Bose Einstein Condensates

studies the Bose-Einstein condensate (BEC) stars in the light of 𝑓 (𝑅, 𝑇) gravity here with Durgapal-Fuloria (DP) metric ansatz. The function under this study features as 𝑓 (𝑅, 𝑇) = 𝑅 + 2𝜂𝑇 , where 𝜂 represents the coupling constant. With the help of it, we have formulated a stellar model describing the isotropic matter here within. Our analysis covers energy conditions, equation of state (EoS) parameter and gradients of the energy-momentum tensor components for a valid BEC stellar framework within 𝑓 (𝑅, 𝑇) gravitational theory with satisfactory results. The model's stability has been validated via multiple stability criteria viz., the velocity of sound, study of adiabatic index and surface redshift where all are found to be lying within the acceptable range for our stellar model. Thus in all the cases we have found our model to be stable and realistic. From the graphical representations the impact of the coupling constant and the parameter of the DP metric potential are clearly visible. Thus we can state that with all the above-mentioned features we have introduced new stellar solutions for BEC stars with enhanced precise results in this modified gravity.

The intrinsic coupling between local polarization vectors and superfluid vorticity represents afundamental aspect of quantum fluid dynamics governed by geometric Berry phase mechanisms. Thisreview examines the unified theoretical framework derived from spinor Gross-Pitaevskii equations,demonstrating how vortex-induced velocity fields induce polarization precession through geometricphase accumulation. The phenomenological evolution equation dP/dt = v_vor × P + Γ·P + F(P,ψ) emerges as the central result, incorporating conservative Berry phase effects and dissipativeprocesses. Applications span spinor Bose-Einstein condensates, superfluid ³He systems, and quantumturbulence in ⁴He. Numerical investigations using pseudo-spectral codes and experimental proposalsprovide pathways for validation of this geometric coupling mechanism with broader implications forquantum hydrodynamics and quantum information processing.

This paper presents a comprehensive analysis of gravitational phase shifts in quantum entangled systems, examining the equation which describes how gravitational fields induce phase modifications in quantum superpositions and entangled states. The work explores the theoretical foundations, derivation, and experimental implications of this phenomenon, which represents a crucial intersection between general relativity and quantum mechanics. Through detailed examination of neutron interferometry, optomechanical systems, neutrino oscillations, and fiber-optic measurements, this paper demonstrates how weak gravitational fields can introduce relative phases that affect quantum correlations, potentially leading to gravitational decoupling effects. The analysis includes experimental proposals for detecting these effects, their implications for quantum gravity tests, and their role in understanding the emergence of spacetime from quantum entanglement. This research contributes to our understanding of semi-classical gravity effects on quantum systems and provides pathways for future experimental verification of quantum gravitational phenomena.

We propose a new formulation for atomic side mode dynamics from super-radiant light scattering of trapped atoms. A detailed analysis of the recently observed super-radiant light scattering from trapped bose gases [S. Inouye et al., Science 285, 571 (1999)] is presented. We find that scattered light intensity can exhibit both oscillatory and exponential growth behaviors depending on densities, pump pulse characteristics, temperatures, and geometric shapes of trapped gas samples. The total photon scattering rate as well as the accompanied matter wave amplification depends explicitly on atom number fluctuations in the condensate. Our formulation allows for natural and transparent interpretations of subtle features in the MIT data, and provides numerical simulations in good agreement with all aspects of the experimental observations.

Theoretical studies of coherent single-atom transport have as yet mainly been restricted to onedimensional model systems with harmonic trapping potentials. Here we investigate this important phenomenon -a prerequsite for a variety of quantum-technology applications based on cold neutral atoms -under much more complex physical circumstances. More specificially yet, we study fast single-atom transport in a moving double-well optical lattice, whose three-dimensional (anharmonic) potential is nonseparable in the x -y plane. We propose specific configurations of acousto-optic modulators that give rise to the moving-lattice effect in an arbitrary direction in this plane. We then determine moving-lattice trajectories that enable single-atom transport using two classes of quantum-control methods: shortcuts to adiabaticity (STA), here utilized in the form of inverse engineering based on a quadratic-in-momentum dynamical invariant of Lewis-Riesenfeld type, and their recently proposed modification termed enhanced STA (eSTA). Subsequently, we quantify the resulting single-atom dynamics by numerically solving the relevant time-dependent Schrödinger equations and compare the efficiency of STA-and eSTA-based transport by evaluating the respective fidelities. We show that -while STA enables somewhat faster transport for shallow lattices -eSTA outperforms it for larger lattice depths. The present work constitutes a large stride towards fully realistic modelling of single-atom transport in complex optically-trapped neutral-atom systems.

We present a mathematical framework based on unified fractal field equations that reproduces the empirical predictions of Einstein's General Relativity while offering a fundamentally different ontological foundation. Unlike Einstein's field equations, which describe how matter-energy determines spacetime curvature through a static relationship, our unified fractal formalism introduces temporal iteration and self-referential dynamics. We demonstrate that the recursive equation generates spacetime geometry through iterative field closure rather than assuming a preexisting manifold. This approach resolves the ontological incompleteness of General Relativity by explaining the origin of spacetime structure itself, while maintaining mathematical equivalence in the classical limit. We show that stable recursive attractors correspond to known solutions of Einstein's equations, while the discrete iteration naturally regularizes singularities and provides a fundamental time scale compatible with quantum mechanics. The framework predicts subtle deviations from General Relativity in extreme regimes, including gravitational wave echoes, modified dispersion relations for high-energy particles, and a dynamically evolving cosmological constant that may explain dark energy observations.

In this paper, we determine the instability effects of a phase twist superposed on a quantum vortex defect governed by the Gross–Pitaevskii equation. For this, we consider the modified form of the equation in two cases: when a uniform phase twist is present everywhere in the condensate, and when the defect is subject to a localized phase twist confined to the defect healing region. In the first case, we show that a secondary, new defect is produced as manifestation of an Aharonov–Bohm type effect. In the second case, we prove that due to energy minimization, the defect changes its configurational energy by converting localized twist to writhe. This mechanism, typical of classical elastic systems, is shown to occur also in quantum defects, and it may find useful applications in science and technology.

Crystal is an important subject of study in a solid with structure, based on this idea it is development a higher order theory for description of this crystal with frontiers, and is studied polymer quantum mechanics with a representation that is noted to be similar in structure. Polymer quantum mechanics is an used idea for understanding of certain macro-scales for space-time that are obtained of micro-scales where are considered in these kinds of representations and are different to usual quantum mechanics. Micro-scales can represent a problem in general because these types of scales are difficult to manage, but an hypothetical Planck scale improves the understanding of polymer quantum mechanics. Using that idea, for this work a crystal is considered to be a base to describe a higher-order theory. Classical mechanics is used to describe solid structure for a crystal, with natural problems, but in polymer quantum mechanics a description with description problems. It is focused on the path integral and, it is including a polymeric quantum mechanics formalism. The path integral and polymer quantum mechanics are interesting themes because one establishes the quantum formulation, with polymeric rules that establish a different formulation. In starting this idea was to establish as an option in construction of quantum mechanics that is used in the formulation of polymeric quantum mechanics that is briefly revised for this the job for construct path integral and to analyze this type of formulation in this frame. An important fact is that the structure with frontiers must be considered, we establish a fractal structure and, perturbations.

Crystal is an important subject of study in a solid with structure, based on this idea it is development a higher order theory for description of this crystal with frontiers, and is studied polymer quantum mechanics with a representation that is noted to be similar in structure. Polymer quantum mechanics is an used idea for understanding of certain macro-scales for space-time that are obtained of micro-scales where are considered in these kinds of representations and are different to usual quantum mechanics. Micro-scales can represent a problem in general because these types of scales are difficult to manage, but an hypothetical Planck scale improves the understanding of polymer quantum mechanics. Using that idea, for this work a crystal is considered to be a base to describe a higher-order theory. Classical mechanics is used to describe solid structure for a crystal, with natural problems, but in polymer quantum mechanics a description with description problems. It is focused on the path integral and, it is including a polymeric quantum mechanics formalism. The path integral and polymer quantum mechanics are interesting themes because one establishes the quantum formulation, with polymeric rules that establish a different formulation. In starting this idea was to establish as an option in construction of quantum mechanics that is used in the formulation of polymeric quantum mechanics that is briefly revised for this the job for construct path integral and to analyze this type of formulation in this frame. An important fact is that the structure with frontiers must be considered, we establish a fractal structure and, perturbations. Keywords harmonic oscillator • string • disengaged • polymeric path integral • destructive resonance * Use footnote for providing further information about author (webpage, alternative address)-not for acknowledging funding agencies.

A quantum liquid in a heterogeneous mixture of 41 K and 87 Rb atoms is studied using the diffusion Monte Carlo method and Density Functional Theory. The perturbative Lee-Huang-Yang term for a heterogeneous mixture is verified and it is proved to be valid only near the gas-liquid transition. Based on the equations of state of the bulk mixture, calculated with diffusion Monte Carlo, extensions to Lee-Huang-Yang corrected mean-field energy functionals (MF+LHY) are presented. Using Density Functional Theory, a systematic comparison between different functionals is performed, focusing on the critical atom number, surface tension, surface width, Tolman length, and compressibility. These results are given as a function of the inter-species interaction strength, within the stability domain of the liquid mixture.

The Bose-stimulated self-organization of a quasi-two dimensional non-equilibrium Bose-Einstein condensate in an in-plane potential is proposed. We obtained the solution of the nonlinear, drivendissipative Gross-Pitaevskii equation for a Bose-Einstein condensate trapped in an external asymmetric parabolic potential within the method of the spectral expansion. We found that, in sharp contrast to previous observations, the condensate can spontaneously acquire a soliton-like shape for spatially homogenous pumping. This condensate soliton performs oscillatory motion in a parabolic trap and, also, can spontaneously rotate. Stability of the condensate soliton in the spatially asymmetric trap is analyzed. In addition to the nonlinear dynamics of non-equilibrium Bose-Einstein condensates of ultra-cold atoms, our findings can be applied to the condensates of quantum well excitons and cavity polaritons in semiconductor heterostructure, and to the condensates of photons.

First, we verify that the physical parameters estimated for the four directly detected gravitational wave (GW) events involving coalescence of binary black holes (BHs) indeed uphold the second law of BH thermodynamics, strengthening further the case for BH physics. Non-spherical gravitational collapse leading to BH formation may entail very high GW luminosities during the final phase of implosion, reaching non-negligible fraction of Dyson luminosity ∼ c/G. Most galaxies harbor supermassive black holes (SMBHs) in their nuclear regions. Several bright quasars detected at redshifts > ∼ 6 are powered by accreting SMBHs of mass > ∼ 10M⊙ when the universe was only ∼ 10 yrs old. We posit that creation of SMBHs occurs due to collapse (on dynamical time scales ∼ 10 yrs) of ultra-light bosonic dark matter (DM) particles that have undergone Bose-Einstein condensation. Furthermore, oscillations in DM Bose-Einstein condensates (BECs) triggered by tidal forces in interacting galaxies can le...

Observed active galactic nuclei at redshifts of about 6 strongly suggest that supermassive black holes (SMBHs) had formed early on. Accretion of matter onto remnants of Population III stars leading to SMBHs is a very slow process, and therefore the model faces difficulties in explaining quasars detected at $ z \gtrsim 6$. In this paper we invoke Bose-Einstein condensation of dark bosons to demonstrate that existence of very light ($m \sim 10^{-23} \ \mbox{eV}$) spinless dark matter particles can not only lead to SMBHs of mass $\gtrsim 10^{10} \ M_\odot$ at $ z \gtrsim 6$ but also such particles can masquerade as dark matter as well as dark energy.

The recent report on the realization of a Bose-Einstein condensate of G-wave molecule made up of bound pairs of Cesium bosons is a surprise. These molecules are created at the G-wave resonance at 19.87G, where the severe three-body loss usually associated with these resonance are found to be reduced significantly when the density of the gas is reduced in a quasi 2D setting. The G-wave molecules produced through this resonance have non-zero angular momentum projections, resulting in the first BEC with a macroscopic intrinsic angular momentum. Here, we show that this intrinsic angular momentum will lead to many new quantum effects. They include a splitting of collective modes in the absence of vortices, an orientation dependent energy shift due to the moment of inertia of the molecules, and a contribution to angular momentum in non-uniform magnetic fields different from that of the Berry phase current. The intrinsic angular momentum also provides a way to probe the half vortices, excitations that are unique to molecular condensates of bosons. The wavefunction giving rise to the intrinsic angular momentum can also be mapped out from the noise correlation.

Discovery of active galactic nuclei at redshifts > ∼ 6 suggests that supermassive black holes (SMBHs) formed early on. Growth of the remnants of Population III stars by accretion of matter, both baryonic as well as collisionless dark matter (DM), leading up to formation of SMBHs is a very slow process. Therefore, such models encounter difficulties in explaining quasars detected at z > ∼ 6. Furthermore, massive particles making up collisionless DM not only have so far eluded experimental detection but they also do not satisfactorily explain gravitational structures on small scales. In recent years, there is a surge in research activities concerning cosmological structure formation that involve coherent, ultra-light bosons in a dark fluid-like or fuzzy cold DM state. In this paper, we study collapse of such ultra-light bosonic halo DM that are in a Bose-Einstein condensate (BEC) phase to give rise to SMBHs on dynamical time scales. Time evolution of such self-gravitating BECs is examined using the Gross-Pitaevskii equation in the framework of time-dependent variational method. Comprised of identical dark bosons of mass m, BECs can collapse to form black holes of mass M ef f on time scales ∼ 10 8 yrs provided m M ef f > ∼ 0.64 m 2 P l. In particular, ultra-light dark bosons of mass ∼ 10 −20 eV can lead to SMBHs with mass > ∼ 10 10 M⊙ at z ≈ 6. Recently observed radio-galaxies in the ELAIS-N1 deep field with aligned jets can also possibly be explained if vortices of a rotating cluster size BEC collapse to form spinning SMBHs with angular momentum J < ∼ 3.6 nW GM 2 c , where nW and M are the winding number and mass of a vortex, respectively.

Correlações e interferência em sistemas atômicos de Bose-Einstein frios 2 Resumo Este trabalho consiste em um estudo teórico da coexistência de condensados de Bose-Einstein atômicos acoplados. Esta mistura de condensados pode consistir em átomos de um mesmo elemento em vários estados hipernos (estado interno).

We construct strongly anisotropic quantum droplets with embedded vorticity in the 3D space, with mutually perpendicular vortex axis and polarization of atomic magnetic moments. Stability of these anisotropic vortex quantum droplets (AVQDs) is verified by means of systematic simulations. Their stability area is identified in the parametric plane of the total atom number and scattering length of the contact interactions. We also construct vortex-antivortex-vortex bound states and find their stability region in the parameter space. The application of a torque perpendicular to the vorticity axis gives rise to robust intrinsic oscillations or rotation of the AVQDs. The effect of three-body losses on the AVQD stability is considered too. The results show that the AVQDs can retain the topological structure (vorticity) for a sufficiently long time if the scattering length exceeds a critical value.

We have investigated spin dynamics in a 2D quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions with superimposed angular density modulations. The density distributions depend on the applied magnetic field and are well explained by a simple Bogoliubov model. We show that the two clouds are anti-correlated in momentum space. The observed momentum correlations pave the way towards the creation of an atom source with non-local Einstein-Podolsky-Rosen entanglement.

Magneto-optical traps on atom chips are usually restricted to small atomic samples due to a limited capture volume caused primarily by distorted field configurations. Here we present a magneto-optical trap with minimized distortions based on a mesoscopic wire structure which provides a loading rate of 8.4 × 10 10 atoms/s and a maximum number of 8.7 × 10 9 captured atoms. The wire structure is placed outside of the vacuum to enable a further adaptation to new scientific objectives. Since all magnetic fields are applied locally without the need for external bias fields, the presented setup will facilitate parallel generation of Bose-Einstein condensates on a conveyor belt with a cycle rate above 1 Hz.

We calculate the excitation spectrum of a one-dimensional self-bound quantum droplet in a twocomponent bosonic mixture described by the Gross-Pitaevskii equation (GPE) with cubic and quadratic nonlinearities. The cubic term originates from the mean-field energy of the mixture proportional to the effective coupling constant δg, whereas the quadratic nonlinearity corresponds to the attractive beyond-mean-field contribution. The droplet properties are governed by a control parameter γ ∝ δgN 2/3 , where N is the particle number. For large γ > 0 the droplet features the flat-top shape with the discrete part of its spectrum consisting of plane-wave Bogoliubov phonons propagating through the flat-density bulk and reflected by edges of the droplet. With decreasing γ these modes cross into the continuum, sequentially crossing the particle-emission threshold at specific critical values. A notable exception is the breathing mode which we find to be always bound. The balance point γ = 0 provides implementation of a system governed by the GPE with an unusual quadratic nonlinearity. This case is characterized by the ratio of the breathing-mode frequency to the particle-emission threshold equal to 0.8904. As γ tends to −∞ this ratio tends to 1 and the droplet transforms into the soliton solution of the integrable cubic GPE.

A new method for the creation of 3D solitary topological modes, corresponding to vortical droplets of a two-component dilute superfluid, is presented. We use the recently introduced system of nonlinearly coupled Gross-Pitaevskii equations, which include contact attraction between the components, and quartic repulsion stemming from the Lee-Huang-Yang correction to the mean-field energy. Self-trapped vortex tori, carrying the topological charges results provide the first example of stable 3D self-trapped states with the double vorticity (1,2 2 m =), in any physical setting. The stable modes are shaped as flat-top ones, with the space between the inner hole, induced by the vorticity, and the outer boundary filled by a nearly constant density. On the other hand, all modes with hidden vorticity, i.e., topological charges of the two components 1 2 1 m m =− = , are unstable. The stability of the droplets with 1,2 1 m = against splitting (which is the main scenario of possible instability) is explained by estimating analytically the energy of the split and un-split states. The predicted results may be implemented, exploiting dilute quantum droplets in mixtures of Bose-Einstein condensates.

Dipolar Bose-Einstein condensates in an array of double-well potentials realize an effective transverse Ising model with peculiar inter-layer interactions, that may result under proper conditions in an anomalous first-order ferromagnetic-antiferromagnetic phase transition, and nontrivial phases due to frustration. The considered setup allows as well for the study of Kibble-Zurek defect formation, whose kink statistics follows that expected from the universality class of the mean-field one-dimensional transverse Ising model. Furthermore, random occupation of each layer of the stack leads to random effective Ising interactions and local transverse fields, that may lead to the Anderson-like localization of imbalance perturbations.

Atomtronics 1, 2 is an emerging interdisciplinary field that seeks new functionality by creating devices and circuits where ultra-cold atoms, often superfluids, play a role analogous to the electrons in electronics. Hysteresis is widely used in electronic circuits, e.g., it is routinely observed in superconducting circuits 3 and is essential in rf-superconducting quantum interference devices [SQUIDs] 4. Furthermore, hysteresis is as fundamental to superfluidity 5 (and superconductivity) as quantized persistent currents 6-8 , critical velocity 9-14 , and Josephson effects 15, 16. Nevertheless, in spite of multiple theoretical predictions 5, 17-19 , hysteresis has not been previously observed in any superfluid, atomic-gas Bose-Einstein condensate (BEC). Here we demonstrate hysteresis in a quantized atomtronic circuit: a ring of superfluid BEC obstructed by a rotating weak link. We directly detect hysteresis between quantized circulation states, in contrast to superfluid liquid helium experiments that observed hysteresis directly in systems where the quantization of flow could not be observed 20 and indirectly in systems that showed quantized flow 21, 22. Our techniques allow us to tune the size of the hysteresis loop and to consider the fundamental excitations that accompany hysteresis. The 1

We demonstrate the occurrence of oscillatory reactions in the ultra-cold chemistry of atom-molecular Bose-Einstein condensate. Nonlinear oscillations in the mean-field dynamics occur for a specific range of elliptic modulus, giving rise to both in- and out-phase modulations in the atom-molecule population density. The reaction front velocity is found to be controlled by photoassociation, which also regulates the condensate density. Two distinct pair of in-phase bright localized gap solitons are found as exact solutions, existence of one of which necessarily requires a background. Cnoidal atomic density-waves in a plane wave molecular background are observed in both attractive and repulsive domains. Role of intra- and inter-species interactions on both existence and stability is explicated in the presence of photoassociation.

Using semion substitution for spin variables we perform an ab initio derivation of effective action for an open quantum two-level system. For this purpose, we introduce, by using the Hubbard-Stratonovich transformation a two-time complex quantum field which average value plays the role of the Green's function for the spin variables. The field thus introduced allows us to develop a diagram technique in a standard way. The proposed formalism is used to study a spin embedded into an Ohmic reservoir as an example of the spin-boson model. Non-Markovian effects in this system are analyzed.

The recent progress in nanotechnology [1, 2] and single-molecule spectroscopy [3-5] paves the way for cost-effective organic quantum optical technologies emergent with a promise to useful devices operating at ambient conditions. We harness a π-conjugated ladder-type polymer strongly coupled to a microcavity forming hybrid light-matter states, so-called exciton-polaritons, to create excitonpolariton condensates with quantum fluid properties. Obeying Bose statistics, exciton-polaritons exhibit an extreme nonlinearity undergoing bosonic stimulation [6] which we have managed to trigger at the single-photon level, thereby providing an efficient way for all-optical ultra-fast control over the macroscopic condensate wavefunction. Here, we utilise stable excitons dressed with high energy molecular vibrations allowing for single-photon nonlinearity operation at ambient conditions. This opens new horizons for practical implementations like sub-picosecond switching, amplification and all-optical logic at the fundamental quantum limit.

We study the formation of large-scale coherent structures (a condensate) for a system of two weakly interacting classical waves. Using the coupled defocusing nonlinear Schrödinger (NLS) equations as a representative model, we focus on condensation in the phase mixing regime. We employ weak turbulence theory to provide a complete thermodynamic description of the classical condensation process. We show that the temperature and the condensate mass fractions are fully determined by the total number of particles in each component and the initial total energy. Moreover, we find that, at higher energies, condensation can occur in only one component. The theory presented provides excellent agreement with results of numerical simulations obtained by directly integrating the dynamical model.

We study the properties of nonlinear Bloch waves in a diamond chain waveguide lattice in the presence of a synthetic magnetic flux. In the linear limit, the lattice exhibits a completely flat (wavevector k-independent) band structure, resulting in perfect wave localization, known as Aharonov–Bohm caging. We find that in the presence of nonlinearity, the Bloch waves become sensitive to k, exhibiting bifurcations and instabilities. Performing numerical beam propagation simulations using the tight-binding model, we show how the instabilities can result in either the spontaneous or controlled formation of localized modes, which are immobile and remain pinned in place due to the synthetic magnetic flux.

, QUANTUS TEAM-Recent proposals for testing foundations of physics assume BECs as source of atom interferometry sensors.In this context, atom chip devices allow to build transportable BEC machines with high flux and high repetition rates,as demonstrated with MAIUS (rocket) micro-gravity experiment. In such experiments, the proximity of the atoms to the chip surface is however, limiting the optical access abd the available interferometry time necessary for high-precision measurements.This justifies the need of very well-designed BEC transport protocols in order to perform long base-line, and thus precise, atom interferometry measurements.We present optimal control theory protocols for the fast, excitation-less transport of BECs with atom chips,engineering transport ramps with duration not exceeding a 200 ms with realistic 3D anharmonic trap.This controlled transport is implemented over large distances, typically of the order of 1-2mm, i.e of about 1,000 times the size of the atomic cloud.The robustness of the transport protocol against experimental imperfections is evaluated, and the advantages over ' shorcut-to-adiabacity' schemes reported by our team will be discussed.Such robust control features are crucial for the success of novel implementation of atom interferometry experiments in space. sirine amri Institut Des Sciences Molculaires d'Orsay

We present a detailed theoretical analysis of the implementation of shortcut-to-adiabaticity protocols for the fast transport of neutral atoms with atom chips. The objective is to engineer transport ramps with durations not exceeding a few hundred milliseconds to provide metrologically relevant input states for an atomic sensor. Aided by numerical simulations of the classical and quantum dynamics, we study the behavior of a Bose-Einstein condensate in an atom chip setup with realistic anharmonic trapping. We detail the implementation of fast and controlled transports over large distances of several millimeters, i.e. distances 1000 times larger than the size of the atomic cloud. A subsequent optimized release and collimation step demonstrates the capability of our transport method to generate ensembles of quantum gases with expansion speeds in the picokelvin regime. The performance of this procedure is analyzed in terms of collective excitations reflected in residual center of mass and size oscillations of the condensate. We further evaluate the robustness of the protocol against experimental imperfections.

Low energy bremsstrahlung formulae are derived for a particle beam of charged bosons forming a Bose-Einsten condensate. The expression for energy radiated consists of two terms in this case. One of them, the larger one in the limit of large numbers of Bosons in the state, is proportional to the number of bosons squared and has the same form as one obtains in a hydrodynamic model of quantum wave mechanics. This term is sensitive to the size and shape of the wave packet especially when the force field causing acceleration is localized in extent. The second term, identical to the single particle scattering formula, is less sensitive to the wave packet size and shape and is proportional to the number of bosons in the condensate. The conclusion is that for a Bose-Einstein condensate the radiated bremsstrahlung is a sensitive function of the wave packet shape which is quite different than for a beam of incoherent particles which do not show very much dependence on the wave packet. Only lowest order radiation is calculated. It is also found that to lowest order there does not exist any situation in which the radiation loss from a coherent state of bosons vanishes completely, so that there is no analog of superconductivity in a particle beam of this type at least within the net of assumptions made in this paper. The amount of radiation can be greatly suppressed however, as it is a sensitive function of the form of the wave function.

We study the ground state of a bosonic ring ladder under a gauge flux in the vortex phase, corresponding to the case where the single-particle dispersion relation has two degenerate minima. By combining exact diagonalization and an approximate fermionization approach we show that the ground state of the system evolves from a fragmented state of two single-particle states at weak interparticle interactions to a fragmented state of two Fermi seas at large interactions. Fragmentation is inferred from the study of the eigenvalues of the reduced single-particle density matrix as well as from the calculation of the fidelity of the states. We characterize these nonclassical states by the momentum distribution, the chiral currents and the current-current correlations.

The advent of controlled experimental accessibility of Bose-Einstein condensates, as realized with e.g. cold atomic gases, exciton-polaritons, and more recently photons in a dye-filled optical microcavity, has paved the way for new studies and tests of a plethora of fundamental concepts in quantum physics. We here describe recent experiments studying a transition between laser-like dynamics and Bose-Einstein condensation of photons in the dye microcavity system. Further, measurements of the second-order coherence of the photon condensate are presented. In the condensed state we observe photon number fluctuations of order of the total particle number, as understood from effective particle exchange with the photo-excitable dye molecules. The observed intensity fluctuation properties give evidence for Bose-Einstein condensation occurring in the grand-canonical statistical ensemble regime.

The advent of controlled experimental accessibility of Bose-Einstein condensates, as realized with e.g. cold atomic gases, exciton-polaritons, and more recently photons in a dye-filled optical microcavity, has paved the way for new studies and tests of a plethora of fundamental concepts in quantum physics. We here describe recent experiments studying a transition between laser-like dynamics and Bose-Einstein condensation of photons in the dye microcavity system. Further, measurements of the second-order coherence of the photon condensate are presented. In the condensed state we observe photon number fluctuations of order of the total particle number, as understood from effective particle exchange with the photo-excitable dye molecules. The observed intensity fluctuation properties give evidence for Bose-Einstein condensation occurring in the grand-canonical statistical ensemble regime.

The leapfrogging of coaxial vortex rings is a famous effect which has been noticed since the times of Helmholtz. Recent advances in ultra-cold atomic gases show that the effect can now be studied in quantum fluids. The strong confinement which characterises these systems motivates the study of leapfrogging of vortices within narrow channels. Using the two-dimensional point vortex model, we show that in the constrained geometry of a two-dimensional channel the dynamics is richer than in an unbounded domain: alongside the known regimes of standard leapfrogging and the absence of it, we identify new regimes of image-driven leapfrogging and periodic orbits. Moreover, by solving the Gross-Pitaevskii equation for a Bose-Einstein condensate, we show that all four regimes exist for quantum vortices too. Finally, we discuss the differences between classical and quantum vortex leapfrogging which appear when the quantum healing length becomes significant compared to the vortex separation or the channel size, and when, due to high velocity, compressibility effects in the condensate becomes significant.

Quantum turbulence is characterized by many degrees of freedom interacting non-linearly to produce disordered states, both in space and in time. In this work, we investigate the decaying regime of quantum turbulence in a trapped Bose–Einstein condensate. We present an alternative way of exploring this phenomenon by defining and computing a characteristic length scale, which possesses relevant characteristics to study the establishment of the quantum turbulent regime. We reconstruct the three-dimensional momentum distributions with the inverse Abel transform, as we have done successfully in other works. We present our analysis with both the two- and three-dimensional momentum distributions, discussing their similarities and differences. We argue that the characteristic length allows us to intuitively visualize the time evolution of the turbulent state.

Francisco Machado∗†1,2, Nicholas Rivera∗2, Hrvoje Buljan, Marin Soljačić, Ido Kaminer Department of Physics, University of California, Berkeley, CA 94720, USA Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA Department of Physics, University of Zagreb, Zagreb 10000, Croatia Department of Electrical Engineering, Technion, Israel Institute of Technology, Haifa 32000, Israel

We study the dynamics of a quantum impurity immersed in a Bose-Einstein condensate as an open quantum system in the framework of the quantum Brownian motion model. We derive a generalized Langevin equation for the position of the impurity. The Langevin equation is an integro-differential equation that contains a memory kernel and is driven by a colored noise. These result from considering the environment as given by the degrees of freedom of the quantum gas, and thus depend on its parameters, e.g. interaction strength between the bosons, temperature, etc. We study the role of the memory on the dynamics of the impurity. When the impurity is untrapped, we find that it exhibits a super-diffusive behavior at long times. We find that back-flow in energy between the environment and the impurity occurs during evolution. When the particle is trapped, we calculate the variance of the position and momentum to determine how they compare with the Heisenberg limit. One important result of this paper is that we find position squeezing for the trapped impurity at long times. We determine the regime of validity of our model and the parameters in which these effects can be observed in realistic experiments.

We present an analytical model for the theoretical analysis of spin dynamics and spontaneous symmetry breaking in a spinor Bose-Einstein condensate (BEC). This allows for an excellent intuitive understanding of the processes and provides good quantitative agreement with the experimental results of Scherer et al. [Phys. Rev. Lett. 105, 135302 (2010)]. It is shown that the dynamics of a spinor BEC initially prepared in an unstable Zeeman state m F = 0 (|0) can be understood by approximating the effective trapping potential for the state |±1 with a cylindrical box potential. The resonances in the creation efficiency of these atom pairs can be traced back to excitation modes of this confinement. The understanding of these excitation modes allows for a detailed characterization of the symmetry-breaking mechanism, showing how a twofold spontaneous breaking of spatial and spin symmetry can occur. In addition, a detailed account of the experimental methods for the preparation and analysis of spinor quantum gases is given.