1,978 research outputs found
Probing the structure of entanglement with entanglement moments
We introduce and define a set of functions on pure bipartite states called
entanglement moments. Usual entanglement measures tell you if two systems are
entangled, while entanglement moments tell you both if and how two systems are
entangled. They are defined with respect to a measurement basis in one system
(e.g., a measuring device), and output numbers describing how a system (e.g., a
qubit) is entangled with that measurement basis. The moments utilize different
distance measures on the Hilbert space of the measured system, and can be
generalized to any N-dimensional Hilbert space. As an application, they can
distinguish between projective and non-projective measurements. As a particular
example, we take the Rabi model's eigenstates and calculate the entanglement
moments as well as the full distribution of entanglement.Comment: 5 pages, 5 figure
Non-analytic behavior of the Casimir force across a Lifshitz transition in a spin-orbit coupled material
We propose the Casimir effect as a general method to observe Lifshitz
transitions in electron systems. The concept is demonstrated with a planar
spin-orbit coupled semiconductor in a magnetic field. We calculate the Casimir
force between two such semiconductors and between the semiconductor and a metal
as a function of the Zeeman splitting in the semiconductor. The Zeeman field
causes a Fermi pocket in the semiconductor to form or collapse by tuning the
system through a topological Lifshitz transition. We find that the Casimir
force experiences a kink at the transition point and noticeably different
behaviors on either side of the transition. The simplest experimental
realization of the proposed effect would involve a metal-coated sphere
suspended from a micro-cantilever above a thin layer of InSb (or another
semiconductor with large -factor). Numerical estimates are provided and
indicate that the effect is well within experimental reach.Comment: 5 pages + 6 page supplement; 5 figure
Tidal and nonequilibrium Casimir effects in free fall
In this work, we consider a Casimir apparatus that is put into free fall (e.g., falling into a black hole). Working in 1 + 1D, we find that two main effects occur: First, the Casimir energy density experiences a tidal effect where negative energy is pushed toward the plates and the resulting force experienced by the plates is increased. Second, the process of falling is inherently nonequilibrium and we treat it as such, demonstrating that the Casimir energy density moves back and forth between the plates after being “dropped,” with the force modulating in synchrony. In this way, the Casimir energy behaves as a classical liquid might, putting (negative) pressure on the walls as it moves about in its container. In particular, we consider this in the context of a black hole and the multiple vacua that can be achieved outside of the apparatus
Quantum interference phenomena in the Casimir effect
We propose a definitive test of whether plates involved in Casimir
experiments should be modeled with ballistic or diffusive electrons--a
prominent controversy highlighted by a number of conflicting experiments. The
unambiguous test we propose is a measurement of the Casimir force between a
disordered quasi-2D metallic plate and a three-dimensional metallic system at
low temperatures, in which disorder-induced weak localization effects modify
the well-known Drude result in an experimentally tunable way. We calculate the
weak localization correction to the Casimir force as a function of magnetic
field and temperature and demonstrate that the quantum interference suppression
of the Casimir force is a strong, observable effect. The coexistence of weak
localization suppression in electronic transport and Casimir pressure would
lend credence to the Drude theory of the Casimir effect, while the lack of such
correlation would indicate a fundamental problem with the existing theory. We
also study mesoscopic disorder fluctuations in the Casimir effect and estimate
the width of the distribution of Casmir energies due to disorder fluctuations.Comment: 9 pages, 9 figure
Remnant Geometric Hall Response in a Quantum Quench
Out-of-equilibrium systems can host phenomena that transcend the usual restrictions of equilibrium systems. Here, we unveil how out-of-equilibrium states, prepared via a quantum quench in a two-band system, can exhibit a nonzero Hall-type current - a remnant Hall response - even when the instantaneous Hamiltonian is time reversal symmetric (in contrast to equilibrium Hall currents). Interestingly, the remnant Hall response arises from the coherent dynamics of the wave function that retain a remnant of its quantum geometry postquench, and can be traced to processes beyond linear response. Quenches in two-band Dirac systems are natural venues for realizing remnant Hall currents, which exist when either mirror or time-reversal symmetry are broken (before or after the quench). Its long time persistence, sensitivity to symmetry breaking, and decoherence-type relaxation processes allow it to be used as a sensitive diagnostic of the complex out-of-equilibrium dynamics readily controlled and probed in cold-atomic optical lattice experiments
Rare regions and avoided quantum criticality in disordered Weyl semimetals and superconductors
Disorder in Weyl semimetals and superconductors is surprisingly subtle, attracting attention and competing theories in recent years. In this brief review, we discuss the current theoretical understanding of the effects of short-ranged, quenched disorder on the low energy-properties of three-dimensional, topological Weyl semimetals and superconductors. We focus on the role of non-perturbative rare region effects on destabilizing the semimetal phase and rounding the expected semimetal-to-diffusive metal transition into a cross over. Furthermore, the consequences of disorder on the resulting nature of excitations, transport, and topology are reviewed. New results on a bipartite random hopping model are presented that confirm previous results in a p+ip Weyl superconductor, demonstrating that particle–hole symmetry is insufficient to help stabilize the Weyl semimetal phase in the presence of disorder. The nature of the avoided transition in a model for a single Weyl cone in the continuum is discussed. We close with a discussion of open questions and future directions
Breakdown of the coherent state path integral: Two simple examples
We show how the time-continuous coherent state path integral breaks down for both the single-site Bose-Hubbard model and the spin-path integral. Specifically, when the Hamiltonian is quadratic in a generator of the algebra used to construct coherent states, the path integral fails to produce correct results following from an operator approach. As suggested by previous authors, we note that the problems do not arise in the time-discretized version of the path integral. © 2011 American Physical Society
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