4,064 research outputs found
Cosmological Vorticity in a Gravity with Quadratic Order Curvature Couplings
We analyse the evolution of the rotational type cosmological perturbation in
a gravity with general quadratic order gravitational coupling terms. The result
is expressed independently of the generalized nature of the gravity theory, and
is simply interpreted as a conservation of the angular momentum.Comment: 5 pages, revtex, no figure
Counterfactual Quantum Cryptography
Quantum cryptography allows one to distribute a secret key between two remote
parties using the fundamental principles of quantum mechanics. The well-known
established paradigm for the quantum key distribution relies on the actual
transmission of signal particle through a quantum channel. This paper shows
that the task of a secret key distribution can be accomplished even though a
particle carrying secret information is not in fact transmitted through the
quantum channel. The proposed protocols can be implemented with current
technologies and provide practical security advantages by eliminating the
possibility that an eavesdropper can directly access the entire quantum system
of each signal particle.Comment: 19 pages, 1 figure; a little ambiguity in the version 1 removed;
abstract, text, references, and appendix revised; suggestions and comments
are highly appreciate
Coulomb Drag near the metal-insulator transition in two-dimensions
We studied the drag resistivity between dilute two-dimensional hole systems,
near the apparent metal-insulator transition. We find the deviations from the
dependence of the drag to be independent of layer spacing and
correlated with the metalliclike behavior in the single layer resistivity,
suggesting they both arise from the same origin. In addition, layer spacing
dependence measurements suggest that while the screening properties of the
system remain relatively independent of temperature, they weaken significantly
as the carrier density is reduced. Finally, we demonstrate that the drag itself
significantly enhances the metallic dependence in the single layer
resistivity.Comment: 6 pages, 5 figures; revisions to text, to appear in Phys. Rev.
Direct sampling of the Susskind-Glogower phase distributions
Coarse-grained phase distributions are introduced that approximate to the
Susskind--Glogower cosine and sine phase distributions. The integral relations
between the phase distributions and the phase-parametrized field-strength
distributions observable in balanced homodyning are derived and the integral
kernels are analyzed. It is shown that the phase distributions can be directly
sampled from the field-strength distributions which offers the possibility of
measuring the Susskind--Glogower cosine and sine phase distributions with
sufficiently well accuracy. Numerical simulations are performed to demonstrate
the applicability of the method.Comment: 10 figures using a4.st
Analytic study of the three-urn model for separation of sand
We present an analytic study of the three-urn model for separation of sand.
We solve analytically the master equation and the first-passage problem. We
find that the stationary probability distribution obeys the detailed balance
and is governed by the {\it free energy}. We find that the characteristic
lifetime of a cluster diverges algebraically with exponent 1/3 at the limit of
stability.Comment: 5pages, 4 figures include
Frictional Drag between Two Dilute Two-Dimensional Hole Layers
We report drag measurements on dilute double layer two-dimensional hole
systems in the regime of r_s=19~39. We observed a strong enhancement of the
drag over the simple Boltzmann calculations of Coulomb interaction, and
deviations from the T^2 dependence which cannot be explained by
phonon-mediated, plasmon-enhanced, or disorder-related processes. We suggest
that this deviation results from interaction effects in the dilute regime.Comment: 4 pages, 3 figures, accepted in Phys. Rev. Lett. Added single layer
transport dat
Third-order cosmological perturbations of zero-pressure multi-component fluids: Pure general relativistic nonlinear effects
Present expansion stage of the universe is believed to be mainly governed by
the cosmological constant, collisionless dark matter and baryonic matter. The
latter two components are often modeled as zero-pressure fluids. In our
previous work we have shown that to the second-order cosmological
perturbations, the relativistic equations of the zero-pressure, irrotational,
multi-component fluids in a spatially near flat background effectively coincide
with the Newtonian equations. As the Newtonian equations only have quadratic
order nonlinearity, it is practically interesting to derive the potential
third-order perturbation terms in general relativistic treatment which
correspond to pure general relativistic corrections. Here, we present pure
general relativistic correction terms appearing in the third-order
perturbations of the multi-component zero-pressure fluids. We show that, as in
a single component situation, the third-order correction terms are quite small
(~ 5 x10^{-5} smaller compared with the relativistic/Newtonian second-order
terms) due to the weak level anisotropy of the cosmic microwave background
radiation. Still, there do exist pure general relativistic correction terms in
third-order perturbations which could potentially become important in future
development of precision cosmology. We include the cosmological constant in all
our analyses.Comment: 20 pages, no figur
Anomalous Rashba spin splitting in two-dimensional hole systems
It has long been assumed that the inversion asymmetry-induced Rashba spin
splitting in two-dimensional (2D) systems at zero magnetic field is
proportional to the electric field that characterizes the inversion asymmetry
of the confining potential. Here we demonstrate, both theoretically and
experimentally, that 2D heavy hole systems in accumulation layer-like single
heterostructures show the opposite behavior, i.e., a decreasing, but nonzero
electric field results in an increasing Rashba coefficient.Comment: 4 pages, 3 figure
Modulation transfer spectroscopy of the D1 transition of potassium: theory and experiment
We report on a study of modulation transfer spectroscopy of the 4S1/2 → 4P1/2 (D1) transition of naturally abundant potassium in a room-temperature vapour cell. This transition is critical for laser cooling and optical pumping of potassium and our study is therefore motivated by the need for robust laser frequency stabilisation. Despite the absence of a closed transition, the small ground-state hyperfine splitting in potassium results in strong crossover features in the D1 modulation transfer spectrum. To emphasise this we compare the D1 and D2 spectra of potassium with those of rubidium. Further, we compare our experimental results with a detailed theoretical simulation, examining different pump–probe polarisation configurations to identify the optimal signals for laser frequency stabilisation. We find good agreement between the experiment and the theory, especially for the lin ∥ lin polarisation configuration
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