We demonstrate quantum bath engineering for a superconducting artificial atom coupled to a microwave cavity. By tailoring the spectrum of microwave photon shot noise in the cavity, we create a dissipative environment that autonomously relaxes the atom to an arbitrarily specified coherent superposition of the ground and excited states. In the presence of background thermal excitations, this mechanism increases state purity and effectively cools the dressed atom state to a low temperature.

No abstract

We study a class of two-dimensional spin models with the Kitaev-type couplings in mosaic structure lattices to implement topological orders. We show that they are exactly solvable by reducing them to some free Majorana fermion models with gauge symmetries. The typical case with a 4-8-8 close packing is investigated in detail to display the quantum phases with Abelian and non-Abelian anyons. Its topological properties characterized by Chern numbers are revealed through the edge modes of its spectrum.Comment: 4 pages, 3 figures. Final version to appear in Phys. Rev. B as a Rapid Communicatio

We study the coherent off-equilibrium spin mixing inside an atomic condensate. Using mean field theory and adopting the single spatial mode approximation (SMA), the condensate spin dynamics is found to be well described by that of a nonrigid pendulum, and displays a variety of periodic oscillations in an external magnetic field. Our results illuminate several recent experimental observations and provide critical insights into the observation of coherent interaction-driven oscillations in a spin-1 condensate. Bose-Einstein condensation (BEC) has been one of the most active topics in physics for over a decade, and yet interest in this field remains impressively high. Recent experiments showcase the rich versatility of control over the atomic superfluid, e.g. the BEC-BCS crossover [1,2], quantized vortices [3,4,5], condensates in optical lattices [6], and low dimensional quantum gases [7,8]. While most of these efforts involve condensates of atoms in a single Zeeman state, activities in spinor condensates [9,10] have recently received significant boost with the addition of three new spin-1 experiments [11,12,13,14].In a spinor condensate, atomic hyperfine spin degree of freedom becomes accessible with the use of a far-off resonant optical trap instead of a magnetic trap. For atoms in the F = 1 ground state manifold, the presence of Zeeman degeneracy and spin dependent atom-atom interactions [9,10,11,15,16,17,18,19] leads to interesting condensate spin dynamics. In this article, we study spin mixing inside a spin-1 condensate [17,19,20], focusing on the interaction-driven coherent oscillations within a mean field description. Unlike the pioneering studies on this subject as in Refs. [17,19], we will highlight the important role of an external magnetic field, which is present in all experiments to date.Recently, a beautiful experiment has finally observed the long predicted Josephson type coherent nonlinear oscillations with a scalar condensate in a spatial double well potential [21].Although spin mixing driven by the internal spindependent interaction (not of the nature of a Rabi oscillation as driven by an external field [22,23]), has been observed in both F = 1 and F = 2 condensates [9,12,14,24], the coherence of this process has not yet been investigated. Over-damped single oscillations in spin populations have been observed in earlier experiments [24] although their interpretation has been limited because evolution from the initial (meta-stable) states was noise-driven. The main experimental obstacles to observe more oscillations are the dissipative atomic collisions among the condensed atoms and the decoherence collisions with noncondensed atoms [12,24]. A promising future direction relies on increased atomic detection sensitivity, thus the use of smaller condensates as in the experiment of Ref. [21], with lower number densities and at lower temperatures, two favorable conditions for the single spatial mode approximation (SMA) [17,19].The initial atomic population distribution in Fig. 1 corresponds to the (equi...