152 research outputs found
Matter waves in a gravitational field: An index of refraction for massive particles in general relativity
We consider the propagation of massive-particle de Broglie waves in a static,
isotropic metric in general relativity. We demonstrate the existence of an
index of refraction that governs the waves and that has all the properties of a
classical index of refraction. We confirm our interpretation with a WKB
solution of the general-relativistic Klein-Gordon equation. Finally, we make
some observations on the significance of the optical action.Comment: 20 pages, latex, ps and pdf. To appear in Am.J.Phys September, 200
Neural Stellar Population Synthesis Emulator for the DESI PROVABGS
The Probabilistic Value-Added Bright Galaxy Survey (PROVABGS) catalog will
provide the posterior distributions of physical properties of million
DESI Bright Galaxy Survey (BGS) galaxies. Each posterior distribution will be
inferred from joint Bayesian modeling of observed photometry and spectroscopy
using Markov Chain Monte Carlo sampling and the [arXiv:2202.01809] stellar
population synthesis (SPS) model. To make this computationally feasible,
PROVABGS will use a neural emulator for the SPS model to accelerate the
posterior inference. In this work, we present how we construct the emulator
using the [arXiv:1911.11778] approach and verify that it can be used to
accurately infer galaxy properties. We confirm that the emulator is in
excellent agreement with the original SPS model with error and is
faster. In addition, we demonstrate that the posteriors of galaxy
properties derived using the emulator are also in excellent agreement with
those inferred using the original model. The neural emulator presented in this
work is essential in bypassing the computational challenge posed in
constructing the PROVABGS catalog. Furthermore, it demonstrates the advantages
of emulation for scaling sophisticated analyses to millions of galaxies.Comment: 9 pages, 5 figures, submitted to ApJ
Relativistically covariant state-dependent cloning of photons
The influence of the relativistic covariance requirement on the optimality of
the symmetric state-dependent 1 -> 2 cloning machine is studied. Namely, given
a photonic qubit whose basis is formed from the momentum-helicity eigenstates,
the change to the optimal cloning fidelity is calculated taking into account
the Lorentz covariance unitarily represented by Wigner's little group. To
pinpoint some of the interesting results, we found states for which the optimal
fidelity of the cloning process drops to 2/3 which corresponds to the fidelity
of the optimal classical cloner. Also, an implication for the security of the
BB84 protocol is analyzed.Comment: corrected, rewritten and accepted in PR
Analogue Of The Fizeau Effect In An Effective Optical Medium
Using a new approach, we propose an analogue of the Fizeau effect for massive and massless particles in an effective optical medium derived from the static, spherically symmetric gravitational field. The medium is naturally perceived as a dispersive medium by matter de Broglie waves. Several Fresnel drag coefficients are worked out, with appropriate interpretations of the wavelengths used. In two cases, it turns out that the coefficients become independent of the wavelength even if the equivalent medium itself is dispersive. A few conceptual issues are also addressed in the process of derivation. It is shown that some of our results complement recent work dealing with real fluid or optical black holes
Squeezing enhancement by damping in a driven atom-cavity system
In a driven atom-cavity coupled system in which the two-level atom is driven
by a classical field, the cavity mode which should be in a coherent state in
the absence of its reservoir, can be squeezed by coupling to its reservoir. The
squeezing effect is enhanced as the damping rate of the cavity is increased to
some extent.Comment: 3 pages and 3 figure
Spatial Localization and Relativistic Transformation of Quantum Spins
The purity of a reduced state for spins that is pure in the rest frame will
most likely appear to degrade because spin and momentum become mixed when
viewed by a moving observer. We show that such a boost-induced decrease in spin
purity observed in a moving reference frame is intrinsically related to the
spatial localization properties of the wave package observed in the rest frame.
Furthermore, we prove that, for any localized pure state with separable spin
and momentum in the rest frame, its reduced density matrix for spins inevitably
appears to be mixed whenever viewed from a moving reference frame.Comment: 5 pages, 1 figur
Quantum state of a free spin-1/2 particle and the inextricable dependence of spin and momentum under Lorentz transformations
We revise the Dirac equation for a free particle and investigate Lorentz
transformations on spinors. We study how the spin quantization axis changes
under Lorentz transformations, and evince the interplay between spin and
momentum in this context.Comment: 14 pages, 3 figures, published as a Review in the IJQ
The entangling side of the Unruh-Hawking effect
We show that the Unruh effect can create net quantum entanglement between
inertial and accelerated observers depending on the choice of the inertial
state. This striking result banishes the extended belief that the Unruh effect
can only destroy entanglement and furthermore provides a new and unexpected
source for finding experimental evidence of the Unruh and Hawking effects.Comment: 4 pages, 4 figures. Added Journal referenc
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