219 research outputs found
Quantum Ratchets for Quantum Communication with Optical Superlattices
We propose to use a quantum ratchet to transport quantum information in a
chain of atoms trapped in an optical superlattice. The quantum ratchet is
created by a continuous modulation of the optical superlattice which is
periodic in time and in space. Though there is zero average force acting on the
atoms, we show that indeed the ratchet effect permits atoms on even and odd
sites to move along opposite directions. By loading the optical lattice with
two-level bosonic atoms, this scheme permits to perfectly transport a qubit or
entangled state imprinted in one or more atoms to any desired position in the
lattice. From the quantum computation point of view, the transport is achieved
by a smooth concatenation of perfect swap gates. We analyze setups with
noninteracting and interacting particles and in the latter case we use the
tools of optimal control to design optimal modulations. We also discuss the
feasibility of this method in current experiments.Comment: Published version, 9 pages, 5 figure
Entanglement detection in coupled particle plasmons
When in close contact, plasmonic resonances interact and become strongly
correlated. In this work we develop a quantum mechanical model, using the
language of continuous variables and quantum information, for an array of
coupled particle plasmons. This model predicts that when the coupling strength
between plasmons approaches or surpasses the local dissipation, a sizable
amount of entanglement is stored in the collective modes of the array. We also
prove that entanglement manifests itself in far-field images of the plasmonic
modes, through the statistics of the quadratures of the field, in what
constitutes a novel family of entanglement witnesses. This protocol is so
robust that it is indeed independent of whether our own model is correct.
Finally, we estimate the amount of entanglement, the coupling strength and the
correlation properties for a system that consists of two or more coupled
nanospheres of silver, showing evidence that our predictions could be tested
using present-day state-of-the-art technology.Comment: 8 pages (6 main text + 2 supplemental), 3 figure
Microwave photonics with Josephson junction arrays: Negative refraction index and entanglement through disorder
We study different architectures for a photonic crystal in the microwave regime based on superconducting transmission lines interrupted by Josephson junctions, both in one and two dimensions. A study of the scattering properties of a single junction in the line shows that the junction behaves as a perfect mirror when the photon frequency matches the Josephson plasma frequency. We generalize our calculations to periodic arrangements of junctions, demonstrating that they can be used for tunable band engineering, forming what we call a quantum circuit crystal. Two applications are discussed in detail. In a two-dimensional structure we demonstrate the phenomenon of negative refraction. We finish by studying the creation of stationary entanglement between two superconducting qubits interacting through a disordered media. © 2012 American Physical Society.This work was supported by Spanish Governement projects FIS2008-01240, FIS2009-10061, FIS2009-12773-C02-01, and FIS2011-25167 coïŹnanced by FEDER funds; CAM research consortium QUITEMAD; Basque Government Grants No. IT472-10, and No. UPV/EHU UFI 11/55; and PROMISCE, SOLID, and CCQED European projects.Peer Reviewe
Split vortices in optically coupled Bose-Einstein condensates
We study a rotating two-component Bose-Einstein condensate in which an
optically induced Josephson coupling allows for population transfer between the
two species. In a regime where separation of species is favored, the ground
state of the rotating system displays domain walls with velocity fields normal
to them. Such a configuration looks like a vortex split into two halves, with
atoms circulating around the vortex and changing their internal state in a
continuous way.Comment: 4 EPS pictures, 4 pages; Some errata have been corrected and thep
resentation has been slightly revise
Construction of exact solutions by spatial traslations in inhomogeneous Nonlinear Schrodinger equations. Applications to Bose-Einstein condensation
In this paper we study a general nonlinear Schr\"odinger equation with a time
dependent harmonic potential. Despite the lack of traslational invariance we
find a symmetry trasformation which, up from any solution, produces infinitely
many others which are centered on classical trajectories. The results presented
here imply that, not only the center of mass of the wave-packet satisfies the
Ehrenfest theorem and is decoupled from the dynamics of the wave-packet, but
also the shape of the solution is independent of the behaviour of the center of
the wave. Our findings have implications on the dynamics of Bose-Einstein
condensates in magnetic trapsComment: Submitted to Phys. Re
Entangled microwaves as a resource for entangling spatially separate solid-state qubits: Superconducting qubits, nitrogen-vacancy centers, and magnetic molecules
13 pågs.; 10 figs.; 2 apps.Quantum correlations present in a broadband two-line squeezed microwave state can induce entanglement in a spatially separated bipartite system consisting of either two single qubits or two-qubit ensembles. By using an appropriate master equation for a bipartite quantum system in contact with two separate but entangled baths, the generating entanglement process in spatially separated quantum systems is thoroughly characterized. Decoherence thermal effects on the entanglement transfer are also discussed. Our results provide evidence that this entanglement transfer by dissipation is feasible, yielding to a steady-state amount of entanglement in the bipartite quantum system which can be optimized for a wide range of realistic physical systems that include state-of-the-art experiments with nitrogen-vacancy centers in diamond, superconducting qubits, or even magnetic molecules embedded in a crystalline matrix. ©2016 American Physical SocietyA.V.G., F.J.R., and L.Q. acknowledge financial support
from Facultad de Ciencias at UniAndes-2015 Project âTransfer
of Correlations from Non-classically Correlated Reservoirs
to Solid State Systemsâ and Project âQuantum Control of
Non-equilibrium Hybrid Systems-Part II,â UniAndes-2015.
J.J.G.R. acknowledges support from Spanish Mineco Project
No. FIS2012-33022, from EU FP7 Project PROMISCE, from
CAM Research Network QUITEMAD+.Peer Reviewe
Fragmented superfluid due to frustration of cold atoms in optical lattices
A one dimensional optical lattice is considered where a second dimension is
encoded in the internal states of the atoms giving effective ladder systems.
Frustration is introduced by an additional optical lattice that induces
tunneling of superposed atomic states. The effects of frustration range from
the stabilization of the Mott insulator phase with ferromagnetic order, to the
breakdown of superfluidity and the formation of a macroscopically fragmented
phase.Comment: New version, more results, about 20 page
Temperature-independent quantum logic for molecular spectroscopy
We propose a fast and non-destructive spectroscopic method for single
molecular ions that implements quantum logic schemes between an atomic ion and
the molecular ion of interest. Our proposal relies on a hybrid coherent
manipulation of the two-ion system, using optical or magnetic forces depending
on the types of molecular levels to be addressed (Zeeman, rotational,
vibrational or electronic degrees of freedom). The method is especially suited
for the non-destructive precision spectroscopy of single molecular ions, and
sets a starting point for new hybrid quantum computation schemes that combine
molecular and atomic ions, covering the measurement and entangling steps.Comment: v3. Substantially enlarged manuscript with details of derivations and
calculations in two appendices. To appear in PR
Anomalous rotational properties of Bose-Einstein condensates in asymmetric traps
We study the rotational properties of a Bose-Einstein condensate confined in
a rotating harmonic trap for different trap anisotropies. Using simple
arguments, we derive expressions for the velocity field of the quantum fluid
for condensates with or without vortices. While the condensed gas describes
open spiraling trajectories, on the frame of reference of the rotating trap the
motion of the fluid is against the trap rotation. We also find explicit
formulae for the angular momentum and a linear and Thomas-Fermi solutions for
the state without vortices. In these two limits we also find an analytic
relation between the shape of the cloud and the rotation speed. The predictions
are supported by numerical simulations of the mean field Gross-Pitaevskii
model.Comment: 4 RevTeX pages, 2 EPS figures; typos fixed, reference adde
From Josephson junction metamaterials to tunable pseudo-cavities
arXiv:1305.4844v1The scattering through a Josephson junction (JJ) interrupting a superconducting line is revisited including power leakage. We also discuss how to make tunable and broadband resonant mirrors by concatenating junctions. As an application, we show how to construct cavities using these mirrors, thus connecting two research fields: JJ quantum metamaterials and coupled-cavity arrays. We finish by discussing the first nonlinear corrections to the scattering and their measurable effects. © 2013 IOP Publishing Ltd.This work was supported by Spanish government projects FIS2009-10061, and FIS2011-25167 conanced by FEDER funds. We thanks Aragon government support to group FENOL, CAM research consortium QUITEMAD and PROMISCE European project.Peer Reviewe
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