Ultracold Atomic Physics Research Articles

Self-ordered supersolid phase beyond Dicke superradiance in a ring cavity

The supersolid phase characterized by the superfluid and long-range spatial periodicity of crystalline order is central to many branches of science ranging from condensed matter physics to ultracold atomic physics. Here we study a self-ordered checkerboard supersolid phase originating from dynamical spin-orbit coupling for a transversely pumped atomic Bose-Einstein condensate trapped in a ring cavity, corresponding to a superradiant anti-Tavis-Cummings phase transition. In particular, an undamped gapless Goldstone mode is observed in contrast to the experimentally realized lattice supersolid with a gapped roton mode for Dicke superradiance. This zero-energy mode reveals the rigidity of the self-ordered superradiant phase, which spontaneously breaks a continuous translational symmetry. Our work will highlight the significant opportunities for exploring long-lived supersolid matter by utilizing dynamical spin-orbit coupling in controllable optical cavities.

Experimental realization of a high precision tunable hexagonal optical lattice.

Hexagonal optical lattices offer a tunable platform to study exotic orbital physics in solid state materials. Here, we present a versatile high-precision scheme to implement a hexagonal optical lattice potential, which is engineered by overlapping two independent triangular optical sublattices generated by laser beams with slightly different wavelengths around 1064 nm. This enables us to precisely control the detailed structure of the hexagonal lattice by adjusting the relative position and the relative lattice depth of the two triangular optical sublattices. Taking advantage of the sensitive dependence of the second Bloch band on small lattice deformations, we propose a strategy to optimize the optical lattice geometry with an extremely high precision. This method can also be extended to other lattice configurations involving more than two sublattices. Our work provides the experimental requirements in the search for novel orbital physics of ultracold atoms, for example, in the flat p-band of the hexagonal optical lattice.

Characterizing ultra-narrow momentum of atoms by standing-wave light-pulse sequences

We propose a method to characterize the ultra-narrow momentum distribution of atomic gases by employing a standing-wave light-pulse sequences beam splitter. The mechanism of beam splitting is analyzed in detail, and the influence of a finite-width momentum distribution on the population of each diffraction order is given. The temperature of ultracold atomic gases can be calibrated by measuring the ratio of population in different diffraction orders after double standing-wave light pulses. We obtain analytical expressions for two typical cases, and demonstrate phase space evolution in the whole process by using the Wigner function. This method is valid for both classical atomic gas and Bose–Einstein condensates, and it is suited for temperature measurement on the space ultracold atomic physics platform, in which the ultra-narrow momentum distribution of atomic gas is of the order of 100 pK or even lower.

Operator spectrum of nonrelativistic CFTs at large charge

We extend and clarify the large-charge expansion of the conformal dimension $\Delta_Q$ of the lowest operator of charge $Q$ in nonrelativistic CFTs using the state-operator correspondence. The latter requires coupling the theory to an external harmonic trap that confines the particles to a spherical cloud, at the edge of which the effective theory breaks down and leads to divergences. Only recently has this issue been overcome by constructing appropriate counterterms at the edge of the cloud in arXiv:2010.07967. In this note, we extend these results by systematically analyzing the degree of divergence of operators in the effective action and show that there always exist appropriate edge counterterms that make the final contributions to $\Delta_Q$ finite. On the other side of the correspondence, this also provides new corrections to the Thomas-Fermi approximation of the unitary Fermi gas, and we comment on their relevance for ultracold atom physics.

Conference on Physics of Ultracold Atoms in Russia – a new step towards deepening international cooperation

Abstract At the end of December 2021, there was held online the annual, fifteenth in a row, All-Russian Conference on Physics of Ultracold Atoms, in which scientists from other countries took part. Over the past years, this conference has changed dramatically: from a one-day workshop of participants in the integration projects of the Siberian Branch of the Russian Academy of Sciences, where the results of the year were summed up, into a full-scale All-Russian conference with a wide geographic coverage of participants from Vladivostok to Voronezh. Foreign scientists also took an active part in the work of the conference, but until recently they were Russianspeaking researchers, and so Russian remained the working language of the conference. In 2021, an important step was taken towards its transition to a full-fledged international format. Russian and English became the working languages, and in order to increase the level and significance of the conference, as well as to deepen international cooperation in this field of physics, a number of foreign scientists were invited.

Universal energy-dependent pseudopotential for the two-body problem of confined ultracold atoms

The two-body scattering amplitude and energy spectrum of confined ultracold atoms are of fundamental importance for both theoretical and experimental studies of ultracold-atom physics. For many systems, one can efficiently calculate these quantities via the zero-range Huang-Yang pseudopotential (HYP), in which the interatomic interaction is characterized by the scattering length $a$. Furthermore, when the scattering length is dependent on the kinetic energy ${\ensuremath{\varepsilon}}_{\mathrm{r}}$ of two-atom relative motion, i.e., $a=a({\ensuremath{\varepsilon}}_{\mathrm{r}})$, the results are applicable for a broad energy region. However, when the free Hamiltonian of atomic internal state (e.g., the Zeeman Hamiltonian) does not commute with the interatomic interaction, or the center-of-mass (c.m.) motion is coupled to the relative motion, the generalization of this technique is still lacking. In this work we solve this problem and construct a reasonable energy-dependent multichannel HYP, which is characterized by a ``scattering length operator'' ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{a}}_{\mathrm{eff}}$, for the above complicated cases. Here, ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{a}}_{\mathrm{eff}}$ is an operator for atomic internal states and c.m. motion, and depends on both the total two-atom energy and the external field as well as the trapping parameter. The effects from the internal-state or c.m.-relative motion coupling can be self-consistently taken into account by ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{a}}_{\mathrm{eff}}$. We further show a method based on the quantum defect theory, with which ${\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{a}}_{\mathrm{eff}}$ can be analytically derived for systems with van der Waals interatomic interaction. To demonstrate our method, we calculate the spectrum of two ultracold fermionic alkaline-earth-like atoms [in electronic $^{1}S_{0}$ $(|g\ensuremath{\rangle})$ and $^{3}P_{0}$ $(|e\ensuremath{\rangle})$ states, respectively] confined in an optical lattice. By comparing our results with the recent experimental measurements for two $^{173}\mathrm{Yb}$ atoms and two $^{171}\mathrm{Yb}$ atoms, we calibrate the scattering lengths ${a}_{\ifmmode\pm\else\textpm\fi{}}$ with respect to antisymmetric and symmetric nuclear-spin states to be ${a}_{+}=2012(19){a}_{0}$ and ${a}_{\ensuremath{-}}=193(4){a}_{0}$ for $^{173}\mathrm{Yb}$, and ${a}_{+}=232(3){a}_{0}$ and ${a}_{\ensuremath{-}}=372(1){a}_{0}$ for $^{171}\mathrm{Yb}$.

Impact of Chen-Ning Yang’s theoretical work on ultracold atomic physics

As early as the 1950s, Prof. Yang and his collaborators realized that the most important interaction effects in a dilute quantum gas can be described by the s-wave scattering length between particles. This insight leads to universal descriptions of the interaction effects without the detailed knowledge of the interaction potential. They derived a formula expanding the energy density in terms of the gas parameter. This formula is later known as the Lee-Huang-Yang correction. However, it took forty years for the experimentalists to overcome several challenges and finally achieve degenerate quantum gases of atoms in 1995. The developments after 1995 have led to an exciting field known as “quantum gases” or “ultracold atomic gases”. The ultracold atom system has flexible tunability, allowing both the scattering length and the dimensionality to vary. The Lee-Huang-Yang corrections were observed from several experiments on ultracold atoms by increasing the scattering length. In addition, by reducing the dimensionality to one-dimension, several experiments on ultracold atoms have confirmed the Yang-Yang thermodynamics for one-dimensional bosons that Prof. Yang obtained in the 1960s and the large-<i>N</i> limit of one-dimensional fermions that Prof. Yang obtained around 2010. By increasing the dimensionality through using the idea of synthetic dimension, the experiment on ultracold atoms has also demonstrated the Yang monopole in the<i> SU</i>(2) non-abelian gauge field proposed by Prof. Yang in the 1970s. All of these experiments show the long-lasting impact of Prof. Yang’s theoretical work over several decades.

Integrated Design and Realization of Two-Dimensional Magneto-Optical Trap for Ultra-Cold Atomic Physics Rack in Space

Integrated Design and Realization of Two-Dimensional Magneto-Optical Trap for Ultra-Cold Atomic Physics Rack in Space

Preface

General Information This volume of the Journal is devoted to the IX International Symposium and Young Scientists School “Modern Problems of Laser Physics” (MPLP-2021)1 that was held in Novosibirsk, Russia, 22-28 August 2021.The MPLP symposium has a long history starting from 1995 and gathers scientists from many courtiers who carrying out their researches in the forefront of laser physics, quantum metrology and high-resolution spectroscopy, physics of ultracold atoms, molecules and ions, atom optics, ultrafast phenomena and attoscience, quantum optics and information, nonlinear optics and applications of laser radiation from THz to UV radiation ranges in medicine, geophysics, chemistry and microbiology. This year the sessions devoted to advances in laboratory space plasma physics with lasers was also included in the list of topics of MPLP symposium.The Scientific Program of MPLP-2021 includes invited and oral talks selected from contributed papers, as well as several Poster Sessions. A Scientific School for Young Scientists was also take place during the Symposium. Following the tradition of MPLP Symposia, the scientific program comprises single sessions of invited and oral presentations for each topic, running sequentially. This year online access to MPLP was provided for participants who can’t attend the symposium in-person and many of the invited talks were done online.List of Organizers, Committees, Chairman of the Symposium, Invited and Oral Speakers, School for Young Scientists and Results are available in this pdf.

Physics of ultracold atoms in Russia: current research

Physics of ultracold atoms in Russia: current research

High-powered optical superlattice with robust phase stability for quantum gas microscopy.

Optical superlattice has a wide range of applications in the study of ultracold atom physics. Especially, it can be used to trap and manipulate thousands of atom pairs in parallel which constitutes a promising system for quantum simulation and quantum computation. In the present work, we report on a high-power optical superlattice formed by a 532-nm and 1064-nm dual-wavelength interferometer with a short lattice spacing of 630 nm. The short-term fluctuation (in 10 seconds) of the relative phase between the short lattice and the long lattice is measured to be 0.003π, which satisfies the needs for performing two-qubit gates among neighboring lattice sites. We further implement this superlattice in a 87Rb experiment with a quantum gas microscope of single-site resolution, where the high-power 532-nm laser is necessary for pinning atoms in the short lattice during imaging, providing a unique platform for engineering quantum states.

Emulation of magneto-optic Faraday effect using ultracold atoms

We propose an arresting scheme for emulating the famous Faraday effect in ultracold atomic gases. Inspired by the similarities between the light field and bosonic atoms, we represent the light propagation in medium by the atomic transport in accompany of the laser-atom interaction. An artificial magneto-optic Faraday effect (MOFE) is readily signaled by the spin imbalance of atoms, with the setup of laser fields offering a high controllability for quantum manipulation. The present scheme is really feasible and can be realized with existing experimental techniques of ultracold atoms. It generalizes the crucial concept of the MOFE to ultracold atomic physics, and opens a new way of quantum emulating and exploring the MOFE and associated intriguing physics.

Dimensional crossover and phase transitions in coupled chains: Density matrix renormalization group results

Quasi-one-dimensional (Q1D) systems, i.e., three- and two-dimensional (3D/2D) arrays composed of weakly coupled one-dimensional lattices of interacting quantum particles, exhibit rich and fascinating physics. They are studied across various areas of condensed matter and ultracold atomic lattice-gas physics, and are often marked by dimensional crossover as the coupling between one-dimensional systems is increased or temperature decreased, i.e., the Q1D system goes from appearing largely 1D to largely 3D. Phase transitions occurring along the crossover can strongly enhance this effect. Understanding these crossovers and associated phase transitions can be challenging due to the very different elementary excitations of 1D systems compared to higher-dimensional ones. In the present work, we combine numerical matrix product state (MPS) methods with mean-field (MF) theory to study paradigmatic cases of dimensional crossovers and the associated phase transitions in systems of both hard-core and soft-core lattice bosons, with relevance to both condensed matter physics and ultracold atomic gases. We show that the superfluid-to-insulator transition is a first order one, as opposed to the isotropic cases and calculate transition temperatures for the superfluid states, finding excellent agreement with analytical theory. At the same time, our MPS+MF approach keeps functioning well where the current analytical framework cannot be applied. We further confirm the qualitative and quantitative reliability of our approach by comparison to exact quantum Monte Carlo calculations for the full 3D arrays.

BCS-BEC Crossover Effects and Pseudogap in Neutron Matter

Due to the large neutron–neutron scattering length, dilute neutron matter resembles the unitary Fermi gas, which lies half-way in the crossover from the BCS phase of weakly coupled Cooper pairs to the Bose–Einstein condensate of dimers. We discuss crossover effects in analogy with the T-matrix theory used in the physics of ultracold atoms, which we generalize to the case of a non-separable finite-range interaction. A problem of the standard Nozières–Schmitt-Rink approach and different ways to solve it are discussed. It is shown that in the strong-coupling regime, the spectral function exhibits a pseudo-gap at temperatures above the critical temperature Tc. The effect of the correlated density on the density dependence of Tc is found to be rather weak, but a possibly important effect due to the reduced quasiparticle weight is identified.

Ideal Weyl semimetal with 3D spin-orbit coupled ultracold quantum gas

There is an immense effort in search for various types of Weyl semimetals, of which the most fundamental phase consists of the minimal number of i.e. two Weyl points, but is hard to engineer in solids. Here we demonstrate how such fundamental Weyl semimetal can be realized in a maneuverable optical Raman lattice, with which the three-dimensional (3D) spin-orbit (SO) coupling is synthesised for ultracold atoms. In addition, a new novel Weyl phase with coexisting Weyl nodal points and nodal ring is also predicted here, and is shown to be protected by nontrivial linking numbers. We further propose feasible techniques to precisely resolve 3D Weyl band topology through 2D equilibrium and dynamical measurements. This work leads to the first realization of the most fundamental Weyl semimetal band and the 3D SO coupling for ultracold quantum gases, which are respectively the significant issues in the condensed matter and ultracold atom physics.

Physics of ultracold atoms in Russia: topical research

Physics of ultracold atoms in Russia: topical research

Bifurcation analysis of stationary solutions of two-dimensional coupled Gross–Pitaevskii equations using deflated continuation

Recently, a novel bifurcation technique known as deflated continuation was applied to the single-component nonlinear Schrödinger (NLS) equation with a parabolic trap in two spatial dimensions. This bifurcation analysis revealed previously unknown solutions, shedding light on this fundamental problem in the physics of ultracold atoms. In the present work, we take this a step further by applying deflated continuation to two coupled NLS equations, which – feature a considerably more complex landscape of solutions. Upon identifying branches of solutions, we construct the relevant bifurcation diagrams and perform spectral stability analysis to identify parametric regimes of stability and instability and to understand the mechanisms by which these branches emerge. The method reveals a remarkable wealth of solutions. These include both well-known states arising from the Cartesian and polar small amplitude limits of the underlying linear problem, but also a significant number of more complex states that arise through (typically pitchfork) bifurcations.

Optically contorting into new dimensions

Topological Optics Creating synthetic dimensions has generated interest in many branches of science, ranging from ultracold atomic physics to photonics. The ability to do so provides a versatile platform for realizing effective gauge potentials and novel topological physics that might be difficult or impossible to realize in real systems. Dutt et al. show that a structured optical ring cavity can sustain more than one synthetic dimension. Under modulation, coupling the different degrees of freedom within the resonator is used synthesize two additional dimensions. The authors are then able to emulate many complex physical phenomena usually associated with condensed matter systems. Science , this issue p. [59][1] [1]: /lookup/doi/10.1126/science.aaz3071

Shell potentials for microgravity Bose\u2013Einstein condensates

Extending the understanding of Bose–Einstein condensate (BEC) physics to new geometries and topologies has a long and varied history in ultracold atomic physics. One such new geometry is that of a bubble, where a condensate would be confined to the surface of an ellipsoidal shell. Study of this geometry would give insight into new collective modes, self-interference effects, topology-dependent vortex behavior, dimensionality crossovers from thick to thin shells, and the properties of condensates pushed into the ultradilute limit. Here we propose to implement a realistic experimental framework for generating shell-geometry BEC using radiofrequency dressing of magnetically trapped samples. Such a tantalizing state of matter is inaccessible terrestrially due to the distorting effect of gravity on experimentally feasible shell potentials. The debut of an orbital BEC machine (NASA Cold Atom Laboratory, aboard the International Space Station) has enabled the operation of quantum-gas experiments in a regime of perpetual freefall, and thus has permitted the planning of microgravity shell-geometry BEC experiments. We discuss specific experimental configurations, applicable inhomogeneities and other experimental challenges, and outline potential experiments.

A single photonic cavity with two independent physical synthetic dimensions.

The concept of synthetic dimensions has generated interest in many branches of science, ranging from ultracold atomic physics to photonics, as it provides a versatile platform for realizing effective gauge potentials and topological physics. Previous experiments have augmented the real-space dimensionality by one additional physical synthetic dimension. In this study, we endow a single ring resonator with two independent physical synthetic dimensions. Our system consists of a temporally modulated ring resonator with spatial coupling between the clockwise and counterclockwise modes, creating a synthetic Hall ladder along the frequency and pseudospin degrees of freedom for photons propagating in the ring. We observe a wide variety of physics, including effective spin-orbit coupling, magnetic fields, spin-momentum locking, a Meissner-to-vortex phase transition, and signatures of topological chiral one-way edge currents, completely in synthetic dimensions. Our experiments demonstrate that higher-dimensional physics can be studied in simple systems by leveraging the concept of multiple simultaneous synthetic dimensions.