822 research outputs found
Ground state properties of a Tonks-Girardeau Gas in a periodic potential
In this paper, we investigate the ground-state properties of a bosonic
Tonks-Girardeau gas confined in a one-dimensional periodic potential. The
single-particle reduced density matrix is computed numerically for systems up
to bosons. Scaling analysis of the occupation number of the lowest
orbital shows that there are no Bose-Einstein Condensation(BEC) for the
periodically trapped TG gas in both commensurate and incommensurate cases. We
find that, in the commensurate case, the scaling exponents of the occupation
number of the lowest orbital, the amplitude of the lowest orbital and the
zero-momentum peak height with the particle numbers are 0, -0.5 and 1,
respectively, while in the incommensurate case, they are 0.5, -0.5 and 1.5,
respectively. These exponents are related to each other in a universal
relation.Comment: 9 pages, 10 figure
Passive faraday mirror attack in practical two-way quantum key distribution system
The faraday mirror (FM) plays a very important role in maintaining the
stability of two way plug-and-play quantum key distribution (QKD) system.
However, the practical FM is imperfect, which will not only introduce
additional quantum bit error rate (QBER) but also leave a loophole for Eve to
spy the secret key. In this paper, we propose a passive faraday mirror attack
in two way QKD system based on the imperfection of FM. Our analysis shows that,
if the FM is imperfect, the dimension of Hilbert space spanned by the four
states sent by Alice is three instead of two. Thus Eve can distinguish these
states with a set of POVM operators belonging to three dimension space, which
will reduce the QBER induced by her attack. Furthermore, a relationship between
the degree of the imperfection of FM and the transmittance of the practical QKD
system is obtained. The results show that, the probability that Eve loads her
attack successfully depends on the degree of the imperfection of FM rapidly,
but the QBER induced by Eve's attack changes with the degree of the
imperfection of FM slightly
Possible Superconductivity at 37 K in Graphite-Sulfur Composite
Sulfur intercalated graphite composites with diamagnetic transitions at 6.7 K
and 37 K are prepared. The magnetization hysteresis loops (MHL), Xray
diffraction patterns, and resistance were measured. From the MHL, a slight
superconducting like penetration process is observed at 15 K in low field
region. The XRD shows no big difference from the mixture of graphite and sulfur
indicating that the volume of the superconducting phase (if any) is very small.
The temperature dependence of resistance shows a typical semiconducting
behavior with a saturation in low temperature region. This saturation is either
induced by the de-localization of conducting electrons or by possible
superconductivity in this system.Comment: CHIN. PHYS.LETT v18 1648 (2001
A New Kind of Shift Operators for Infinite Circular and Spherical Wells
A new kind of shift operators for infinite circular and spherical wells is identified. These shift operators depend on all spatial variables of quantum systems and connect some eigenstates of confined systems of different radii R sharing energy levels with a common eigenvalue. In circular well, the momentum operators P±=Px±iPy play the role of shift operators. The Px and Py operators, the third projection of the orbital angular momentum operator Lz, and the Hamiltonian H form a complete set of commuting operators with the SO(2) symmetry. In spherical well, the shift operators establish a novel relation between ψlm(r) and ψ(l ± 1)(m±1)(r)
Levinson's Theorem for the Klein-Gordon Equation in Two Dimensions
The two-dimensional Levinson theorem for the Klein-Gordon equation with a
cylindrically symmetric potential is established. It is shown that
, where denotes
the difference between the number of bound states of the particle
and the ones of antiparticle with a fixed angular momentum , and
the is named phase shifts. The constants and
are introduced to symbol the critical cases where the half bound
states occur at .Comment: Revtex file 14 pages, submitted to Phys. Rev.
Strong quantum fluctuation of vortices in the new superconductor
By using transport and magnetic measurement, the upper critical field
and the irreversibility line has been determined. A
big separation between and has been found showing the
existence of a quantum vortex liquid state induced by quantum fluctuation of
vortices in the new superconductor . Further investigation on the
magnetic relaxation shows that both the quantum tunneling and the thermally
activated flux creep weakly depends on temperature. But when the melting field
is approached, a drastic rising of the relaxation rate is observed.
This may imply that the melting of the vortex matter at a finite temperature is
also induced by the quantum fluctuation of vortices.Comment: 4 pages, 4 figure
Production of the neutral top-pion in association with a high- jet at the
In the framework of the topcolor-assisted technicolor model, we study
production of the neutral top-pion in association with a
high- jet at the , which proceeds via the partonic processes
, ,
, , and . We find
that it is very challenging to detect the neutral top-pion via
the process , while the
possible signatures of might be detected via the process
at the .Comment: 13 pages, 4 figures; typos correcte
Universal role of correlation entropy in critical phenomena
In statistical physics, if we successively divide an equilibrium system into
two parts, we will face a situation that, within a certain length , the
physics of a subsystem is no longer the same as the original system. Then the
extensive properties of the thermal entropy ABAB is
violated. This observation motivates us to introduce the concept of correlation
entropy between two points, as measured by mutual information in the
information theory, to study the critical phenomena. A rigorous relation is
established to display some drastic features of the non-vanishing correlation
entropy of the subsystem formed by any two distant particles with long-range
correlation. This relation actually indicates the universal role of the
correlation entropy in understanding critical phenomena. We also verify these
analytical studies in terms of two well-studied models for both the thermal and
quantum phase transitions: two-dimensional Ising model and one-dimensional
transverse field Ising model. Therefore, the correlation entropy provides us
with a new physical intuition in critical phenomena from the point of view of
the information theory.Comment: 10 pages, 9 figure
Smart Machine Vision for Universal Spatial Mode Reconstruction
Structured light beams, in particular those carrying orbital angular momentum
(OAM), have gained a lot of attention due to their potential for enlarging the
transmission capabilities of communication systems. However, the use of
OAM-carrying light in communications faces two major problems, namely
distortions introduced during propagation in disordered media, such as the
atmosphere or optical fibers, and the large divergence that high-order OAM
modes experience. While the use of non-orthogonal modes may offer a way to
circumvent the divergence of high-order OAM fields, artificial intelligence
(AI) algorithms have shown promise for solving the mode-distortion issue.
Unfortunately, current AI-based algorithms make use of large-amount
data-handling protocols that generally lead to large processing time and high
power consumption. Here we show that a low-power, low-cost image sensor can
itself act as an artificial neural network that simultaneously detects and
reconstructs distorted OAM-carrying beams. We demonstrate the capabilities of
our device by reconstructing (with a 95 efficiency) individual Vortex,
Laguerre-Gaussian (LG) and Bessel modes, as well as hybrid (non-orthogonal)
coherent superpositions of such modes. Our work provides a potentially useful
basis for the development of low-power-consumption, light-based communication
devices
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