158 research outputs found
Influence of modal loss on the quantum state generation via cross-Kerr nonlinearity
In this work we investigate an influence of decoherence effects on quantum
states generated as a result of the cross-Kerr nonlinear interaction between
two modes. For Markovian losses (both photon loss and dephasing), a region of
parameters when losses still do not lead to destruction of non-classicality is
identified. We emphasize the difference in impact of losses in the process of
state generation as opposed to those occurring in propagation channel. We show
moreover, that correlated losses in modern realizations of schemes of large
cross-Kerr nonlinearity might lead to enhancement of non-classicality.Comment: To appear in PR
Optimizing the computation of overriding
We introduce optimization techniques for reasoning in DLN---a recently
introduced family of nonmonotonic description logics whose characterizing
features appear well-suited to model the applicative examples naturally arising
in biomedical domains and semantic web access control policies. Such
optimizations are validated experimentally on large KBs with more than 30K
axioms. Speedups exceed 1 order of magnitude. For the first time, response
times compatible with real-time reasoning are obtained with nonmonotonic KBs of
this size
Robustness of Light-Transport Processes to Bending Deformations in Graded-Index Multimode Waveguides
Light transport through a multimode optical waveguide undergoes changes when subjected to bending deformations. We show that optical waveguides with a perfectly parabolic refractive index profile are almost immune to bending, conserving the structure of propagation-invariant modes. Moreover, we show that changes to the transmission matrix of parabolic-index fibers due to bending can be expressed with only two free parameters, regardless of how complex a particular deformation is. We provide detailed analysis of experimentally measured transmission matrices of a commercially available graded-index fiber as well as a gradient-index rod lens featuring a very faithful parabolic refractive index profile. Although parabolic-index fibers with a sufficiently precise refractive index profile are not within our reach, we show that imaging performance with standard commercially available graded-index fibers is significantly less influenced by bending deformations than step-index types under the same conditions. Our work thus predicts that the availability of ultraprecise parabolic-index fibers will make endoscopic applications with flexible probes feasible and free from extremely elaborate computational challenges
Recommended from our members
Robustness of Light-Transport Processes to Bending Deformations in Graded-Index Multimode Waveguides
Light transport through a multimode optical waveguide undergoes changes when subjected to bending deformations. We show that optical waveguides with a perfectly parabolic refractive index profile are almost immune to bending, conserving the structure of propagation-invariant modes. Moreover, we show that changes to the transmission matrix of parabolic-index fibers due to bending can be expressed with only two free parameters, regardless of how complex a particular deformation is. We provide detailed analysis of experimentally measured transmission matrices of a commercially available graded-index fiber as well as a gradient-index rod lens featuring a very faithful parabolic refractive index profile. Although parabolic-index fibers with a sufficiently precise refractive index profile are not within our reach, we show that imaging performance with standard commercially available graded-index fibers is significantly less influenced by bending deformations than step-index types under the same conditions. Our work thus predicts that the availability of ultraprecise parabolic-index fibers will make endoscopic applications with flexible probes feasible and free from extremely elaborate computational challenges
Entanglement of superconducting charge qubits by homodyne measurement
We present a scheme by which projective homodyne measurement of a microwave
resonator can be used to generate entanglement between two superconducting
charge qubits coupled to this resonator. The non-interacting qubits are
initialised in a product of their ground states, the resonator is initialised
in a coherent field state, and the state of the system is allowed to evolve
under a rotating wave Hamiltonian. Making a homodyne measurement on the
resonator at a given time projects the qubits into an state of the form (|gg> +
exp(-i phi)|ee>)/sqrt(2). This protocol can produce states with a fidelity as
high as required, with a probability approaching 0.5. Although the system
described is one that can be used to display revival in the qubit oscillations,
we show that the entanglement procedure works at much shorter timescales.Comment: 17 pages, 7 figure
Controlled Quantum Secret Sharing
We present a new protocol in which a secret multiqubit quantum state
is shared by players and controllers, where
is the encoding state of a quantum secret sharing scheme. The players may be
considered as field agents responsible for carrying out a task, using the
secret information encrypted in , while the controllers are
superiors who decide if and when the task should be carried out and who to do
it. Our protocol only requires ancillary Bell states and Bell-basis
measurements.Comment: 6 pages, 0 figure, RevTeX4; published version with minor change
Highly non-Gaussian states created via cross-Kerr nonlinearity
We propose a feasible scheme for generation of strongly non-Gaussian states
using the cross-Kerr nonlinearity. The resultant states are highly
non-classical states of electromagnetic field and exhibit negativity of their
Wigner function, sub-Poissonian photon statistics, and amplitude squeezing.
Furthermore, the Wigner function has a distinctly pronounced ``banana'' or
``crescent'' shape specific for the Kerr-type interactions, which so far was
not demonstrated experimentally. We show that creating and detecting such
states should be possible with the present technology using electromagnetically
induced transparency in a four-level atomic system in N-configuration.Comment: 12 pages, 7 figure
Quantum Computation by Communication
We present a new approach to scalable quantum computing--a ``qubus
computer''--which realises qubit measurement and quantum gates through
interacting qubits with a quantum communication bus mode. The qubits could be
``static'' matter qubits or ``flying'' optical qubits, but the scheme we focus
on here is particularly suited to matter qubits. There is no requirement for
direct interaction between the qubits. Universal two-qubit quantum gates may be
effected by schemes which involve measurement of the bus mode, or by schemes
where the bus disentangles automatically and no measurement is needed. In
effect, the approach integrates together qubit degrees of freedom for
computation with quantum continuous variables for communication and
interaction.Comment: final published versio
Quantum Optical Systems for the Implementation of Quantum Information Processing
We review the field of Quantum Optical Information from elementary
considerations through to quantum computation schemes. We illustrate our
discussion with descriptions of experimental demonstrations of key
communication and processing tasks from the last decade and also look forward
to the key results likely in the next decade. We examine both discrete (single
photon) type processing as well as those which employ continuous variable
manipulations. The mathematical formalism is kept to the minimum needed to
understand the key theoretical and experimental results
On the self-consistent spin-wave theory of layered Heisenberg magnets
The versions of the self-consistent spin-wave theories (SSWT) of
two-dimensional (2D) Heisenberg ferro- and antiferromagnets with a weak
interlayer coupling and/or magnetic anisotropy, that are based on the
non-linear Dyson-Maleev, Schwinger, and combined boson-pseudofermion
representations, are analyzed. Analytical results for the temperature
dependences of (sublattice) magnetization and short-range order parameter, and
the critical points are obtained. The influence of external magnetic field is
considered. Fluctuation corrections to SSWT are calculated within a
random-phase approximation which takes into account correctly leading and
next-leading logarithmic singularities. These corrections are demonstrated to
improve radically the agreement with experimental data on layered perovskites
and other systems. Thus an account of these fluctuations provides a
quantitative theory of layered magnets.Comment: 46 pages, RevTeX, 7 figure
- …