Directional `superradiant' collisions: bosonic amplification of atom pairs emitted from an elongated Bose-Einstein condensate

We study spontaneous directionality in the bosonic amplification of atom pairs emitted from an elongated Bose-Einstein condensate (BEC), an effect analogous to `superradiant' emission of atom-photon pairs. Using a simplified model, we make analytic predictions regarding directional effects for both atom-atom and atom-photon emission. These are confirmed by numerical mean-field simulations, demonstrating the the feasibility of nearly perfect directional emission along the condensate axis. The dependence of the emission angle on the pump strength for atom-atom pairs is significantly different than for atom-photon pairs

Projective non-Abelian Statistics of Dislocation Defects in a Z_N Rotor Model

Non-Abelian statistics is a phenomenon of topologically protected non-Abelian Berry phases as we exchange quasiparticle excitations. In this paper, we construct a Z_N rotor model that realizes a self-dual Z_N Abelian gauge theory. We find that lattice dislocation defects in the model produce topologically protected degeneracy. Even though dislocations are not quasiparticle excitations, they resemble non-Abelian anyons with quantum dimension sqrt(N). Exchanging dislocations can produces topologically protected projective non-Abelian Berry phases. The dislocations, as projective non-Abelian anyons can be viewed as a generalization of the Majorana zero modes.Comment: 4 pages + refs, 4 figures. RevTeX

Effective Hamiltonian Approach to the Master Equation

A method of exactly solving the master equation is presented in this letter. The explicit form of the solution is determined by the time evolution of a composite system including an auxiliary system and the open system in question. The effective Hamiltonian governing the time evolution of the composed system are derived from the master equation. Two examples, the dissipative two-level system and the damped harmonic oscillator, are presented to illustrate the solving procedure. PACS number(s): 05.30.-d, 05.40.+j, 42.50.CtComment: 4 pages, no figure

Doping a spin-orbit Mott Insulator: Topological Superconductivity from the Kitaev-Heisenberg Model and possible application to (Na2/Li2)IrO3

We study the effects of doping a Mott insulator on the honeycomb lattice where spins interact via direction dependent Kitaev couplings J_K, and weak antiferromagnetic Heisenberg couplings J. This model is known to have a spin liquid ground state and may potentially be realized in correlated insulators with strong spin orbit coupling. The effect of hole doping is studied within a t-J-J_K model, treated using the SU(2) slave boson formulation, which correctly captures the parent spin liquid. We find superconductor ground states with spin triplet pairing that spontaneously break time reversal symmetry. Interestingly, the pairing is qualitatively different at low and high dopings, and undergoes a first order transition with doping. At high dopings, it is smoothly connected to a paired state of electrons propagating with the underlying free particle dispersion. However, at low dopings the dispersion is strongly influenced by the magnetic exchange, and is entirely different from the free particle band structure. Here the superconductivity is fully gapped and topological, analogous to spin polarized electrons with px+ipy pairing. These results may be relevant to honeycomb lattice iridates such as A2IrO3 (A=Li or Na) on doping.Comment: 8 pages + 6 pages supplementary material; 5 figures, 3 tabl

The direct algorithm to construct the Davey-Stewartson hierarchy by two scalar pseudo-differential operators

The infinite many symmetries of DS(Davey-Stewartson) system are closely connected to the integrable deformations of surfaces in $\mathbb{R}^{4}$. In this paper, we give a direct algorithm to construct the expression of the DS(Davey-Stewartson) hierarchy by two scalar pseudo-differential operators involved with $\partial$ and $\hat{\partial}$.Comment: 16 page