21,372 research outputs found
Linear-optical processing cannot increase photon efficiency
We answer the question whether linear-optical processing of the states
produced by one or multiple imperfect single-photon sources can improve the
single-photon fidelity. This processing can include arbitrary interferometers,
coherent states, feedforward, and conditioning on results of detections. We
show that without introducing multiphoton components, the single-photon
fraction in any of the single-mode states resulting from such processing cannot
be made to exceed the efficiency of the best available photon source. If
multiphoton components are allowed, the single-photon fidelity cannot be
increased beyond 1/2. We propose a natural general definition of the
quantum-optical state efficiency, and show that it cannot increase under
linear-optical processing.Comment: 4 pages, 3 figure
Semiclassical Analysis of the Supershell Effect in Reflection-Asymmetric Superdeformed Oscillator
An oscillatory pattern in the smoothed quantum spectrum, which is unique for
single-particle motions in a reflection-asymmetric superdeformed oscillator
potential, is investigated by means of the semiclassical theory of shell
structure. Clear correspondence between the oscillating components of the
smoothed level density and the classical periodic orbits is found. It is shown
that an interference effect between two families of the short periodic orbits,
called supershell effect, develops with increasing reflection-asymmetric
deformations. Possible origins of this enhancement phenomena as well as quantum
signatures of period-multipling bifurcations are discussed in connection with
stabilities of the classical periodic orbits.Comment: 27 pages, REVTeX, 12 postscript figures are available from the author
upon reques
Efficiency limits for linear optical processing of single photons and single-rail qubits
We analyze the problem of increasing the efficiency of single-photon sources
or single-rail photonic qubits via linear optical processing and destructive
conditional measurements. In contrast to previous work we allow for the use of
coherent states and do not limit to photon-counting measurements. We conjecture
that it is not possible to increase the efficiency, prove this conjecture for
several important special cases, and provide extensive numerical results for
the general case.Comment: 10 pages, 4 figure
Interconvertibility of single-rail optical qubits
We show how to convert between partially coherent superpositions of a single
photon with the vacuum using linear optics and postselection based on homodyne
measurements. We introduce a generalized quantum efficiency for such states and
show that any conversion that decreases this quantity is possible. We also
prove that our scheme is optimal by showing that no linear optical scheme with
generalized conditional measurements, and with one single-rail qubit input can
improve the generalized efficiency.Comment: 3 pages, 2 figure
Efficiencies of Quantum Optical Detectors
We propose a definition for the efficiency that can be universally applied to
all classes of quantum optical detectors. This definition is based on the
maximum amount of optical loss that a physically plausible device can
experience while still replicating the properties of a given detector. We prove
that detector efficiency cannot be increased using linear optical processing.
That is, given a set of detectors, as well as arbitrary linear optical elements
and ancillary light sources, it is impossible to construct detection devices
that would exhibit higher efficiencies than the initial set.Comment: 5 pages, 3 figure
Modified Reconstruction of Standard Model in Non-Commutative Differential Geometry
Sogami recently proposed the new idea to express Higgs particle as a kind of
gauge particle by prescribing the generalized covariant derivative with gauge
and Higgs fields operating on quark and lepton fields. The field strengths for
both the gauge and Higgs fields are defined by the commutators of the covariant
derivative by which he could obtain the Yang-Mills Higgs Lagrangian in the
standard model. Inspired by Sogami's work, we present a modification of our
previous scheme to formulate the spontaneously broken gauge theory in
non-commutative geometry on the discrete space; Minkowski space multiplied by
two points space by introducing the generation mixing matrix in operation of
the generalized derivative on the more fundamental fields a_i(x,y) which
compose the gauge and Higgs fields. The standard model is reconstructed
according to the modified scheme, which does not yields not only any special
relations between the particle masses but also the special restriction on the
Higgs potential.Comment: 21 page
Phase Space Evolution and Discontinuous Schr\"odinger Waves
The problem of Schr\"odinger propagation of a discontinuous wavefunction
-diffraction in time- is studied under a new light. It is shown that the
evolution map in phase space induces a set of affine transformations on
discontinuous wavepackets, generating expansions similar to those of wavelet
analysis. Such transformations are identified as the cause for the
infinitesimal details in diffraction patterns. A simple case of an evolution
map, such as SL(2) in a two-dimensional phase space, is shown to produce an
infinite set of space-time trajectories of constant probability. The
trajectories emerge from a breaking point of the initial wave.Comment: Presented at the conference QTS7, Prague 2011. 12 pages, 7 figure
Periodic-Orbit Bifurcation and Shell Structure in Reflection-Asymmetric Deformed Cavity
Shell structure of the single-particle spectrum for reflection-asymmetric
deformed cavity is investigated. Remarkable shell structure emerges for certain
combinations of quadrupole and octupole deformations. Semiclassical
periodic-orbit analysis indicates that bifurcation of equatorial orbits plays
an important role in the formation of this new shell structure.Comment: 5 pages, latex including 5 postscript figures, submitted to Physics
Letters
Vector Potential and Berry phase-induced Force
We present a general theoretical framework for the exact treatment of a
hybrid system that is composed of a quantum subsystem and a classical
subsystem. When the quantum subsystem is dynamically fast and the classical
subsystem is slow, a vector potential is generated with a simple canonical
transformation. This vector potential, on one hand, gives rise to the familiar
Berry phase in the fast quantum dynamics; on the other hand, it yields a
Lorentz-like force in the slow classical dynamics. In this way, the pure phase
(Berry phase) of a wavefunction is linked to a physical force.Comment: 4 pages, 1 figur
Gravitational wave energy spectrum of a parabolic encounter
We derive an analytic expression for the energy spectrum of gravitational
waves from a parabolic Keplerian binary by taking the limit of the Peters and
Matthews spectrum for eccentric orbits. This demonstrates that the location of
the peak of the energy spectrum depends primarily on the orbital periapse
rather than the eccentricity. We compare this weak-field result to strong-field
calculations and find it is reasonably accurate (~10%) provided that the
azimuthal and radial orbital frequencies do not differ by more than ~10%. For
equatorial orbits in the Kerr spacetime, this corresponds to periapse radii of
rp > 20M. These results can be used to model radiation bursts from compact
objects on highly eccentric orbits about massive black holes in the local
Universe, which could be detected by LISA.Comment: 5 pages, 3 figures. Minor changes to match published version; figure
1 corrected; references adde
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