697 research outputs found
Enhancement of entanglement transfer in a spin chain by phase shift-control
We study the effect of a phase shift on the amount of transferrable two-spin
entanglement in a spin chain. We consider a ferromagnetic Heisenberg/XY spin
chain, both numerically and analytically, and two mechanisms to generate a
phase shift, the Aharonov-Casher effect and the Dzyaloshinskii-Moriya
interaction. In both cases, the maximum attainable entanglement is shown to be
significantly enhanced, suggesting its potential usefulness in quantum
information processing.Comment: 7 pages, 5 figures. v2: a fig added, the main text modified a bi
Acoustic Radiation Force and Torque on Small Particles as Measures of the Canonical Momentum and Spin Densities
We examine acoustic radiation force and torque on a small (subwavelength)
absorbing isotropic particle immersed in a monochromatic (but generally
inhomogeneous) sound-wave field. We show that by introducing the monopole and
dipole polarizabilities of the particle, the problem can be treated in a way
similar to the well-studied optical forces and torques on dipole Rayleigh
particles. We derive simple analytical expressions for the acoustic force
(including both the gradient and scattering forces) and torque. Importantly,
these expressions reveal intimate relations to the fundamental field properties
introduced recently for acoustic fields: the canonical momentum and spin
angular momentum densities. We compare our analytical results with previous
calculations and exact numerical simulations. We also consider an important
example of a particle in an evanescent acoustic wave, which exhibits the
mutually-orthogonal scattering (radiation-pressure) force, gradient force, and
torque from the transverse spin of the field.Comment: 7 pages, 3 figures, Supplemental Material, to appear in Phys. Rev.
Let
Detectable inertial effects on Brownian transport through narrow pores
We investigate the transport of suspended Brownian particles dc driven along
corrugated narrow channels in a regime of finite damping. We demonstrate that
inertial corrections cannot be neglected as long as the width of the channel
bottlenecks is smaller than an appropriate particle diffusion length, which
depends on both, the temperature and the strength of the dc drive. Therefore,
transport through sufficiently narrow constrictions turns out to be sensitive
to the viscosity of the suspension fluid. Applications to colloidal systems are
discussed
Spin-Hall effect and circular birefringence of a uniaxial crystal plate
The linear birefringence of uniaxial crystal plates is known since the 17th
century, and it is widely used in numerous optical setups and devices. Here we
demonstrate, both theoretically and experimentally, a fine lateral circular
birefringence of such crystal plates. This effect is a novel example of the
spin-Hall effect of light, i.e., a transverse spin-dependent shift of the
paraxial light beam transmitted through the plate. The well-known linear
birefringence and the new circular birefringence form an interesting analogy
with the Goos-H\"anchen and Imbert-Fedorov beam shifts that appear in the light
reflection at a dielectric interface. We report the experimental observation of
the effect in a remarkably simple system of a tilted half-wave plate and
polarizers using polarimetric and quantum-weak-measurement techniques for the
beam-shift measurements. In view of great recent interest in spin-orbit
interaction phenomena, our results could find applications in modern
polarization optics and nano-photonics.Comment: 16 pages, 8 figures, to appear in Optic
Switchable resonant coupling of flux qubits
We propose a coupling scheme, where two or more flux qubits with different
eigenfrequencies share Josephson junctions with a coupler loop devoid of its
own quantum dynamics. Switchable two-qubit coupling is realized by tuning the
frequency of the AC magnetic flux through the coupler to a combination
frequency of two of the qubits. The coupling allows any or all of the qubits to
be simultaneously at the degeneracy point and can change sign.Comment: REVTeX 4, 4 pages, 2 figures, v2: reference added, v3: final version
published in Phys. Rev.
- …