In this paper, we numerically studied the effects of mechanical vibration and magnetic fields on evaporative cooling process carried in space station by direct simulation Monte Carlo method. Simulated with the vibration data of international space station, we found that the cooling process would suffer great atomic losses until the accelerations reduced tenfold at least. In addition, if we enlarge the s-wave scattering length five times by Feshbach resonance, the PSD increased to 50 compared to 3 of no magnetic fields situation after 5 seconds evaporative cooling. We also simulated the two stages crossed beam evaporative cooling process (TSCBC) under both physical impacts and obtain $4\times10^5$ $^{85}$Rb atoms with a temperature of 8 pK. These results are of significance to the cold atom experiments carried out on space station in the future.
To achieve Bose-Einstein condensation, one may implement evaporative cooling by dynamically regulating the power of laser beams forming the optical dipole trap. We propose and experimentally demonstrate a protocol of Bayesian optimization of Bose-Einstein condensation via the evaporative cooling model. Applying this protocol, pure Bose-Einstein condensate of 87Rb with 2.4X10e4 atoms can be produced via evaporative cooling from the initial stage when the number of atoms is 6.0X10e5 at a temperature of 12μK. In comparison with Bayesian optimization via blackbox experiment, our protocol only need…
We demonstrate experimentally the evaporative cooling of a few hundred rubidium 87 atoms in a single-beam microscopic dipole trap. Starting from 800 atoms at a temperature of 125microKelvins, we produce an unpolarized sample of 40 atoms at 110nK, within 3s. The phase-space density at the end of the evaporation reaches unity, close to quantum degeneracy. The gain in phase-space density after evaporation is 10^3. We find that the scaling laws used for much larger numbers of atoms are still valid despite the small number of atoms involved in the evaporative cooling process. We also compare our re…
We present a combined computational and experimental study to optimize the efficiency of evaporative cooling for atoms in optical dipole traps. By employing a kinetic model of evaporation, we provide a strategy for determining the optimal relation between atom temperature, trap depth, and average trap frequency during evaporation given experimental initial conditions. We then experimentally implement a highly efficient evaporation process in an optical dipole trap, showing excellent agreement between the theory and experiment. This method has allowed the creation of pure Bose-Einstein condensa…
Recent experimental developments in the loading of ultracold KRb molecules into quasi-two-dimensional traps, combined with the ability to tune the ratio between elastic and loss (inelastic/reactive) collisions through application of an external electric field, are opening the door to achieving efficient evaporative cooling of reactive polar molecules. In this paper, we use Monte Carlo simulations and semianalytic models to study theoretically the experimental parameter regimes in which evaporative cooling is feasible under current trapping conditions. We investigate the effect of the anisotrop…
Atomic physics was revolutionized by the development of forced evaporative cooling: it led directly to the observation of Bose-Einstein condensation, quantum-degenerate Fermi gases, and ultracold optical lattice simulations of condensed matter phenomena. More recently, great progress has been made in the production of cold molecular gases, whose permanent electric dipole moment is expected to generate rich, novel, and controllable phases, dynamics, and chemistry in these ultracold systems. However, while many strides have been made in both direct cooling and cold-association techniques, evapor…
In recent years, cold atoms could prove their scientific impact not only on ground but in microgravity environments such as the drop tower in Bremen, sounding rockets and parabolic flights. We investigate the preparation of cold atoms in an optical dipole trap, with an emphasis on evaporative cooling under microgravity. Up to $ 1\times10^{6} $ rubidium-87 atoms were optically trapped from a temporarily dark magneto optical trap during free fall in the droptower in Bremen. The efficiency of evaporation is determined to be equal with and without the effect of gravity. This is confirmed using num…
We report the realization of Bose-Einstein condensates of 39K atoms without the aid of an additional atomic coolant. Our route to Bose-Einstein condensation comprises Sub Doppler laser cooling of large atomic clouds with more than 10^10 atoms and evaporative cooling in optical dipole traps where the collisional cross section can be increased using magnetic Feshbach resonances. Large condensates with almost 10^6 atoms can be produced in less than 15 seconds. Our achievements eliminate the need for sympathetic cooling with Rb atoms which was the usual route implemented till date due to the unfav…
We calculate the evaporative cooling dynamics of trapped one-dimensional Bose-Einstein condensates for parameters leading to a range of condensates and quasicondensates in the final equilibrium state. We confirm that solitons are created during the evaporation process, but always eventually dissipate during thermalisation. The distance between solitons at the end of the evaporation ramp matches the coherence length in the final thermal state. Calculations were made using the classical fields method. They bridge the gap between the phase defect picture of the Kibble-Zurek mechanism and the long…
We theoretically show how to obtain a long one-dimensional crystal near its quantum ground state. We rely on an evaporative cooling scheme applicable to many-body systems with nonzero-ranged interactions. Despite the absence of periodic potentials, the final state is a crystal which exhibits long-range spatial order. We describe the scheme thermodynamically, applying the truncated Boltzmann distribution to the collective excitations of the chain, and show that it leads to a novel quasi-equilibrium many-body state. For longer chains, comprising about 1000 atoms, we emphasize the quasi-universal…
The fluctuations in thermodynamic and transport properties in many-body systems gain importance as the number of constituent particles is reduced. Ultracold atomic gases provide a clean setting for the study of mesoscopic systems; however, the detection of temporal fluctuations is hindered by the typically destructive detection, precluding repeated precise measurements on the same sample. Here, we overcome this hindrance by utilizing the enhanced light--matter coupling in an optical cavity to perform a minimally invasive continuous measurement and track the time evolution of the atom number in…
Ultracold polar molecules possess long-range, anisotropic, and tunable dipolar interactions, providing the opportunities to probe quantum phenomena inaccessible with existing cold gas platforms. However, experimental progress has been hindered by the dominance of two-body loss over elastic interactions, which prevents efficient evaporative cooling. Though recent work has demonstrated controlled interactions by confining molecules to a two-dimensional geometry, a general approach for tuning molecular interactions in a three-dimensional (3D), stable system has been lacking. Here, we demonstrate …
We demonstrate direct laser cooling of a gas of rubidium 87 atoms to quantum degeneracy. The method does not involve evaporative cooling, is fast, and induces little atom loss. The atoms are trapped in a two-dimensional optical lattice that enables cycles of cloud compression to increase the density, followed by degenerate Raman sideband cooling to decrease the temperature. Light-induced loss at high atomic density is substantially reduced by using far red detuned optical pumping light. Starting with 2000 atoms, we prepare 1400 atoms in 300 ms at quantum degeneracy, as confirmed by the appeara…
We study depletion dynamics of an open system of weakly interacting fermions with two-body random interactions. In this model fermions are escaping from the high-energy one-particle orbitals, that mimics the evaporation process used in laboratory experiments with neutral atoms to cool them to ultra-low temperatures. It is shown that due to dynamical thermalization the system instantaneously adjusts to the new chemical potential and temperature, so that occupation numbers of the one-particle orbitals always obey the Fermi-Dirac distribution. In this way we are able to describe the evaporation p…
Semi-classical evaporative cooling: classical and quantum distributions
Centro de Investigación en Computación, Instituto Politénico Nacional（国家理工学院计算研究中心）；Facultad de Ciencias, Universidad Nacional Autónoma de México（墨西哥国立自治大学理学院）；Instituto de Química, Universidad Nacional Autónoma de México（墨西哥国立自治大学化学研究所）；Instituto de Física, Universidad Nacional Autónoma de México（墨西哥国立自治大学物理研究所）；Investigador por México - Instituto de Física, Universidad Nacional Autónoma de México（墨西哥研究者计划-墨西哥国立自治大学物理研究所）
Degenerate quantum gases are instrumental in advancing many-body quantum physics and underpin emerging precision sensing technologies. All state-of-the-art experiments use evaporative cooling to achieve the ultracold temperatures needed for quantum degeneracy, yet evaporative cooling is extremely lossy: more than 99.9% of the gas is discarded. Such final particle number limitations constrain imaging resolution, gas lifetime, and applications leveraging macroscopic quantum coherence. Here we show that atomic Bose gases can be cooled to quantum degeneracy using real-time feedback, an entirely ne…
The preparation of low-entropy starting conditions is a key requirement for many experiments involving neutral atoms. Here, we propose a method to autonomously assemble arbitrary spatial configurations of atoms within arrays of optical tweezers or lattice sites, enabled by a combination of tunneling and ground-state laser cooling. In contrast to previous methods, our protocol does not rely on either imaging or evaporative cooling. This circumvents limitations associated with imaging fidelity and loss, especially in systems with small spatial scales, while providing a substantial improvement in…
We report on the attainment of Bose-Einstein condensation with ultracold strontium atoms. We use the 84Sr isotope, which has a low natural abundance but offers excellent scattering properties for evaporative cooling. Accumulation in a metastable state using a magnetic-trap, narrowline cooling, and straightforward evaporative cooling in an optical trap lead to pure condensates containing 1.5x10^5 atoms. This puts 84Sr in a prime position for future experiments on quantum-degenerate gases involving atomic two-electron systems.
This brief review presents the emerging field of mesoscopic physics with cold atoms, with an emphasis on thermal and 'thermoelectric' transport, i.e. coupled transport of particle and entropy. We review in particular the comparison between theoretically predited and experimentally observed thermoelectric effects in such systems. We also show how combining well designed transport properties and evaporative cooling leads to an equivalent of the Peltier effect with cold atoms, which can be used as a new cooling procedure with improved cooling power and efficiency compared to the evaporative cooli…
We report the realisation of Bose-Einstein condensation (BEC) of metastable helium atoms using an in-vacuum coil magnetic trap and a crossed beam optical dipole trap. A novel quadrupole-Ioffe configuration (QUIC) magnetic trap made from in-vacuum hollow copper tubes provides fast switching times while generating traps with a 10G bias, without compromising optical access. The bias enables in-trap 1D doppler cooling to be used, which is the only cooling stage between the magneto-optic trap (MOT) and the optical dipole trap. This allows direct transfer to the dipole trap without the need for any …
We report the simultaneous production of Bose-Einstein condensates (BECs) of $^{87}$Rb and $^{133}$Cs atoms in separate optical traps. The two samples are mixed during laser cooling and loading but are separated by $400 μ$m for the final stage of evaporative cooling. This is done to avoid considerable interspecies three-body recombination, which causes heating and evaporative loss. We characterize the BEC production process, discuss limitations, and outline the use of the dual-species BEC in future experiments to produce rovibronic ground state molecules, including a scheme facilitated by the …
We optimize a collision-induced cooling process for ultracold atoms in the nondegenerate regime. It makes use of a Feshbach resonance, instead of rf radiation in evaporative cooling, to selectively expel hot atoms from a trap. Using functional minimization we analytically show that for the optimal cooling process the resonance energy must be tuned such that it linearly follows the temperature. Here, optimal cooling is defined as maximizing the phase-space density after a fixed cooling duration. The analytical results are confirmed by numerical Monte-Carlo simulations. In order to simulate more…
We present an evaporative cooling technique for atoms trapped in an optical dipole trap that benefits from narrow optical transitions. For an appropriate choice of wavelength and polarization, a single laser beam leads to opposite light-shifts in two internal states of the lowest energy manifold. Radio-frequency coupling between these two states results in evaporative cooling at a constant trap stiffness. The evaporation protocol is well adapted to several atomic species, in particular to the case of Lanthanides such as Er, Dy, and fermionic Yb, but also to alkali-earth metals such as fermioni…
Forced evaporative cooling in a far-off-resonance optical dipole trap is proved to be an efficient method to produce fermionic- or bosonic-degenerated gases. However in most of the experiences, the reduction of the potential height occurs with a diminution of the collision elastic rate. Taking advantage of a long-living excited state, like in two-electron atoms, I propose a new scheme, based on an optical knife, where the forced evaporation can be driven independently of the trap confinement. In this context, the runaway regime might be achieved leading to a substantial improvement of the cool…
We detail the cooling mechanisms of a Fermionic strontium-87 gas in order to study its evolution under a non-Abelian gauge field. In contrast to our previous work reported in Ref. [1], we emphasize here on the finite temperature effect of the gas. In addition, we provide the detail characterization for the efficiency of atoms loading in the cross-dipole trap, the quantitative performance of the evaporative cooling, and the characterization of a degenerate Fermi gas using a Thomas-Fermi distribution.
