6,718 research outputs found
Thermodynamics of rotating Bose gases in a trap
Novel ground state properties of rotating Bose gases have been intensively
studied in the context of neutral cold atoms. We investigate the rotating Bose
gas in a trap from a thermodynamic perspective, taking the charged ideal Bose
gas in magnetic field (which is equivalent to a neutral gas in a synthetic
magnetic field) as an example. It is indicated that the Bose-Einstein
condensation temperature is irrelevant to the magnetic field, conflicting with
established intuition that the critical temperature decreases with the field
increasing. The specific heat and Landau diamagnetization also exhibit
intriguing behaviors. In contrast, we demonstrate that the condensation
temperature for neutral Bose gases in a rotating frame drops to zero in the
fast rotation limit, signaling a non-condensed quantum phase in the ground
state.Comment: 4 pages, 1 figur
Deterministic Quantum Key Distribution Using Gaussian-Modulated Squeezed States
A continuous variable ping-pong scheme, which is utilized to generate
deterministically private key, is proposed. The proposed scheme is implemented
physically by using Gaussian-modulated squeezed states. The deterministic way,
i.e., no basis reconciliation between two parties, leads a two-times efficiency
comparing to the standard quantum key distribution schemes. Especially, the
separate control mode does not need in the proposed scheme so that it is
simpler and more available than previous ping-pong schemes. The attacker may be
detected easily through the fidelity of the transmitted signal, and may not be
successful in the beam splitter attack strategy.Comment: 7 pages, 4figure
Ultrafast optical spin echo for electron spins in semiconductors
Spin-based quantum computing and magnetic resonance techniques rely on the
ability to measure the coherence time, T2, of a spin system. We report on the
experimental implementation of all-optical spin echo to determine the T2 time
of a semiconductor electron-spin system. We use three ultrafast optical pulses
to rotate spins an arbitrary angle and measure an echo signal as the time
between pulses is lengthened. Unlike previous spin-echo techniques using
microwaves, ultrafast optical pulses allow clean T2 measurements of systems
with dephasing times T2* fast in comparison to the timescale for microwave
control. This demonstration provides a step toward ultrafast optical dynamic
decoupling of spin-based qubits.Comment: 4 pages, 3 figure
Experimental tests on the lifetime Asymmetry
The experimental test problem of the left-right polarization-dependent
lifetime asymmetry is discussed. It shows that the existing experiments cannot
demonstrate the lifetime asymmetry to be right or wrong after analyzing the
measurements on the neutron, the muon and the tau lifetime, as well as the
experiment. However, It is pointed out emphatically that the SLD and the
E158 experiments, the measurements of the left-right integrated cross section
asymmetry in boson production by collisions and by
electron-electron M{\o}ller scattering, can indirectly demonstrate the lifetime
asymmetry. In order to directly demonstrate the lifetime asymmetry, we propose
some possible experiments on the decays of polarized muons. The precise
measurement of the lifetime asymmetry could have important significance for
building a muon collider, also in cosmology and astrophysics. It would provide
a sensitive test of the standard model in particle physics and allow for
exploration of the possible interactions.Comment: 11 pages, 1 figur
A Modified Synchrotron Model for Knots in the M87 Jet
For explaining the broadband spectral shape of knots in the M87 jet from
radio through optical to X-ray, we propose a modified synchrotron model that
considers the integrated effect of particle injection from different
acceleration sources in the thin acceleration region. This results in two break
frequencies at two sides of which the spectral index of knots in the M87 jet
changes. We discuss the possible implications of these results for the physical
properties in the M87 jet. The observed flux of the knots in the M87 jet from
radio to X-ray can be satisfactorily explained by the model, and the predicted
spectra from ultraviolet to X-ray could be further tested by future
observations. The model implies that the knots D, E, F, A, B, and C1 are
unlikely to be the candidate for the TeV emission recently detected in M87.Comment: 12 pages, 1 figure, 2 tables, Accepted for publication in ApJ Letter
Experimental Decoy Quantum Key Distribution Up To 130KM Fiber
Decoy State Quantum Key Distribution (QKD), being capable of beating PNS
attack and uncon- ditionally secure, have become an attractive one recently.
But, in many QKD systems, disturbances of transmission channel make quantum bit
error rate (QBER) increase which limits both security distance and key bit rate
of real-life decoy state QKD systems. We demonstrate the two-intensity decoy
QKD with one-way Faraday-Michelson phase modulation system, which is free of
channel dis- turbance and keeps interference fringe visibility (99%) long
period, near 130KM single mode optical fiber in telecom (1550 nm) wavelength.
This is longest distance fiber decoy state QKD system based on two intensity
protocol.Comment: 4 pages, 2figure
Quark deconfinement phase transition in nuclear matter for improved quark mass density-dependent model
The improved quark mass density-dependent (IQMDD) model, which has been
successfully used to describe the properties of both infinite nuclear matter
and finite nuclei, is applied to investigate the properties of quark
deconfinement phase transition. By using the finite-temperature quantum field
theory, we calculate the finite temperature effective potential and extend the
IQMDD model to finite temperature and finite nuclear matter density. The
critical temperature and the critical density of nuclear matter are given and
the QCD phase diagram is addressed. It is shown that this model can not only
describe the saturation properties of nuclear matter, but also explain the
quark deconfinement phase transition successfully
Left-Right Asymmetry of Weak Interaction Mass of Polarized Fermions in Flight
The left-right polarization-dependent asymmetry of the weak interaction mass
is investigated. Based on the Standard Model, the calculation shows that the
weak interaction mass of left-handed polarized fermions is always greater than
that of right-handed polarized fermions in flight with the same velocity in any
inertial frame. The asymmetry of the weak interaction mass might be very
important to the investigation of neutrino mass and would have an important
significance for understanding the parity nonconservation in weak interactions.Comment: 8 pages, 2 figures, corrected calculatio
Efficient quantum direct communication with authentication
Two protocols of quantum direct communication with authentication [Phys. Rev.
A 73, 042305(2006)] were recently indicated to be insecure against the
authenticator Trent's attacks [Phys. Rev. A 75, 026301(2007)]. We present two
efficient protocols by using four Pauli operations, which are secure against
inner Trent's attacks as well as outer Eve's attacks. Finally, we generalize
them to multiparty quantum direction communication.Comment: 4 pages, 4 table
- …