545 research outputs found
Creation of resilient entangled states and a resource for measurement-based quantum computation with optical superlattices
We investigate how to create entangled states of ultracold atoms trapped in
optical lattices by dynamically manipulating the shape of the lattice
potential. We consider an additional potential (the superlattice) that allows
both the splitting of each site into a double well potential, and the control
of the height of potential barrier between sites. We use superlattice
manipulations to perform entangling operations between neighbouring qubits
encoded on the Zeeman levels of the atoms without having to perform transfers
between the different vibrational states of the atoms. We show how to use
superlattices to engineer many-body entangled states resilient to collective
dephasing noise. Also, we present a method to realize a 2D resource for
measurement-based quantum computing via Bell-pair measurements. We analyze
measurement networks that allow the execution of quantum algorithms while
maintaining the resilience properties of the system throughout the computation.Comment: 23 pages, 6 figures, IOP style, published in New Journal of Physics.
Minor corrections/few typos remove
Fast initialization of a high-fidelity quantum register using optical superlattices
We propose a method for the fast generation of a quantum register of
addressable qubits consisting of ultracold atoms stored in an optical lattice.
Starting with a half filled lattice we remove every second lattice barrier by
adiabatically switching on a superlattice potential which leads to a long
wavelength lattice in the Mott insulator state with unit filling. The larger
periodicity of the resulting lattice could make individual addressing of the
atoms via an external laser feasible. We develop a Bose-Hubbard-like model for
describing the dynamics of cold atoms in a lattice when doubling the lattice
periodicity via the addition of a superlattice potential. The dynamics of the
transition from a half filled to a commensurately filled lattice is analyzed
numerically with the help of the Time Evolving Block Decimation algorithm and
analytically using the Kibble-Zurek theory. We show that the time scale for the
whole process, i.e. creating the half filled lattice and subsequent doubling of
the lattice periodicity, is significantly faster than adiabatic direct quantum
freezing of a superfluid into a Mott insulator for large lattice periods. Our
method therefore provides a high fidelity quantum register of addressable
qubits on a fast time scale.Comment: 22 pages, 9 figures, IOP style. Revised version to appear in NJ
Ultra-large Rydberg dimers in optical lattices
We investigate the dynamics of Rydberg electrons excited from the ground
state of ultracold atoms trapped in an optical lattice. We first consider a
lattice comprising an array of double-well potentials, where each double well
is occupied by two ultracold atoms. We demonstrate the existence of molecular
states with equilibrium distances of the order of experimentally attainable
inter-well spacings and binding energies of the order of 10^3 GHz. We also
consider the situation whereby ground-state atoms trapped in an optical lattice
are collectively excited to Rydberg levels, such that the charge-density
distributions of neighbouring atoms overlap. We compute the hopping rate and
interaction matrix elements between highly-excited electrons separated by
distances comparable to typical lattice spacings. Such systems have tunable
interaction parameters and a temperature ~10^{-4} times smaller than the Fermi
temperature, making them potentially attractive for the study and simulation of
strongly correlated electronic systems.Comment: 10 pages, 6 figures, PRA format, version to be published in PR
Dynamic optical lattices: two-dimensional rotating and accordion lattices for ultracold atoms
We demonstrate a novel experimental arrangement which rotates a 2D optical
lattice at frequencies up to several kilohertz. Ultracold atoms in such a
rotating lattice can be used for the direct quantum simulation of strongly
correlated systems under large effective magnetic fields, allowing
investigation of phenomena such as the fractional quantum Hall effect. Our
arrangement also allows the periodicity of a 2D optical lattice to be varied
dynamically, producing a 2D accordion lattice.Comment: 7 pages, 5 figures, final versio
A Single Atom Transistor in a 1D Optical Lattice
We propose a scheme utilising a quantum interference phenomenon to switch the
transport of atoms in a 1D optical lattice through a site containing an
impurity atom. The impurity represents a qubit which in one spin state is
transparent to the probe atoms, but in the other acts as a single atom mirror.
This allows a single-shot quantum non-demolition measurement of the qubit spin.Comment: RevTeX 4, 5 Figures, 4 Page
Transport enhancement from incoherent coupling between one-dimensional quantum conductors
We study the non-equilibrium transport properties of a highly anisotropic
two-dimensional lattice of spin-1/2 particles governed by a Heisenberg XXZ
Hamiltonian. The anisotropy of the lattice allows us to approximate the system
at finite temperature as an array of incoherently coupled one-dimensional
chains. We show that in the regime of strong intrachain interactions, the weak
interchain coupling considerably boosts spin transport in the driven system.
Interestingly, we show that this enhancement increases with the length of the
chains, which is related to superdiffusive spin transport. We describe the
mechanism behind this effect, compare it to a similar phenomenon in single
chains induced by dephasing, and explain why the former is much stronger
Generation of GHZ entangled states of photons in multiple cavities via a superconducting qutrit or an atom through resonant interaction
We propose an efficient method to generate a GHZ entangled state of n photons
in n microwave cavities (or resonators) via resonant interaction to a single
superconducting qutrit. The deployment of a qutrit, instead of a qubit, as the
coupler enables us to use resonant interactions exclusively for all
qutrit-cavity and qutrit-pulse operations. This unique approach significantly
shortens the time of operation which is advantageous to reducing the adverse
effects of qutrit decoherence and cavity decay on fidelity of the protocol.
Furthermore, the protocol involves no measurement on either the state of qutrit
or cavity photons. We also show that the protocol can be generalized to other
systems by replacing the superconducting qutrit coupler with different types of
physical qutrit, such as an atom in the case of cavity QED, to accomplish the
same task.Comment: 11 pages, 5 figures, accepted by Phys. Rev.
Ultracold atoms in optical lattices generated by quantized light fields
We study an ultracold gas of neutral atoms subject to the periodic optical
potential generated by a high- cavity mode. In the limit of very low
temperatures, cavity field and atomic dynamics require a quantum description.
Starting from a cavity QED single atom Hamiltonian we use different routes to
derive approximative multiparticle Hamiltonians in Bose-Hubbard form with
rescaled or even dynamical parameters. In the limit of large enough cavity
damping the different models agree. Compared to free space optical lattices,
quantum uncertainties of the potential and the possibility of atom-field
entanglement lead to modified phase transition characteristics, the appearance
of new phases or even quantum superpositions of different phases. Using a
corresponding effective master equation, which can be numerically solved for
few particles, we can study time evolution including dissipation. As an example
we exhibit the microscopic processes behind the transition dynamics from a Mott
insulator like state to a self-ordered superradiant state of the atoms, which
appears as steady state for transverse atomic pumping.Comment: 17 pages, 10 figures, Published versio
Quantum Logic for Trapped Atoms via Molecular Hyperfine Interactions
We study the deterministic entanglement of a pair of neutral atoms trapped in
an optical lattice by coupling to excited-state molecular hyperfine potentials.
Information can be encoded in the ground-state hyperfine levels and processed
by bringing atoms together pair-wise to perform quantum logical operations
through induced electric dipole-dipole interactions. The possibility of
executing both diagonal and exchange type entangling gates is demonstrated for
two three-level atoms and a figure of merit is derived for the fidelity of
entanglement. The fidelity for executing a CPHASE gate is calculated for two
87Rb atoms, including hyperfine structure and finite atomic localization. The
main source of decoherence is spontaneous emission, which can be minimized for
interaction times fast compared to the scattering rate and for sufficiently
separated atomic wavepackets. Additionally, coherent couplings to states
outside the logical basis can be constrained by the state dependent trapping
potential.Comment: Submitted to Physical Review
Thermodynamics of quantum degenerate gases in optical lattices
The entropy-temperature curves are calculated for non-interacting Bose and
Fermi gases in a 3D optical lattice. These curves facilitate understanding of
how adiabatic changes in the lattice depth affect the temperature, and we
demonstrate regimes where the atomic sample can be significantly heated or
cooled by the loading process. We assess the effects of interactions on a Bose
gas in a deep optical lattice, and show that interactions ultimately limit the
extent of cooling that can occur during lattice loading.Comment: 6 pages, 4 figures. Submitted to proceedings of Laser Physics 2006
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