1,400 research outputs found
Dispersion and fidelity in quantum interferometry
We consider Mach-Zehnder and Hong-Ou-Mandel interferometers with nonclassical
states of light as input, and study the effect that dispersion inside the
interferometer has on the sensitivity of phase measurements. We study in detail
a number of different one- and two-photon input states, including Fock, dual
Fock, N00N states, and photon pairs from parametric downconversion. Assuming
there is a phase shift in one arm of the interferometer, we compute
the probabilities of measurement outcomes as a function of , and then
compute the Shannon mutual information between and the measurements.
This provides a means of quantitatively comparing the utility of various input
states for determining the phase in the presence of dispersion. In addition, we
consider a simplified model of parametric downconversion for which
probabilities can be explicitly computed analytically, and which serves as a
limiting case of the more realistic downconversion model.Comment: 12 pages, 14 figures. Submitted to Physical Review
Goldstone-Mode Phonon Dynamics in the Pyrochlore Cd2Re2O7
We have measured the polarized Raman scattering spectra of Cd2Re2O7, the
first superconducting pyrochlore, as a function of temperature. For
temperatures below the cubic-to-tetragonal structural phase transition (SPT) at
200K, a peak with B1 symmetry develops at zero frequency with divergent
intensity. We identify this peak as the first observation of the Goldstone
phonon in a crystalline solid. The Goldstone phonon is a collective excitation
that exists due to the breaking of the continuous symmetry with the SPT. Its
emergence coincides with that of a Raman-active soft mode. The order parameter
for both features derives from an unstable doubly-degenerate vibration (with Eu
symmetry) of the O1 atoms which drives the SPT.Comment: 4+ pages, 4 figures. Updated figures and text. Accepted to PR
Generating Polarization-Entangled Photon Pairs with Arbitrary Joint Spectrum
We present a scheme for generating polarization-entangled photons pairs with
arbitrary joint spectrum. Specifically, we describe a technique for spontaneous
parametric down-conversion in which both the center frequencies and the
bandwidths of the down-converted photons may be controlled by appropriate
manipulation of the pump pulse. The spectral control offered by this technique
permits one to choose the operating wavelengths for each photon of a pair based
on optimizations of other system parameters (loss in optical fiber, photon
counter performance, etc.). The combination of spectral control, polarization
control, and lack of group-velocity matching conditions makes this technique
particularly well-suited for a distributed quantum information processing
architecture in which integrated optical circuits are connected by spans of
optical fiber.Comment: 6 pages, 3 figure
Metallic "Ferroelectricity" in the Pyrochlore Cd2Re2O7
A class of materials known as ``ferroelectric metals'' was discussed
theoretically by Anderson and Blount in 1965 [Phys. Rev. Lett. 14, 217 (1965)],
but to date no examples of this class have been reported. Here we present
measurements of the elastic moduli of Cd2Re2O7 through the 200 K
cubic-to-tetragonal phase transition. A Landau analysis of the moduli reveals
that the transition is consistent with Cd2Re2O7 being classified as a
``ferroelectric metal'' in the weaker sense described by Anderson and Blount
(loss of a center of symmetry). First-principles calculations of the lattice
instabilities indicate that the dominant lattice instability corresponds to a
two-fold degenerate mode with Eu symmetry, and that motions of the O ions
forming the O octahedra dominate the energetics of the transition.Comment: 4 pages, 2 figure
Symmetric Autocompensating Quantum Key Distribution
We present quantum key distribution schemes which are autocompensating
(require no alignment) and symmetric (Alice and Bob receive photons from a
central source) for both polarization and time-bin qubits. The primary benefit
of the symmetric configuration is that both Alice and Bob may have passive
setups (neither Alice nor Bob is required to make active changes for each run
of the protocol). We show that both the polarization and the time-bin schemes
may be implemented with existing technology. The new schemes are related to
previously described schemes by the concept of advanced waves.Comment: 4 pages, 2 figur
Two-Photon Spiral Imaging with Correlated Orbital Angular Momentum States
The concept of correlated two-photon spiral imaging is introduced. We begin
by analyzing the joint orbital angular momentum (OAM) spectrum of correlated
photon pairs. The mutual information carried by the photon pairs is evaluated,
and it is shown that when an object is placed in one of the beam paths the
value of the mutual information is strongly dependent on object shape and is
closely related to the degree of rotational symmetry present. After analyzing
the effect of the object on the OAM correlations, the method of correlated
spiral imaging is described. We first present a version using parametric
downconversion, in which entangled pairs of photons with opposite OAM values
are produced, placing an object in the path of one beam. We then present a
classical (correlated, but non-entangled) version. The relative problems and
benefits of the classical versus entangled configurations are discussed. The
prospect is raised of carrying out compressive imaging via twophoton OAM
detection to reconstruct sparse objects with few measurements
Odd-Order Aberration-Cancellation in Correlated-Photon Imaging
We discuss a correlated two-photon imaging apparatus that is capable of
producing images that are free of the effects of odd-order aberration
introduced by the optical system. We show that both quantum-entangled and
classically correlated light sources are capable of producing the desired
spatial-aberration cancelation
Twin-Photon Confocal Microscopy
A recently introduced two-channel confocal microscope with correlated
detection promises up to 50% improvement in transverse spatial resolution
[Simon, Sergienko, Optics Express {\bf 18}, 9765 (2010)] via the use of photon
correlations. Here we achieve similar results in a different manner,
introducing a triple-confocal correlated microscope which exploits the
correlations present in optical parametric amplifiers. It is based on tight
focusing of pump radiation onto a thin sample positioned in front of a
nonlinear crystal, followed by coincidence detection of signal and idler
photons, each focused onto a pinhole. This approach offers further resolution
enhancement in confocal microscopy
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