1,392 research outputs found
Quantum communication and the creation of maximally entangled pairs of atoms over a noisy channel
We show how to create maximally entangled EPR pairs between spatially distant
atoms, each of them inside a high-Q optical cavity, by sending photons through
a general, noisy channel, such as a standard optical fiber. An error correction
scheme that uses few auxiliary atoms in each cavity effectively eliminates
photoabsorption and other transmission errors. This realizes the `absorption
free channel.' A concatenation protocol using the absorption free channel
allows for quantum communication with single qubits over distances much larger
than the coherence length of the channel.Comment: 12 pages, latex, rspublic.sty, 4 figures, uses epsf macro. For the
Royal Society meeting on quantum computatio
Dissipation-induced d-Wave Pairing of Fermionic Atoms in an Optical Lattice
We show how dissipative dynamics can give rise to pairing for two-component
fermions on a lattice. In particular, we construct a "parent" Liouvillian
operator so that a BCS-type state of a given symmetry, e.g. a d-wave state, is
reached for arbitrary initial states in the absence of conservative forces. The
system-bath couplings describe single-particle, number conserving and
quasi-local processes. The pairing mechanism crucially relies on Fermi
statistics. We show how such Liouvillians can be realized via reservoir
engineering with cold atoms representing a driven dissipative dynamics.Comment: 5 pages, 3 figures. Replaced with the published versio
Quantum Spin Lenses in Atomic Arrays
We propose and discuss `quantum spin lenses', where quantum states of
delocalized spin excitations in an atomic medium are `focused' in space in a
coherent quantum process down to (essentially) single atoms. These can be
employed to create controlled interactions in a quantum light-matter interface,
where photonic qubits stored in an atomic ensemble are mapped to a quantum
register represented by single atoms. We propose Hamiltonians for quantum spin
lenses as inhomogeneous spin models on lattices, which can be realized with
Rydberg atoms in 1D, 2D and 3D, and with strings of trapped ions. We discuss
both linear and non-linear quantum spin lenses: in a non-linear lens, repulsive
spin-spin interactions lead to focusing dynamics conditional to the number of
spin excitations. This allows the mapping of quantum superpositions of
delocalized spin excitations to superpositions of spatial spin patterns, which
can be addressed by light fields and manipulated. Finally, we propose
multifocal quantum spin lenses as a way to generate and distribute entanglement
between distant atoms in an atomic lattice array.Comment: 13 pages, 9 figure
Quantum Field Theory for the Three-Body Constrained Lattice Bose Gas -- Part I: Formal Developments
We develop a quantum field theoretical framework to analytically study the
three-body constrained Bose-Hubbard model beyond mean field and non-interacting
spin wave approximations. It is based on an exact mapping of the constrained
model to a theory with two coupled bosonic degrees of freedom with polynomial
interactions, which have a natural interpretation as single particles and
two-particle states. The procedure can be seen as a proper quantization of the
Gutzwiller mean field theory. The theory is conveniently evaluated in the
framework of the quantum effective action, for which the usual symmetry
principles are now supplemented with a ``constraint principle'' operative on
short distances. We test the theory via investigation of scattering properties
of few particles in the limit of vanishing density, and we address the
complementary problem in the limit of maximum filling, where the low lying
excitations are holes and di-holes on top of the constraint induced insulator.
This is the first of a sequence of two papers. The application of the formalism
to the many-body problem, which can be realized with atoms in optical lattices
with strong three-body loss, is performed in a related work [14].Comment: 21 pages, 5 figure
Reservoir engineering and dynamical phase transitions in optomechanical arrays
We study the driven-dissipative dynamics of photons interacting with an array
of micromechanical membranes in an optical cavity. Periodic membrane driving
and phonon creation result in an effective photon-number conserving non-unitary
dynamics, which features a steady state with long-range photonic coherence. If
the leakage of photons out of the cavity is counteracted by incoherent driving
of the photonic modes, we show that the system undergoes a dynamical phase
transition to the state with long-range coherence. A minimal system, composed
of two micromechanical membranes in a cavity, is studied in detail, and it is
shown to be a realistic setup where the key processes of the driven-dissipative
dynamics can be seen.Comment: 16 pages, 9 figure
Stabilization of the p-wave superfluid state in an optical lattice
It is hard to stabilize the p-wave superfluid state of cold atomic gas in
free space due to inelastic collisional losses. We consider the p-wave Feshbach
resonance in an optical lattice, and show that it is possible to have a stable
p-wave superfluid state where the multi-atom collisional loss is suppressed
through the quantum Zeno effect. We derive the effective Hamiltonian for this
system, and calculate its phase diagram in a one-dimensional optical lattice.
The results show rich phase transitions between the p-wave superfluid state and
different types of insulator states induced either by interaction or by
dissipation.Comment: 5 pages, 5 figure
Nonequilibrium Phase Diagram of a Driven-Dissipative Many-Body System
We study the nonequilibrium dynamics of a many-body bosonic system on a
lattice, subject to driving and dissipation. The time-evolution is described by
a master equation, which we treat within a generalized Gutzwiller mean field
approximation for density matrices. The dissipative processes are engineered
such that the system, in the absence of interaction between the bosons, is
driven into a homogeneous steady state with off-diagonal long range order. We
investigate how the coherent interaction affects qualitatively the properties
of the steady state of the system and derive a nonequilibrium phase diagram
featuring a phase transition into a steady state without long range order. The
phase diagram exhibits also an extended domain where an instability of the
homogeneous steady state gives rise to a persistent density pattern with
spontaneously broken translational symmetry. In the limit of small particle
density, we provide a precise analytical description of the time-evolution
during the instability. Moreover, we investigate the transient following a
quantum quench of the dissipative processes and we elucidate the prominent role
played by collective topological variables in this regime.Comment: 23 pages, 15 figure
Quantum Computation Using Vortices and Majorana Zero Modes of a + Superfluid of Fermionic Cold Atoms
We propose to use the recently predicted two-dimensional `weak-pairing' superfluid state of fermionic cold atoms as a platform for topological
quantum computation. In the core of a vortex, this state supports a zero-energy
Majorana mode, which moves to finite energy in the corresponding topologically
trivial `strong-pairing' state. By braiding vortices in the `weak-pairing'
state, unitary quantum gates can be applied to the Hilbert space of Majorana
zero-modes. For read-out of the topological qubits, we propose realistic
schemes suitable for atomic superfluids
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