Pumping of twin-trap Bose-Einstein condensates

Two-Dimensional Thouless Pumping of Ultracold Fermions in Obliquely Introduced Optical Superlattice

We propose a two-dimensional (2D) version of Thouless pumping that can be realized by using ultracold atoms in optical lattices. To be specific, we consider a 2D square lattice tight-binding model with an obliquely introduced superlattice. It is demonstrated that quantized particle transport occurs in this system, and that the transport is expressed as a solution of a Diophantine equation. This topological nature can be understood by mapping the Hamiltonian to a three-dimensional (3D) cubic lattice model with a homogeneous magnetic field. We also propose a continuum model with obliquely introd…

Dynamics of a Bose-Einstein condensate in a symmetric triple-well trap

We present a complete analysis of the dynamics of a Bose-Einstein condensate trapped in a symmetric triple-well potential. Our classical analogue treatment, based on a time-dependent variational method using SU(3) coherent states, includes the parameter dependence analysis of the equilibrium points and their local stability, which is closely related to the condensate collective behaviour. We also consider the effects of off-site interactions, and how these "cross-collisions" may become relevant for a large number of trapped bosons. Besides, we have shown analytically, by means of a simple basi…

Generation of a maximally entangled state using collective optical pumping

We propose and implement a novel scheme for dissipatively pumping two qubits into a singlet Bell state. The method relies on a process of collective optical pumping to an excited level, to which all states apart from the singlet are coupled. We apply the method to deterministically entangle two trapped ${}^{40}\text{Ca}^+$ ions with a fidelity of $93(1)\%$. We theoretically analyze the performance and error susceptibility of the scheme and find it to be insensitive to a large class of experimentally relevant noise sources.

Unconventional magnetism via optical pumping of interacting spin systems

We consider strongly interacting systems of effective spins, subject to dissipative spin-flip processes associated with optical pumping. We predict the existence of novel magnetic phases in the steady-state of this system, which emerge due to the competition between coherent and dissipative processes. Specifically, for strongly anisotropic spin-spin interactions, we find ferromagnetic, antiferromagnetic, spin-density-wave, and staggered-XY steady states, which are separated by nonequilibrium phase transitions meeting at a Lifshitz point. These transitions are accompanied by quantum correlation…

Pulsed pumping of a Bose-Einstein condensate

In this work, we examine a system for coherent transfer of atoms into a Bose-Einstein condensate. We utilize two spatially separate Bose-Einstein condensates in different hyperfine ground states held in the same dc magnetic trap. By means of a pulsed transfer of atoms, we are able to show a clear resonance in the timing of the transfer, both in temperature and number, from which we draw conclusions about the underlying physical process. The results are discussed in the context of the recently demonstrated pumped atom laser.

Characterizing twin-particle entanglement in double-well potentials

We consider a pair of twin atoms trapped in double-well potentials. For each atom, two orthogonal spatial modes are accessible: the states $ |L\rangle$ and $|R\rangle$ spatially localized in the left and right wells respectively. Furthermore the twin atoms are distinguishable thanks to an additional degree of freedom. We propose a method for experimentally quantifying the particle entanglement between these atoms which allows us to probe a violation of Bell's inequality. It is based on measuring the correlations in the atoms' momentum distribution. If the tunneling and the energy difference be…

Two dipolar atoms in a harmonic trap

Two identical dipolar atoms moving in a harmonic trap without an external magnetic field are investigated. Using the algebra of angular momentum a semi - analytical solutions are found. We show that the internal spin - spin interactions between the atoms couple to the orbital angular momentum causing an analogue of Einstein - de Haas effect. We show a possibility of adiabatically pumping our system from the s-wave to the d-wave relative motion. The effective spin-orbit coupling occurs at anti-crossings of the energy levels.

通过将自旋量子比特泵浦穿过量子点环路来测量非阿贝尔Berry相的协议

Protocols to measure the non-Abelian Berry phase by pumping a spin qubit through a quantum-dot loop

提出通过将自旋量子比特泵浦穿过量子点环路来测量非阿贝尔Berry相的协议，以评估holonomic quantum gates在量子信息处理中的潜力。

Continuous Loading of a Conservative Trap from an Atomic Beam

We demonstrate the fast accumulation of Cr atoms in a conservative potential from a magnetically guided atomic beam. Without laser cooling on a cycling transition, a single dissipative step realized by optical pumping allows to load atoms at a rate of 2*10^7 1/s in the trap. Within less than 100 ms we reach the collisionally dense regime, from which we directly produce a Bose-Einstein condensate with subsequent evaporative cooling. This constitutes a new approach to degeneracy where, provided a slow beam of particles can be produced by some means, Bose-Einstein condensation can be reached for …

Optimized Bose-Einstein-condensate production in a dipole trap based on a 1070-nm multifrequency laser: Influence of enhanced two-body loss on the evaporation process

We present an optimized strategy for the production of tightly confined Bose-Einstein condensates (BEC) of 87Rb in a crossed dipole trap with direct loading from a magneto-optical trap. The dipole trap is created with light of a multifrequency fiber laser with a center wavelength of 1070nm. Evaporative cooling is performed by ramping down the laser power only. A comparison of the resulting atom number in an almost pure BEC to the initial atom number and the value for the gain in phase space density per atom lost confirm that this straightforward strategy is very efficient. We observe that the …

Multi-stability and condensation of exciton-polaritons below threshold

Exciton-polaritons can condense to a macroscopic quantum state through a non-equilibrium process of pumping and decay. In recent experiments, polariton condensates are used to observe, for a short time, nonlinear Josephson phenomena by coupling two condensates. However, it is still not clear how these phenomena are affected by the pumping and decay at long times and how the coupling alters the polariton condensation. Here, we consider a polariton Josephson junction pumped on one side and study its dynamics within a mean-field theory. The Josephson current is found to give rise to multi-stabili…

量子机制下的声子激光器

A phonon laser in the quantum regime

本文在囚禁离子系统中通过两个独立耗散通道实现量子机制下的声子激光，平均声子数小于10，并展示了相位锁定与相位扩散的量子态重建。