Bose-Einstein Condensate Of Dilute Gas Research Articles

Galilean invariant dynamics in an emergent spin-orbit coupled Zeeman lattice

Periodic band structures are a hallmark phenomenon of condensed matter physics. While often imposed by external potentials, periodicity can also arise through the interplay of couplings that are not necessarily spatially periodic on their own, but this option is generally less explored than the fully-periodic counterpart. Here, we investigate dynamics in a lattice structure that emerges from the simultaneous application of Raman and radio frequency coupling to a dilute-gas Bose-Einstein condensate. We elaborate on the role of Galilean invariance in this system and demonstrate a variety of techniques, including Bloch oscillations and lattice shaking with spin and momentum resolved measurements. This combined coupling scheme allows for tunability and control, enabling future investigations into unconventional band structures such as quasi-flat ground bands and those with semimetal-like band gaps.

Stability in turbulence: The interplay between shocks and vorticity in a superfluid with higher-order dispersion

Higher-order dispersion can lead to intriguing dynamics that are becoming a focus of modern hydrodynamics research. Such systems occur naturally, for example in shallow water waves and nonlinear optics, for which several types of novel dispersive shocks structures have been identified. Here we introduce ultracold atoms as a tunable quantum simulations platform for higher-order systems. Degenerate quantum gases are well controlled model systems for the experimental study of dispersive hydrodynamics in superfluids and have been used to investigate phenomena such as vortices, solitons, dispersive shock waves and quantum turbulence. With the advent of Raman-induced spin-orbit coupling, the dispersion of a dilute gas Bose-Einstein condensate can be modified in a flexible way, allowing for detailed investigations of higher-order dispersion dynamics. Here we present a combined experimental and theoretical study of shock structures generated in such a system. The breaking of Galilean invariance by the spin-orbit coupling allows two different types of shock structures to emerge simultaneously in a single system. Numerical simulations suggest that the behavior of these shock structures is affected by interactions with vortices in a manner reminiscent of emerging viscous hydrodynamics due to an underlying quantum turbulence in the system. This result suggests that spin-orbit coupling can be used as a powerful means to tun the effective viscosity in cold-atom experiments serving as quantum simulators of turbulent hydrodynamics, with applications from condensed matter and optics to quantum simulations of neutron stars.

Three-Component Soliton States in Spinor F=1 Bose-Einstein Condensates.

Dilute-gas Bose-Einstein condensates are an exceptionally versatile test bed for the investigation of novel solitonic structures. While matter-wave solitons in one- and two-component systems have been the focus of intense research efforts, an extension to three components has never been attempted in experiments. Here, we experimentally demonstrate the existence of robust dark-bright-bright (DBB) and dark-dark-bright solitons in a multicomponent F=1 condensate. We observe lifetimes on the order of hundreds of milliseconds for these structures. Our theoretical analysis, based on a multiscale expansion method, shows that small-amplitude solitons of these types obey universal long-short wave resonant interaction models, namely, Yajima-Oikawa systems. Our experimental and analytical findings are corroborated by direct numerical simulations highlighting the persistence of, e.g., the DBB soliton states, as well as their robust oscillations in the trap.

Overlap of exact and Gross-Pitaevskii wave functions in Bose-Einstein condensates of dilute gases

It has been proven theoretically for bosons with two-body repulsive interaction potentials in the dilute limit that the Gross-Pitaevskii equation provides the exact energy and density per particle as does the basic many-particle Schr\"odinger equation [E. H. Lieb and R. Seiringer, Phys. Rev. Lett. 88, 170409 (2002)]. Here, we investigate the overlap of the Gross-Pitaevskii and exact ground-state wave functions. It is found that this overlap is always smaller than unity and may even vanish despite the fact that both wave functions provide the same energy and density per particle. Consequences are discussed.

Reservoir interactions of a vortex in a trapped three-dimensional Bose-Einstein condensate

We simulate the dissipative evolution of a vortex in a trapped finite-temperature dilute-gas Bose-Einstein condensate using first-principles open-systems theory. Simulations of the complete stochastic projected Gross-Pitaevskii equation for a partially condensed Bose gas containing a single quantum vortex show that the transfer of condensate energy to the incoherent thermal component without population transfer provides an important channel for vortex decay. For the lower temperatures considered, this effect is significantly larger that the population transfer process underpinning the standard theory of vortex decay, and is the dominant determinant of the vortex lifetime. A comparison with the Zaremba-Nikuni-Griffin kinetic (two-fluid) theory further elucidates the role of the particle transfer interaction, and suggests the need for experimental testing of reservoir interaction theory. The dominance of this particular energetic decay mechanism for this open quantum system should be testable with current experimental setups, and its observation would have broad implications for the dynamics of atomic matter waves and experimental studies of dissipative phenomena.

К теории рассеяния света бозе-эйнштейновским конденсатом разреженного газа

К теории рассеяния света бозе-эйнштейновским конденсатом разреженного газа

Experimental Realization of Josephson Junctions for an Atom SQUID

We report the creation of a pair of Josephson junctions on a toroidal dilute gas Bose-Einstein condensate (BEC), a configuration that is the cold atom analog of the well-known dc superconducting quantum interference device (SQUID). We observe Josephson effects, measure the critical current of the junctions, and find dynamic behavior that is in good agreement with the simple Josephson equations for a tunnel junction with the ideal sinusoidal current-phase relation expected for the parameters of the experiment. The junctions and toroidal trap are created with the painted potential, a time-averaged optical dipole potential technique which will allow scaling to more complex BEC circuit geometries than the single atom-SQUID case reported here. Since rotation plays the same role in the atom SQUID as magnetic field does in the dc SQUID magnetometer, the device has potential as a compact rotation sensor.

Two polaron flavors of the Bose-Einstein condensate impurity

We show that repulsive neutral-atom impurities in a dilute gas Bose-Einstein condensate (BEC) can self-localize in bubble polaron states formally analogous to electron bubbles in helium. The BEC is then the first impurity host medium known to exhibit both Landau-Pekar polaron states akin to that of self-localized electrons in a dielectric lattice and self-localized bubble polaron states. We find that the neutral BEC-impurity system is fully characterized by only two dimensionless coupling constants and that a single BEC impurity can be steered adiabatically from the Landau-Pekar to the bubble region. The adiabatic change is that of a crossover, not a transition.

Repulsive Nonlinear Schrödinger Equation and Bose-Einstein Condensate in Phase Space

Within the framework of the quantum phase-space representation established by Torres-Vega and Frederick, the rigorous solutions of repulsive nonlinear Schrödinger equation are solved, which models the dilute-gas Bose-Einstein condensate. The eigenfunctions in position and momentum spaces can be obtained through the “Fourier-like” projection transformation from the phase-space eigenfunctions. It shows that the wave-mechanics method in the phase-space representation could be extended to the nonlinear Schrödinger equations. The research provides the foundation for the approximate calculation in future.

Dark-dark solitons and modulational instability in miscible two-component Bose-Einstein condensates

We investigate the dynamics of two miscible superfluids experiencing fast counterflow in a narrow channel. The superfluids are formed by two distinguishable components of a trapped dilute-gas Bose-Einstein condensate (BEC). The onset of counterflow-induced modulational instability throughout the cloud is observed and shown to lead to the proliferation of dark-dark vector solitons. These solitons do not exist in single-component systems, exhibit intriguing beating dynamics, and can experience a transverse instability leading to vortex line structures. Experimental results and multidimensional numerical simulations are presented.

Guiding-center dynamics of vortex dipoles in Bose-Einstein condensates

A quantized vortex dipole is the simplest vortex molecule, comprising two counter-circulating vortex lines in a superfluid. Although vortex dipoles are endemic in two-dimensional superfluids, the precise details of their dynamics have remained largely unexplored. We present here several striking observations of vortex dipoles in dilute-gas Bose-Einstein condensates, and develop a vortex-particle model that generates vortex line trajectories that are in good agreement with the experimental data. Interestingly, these diverse trajectories exhibit essentially identical quasi-periodic behavior, in which the vortex lines undergo stable epicyclic orbits.

Stability of exact solutions of the cubic-quintic nonlinear Schrödinger equation with periodic potential

The nonlinear Schrodinger equation with attractive quintic nonlinearity in periodic potential in 1D, modeling a dilute-gas Bose–Einstein condensate in a lattice potential, is considered and one family of exact stationary solutions is discussed. Some of these solutions have an analog neither in the linear Schrodinger equation nor in the integrable nonlinear Schrodinger equation. Their stability is examined analytically and numerically.

Resource Article: Experiments with Vortices in Superfluid Atomic Gases

Observations of quantized vortices in dilute-gas Bose-Einstein condensates were first reported in 1999. Over the next 10 years, more than 70 papers describing experiments involving vortices in superfluid atomic gases were published in scientific journals. This resource article provides a guide to the published experimental studies related to quantized vortices in atomic Bose-Einstein condensates and superfluid Fermi gases. A BibTex-formatted bibliography document listing these published studies is also available electronically.

Observing the dance of a vortex−antivortex pair, step by step

The investigation of vortices in superfluids is a fascinating and active line of research that, by now, has a history spanning over half a century. Starting from the first observations of quantized circulation in liquid helium in the 1950s [1], the field has undergone tremendous progress. Nowadays, dilute-gas Bose-Einstein condensates (BECs) provide a powerful tool with which vortex research can be pushed into new regimes, and several hallmark results have been obtained, reaching from interferometric measurements of the quantum mechanical phase of individual vortices to the direct imaging of large vortex lattices containing over 300 vortices in a regular array [2]. Now Tyler Neely and collaborators at the University of Arizona in the US, the Jack Dodd Center for Quantum Technology in New Zealand, and the University of Queensland in Australia [3] are adding another chapter to the story of vortices in superfluids. They have succeeded in creating vortex dipoles, consisting of a vortex paired with an antivortex, in such a controlled way that the dynamics can be studied in detail. An antivortex differs from a vortex only in the orientation of the circular fluid flow. When a vortex and an antivortex meet in a harmonic trap (such as the one holding the BEC in the Neely experiment), they can pair up to form a vortex dipole and then perform an enchanting dance that has now been imaged for the first time. The long lifetime of the vortex dipole and the stability of the observed dynamics are quite intriguing, indicating that such dynamics may also play a key role in other situations where vortices and antivortices emerge, e.g., superfluid turbulence. In another recent paper, periodic streets of vortex pairs in BECs have been studied numerically by Sasaki et al. [4]. Vortex physics also exists in systems as diverse as superfluid Fermi systems, magnetic flux lines in superconductors, and neutron stars. Thus a precise understanding of vortex dynamics is highly desirable, and BECs can lead the way in elucidating the physics of vortices in a well-controlled environment. Vortices emerge when a superfluid is subjected to rotation. At first sight, it may seem surprising that something as apparently simple as inducing rotation would lead to interesting dynamics. To see why this is the case, recall that the velocity of a superfluid is proportional to the gradient of the phase of the underlying macroscopic wave function. The curl of a gradient field is generally zero and thus the flow is irrotational. Consequently, interesting dynamics are bound to occur when the irrotational fluid is subjected to rotation. The outcome is best understood by first considering the flow of water in a sink after the drain plug has been pulled. The water starts rushing down the drain and after a short while forms a rather stable vortex above the drain. If a little paper boat is placed into the swirling water, the boat spirals around the drain in such a way that its bow always points into the same direction. This is due to the fact that conservation of angular momentum of the water spiraling towards the drain leads to a 1/r dependence of the fluid velocity on the distance r from the drain, “compensating” for the rotation of the fluid around the drain. So the flow is irrotational, even though the stream is clearly curved. If, on the other hand, the boat is placed such that it stretches across the central eddy, then it is found to rapidly spin around its vertical axis. For a rotating superfluid, the situation is quite similar: based on the requirement of a uniquely valued wave function, similar 1/r dependence can be derived. Vorticity, defined as the curl of the velocity field, is concentrated in the vortex core where the superfluid density goes to zero. Everywhere else the fluid is irrotational, as expected for a superfluid. Over the past decade, many experimental techniques have been devised and implemented to generate vorticity in BECs [2]. Most of these techniques either create vortices that all spin in the same way (i.e., no antivortices), or offer little to no control over the vor-

Observation of Vortex Dipoles in an Oblate Bose-Einstein Condensate

We report experimental observations and numerical simulations of the formation, dynamics, and lifetimes of single and multiply charged quantized vortex dipoles in highly oblate dilute-gas Bose-Einstein condensates (BECs). We nucleate pairs of vortices of opposite charge (vortex dipoles) by forcing superfluid flow around a repulsive Gaussian obstacle within the BEC. By controlling the flow velocity we determine the critical velocity for the nucleation of a single vortex dipole, with excellent agreement between experimental and numerical results. We present measurements of vortex dipole dynamics, finding that the vortex cores of opposite charge can exist for many seconds and that annihilation is inhibited in our trap geometry. For sufficiently rapid flow velocities, clusters of like-charge vortices aggregate into long-lived multiply charged dipolar flow structures.

The volume superradiant reflection from Bose-Einstein condensate of dilute gas

Here we give a theoretical estimation of the volume superradiant reflection from Bose-Einstein condensate of dilute gas and compare it with Fresnel’s one.

Formation of Dispersive Shock Waves by Merging and Splitting Bose-Einstein Condensates

The processes of merging and splitting dilute-gas Bose-Einstein condensates are studied in the nonadiabatic, high-density regime. Rich dynamics are found. Depending on the experimental parameters, uniform soliton trains containing more than ten solitons or the formation of a high-density bulge as well as dispersive shock waves are observed experimentally within merged BECs. Our numerical simulations indicate the formation of many vortex rings. In the case of splitting a BEC, the transition from sound-wave formation to dispersive shock-wave formation is studied by use of increasingly stronger splitting barriers. These experiments realize prototypical dispersive shock situations.

Maxwell-Schrödinger equations for a dilute gas Bose-Einstein condensate coupled to an electromagnetic field

We give a general formulation of the semiclassical approach to solving the problem of interaction between a Bose-Einstein condensate of dilute gas and electromagnetic radiation without using the commonly applied mean-field approximation. We suggest variants of the systems of Maxwell-Schrodinger equations whose solution describes such effects as superradiant light scattering, light beam amplification, atomic wave (atomic laser) amplification, induced transparency, and reduction in the group velocity of light.

Limits to the analog Hawking temperature in a Bose-Einstein condensate

Quasi-one-dimensional outflow from a dilute gas Bose-Einstein condensate reservoir is a promising system for the creation of analog Hawking radiation. We use numerical modeling to show that stable sonic horizons exist in such a system under realistic conditions, taking into account the transverse dimensions and three-body loss. We find that loss limits the analog Hawking temperatures achievable in the hydrodynamic regime, with sodium condensates allowing the highest temperatures. A condensate of $30\phantom{\rule{0.2em}{0ex}}000$ atoms, with transverse confinement frequency ${\ensuremath{\omega}}_{\ensuremath{\perp}}=6800\ifmmode\times\else\texttimes\fi{}2\ensuremath{\pi}\phantom{\rule{0.3em}{0ex}}\mathrm{Hz}$, yields horizon temperatures of about $20\phantom{\rule{0.3em}{0ex}}\mathrm{nK}$ over a period of $50\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$. This is at least four times higher than for other atoms commonly used for Bose-Einstein condensates.

Acoustic Attenuation Probe for Fermion Superfluidity in Ultracold-Atom Gases

Dilute gas Bose-Einstein condensates (BEC's), currently used to cool fermionic atoms in atom traps, can also probe the superfluidity of these fermions. The damping rate of BEC-acoustic excitations (phonon modes), measured in the middle of the trap as a function of the phonon momentum, yields an unambiguous signature of BCS-like superfluidity, provides a measurement of the superfluid gap parameter, and gives an estimate of the size of the Cooper pairs in the BEC-BCS crossover regime. We also predict kinks in the momentum dependence of the damping rate which can reveal detailed information about the fermion quasiparticle dispersion relation.