20,494 research outputs found
Equivalence between two-mode spin squeezed states and pure entangled states with equal spin
We prove that a pure entangled state of two subsystems with equal spin is
equivalent to a two-mode spin-squeezed state under local operations except for
a set of bipartite states with measure zero, and we provide a counterexample to
the generalization of this result to two subsystems of unequal spin.Comment: 6 pages, no figure
STUDIES ON ABLATION OF OBJECTS TRAVERSING AN ATMOSPHERE
Ablation-type thermal protection of objects traversing an atmosphere - earth and mar
Statistical Properties of Many Particle Eigenfunctions
Wavefunction correlations and density matrices for few or many particles are
derived from the properties of semiclassical energy Green functions. Universal
features of fixed energy (microcanonical) random wavefunction correlation
functions appear which reflect the emergence of the canonical ensemble as the
number of particles approaches infinity. This arises through a little known
asymptotic limit of Bessel functions. Constraints due to symmetries,
boundaries, and collisions between particles can be included.Comment: 13 pages, 4 figure
Quantum enhanced spectroscopy with entangled multi-photon states
Traditionally, spectroscopy is performed by examining the position of
absorption lines. However, at frequencies near the transition frequency,
additional information can be obtained from the phase shift. In this work we
consider the information about the transition frequency obtained from both the
absorption and the phase shift, as quantified by the Fisher information in an
interferometric measurement. We examine the use of multiple single-photon
states, NOON states, and numerically optimized states that are entangled and
have multiple photons. We find the optimized states that improve over the
standard quantum limit set by independent single photons for some atom number
densities.Comment: 6 pages, 8 figures, comments are welcom
Quantum dots in graphene
We suggest a way of confining quasiparticles by an external potential in a
small region of a graphene strip. Transversal electron motion plays a crucial
role in this confinement. Properties of thus obtained graphene quantum dots are
investigated theoretically for different types of the boundary conditions at
the edges of the strip. The (quasi)bound states exist in all systems
considered. At the same time, the dependence of the conductance on the gate
voltage carries an information about the shape of the edges.Comment: 4 pages, 3 figure
Superconductor-proximity effect in chaotic and integrable billiards
We explore the effects of the proximity to a superconductor on the level
density of a billiard for the two extreme cases that the classical motion in
the billiard is chaotic or integrable. In zero magnetic field and for a uniform
phase in the superconductor, a chaotic billiard has an excitation gap equal to
the Thouless energy. In contrast, an integrable (rectangular or circular)
billiard has a reduced density of states near the Fermi level, but no gap. We
present numerical calculations for both cases in support of our analytical
results. For the chaotic case, we calculate how the gap closes as a function of
magnetic field or phase difference.Comment: 4 pages, RevTeX, 2 Encapsulated Postscript figures. To be published
by Physica Scripta in the proceedings of the "17th Nordic Semiconductor
Meeting", held in Trondheim, June 199
Classical to Quantum Transition of a Driven Nonlinear Nanomechanical Resonator
We seek the first indications that a nanoelectromechanical system (NEMS) is
entering the quantum domain as its mass and temperature are decreased. We find
them by studying the transition from classical to quantum behavior of a driven
nonlinear Duffing resonator. Numerical solutions of the equations of motion,
operating in the bistable regime of the resonator, demonstrate that the quantum
Wigner function gradually deviates from the corresponding classical phase-space
probability density. These clear differences that develop due to nonlinearity
can serve as experimental evidence, in the near future, that NEMS resonators
are entering the quantum domain
Adaptive homodyne measurement of optical phase
We present an experimental demonstration of the power of real-time feedback
in quantum metrology, confirming a theoretical prediction by Wiseman regarding
the superior performance of an adaptive homodyne technique for single-shot
measurement of optical phase. For phase measurements performed on weak coherent
states with no prior knowledge of the signal phase, we show that the variance
of adaptive homodyne estimation approaches closer to the fundamental quantum
uncertainty limit than any previously demonstrated technique. Our results
underscore the importance of real-time feedback for reaching quantum
performance limits in coherent telecommunication, precision measurement and
information processing.Comment: RevTex4, color PDF figures (separate files), submitted to PR
Chirality in Quantum Computation with Spin Cluster Qubits
We study corrections to the Heisenberg interaction between several lateral,
single-electron quantum dots. We show, using exact diagonalization, that
three-body chiral terms couple triangular configurations to external sources of
flux rather strongly. The chiral corrections impact single qubit encodings
utilizing loops of three or more Heisenberg coupled quantum dots.Comment: 5 pages, 2 figure
Temperature profiles in high gradient furnaces
Accurate temperature measurement of the furnace environment is very important in both the science and technology of crystal growth as well as many other materials processing operations. A high degree of both accuracy and precision is acutely needed in the directional solidification of compound semiconductors in which the temperature profiles control the freezing isotherm which, in turn, affects the composition of the growth with a concomitant feedback perturbation on the temperature profile. Directional solidification requires a furnace configuration that will transport heat through the sample being grown. A common growth procedure is the Bridgman Stockbarger technique which basically consists of a hot zone and a cold zone separated by an insulator. In a normal growth procedure the material, contained in an ampoule, is melted in the hot zone and is then moved relative to the furnace toward the cold zone and solidification occurs in the insulated region. Since the primary path of heat between the hot and cold zones is through the sample, both axial and radial temperature gradients exist in the region of the growth interface. There is a need to know the temperature profile of the growth furnace with the crystal that is to be grown as the thermal load. However it is usually not feasible to insert thermocouples inside an ampoule and thermocouples attached to the outside wall of the ampoule have both a thermal and a mechanical contact problem as well as a view angle problem. The objective is to present a technique of calibrating a furnace with a thermal load that closely matches the sample to be grown and to describe procedures that circumvent both the thermal and mechanical contact problems
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