3,701 research outputs found
Teleportation of continuous quantum variables
Quantum teleportation is analyzed for states of dynamical variables with continuous spectra, in contrast to previous work with discrete (spin) variables. The entanglement fidelity of the scheme is computed, including the roles of finite quantum correlation and nonideal detection efficiency. A protocol is presented for teleporting the wave function of a single mode of the electromagnetic field with high fidelity using squeezed-state entanglement and current experimental capability
Shape-resonance-induced non-Franck–Condon effects in (2+1) resonance enhanced multiphoton ionization of the C 3Πg state of O2
We show that strong non-Franck–Condon effects observed in (2+1) resonance enhanced multiphoton ionization of the C 3Pig state of O2 are due to the ksigmau shape resonance previously observed in single-photon studies of diatomic molecules. Calculated vibrational branching ratios for the v=2,3 levels of the C 3Πg state are in reasonable agreement with experiment. Certain discrepancies remain in comparing theoretical results with the measured spectra, and possible electron-correlation effects which underly this are discussed
Optical implementation of continuous-variable quantum cloning machines
We propose an optical implementation of the Gaussian continuous-variable
quantum cloning machines. We construct a symmetric N -> M cloner which
optimally clones coherent states and we also provide an explicit design of an
asymmetric 1 -> 2 cloning machine. All proposed cloning devices can be built
from just a single non-degenerate optical parametric amplifier and several beam
splitters.Comment: 4 pages, 3 figures, REVTe
The Scalar Curvature of the Bures Metric on the Space of Density Matrices
The Riemannian Bures metric on the space of (normalized) complex positive
matrices is used for parameter estimation of mixed quantum states based on
repeated measurements just as the Fisher information in classical statistics.
It appears also in the concept of purifications of mixed states in quantum
physics. Here we determine its scalar curvature and Ricci tensor and prove a
lower bound for the curvature on the submanifold of trace one matrices. This
bound is achieved for the maximally mixed state, a further hint for the quantum
statistical meaning of the scalar curvature.Comment: Latex, 9 page
Generalized uncertainty relations: Theory, examples, and Lorentz invariance
The quantum-mechanical framework in which observables are associated with
Hermitian operators is too narrow to discuss measurements of such important
physical quantities as elapsed time or harmonic-oscillator phase. We introduce
a broader framework that allows us to derive quantum-mechanical limits on the
precision to which a parameter---e.g., elapsed time---may be determined via
arbitrary data analysis of arbitrary measurements on identically prepared
quantum systems. The limits are expressed as generalized Mandelstam-Tamm
uncertainty relations, which involve the operator that generates displacements
of the parameter---e.g., the Hamiltonian operator in the case of elapsed time.
This approach avoids entirely the problem of associating a Hermitian operator
with the parameter. We illustrate the general formalism, first, with
nonrelativistic uncertainty relations for spatial displacement and momentum,
harmonic-oscillator phase and number of quanta, and time and energy and,
second, with Lorentz-invariant uncertainty relations involving the displacement
and Lorentz-rotation parameters of the Poincar\'e group.Comment: 39 pages of text plus one figure; text formatted in LaTe
Weak force detection with superposed coherent states
We investigate the utility of non classical states of simple harmonic
oscillators, particularly a superposition of coherent states, for sensitive
force detection. We find that like squeezed states a superposition of coherent
states allows displacement measurements at the Heisenberg limit. Entangling
many superpositions of coherent states offers a significant advantage over a
single mode superposition states with the same mean photon number.Comment: 6 pages, no figures: New section added on entangled resources.
Changes to discussions and conclusio
A Quantum Teleportation Game
We investigate a game where a sender (Alice) teleports coherent states to two
receivers (Bob and Charlie) through a tripartite Gaussian state. The aim of the
receivers is to optimize their teleportation fidelities by means of local
operations and classical communications. We show that a non-cooperative
strategy, corresponding to the standard telecloning protocol, can be
outperformed by a cooperative strategy, which gives rise to a novel
(cooperative) telecloning protocol.Comment: Typographic corrections 4 pages, 4 figure
Entropy inequalities and Bell inequalities for two-qubit systems
Sufficient conditions for (the non-violation of) the Bell-CHSH inequalities
in a mixed state of a two-qubit system are: 1) The linear entropy of the state
is not smaller than 0.5, 2) The sum of the conditional linear entropies is
non-negative, 3) The von Neumann entropy is not smaller than 0.833, 4) The sum
of the conditional von Neumann entropies is not smaller than 0.280.Comment: Errors corrected. See L. Jakobcyk, quant-ph/040908
How to measure squeezing and entanglement of Gaussian states without homodyning
We propose a scheme for measuring the squeezing, purity, and entanglement of
Gaussian states of light that does not require homodyne detection. The
suggested setup only needs beam splitters and single-photon detectors. Two-mode
entanglement can be detected from coincidences between photodetectors placed on
the two beams.Comment: 4 pages, 2 figures, RevTe
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