229,786 research outputs found
Gauge field in ultra-cold bipartite atoms
The effects of entanglement and spin-spin collision on the gauge field in
ultracold atoms are presented in this paper. Two gauge fields are calculated
and discussed. One of the fields comes from space dependent spin-spin
collisions in ultra-cold atoms, while another results from the usual
Born-Oppenheimer method, which separates the center-of-mass motion from the
relative motion in the two-body problem. Adiabatic conditions that lead to the
key results of this paper are also presented and discussed. Entanglement shared
between the two atoms is shown to affect the atomic motion. In the presence of
entanglement, the additional scalar potential disappears, this is different
from the case of atoms in separable states.Comment: 4 pages, 1 figur
Thermal spin current and spin accumulation at ferromagnetic insulator/nonmagnetic metal interface
Spin current injection and spin accumulation near a ferromagnetic insulator
(FI)/nonmagnetic metal (NM) bilayer film under a thermal gradient is
investigated theoretically. Using the Fermi golden rule and the Boltzmann
equations, we find that FI and NM can exchange spins via interfacial
electron-magnon scattering because of the imbalance between magnon emission and
absorption caused by either non-equilibrium distribution of magnons or
non-equilibrium between magnons and electrons. A temperature gradient in FI
and/or a temperature difference across the FI/NM interface generates a spin
current which carries angular momenta parallel to the magnetization of FI from
the hotter side to the colder one. Interestingly, the spin current induced by a
temperature gradient in NM is negligibly small due to the nonmagnetic nature of
the non-equilibrium electron distributions. The results agree well with all
existing experiments.Comment: 8 pages, 2 figure
Effect of near-earth thunderstorms electric field on the intensity of ground cosmic ray positrons/electrons in Tibet
Monte Carlo simulations are performed to study the correlation between the
ground cosmic ray intensity and near-earth thunderstorms electric field at YBJ
(4300 m a.s.l., Tibet, China). The variations of the secondary cosmic ray
intensity are found to be highly dependent on the strength and polarity of the
electric field. In negative fields and in positive fields greater than 600
V/cm, the total number of ground comic ray positrons and electrons increases
with increasing electric field strength. And these values increase more
obviously when involving a shower with lower primary energy or a higher zenith
angle. While in positive fields ranging from 0 to 600 V/cm, the total number of
ground comic ray positrons and electrons declines and the amplitude is up to
3.1% for vertical showers. A decrease of intensity occurs for inclined showers
in positive fields less than 500 V/cm, which is accompanied by smaller
amplitudes. In this paper, the intensity changes are discussed, especially
concerning the decreases in positive electric fields. Our simulation results
are in good agreement with ground-based experimental results obtained from
ARGO-YBJ and the Carpet air shower array. These results could be helpful in
understanding the acceleration mechanisms of secondary charged particles caused
by an atmospheric electric field.Comment: 17pages,15figure
Dissipative preparation of tripartite singlet state in coupled arrays of cavities via quantum feedback control
We propose an experimentally feasible scheme for dissipative preparation of
tripartite entangled state with atoms separately trapped in an array of three
coupled cavities. The combination of coherent driving fields and
quantum-jump-based feedback control will drive the system into a
non-equilibrium steady state, which has a nearly perfect overlap with the
genuine three-atom singlet state. Different control strategies are investigated
and the corresponding optimal parameters are confirmed. Moreover, the fidelity
of target state is insensitive to detection inefficiencies, and it oversteps
90\% for a wide range of decoherence parameters as long as the single-atom
cooperativity parameter .Comment: 7 pages, 5 figures, comments are welcom
Breaking the current density threshold in spin-orbit-torque magnetic random access memory
Spin-orbit-torque magnetic random access memory (SOT-MRAM) is a promising
technology for the next generation of data storage devices. The main bottleneck
of this technology is the high reversal current density threshold. This
outstanding problem of SOT-MRAM is now solved by using a current density of
constant magnitude and varying flow direction that reduces the reversal current
density threshold by a factor of more than the Gilbert damping coefficient. The
Euler-Lagrange equation for the fastest magnetization reversal path and the
optimal current pulse are derived for an arbitrary magnetic cell. The
theoretical limit of minimal reversal current density and current density for a
GHz switching rate of the new reversal strategy for CoFeB/Ta SOT-MRAMs are
respectively of the order of A/cm and A/cm far below
A/cm and A/cm in the conventional strategy. Furthermore,
no external magnetic field is needed for a deterministic reversal in the new
strategy
Canonical Form and Separability of PPT States in 2xMxN Composite Quantum Systems
We investigate the canonical forms of positive partial transposition (PPT)
density matrices in
composite quantum systems with rank . A general expression for these PPT
states are explicitly obtained. From this canonical form a sufficient
separability condition is presented.Comment: 11 pages, Late
The half-quantum group U^>=0
Let U^>=0 denote the half quantum group for a fixed simple Lie algebra. We
examine some properties and representation of U^>=0. We prove that the Hopf
algebra U^>=0 is not quasi-cocommutative, and hence the category of left
U^>=0-module is not a braided monoidal category. In the weight module category
W, we describe all the simple objects and the projective objects. We also
describe all simple Yetter-Drinfel'd U^>=0-weight modules.Comment: 16page
Representation theory of a Class of Hopf algebras
The representations of the pointed Hopf algebras and \su are described,
where and \su can be regarded as deformations of the usual quantized
enveloping algebras and the small quantum groups
respectively. It is illustrated that these representations have a close
connection with those of the quantized enveloping algebras
and those of the half quantum groups of
.Comment: 20page
Magnetic and transport properties in GdSrCoO (= 0.10-0.70)
Magnetic and transport properties of polycrystalline
GdSrCoO (= 0.10-0.70) are investigated systemically.
Cluster-glass magnetism for 0.45 and long-range ferromagnetic order in
higher doping level are observed. Transport measurements indicate
insulator-like behaviors for the samples with 0.30, and an
insulator-metal (IM) transition around = 0.35, and metallic behaviors for
higher samples. In contrast to LaSrCOO, the striking
feature is that the system reenters insulator-like state for 0.60, and
the long-range ferromagnetic order and IM transition take place in samples with
higher Sr content. It could be attributed to the enhancement of low-spin state
stability for the trivalent Co ions due to the small radius of Gd ion.Comment: 8 pages, 9 figure
Current-Driven Domain Wall Depinning and Propagation in Notched Nanowires
Adiabatic spin transfer torque induced domain wall (DW) depinning from a
notch and DW propagation in a nanowire with a series of notches is
investigated. Surprisingly, notches help a current to depin a DW and make a DW
easier to propagate along a wire. Following fascinating results on DW dynamics
are found. 1) The depinning current density of a DW in a notch is substantially
lower than the intrinsic threshold value below which a sustainable DW
propagation doesn't exist in a homogeneous wire. 2) The DW displacement from a
notch is insensitive to notch geometry and current density when it is between
the depinning and the intrinsic threshold current density. 3) A current density
below the intrinsic threshold value can induce a sustainable DW propagation
along notched nanowires. These findings not only reveal interesting and
complicated interaction between a current and a DW, but also have profound
implications in our current understanding of current-driven DW dynamics as well
as in the design of spintronic devices.Comment: 5 pages, 5 figure
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