtures with both attractive and repulsive interactions and highlight the role of symmetry in this effect.

In this mini-review, we briefly summarize some of the main concepts and ideas behind highly dilute self-bound quantum droplets of both binary and dipolar character. The latter type of systems has more recently led to the experimental discovery of a dipolar supersolid state that allows entirely new insights on this long-sought purely quantum state of matter, with exciting prospects for fundamental research as well as future applied quantum sensing technologies. The first half of the review provides a brief history of droplets and supersolidity in various settings and also discusses the self-binding in binary quantum gases, and the second half of the review summarizes our own recent work in the field, presented at the 2022 FQMT conference in Prague. [ABSTRACT FROM AUTHOR]

Detecting ammonia gas in low concentration with proper selectivity is crucial due to its harmful effects on human health and industry. Even low ammonia concentrations can cause a rapid burning sensation in the eyes, nose, and throat. In addition, it can react with copper, silver, and other heavy metals. Hence, it is essential to detect low concentrations of ammonia gas with proper selectivity. Hexagonal boron nitride quantum dots have introduced new properties and potentials for engineering applications and gas-sensing devices. A small perturbation from gas molecules can drastically alter the band structure of quantum dots. When NH3 is attached to BNQD, under the influence of the Coulomb force created between the gas and the quantum dot, the length of the bonds varies, and then the energy levels change, resulting in the band gap reduction. These changes in sub-bands can be easily detected using the optical absorption spectrum. In the present study, the changes in the optical properties of hexagonal boron nitride quantum dots in the presence of ammonia gas molecules are studied, Using density functional theory. Results show that different ammonia concentrations can alter the maximum optical absorption to higher energies. In addition, a few peaks are observed related to the transitions due to ammonia molecules in the system. The selectivity of the different gas molecules is also investigated. Moreover, the size of quantum dots was increased from 32 to 168 atoms, and it was concluded that by increasing their size, similar properties could be achieved. As a result, the present paper not only provides insight into the optical properties of hexagonal boron nitride quantum dots, but also brings up the novel idea of designing gas sensors based on such structures. [ABSTRACT FROM AUTHOR]

In this research, we use the generalized quantum multistream model to describe collective qusiparticle excitations in electron gas with arbitrary degree of degeneracy and relativity. The effective Schrödinger–Poisson and square-root Klein–Gordon–Poisson models are applied to study the energy band structure and statistical parameters of finite temperature quantum and relativistic quantum electron gas in neutralizing background charge. Based on the plasmon energy bandgap appearing above the Fermi level, a new equation of state for quasiparticle (collective) excitations with new plasma parameter definition is suggested for dense plasmas applicable to a wide range of electron temperature and density. The new criterion for quasiparticle excitations reveals some interesting aspects of relativistic quantum matter at extreme condition, such as the plasmon blackout and collective quantum pressure collapse, which are studied in the frameworks of both non-relativistic and relativistic quantum phenomena. Current quasiparticle model predicts density-temperature regimes in warm-dense matter for which collective excitations become ineffective. On the other hand, the energy band structure model predicts the quasiparticle pressure collapse in temperature–density regime close to that of white dwarf stars. The energy band structure is a powerful concept in condensed matter physics and is shown to have applications for collective quantum excitations in electron gas. It can also have direct applications in quasiparticle dielectric response and thermodynamic properties of electron gas in inertial confinement fusion, stellar core, compact stars, and charged relativistic quantum environments. It is interesting that the basic thermodynamic behavior of non-relativistic and relativistic quantum electron gases closely match up to temperature and number density of typical white dwarfs where the gravitational collapse is prone to occur. This evidently confirms the relevance of non-relativistic quantum plasmon model to study the collective excitations in warm dense matter and white dwarfs. [ABSTRACT FROM AUTHOR]

We present a highly efficient method for the numerical solution of coupled Gross–Pitaevskii equations describing the evolution dynamics of a multi-species mixture of Bose–Einstein condensates in time-dependent potentials. This method, based on a moving and expanding reference frame, compares favorably to a more standard but much more computationally expensive solution based on a frozen frame. It allows an accurate description of the long-time behavior of interacting, multi-species quantum mixtures including the challenging problem of long free expansions relevant to microgravity and space experiments. We demonstrate a successful comparison to experimental measurements of a binary Rb–K mixture recently performed with the payload of a sounding rocket experiment. [ABSTRACT FROM AUTHOR]

We review methods that allow one to detect and characterize quantum correlations in many-body systems, with a special focus on approaches which are scalable. Namely, those applicable to systems with many degrees of freedom, without requiring a number of measurements or computational resources to analyze the data that scale exponentially with the system size. We begin with introducing the concepts of quantum entanglement, Einstein–Podolsky–Rosen steering, and Bell nonlocality in the bipartite scenario, to then present their multipartite generalization. We review recent progress on characterizing these quantum correlations from partial information on the system state, such as through data-driven methods or witnesses based on low-order moments of collective observables. We then review state-of-the-art experiments that demonstrate the preparation, manipulation and detection of highly-entangled many-body systems. For each platform (e.g. atoms, ions, photons, superconducting circuits) we illustrate the available toolbox for state preparation and measurement, emphasizing the challenges that each system poses. To conclude, we present a list of timely open problems in the field. [ABSTRACT FROM AUTHOR]

We consider a heavy external object moving in an ideal gas of light particles. Collisions with the gas particles transfer momentum to the object, leading to a force that is proportional to the object's velocity but in the opposite direction. In an ideal classical gas at temperature T, the force acting on the object is proportional to T . Quantum statistics causes a deviation from the T -dependence and shows that the force scales with T2 at low temperatures. At T = 0, the force vanishes in a Bose gas but is finite in a Fermi gas. [ABSTRACT FROM AUTHOR]

In the context of quantum gases, we obtain a many-body Hamiltonian for spin-3/2 atoms with general multipole (spin, quadrupole, and octupole) exchange interaction by employing the apparatus of irreducible spherical tensor operators. This Hamiltonian implies the finite-range interaction, whereas, for zero-range (contact) potentials parameterized by the s -wave scattering length, the multipole exchange interaction becomes irrelevant. Following the reduced description method for quantum systems, we derive the quantum kinetic equation for spin-3/2 atoms in a magnetic field and apply it to examine the high-frequency oscillations known as zero sound. [ABSTRACT FROM AUTHOR]

This article reviews the recent developments in the theory of generalised hydrodynamics (GHD) with emphasis on the repulsive one-dimensional Bose gas. We discuss the implications of GHD on the mechanisms of thermalisation in integrable quantum many-body systems as well as its ability to describe far-from-equilibrium behaviour of integrable and near-integrable systems in a variety of quantum quench scenarios. We outline the experimental tests of GHD in cold-atom gases and its benchmarks with other microscopic theoretical approaches. Finally, we offer some perspectives on the future direction of the development of GHD. [ABSTRACT FROM AUTHOR]

This paper is aimed at studying the thermodynamic properties of quantum gases confined to a torus. To do that, we consider noninteracting gases within the grand canonical ensemble formalism. In this context, fermions and bosons are taken into account and the calculations are properly provided in both analytical and numerical manners. In particular, the system turns out to be sensitive to the topological parameter under consideration: the winding number. Furthermore, we also derive a model in order to take into account interacting quantum gases. To corroborate our results, we implement such a method for two different scenarios: a ring and a torus. [ABSTRACT FROM AUTHOR]

Recent research works on ultra cold quantum gases demonstrated that dipolar Bose–Einstein condensates (BECs) exhibit rich spatiotemporal dynamic where both local and nonlocal interactions are considered. We explore theoretically the possibility of controlling the formation and dynamics of soliton molecules in binary dipolar condensates with spin-orbit coupling (SOC). We exploit the variational technique to derive the new equations of motion for the widths and amplitudes, the effective potential and the oscillation frequency of the molecules. Our study confirms the existence of stable localized bound states in an optical potential. We find that the integrity of the molecules is influenced by the physical parameters, notably the local and nonlocal interactions with the SOC. These parameters are carefully chosen by the Vakhitov–Kolokolov (VK) criterion to ensure the stability of the molecules. We present the results of numerical experiments and confirm the analytical predictions. Moreover, we show the soliton–soliton interaction in each molecule when the local interactions are strong. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 6 L i atomic gases and find good agreements. [ABSTRACT FROM AUTHOR]

A sustainable and healthy environment for human settlement depends on clean air. There is high demand for effective treatment techniques for hazardous gases produced by industry since they are important contributors to air pollution. Here, we use density functional theory to examine the electronic and optical characteristics of two-dimensional zinc sulfide (2D-ZnS) quantum dots as well as their interactions with the three most harmful gases, carbon monoxide (CO), nitrogen monoxide (NO), and methane (CH4). The electronic energy gap, dipole moment, chemical potential, electronegativity, chemical hardness, and adsorption energy are estimated. Planar ZnS quantum dots show high capability for intermolecular bonding with several hazardous gases. The energy gap decreases and the reactivity increases by bonding with the hazardous gases. The UV–Vis spectra confirm the redshift to lower energies by the adsorption of CO and NO. [ABSTRACT FROM AUTHOR]

In quantum gas microscopy experiments, reconstructing the site-resolved lattice occupation with high fidelity is essential for the accurate extraction of physical observables. For short interatomic separations and limited signal-to-noise ratio, this task becomes increasingly challenging. Common methods rapidly decline in performance as the lattice spacing is decreased below half the imaging resolution. Here, we present an algorithm based on deep convolutional neural networks to reconstruct the site-resolved lattice occupation with high fidelity. The algorithm can be directly trained in an unsupervised fashion with experimental fluorescence images and allows for a fast reconstruction of large images containing several thousand lattice sites. We benchmark its performance using a quantum gas microscope with cesium atoms that utilizes short-spaced optical lattices with lattice constant 383.5 nm and a typical Rayleigh resolution of 850 nm. We obtain promising reconstruction fidelities ≳ 96% across all fillings based on a statistical analysis. We anticipate this algorithm to enable novel experiments with shorter lattice spacing, boost the readout fidelity and speed of lower-resolution imaging systems, and furthermore find application in related experiments such as trapped ions. Quantum gas microscopy is an in-situ imaging technique used to investigate many-body phenomena in cold-atom quantum simulators and can provide resolution at the single-particle level; however, limiting factors, such as short lattice constants and finite signal-to-noise ratios, weaken image resolution. Here, the authors develop an algorithm based on unsupervised deep learning that can reconstruct the occupation of an optical lattice of Cs atoms from fluorescence images with high fidelity. [ABSTRACT FROM AUTHOR]

We study the high and low-temperature thermo-statistical properties of ideal Fermi gases by taking into account the effect of generalized uncertainty principle (GUP). Starting with the logarithm of the grand partition function of ideal Fermi system, we derive the total number of particles, internal energy, entropy, and heat capacity under the GUP. For high temperatures, by obtaining a virial expansion of the equation of state of the system, the fist three virial coefficients are calculated. For low temperatures, by using the chemical potential of the system, the susceptibility for Pauli paramagnetism is derived. [ABSTRACT FROM AUTHOR]

We propose simple rectangular cross-section, few-cm long SiN waveguide designs capable of generating ultra-broadband frequency-correlated photon pairs via SFWM, exceeding an octave in bandwidth spanning the visible-to-telecom wavelengths (∼ 700–1700 nm for ∼ 1- μ m pump) with a spectral brightness of > 2.5 × 10 4 photon pairs/s/nm/mW 2 . Such compact sources, spanning the entire telecom spectrum (across O, E, S, C, L, and U bands) on one side and covering most of the major atomic transitions used in ultracold gases and solid-state based quantum memories on the other side, could potentially be employed in large-scale multi-channel hybrid (free space + fiber) quantum networking schemes in addition to the heralding of telecom single photons by utilizing high efficiency visible detectors. [ABSTRACT FROM AUTHOR]

This workshop brought together experts on the analysis of quantum many-body problems and quantum statistical mechanics, with the goal of discussing the state-of-the-art of the field, recent developments as well as challenges for the future. The main topics of discussion concerned the equilibrium and dynamical behavior of (bosonic or fermionic) quantum gases, quantum spin systems, as well as quantum field theory models like the Nelson or Fröhlich model. [ABSTRACT FROM AUTHOR]

We study the statistical properties of a gas of interacting bosons trapped in a box potential in two and three dimensions. Our primary focus is the characteristic temperature Tp, i.e., the temperature at which the fluctuations of the number of condensed atoms (or, in 2D, the number of motionless atoms) are maximal. Using the Fock state sampling method, we show that Tp increases due to interaction. In 3D, this temperature converges to the critical temperature in the thermodynamic limit. In 2D, we show the general applicability of the method by obtaining a generalized dependence of the characteristic temperature on the interaction strength. Finally, we discuss the experimental conditions necessary for the verification of our theoretical predictions. [ABSTRACT FROM AUTHOR]

The precise control of direct current (dc) magnetic fields is crucial in a wide range of experimental platforms, from ultracold quantum gases and nuclear magnetic resonance to precision measurements. In each of these cases, the Zeeman effect causes quantum states to shift in energy as a function of the magnetic field. The development of low-noise current sources is essential because electromagnets are the preferred tool to dynamically control the magnetic field. Here, we describe an ultra-low noise bipolar current source using pairs of complementary n- and p-channel metal–oxide–semiconductor field-effect transistors controlled by zero-drift operational amplifiers. Our source has a 90 kHz inherent bandwidth and provides current from −20 to 20 A with noise (0.1 Hz to 100 kHz) of 140 µA at ±20 A. [ABSTRACT FROM AUTHOR]

We analytically study the dynamics of a solitonic vortex (SV) in a superfluid confined in a non-axisymmetric harmonic trap. The study provides a framework for analyzing the role of the trap anisotropy in the oscillation of SVs observed in recent experiments on atomic Bose and Fermi superfluids. The emergence of common and statistics-dependent features is traced in a unified approach to both types of fluid. Our description, built in the hydrodynamic formalism, is based on a Lagragian approach which incorporates the vortex location as dynamical parameters of a variational ansatz. Previous operative Hamiltonian pictures are recovered through a canonically traced procedure. Our results improve the understanding of the experimental findings. Some of the observed features are shown to be specific to the tri-axial anisotropy of the trap. In particular, we characterize the nontrivial dependence of the oscillation frequency on the trapping transversal to the vortical line. The study reveals also the crucial role played by the nonlinear character of the dynamics in the observed oscillation: for the considered experimental conditions, the frequency, and, in turn, the effective inertial mass of the vortex, are found to significantly depend on the amplitude of the generated motion. It is also uncovered how the coupling with collective modes of the fluid induces a non-negligible shift in the oscillation frequency. The appearance of fine-structure features in the SV trajectory is predicted. [ABSTRACT FROM AUTHOR]