One-body Loss Research Articles

High efficient Raman sideband cooling and strong three-body recombination of atoms

We report a highly efficient three-dimensional degenerated Raman sideband cooling (3D dRSC) that enhances the loading of a magnetically levitated optical dipole trap, and observe the strong atom loss due to the three-body recombination. The 3D dRSC is implemented to obtain 5 × 107 Cs atoms with the temperature of ∼ 480 nK. The cold temperature enables 1.8 × 107 atoms loaded into a crossed dipole trap with an optimized excessive levitation magnetic gradient. Compared to the loading of atoms from a bare magneto-optical trap or the gray-molasses cooling, there is a significant increase in the number of atoms loaded into the optical dipole trap. We derive for the three-body recombination coefficient of L 3 = 7.73 × 10−25 cm6/s by analyzing the strong atom loss at a large scattering length of 1418 Bohr radius, and discover the transition from the strong three-body loss to the dominant one-body loss. Our result indicates that the lifetime of atoms in the optical dipole trap is finally decided by the one-body loss after the initial strong three-body loss.

Understanding one-body losses in magnetically trapped metastable europium atoms

We report the measurement of one-body loss rates for magnetically trapped metastable europium atoms and the study of their loss mechanism. The loss of atoms observed in a magneto-optical trap is not fully understood because of the indivisibility of the loss regarding optical pumpings due to the presence of cooling laser beams. We magnetically trapped the atoms by directly loading from the magneto-optical trap and observed almost identical one-body loss rates of approximately 2.6s−1 for two isotopes: 151Eu and 153Eu. Our rate-equation-based model, combined with loss rate measurements carried out with repumpers, shows that blackbody radiation at room temperature drives E1 transitions and induces the observed losses.

Topological Bose-Mott insulators in one-dimensional non-Hermitian superlattices

We study the topological properties of Bose-Mott insulators in one-dimensional non-Hermitian superlattices, which may serve as effective Hamiltonians for cold atomic optical systems with either two-body loss or one-body loss. We find that in the strongly repulsive limit, the Mott insulator states of the Bose-Hubbard model with a finite two-body loss under integer fillings are topological insulators characterized by a finite charge gap, nonzero integer Chern numbers, and nontrivial edge modes in a low-energy excitation spectrum under an open boundary condition. The two-body loss suppressed by the strong repulsion results in a stable topological Bose-Mott insulator which has shares features similar to the Hermitian case. However, for the non-Hermitian model related to the one-body loss, we find the non-Hermitian topological Mott insulators are unstable with a finite imaginary excitation gap. Finally, we also discuss the stability of the Mott phase in the presence of two-body loss by solving the Lindblad master equation.

Nonequilibrium steady states of Bose-Einstein condensates with a local particle loss in double potential barriers

We investigate stability of non-equilibrium steady states of Bose-Einstein condensates with a local one-body loss in the presence of double potential barriers. We construct an exactly solvable mean-field model, in which the local loss and the potential barriers take the form of a delta function. Using the exact solutions of our model, we show that there are parameter regions in which two steady-state solutions are dynamically stable, i.e., the model exhibits bistability. We also find that unidirectional hysteresis phenomena appear when the local-loss rate is varied in some parameter region.

Excitations and correlations in the driven-dissipative Bose-Hubbard model

Using a field-theoretic approach within the Schwinger-Keldysh formalism, we study a Bose-Hubbard model in the presence of a driving field and dissipation due to one-body losses. We recover the bistability diagram from the Gross-Pitaevski equation and analyze the different phases with respect to their elementary excitations and correlations. We find the low-density solution to be subdivided into a dynamically instable, a gapped, and a gapless regime. The correlations decay exponentially, but a substantial increase of correlation length marks the regime of gapless excitations.

Multi-second magnetic coherence in a single domain spinor Bose–Einstein condensate

We describe a compact, robust and versatile system for studying the macroscopic spin dynamics in a spinor Bose–Einstein condensate. Condensates of are produced by all-optical evaporation in a 1560 nm optical dipole trap, using a non-standard loading sequence that employs an ancillary 1529 nm beam for partial compensation of the strong differential light-shift induced by the dipole trap itself. We use near-resonant Faraday rotation probing to non-destructively track the condensate magnetization, and demonstrate few-Larmor-cycle tracking with no detectable degradation of the spin polarization. In the ferromagnetic F = 1 ground state, we observe the spin orientation between atoms in the condensate is preserved, such that they precess all together like one large spin in the presence of a magnetic field. We characterize this dynamics in terms of the single-shot magnetic coherence times and , and observe them to be of several seconds, limited only by the residence time of the atoms in the trap. At the densities used, this residence is restricted only by one-body losses set by the vacuum conditions.

Squeezing and entanglement in two-mode Bose–Einstein condensates

We investigate the influence of one-body losses on the dynamics of squeezing and entanglement in two-mode Bose–Einstein condensates. We show that one-body losses play an important role in the dynamical process of generating squeezing and quantum entanglement. The stronger one-body losses induce smaller squeezing and lesser entanglement, but maintain in a longer time interval.

Ultracold atom interferometry with pulses of variable duration

We offer interferometry models for thermal ensembles with one-body losses and the phenomenological inclusion of perturbations covering most of the thermal atom experiments. A possible extension to the many-body case is briefly discussed. The Ramsey pulses are assumed to have variable durations and the detuning during the pulses is distinguished from the detuning during evolution. Consequently, the pulses are not restricted to resonant operation and give more flexibility to optimize the interferometer to particular experimental conditions. On this basis another model is devised in which the contrast loss due to the unequal one-body population decays is cancelled by the application of a non-standard splitting pulse. For the importance of its practical implications, an analogous spin-echo model is also provided. The developed models are suitable for the analysis of atomic clocks and a broad range of sensing applications, they are particularly useful for trapped-atom interferometers.

Entanglement in Bose-Einstein Condensates with One-Body Losses

We investigate quantum entanglement in two mutually non-interacting and spatially non-overlapping Bose-Einstein condensates in two harmonic potentials with one-body losses. One-body losses play an important role in the dynamical process of generating quantum entanglement. The stronger one-body losses induce more entanglement and maintain in a longer time interval.

Ensemble master equation for a trapped-atom clock with one- and two-body losses

An ensemble density matrix model that includes one- and two-body losses is derived for a trapped-atom clock. A trapped-atom clock is mainly affected by one- and two-body losses, generally giving nonexponential decays of populations; nevertheless, three-body recombination is also quantitatively analyzed to demonstrate the boundaries of its practical relevance. The importance of one-body losses is highlighted without which population trapping behavior would be observed. The model is written with decay constants expressed through experimental parameters. It can complement, e.g., the ISRE (identical spin rotation effect) model to improve its predictions: ISRE dramatically increases the ensemble coherence time, hence it enables one to observe the influence of two-body losses on the interferometry contrast envelope. The presented model is useful for Ramsey interferometry and is ready for immediate experimental verification in existing systems.

Nonexponential one-body loss in a Bose-Einstein condensate

We have studied the decay of a Bose-Einstein condensate of metastable helium atoms in an optical dipole trap. In the regime where two- and three-body losses can be neglected we show that the Bose-Einstein condensate and the thermal cloud show fundamentally different decay characteristics. The total number of atoms decays exponentially with time constant tau; however, the thermal cloud decays exponentially with time constant (4/3)tau and the condensate decays much faster, and non-exponentially. We show that this behaviour, which should be present for all BECs in thermal equilibrium with a considerable thermal fraction, is due to a transfer of atoms from the condensate to the thermal cloud during its decay.

Optimum Spin Squeezing in Bose-Einstein Condensates with Particle Losses

The problem of spin squeezing with a bimodal condensate in the presence of particle losses is solved analytically by the Monte Carlo wave function method. We find the largest obtainable spin squeezing as a function of the one-body loss rate, the two-body and three-body rate constants, and the s-wave scattering length.