Transparent, Non-local, Species-selective Transport in an Optical Superlattice Containing Two Interacting Atom Species

In an optical superlattice of triple wells, containing two mutually interacting atom species in adjacent wells, we show that one species can be transported through the positions of the other species, yet avoiding significant overlap and direct interaction. The transfer protocol is optimized to be robust against missing atoms of either species in any lattice site, as well as against lattice fluctuations. The degree and the duration of the inter-species overlap during passage can be tuned, making possible controlled large-scale interaction-induced change of internal states.Comment: 7 pages and 5 figure

Entangled Collective Spin States of Two Species Ultracold atoms in a Ring

We study the general quantum Hamiltonian that can be realized with two species of mutually interacting degenerate ultracold atoms in a ring-shaped trap, with the options of rotation and an azimuthal lattice. We examine the spectrum and the states with a collective spin picture in a Dicke state basis. The system can generate states with a high degree of entanglement gauged by the von Neumann entropy. The Hamiltonian has two components, a linear part that can be controlled and switched on via rotation or the azimuthal lattice, and an interaction-dependent quadratic part. Exact solutions are found for the quadratic part for equal strengths of intra-species and the inter-species interactions, but for generally different particle numbers in the two species. The quadratic Hamiltonian has a degenerate ground state when the two species have unequal number of particles, but non-degenerate when equal. We determine the impact on the entanglement entropy of deviations from equal particle numbers as well as deviations from the assumption of equal interaction strengths. Limiting cases are shown to display features of a beam-splitter and spin-squeezing that can find utility in interferometry. The density of states for the full Hamiltonian shows features as of phase transition in varying between linear and quadratic limits.Comment: 8 pages, 6 figure

Sampling the canonical phase from phase-space functions

We discuss the possibility of sampling exponential moments of the canonical phase from the s-parametrized phase space functions. We show that the sampling kernels exist and are well-behaved for any s>-1, whereas for s=-1 the kernels diverge in the origin. In spite of that we show that the phase space moments can be sampled with any predefined accuracy from the Q-function measured in the double-homodyne scheme with perfect detectors. We discuss the effect of imperfect detection and address sampling schemes using other measurable phase-space functions. Finally, we discuss the problem of sampling the canonical phase distribution itself.Comment: 10 pages, 7 figures, REVTe

Quantum inference of states and processes

The maximum-likelihood principle unifies inference of quantum states and processes from experimental noisy data. Particularly, a generic quantum process may be estimated simultaneously with unknown quantum probe states provided that measurements on probe and transformed probe states are available. Drawbacks of various approximate treatments are considered.Comment: 7 pages, 4 figure

Maximum likelihood estimation of photon number distribution from homodyne statistics

We present a method for reconstructing the photon number distribution from the homodyne statistics based on maximization of the likelihood function derived from the exact statistical description of a homodyne experiment. This method incorporates in a natural way the physical constraints on the reconstructed quantities, and the compensation for the nonunit detection efficiency.Comment: 3 pages REVTeX. Final version, to appear in Phys. Rev. A as a Brief Repor

Wigner-function description of quantum teleportation in arbitrary dimensions and continuous limit

We present a unified approach to quantum teleportation in arbitrary dimensions based on the Wigner-function formalism. This approach provides us with a clear picture of all manipulations performed in the teleportation protocol. In addition within the framework of the Wigner-function formalism all the imperfections of the manipulations can be easily taken into account.Comment: 8 pages, LaTeX, 1 figure (included). Accepted for publication in Phys. Rev. A A minor correction added on May 2