10,943 research outputs found
Enhancing the Radiative Rate in III-V Semiconductor Plasmonic Core-Shell Nanowire Resonators
We investigate the radiative properties of plasmonic core-shell nanowire resonators and, using boundary element method calculations,
demonstrate enhanced radiative decay rate by up to 3500 times in
nanoscale compound semi-conductor/metal cavities. Calculation of the
local density of optical states enables identification of new types of
modes in cavities with mode volumes on the order of
10^(-4)(λ/n)^3. These modes dramatically enhance the radiative
decay rate and significantly modify the polarization of far-field
emission
Uncertainty characteristics of generalized quantum measurements
The effects of any quantum measurement can be described by a collection of
measurement operators {M_m} acting on the quantum state of the measured system.
However, the Hilbert space formalism tends to obscure the relationship between
the measurement results and the physical properties of the measured system. In
this paper, a characterization of measurement operators in terms of measurement
resolution and disturbance is developed. It is then possible to formulate
uncertainty relations for the measurement process that are valid for arbitrary
input states. The motivation of these concepts is explained from a quantum
communication viewpoint. It is shown that the intuitive interpretation of
uncertainty as a relation between measurement resolution and disturbance
provides a valid description of measurement back action. Possible applications
to quantum cryptography, quantum cloning, and teleportation are discussed.Comment: 8 pages, small additions on cloning and on definitions of delta A_mf,
et
Quantum phase gate for photonic qubits using only beam splitters and post-selection
We show that a beam splitter of reflectivity one-third can be used to realize
a quantum phase gate operation if only the outputs conserving the number of
photons on each side are post-selected.Comment: 6 pages RevTex, including one figur
Renormalization of the baryon axial vector current in large-N_c chiral perturbation theory
The baryon axial vector current is computed at one-loop order in heavy baryon
chiral perturbation theory in the large-N_c limit, where N_c is the number of
colors. Loop graphs with octet and decuplet intermediate states cancel to
various orders in N_c as a consequence of the large-N_c spin-flavor symmetry of
QCD baryons. These cancellations are explicitly shown for the general case of
N_f flavors of light quarks. In particular, a new generic cancellation is
identified in the renormalization of the baryon axial vector current at
one-loop order. A comparison with conventional heavy baryon chiral perturbation
theory is performed at the physical values N_c=3, N_f=3.Comment: REVTex4, 29 pages, 2 figures, 6 tables. Equations (32) and (81)
corrected. Some typos fixed. Results and conclusions remain unchange
Nuclear fission: The "onset of dissipation" from a microscopic point of view
Semi-analytical expressions are suggested for the temperature dependence of
those combinations of transport coefficients which govern the fission process.
This is based on experience with numerical calculations within the linear
response approach and the locally harmonic approximation. A reduced version of
the latter is seen to comply with Kramers' simplified picture of fission. It is
argued that for variable inertia his formula has to be generalized, as already
required by the need that for overdamped motion the inertia must not appear at
all. This situation may already occur above T=2 MeV, where the rate is
determined by the Smoluchowski equation. Consequently, comparison with
experimental results do not give information on the effective damping rate, as
often claimed, but on a special combination of local stiffnesses and the
friction coefficient calculated at the barrier.Comment: 31 pages, LaTex, 9 postscript figures; final, more concise version,
accepted for publication in PRC, with new arguments about the T-dependence of
the inertia; e-mail: [email protected]
Composition at the CuInSe2 ZnO interface copper depletion induced by diethyl zinc
Abstract The interface formation between epitaxial CuInSe2 112 films and ZnO deposited by metal organic MBE is investigated by photoelectron spectroscopy. Reaction of diethyl zinc with CuInSe2 leads to the formation of an intrinsic ZnSe layer and copper depletion of the interface. This is associated with Zn doping of the chalcopyrite surface and a Fermi level shift towards the conduction band. The implications on the band alignment are discussed
Causality in quantum teleportation: information extraction and noise effects in entanglement distribution
Quantum teleportation is possible because entanglement allows a definition of
precise correlations between the non-commuting properties of a local system and
corresponding non-commuting properties of a remote system. In this paper, the
exact causality achieved by maximal entanglement is analyzed and the results
are applied to the transfer of effects acting on the entanglement distribution
channels to the teleported output state. In particular, it is shown how
measurements performed on the entangled system distributed to the sender
provide information on the teleported state while transferring the
corresponding back-action to the teleported quantum state.Comment: 14 pages, including three figures, discussion of fidelity adde
Quantum Maxwell-Bloch equations for spatially inhomogeneous semiconductor lasers
We present quantum Maxwell-Bloch equations (QMBE) for spatially inhomogeneous
semiconductor laser devices. The QMBE are derived from fully quantum mechanical
operator dynamics describing the interaction of the light field with the
quantum states of the electrons and the holes near the band gap. By taking into
account field-field correlations and field-dipole correlations, the QMBE
include quantum noise effects which cause spontaneous emission and amplified
spontaneous emission. In particular, the source of spontaneous emission is
obtained by factorizing the dipole-dipole correlations into a product of
electron and hole densities. The QMBE are formulated for general devices, for
edge emitting lasers and for vertical cavity surface emitting lasers, providing
a starting point for the detailed analysis of spatial coherence in the near
field and far field patterns of such laser diodes. Analytical expressions are
given for the spectra of gain and spontaneous emission described by the QMBE.
These results are applied to the case of a broad area laser, for which the
frequency and carrier density dependent spontaneous emission factor beta and
the evolution of the far field pattern near threshold are derived.Comment: 22 pages RevTex and 7 figures, submitted to Phys.Rev.A, revisions in
abstract and in the discussion of temporal coherenc
Weak measurement of photon polarization by back-action induced path interference
The essential feature of weak measurements on quantum systems is the
reduction of measurement back-action to negligible levels. To observe the
non-classical features of weak measurements, it is therefore more important to
avoid additional back-action errors than it is to avoid errors in the actual
measurement outcome. In this paper, it is shown how an optical weak measurement
of diagonal (PM) polarization can be realized by path interference between the
horizontal (H) and vertical (V) polarization components of the input beam. The
measurement strength can then be controlled by rotating the H and V
polarizations towards each other. This well-controlled operation effectively
generates the back-action without additional decoherence, while the visibility
of the interference between the two beams only limits the measurement
resolution. As the experimental results confirm, we can obtain extremely high
weak values, even at rather low visibilities. Our method therefore provides a
realization of weak measurements that is extremely robust against experimental
imperfections.Comment: 11 pages, 3 figure
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