7 research outputs found
Transport and Entanglement Generation in the Bose-Hubbard Model
We study entanglement generation via particle transport across a
one-dimensional system described by the Bose-Hubbard Hamiltonian. We analyze
how the competition between interactions and tunneling affects transport
properties and the creation of entanglement in the occupation number basis.
Alternatively, we propose to use spatially delocalized quantum bits, where a
quantum bit is defined by the presence of a particle either in a site or in the
adjacent one. Our results can serve as a guidance for future experiments to
characterize entanglement of ultracold gases in one-dimensional optical
lattices.Comment: 14 pages, 6 figure
Efficient quantum state transfer in spin chains via adiabatic passage
We propose a method for quantum state transfer in spin chains using an
adiabatic passage technique. Modifying even and odd nearest-neighbour couplings
in time allows to achieve transfer fidelities arbitrarily close to one, without
the need for a precise control of coupling strengths and timing. We study in
detail transfer by adiabatic passage in a spin-1 chain governed by a
generalized Heisenberg Hamiltonian. We consider optimization of the transfer
process applying optimal control techniques. We discuss a realistic
experimental implementation using cold atomic gases confined in deep optical
lattices.Comment: 14 pages, 6 figures, to be published in New J. Phy
Decoherence by engineered quantum baths
We introduce, and determine decoherence for, a wide class of non-trivial
quantum spin baths which embrace Ising, XY and Heisenberg universality classes
coupled to a two-level system. For the XY and Ising universality classes we
provide an exact expression for the decay of the loss of coherence beyond the
case of a central spin coupled uniformly to all the spins of the baths which
has been discussed so far in the literature. In the case of the Heisenberg spin
bath we study the decoherence by means of the time-dependent density matrix
renormalization group. We show how these baths can be engineered, by using
atoms in optical lattices.Comment: 4 pages, 4 figure
Mean-field phase diagram of disordered bosons in a lattice at non-zero temperature
Bosons in a periodic lattice with on-site disorder at low but non-zero
temperature are considered within a mean-field theory. The criteria used for
the definition of the superfluid, Mott insulator and Bose glass are analysed.
Since the compressibility does never vanish at non-zero temperature, it can not
be used as a general criterium. We show that the phases are unambiguously
distinguished by the superfluid density and the density of states of the
low-energy exitations. The phase diagram of the system is calculated. It is
shown that even a tiny temperature leads to a significant shift of the boundary
between the Bose glass and superfluid
Magnetism and Hund's rule in an optical lattice with cold fermions
We demonstrate that a two-dimensional (2D) optical lattice loaded with repulsive, contact-interacting fermions shows a rich and systematic magnetic phase diagram. Trapping a few (N ? 12) fermions in each of the single-site minima of the optical lattice, we find that the shell structure in these quantum wells determines the magnetism. In a shallow lattice, the tunnelling between the single wells is strong, and the lattice is non-magnetic (NM). For deeper lattices, however, the shell filling of the single wells with fermionic atoms determines the magnetism. As a consequence of Hund's first rule, the interaction energy is lowered by maximizing the number of atoms of the same species. This leads to a systematic sequence of NM, ferromagnetic (F) and antiferromagnetic (AF) phases