22,020 research outputs found
Influence of inelastic relaxation time on intrinsic spin Hall effects in a disordered two-dimensional electron gas
The influence of inelastic relaxation time on the intrinsic spin Hall effects
in a disordered two-dimensional electron gas with Rashba interaction is
studied, which clarifies the controversy of impurity effects in the system. We
reveal that, due to the existence of inelastic scattering, the spin Hall
conductivity does not vanish when the impurity concentration diminishes to zero
no matter it is non-magnetically or magnetically disordered. The spin
accumulation is evaluated by using the obtained spin Hall conductivity, and an
alternate route is suggested to verify the intrinsic spin Hall effect by
measuring the spin accumulation at different ratios.Comment: Revtex 6 pages, 1 figure, extended with more detail
Towards practical high-speed high dimensional quantum key distribution using partial mutual unbiased basis of photon's orbital angular momentum
Quantum Key Distribution (QKD) guarantees the security of communication with
quantum physics. Most of widely adopted QKD protocols currently encode the key
information with binary signal format---qubit, such as the polarization states.
Therefore the transmitted information efficiency of the quantum key is
intrinsically upper bounded by 1 bit per photon. High dimensional quantum
system is a potential candidate for increasing the capacity of single photon.
However, due to the difficulty in manipulating and measuring high dimensional
quantum systems, the experimental high dimensional QKD is still at its infancy.
Here we propose a sort of practical high-speed high dimensional QKD using
partial mutual unbiased basis (PMUB) of photon's orbital angular momentum
(OAM). Different from the previous OAM encoding, the high dimensional Hilbert
space we used is expanded by the OAM states with same mode order, which can be
extended to considerably high dimensions and implemented under current state of
the art. Because all the OAM states are in the same mode order, the coherence
will be well kept after long-distance propagation, and the detection can be
achieved by using passive linear optical elements with very high speed. We show
that our protocol has high key generation rate and analyze the anti-noise
ability under atmospheric turbulence. Furthermore, the security of our protocol
based on PMUB is rigorously proved. Our protocol paves a brand new way for the
application of photon's OAM in high dimensional QKD field, which can be a
breakthrough for high efficiency quantum communications.Comment: Comments are welcom
Momentum distribution functions in ensembles: the inequivalence of microcannonical and canonical ensembles in a finite ultracold system
It is demonstrated that in many thermodynamic textbooks the equivalence of
the different ensembles is achieved in the thermodynamic limit. In this present
work we remark the inequivalence of microcannonical and canonical ensembles in
a finite ultracold system at low energies. We calculate the microcanonical
momentum distribution function (MDF) in a system of identical fermions
(bosons). We find that, the microcanonical MDF deviates from the canonical one,
which is the Fermi-Dirac (Bose-Einstein) function, in a finite system at low
energies where the single-particle density of states and its inverse are
finite.Comment: 6 pages, 3 figure
Identifying the closeness of eigenstates in quantum many-body systems
We propose a new quantity called modulus fidelity to measure the closeness of
two quantum pure states. Especially, we use it to investigate the closeness of
eigenstates of quantum many-body systems. When the system is integrable, the
modulus fidelity of neighbor eigenstates displays a large fluctuation. But the
modulus fidelity is close to a constant when system becomes non-integrable with
fluctuation reduced drastically. Average modulus fidelity of neighbor
eigenstates increases with the increase of parameters that destroy the
integrability, which also indicates the integrable-chaos transition. In
non-integrable case, it is found two eigenstates are closer to each other if
their level spacing is small. We also show that the closeness of eigenstates in
non-integrable domain is the underlying mechanism of \emph{eigenstate
thermalization hypothesis} (ETH) which explains the thermalization in
nonintegrable system we studied.Comment: 7 pages, 4 figure
Nonvanishing spin Hall currents in the presence of magnetic impurities
The intrinsic spin Hall conductivity in a two dimensional electron gas with
Rashba spin-orbit coupling is evaluated by taking account of anisotropic
coupling between magnetic impurities and itinerant electrons. In our
calculation Kubo's linear response formalism is employed and the vertex
correction is considered. In the semiclassical limit , a
non-vanishing spin Hall conductivity is found to depend on the
momentum relaxation time , spin-orbit splitting and the
anisotropic coefficient of interaction between itinerant electrons and magnetic
impurities. The clean limit of is in the region of , depending on the anisotropic coefficient.Comment: Revtex, 6 pages, 4 figures, version to appear in PR
Synchronous phase clustering in a network of neurons with spatially decaying excitatory coupling
Synchronization is studied in a spatially-distributed network of
weekly-coupled, excitatory neurons of Hodgkin-Huxley type. All neurons are
coupled to each other synaptically with a fixed time delay and a coupling
strength inversely proportional to the distance between two neurons. We found
that a robust, noise-resistant phase clustering state occurred regardless of
the initial phase distribution. This has not been shown in previous studies
where similar clustering states were found only when the coupling was
inhibitory. The spatial distribution of neurons in each synchronous cluster is
determined by the spatial distribution of the coupling strength.
Phase-interaction properties of the model neurons in the network are used to
explain why can such a clustering state be robust
Correlations of spin-polarized and entangled electrons with Berry phase
The correlation and fluctuation of both entangled electrons and
spin-polarized pairs affected by two rotating magnetic fields in a setup
proposed by J. Carlos Egues etc. (Phys. Rev. Lett. {\bf 89}(2002) 176401) are
studied theoretically by using scattering approach. Differing from polarized
pair, the entangled electron pairs are shown to behave like a composite
particle with the total spins and its components. The singlet and triplet
states exhibit different bunching and antibunching features, which can be
easily adjusted by the magnetic fields. The correlations and variances can show
up distinguish output signals for the four incident states. Our results are
expected to be tested by using coincident technique.Comment: 11 pages, 12 figures, 3 table
Three-body force effect on nucleon momentum distributions in asymmetric nuclear matter within the framework of the extended BHF approach
We have investigated the three-body force (TBF) effect on the neutron and
proton momentum distributions in asymmetric nuclear matter within the framework
of the extended Brueckner-Hartree-Fock approach by adopting the two-body
interaction plus a microscopic TBF. In asymmetric nuclear matter, it is shown
that the neutron and proton momentum distributions become different from their
common distribution in symmetric nuclear matter. The predicted depletion of the
proton hole states increases while the neutron one decreases as a function of
isospin-asymmetry. The TBF effect on the neutron and proton momentum
distributions turns out to be negligibly weak at low densities around and below
the normal nuclear density. The TBF effect is found to become sizable only at
high densities well above the saturation density, and inclusion of the TBF
leads to an overall enhancement of the depletion of the neutron and proton
Fermi seas.Comment: 9 pages, 4 figure
Numerically Fitting The Electron Fermi Energy and The Electron Fraction in A Neutron Star
Based on the basic definition of Fermi energy of degenerate and relativistic
electrons, we obtain a special solution to electron Fermi energy, , and express as a function of electron fraction, ,
and matter density, . Several useful analytical formulae for and
within classical models and the work of Dutra et al. 2014 (Type-2) in
relativistic mean field theory are obtained using numerically fitting. When
describing the mean-field Lagrangian, density, we adopt the TMA parameter set,
which is remarkably consistent with with the updated astrophysical observations
of neutron stars. Due to the importance of the density dependence of the
symmetry energy, , in nuclear astrophysics, a brief discussion on the
symmetry parameters and (the slope of ) is presented. Combining
these fit formulae with boundary conditions for different density regions, we
can evaluate the value of in any given matter density, and
obtain a schematic diagram of as a continuous function of
. Compared with previous study on the electron Fermi energy in other
models, our methods of calculating are more simple and
convenient, and can be universally suitable for the relativistic electron
regions in the circumstances of common neutron stars. We have deduced a general
expression of and , which could be used to indirectly
test whether one EoS of a NS is correct in our future studies on neutron star
matter properties. Since URCA reactions are expected in the center of a massive
star due to high-value electron Fermi energy and electron fraction, this study
could be useful in the future studies on the NS thermal evolution.Comment: 30 pages, 14 figure
Robust Room-Temperature Quantum Spin Hall Effect in Methyl-functionalized InBi honeycomb film
Two-dimensional (2D) group-III-V honeycomb films have attracted significant
interest for their potential application in fields of quantum computing and
nanoeletronics. Searching for 2D III-V films with high structural stability and
large-gap are crucial for the realizations of dissipationless transport edge
states using quantum spin Hall (QSH) effect. Based on first-principles
calculations, we predict that the methyl-functionalized InBi monolayer
(InBiCH3) has no dynamic instability, and host a QSH state with a band gap as
large as 0.29 eV, exhibiting an interesting electronic behavior viable for
room-temperature applications. The topological characteristic is confirmed by
s-pxy bands inversion, topological invariant Z2 number, and the time-reversal
symmetry protected helical edge states. Noticeably, the QSH states are tunable
and robust against the mechanical strain, electric field and different levels
of methyl coverages. We also find that InBiCH3 supported on h-BN substrate
maintains a nontrivial QSH state, which harbors the edge states lying within
the band gap of substrate. These findings demonstrate that the
methyl-functionalized III-V films may be a good QSH platform for device design
and fabrication in spintronics.Comment: 24 pages, 6 figure
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