4,077 research outputs found
Entangled SU(2) and SU(1,1) coherent states
Entangled SU(2) and SU(1,1) coherent states are developed as superpositions
of multiparticle SU(2) and SU(1,1) coherent states. In certain cases, these are
coherent states with respect to generalized su(2) and su(1,1) generators, and
multiparticle parity states arise as a special case. As a special example of
entangled SU(2) coherent states, entangled binomial states are introduced and
these entangled binomial states enable the contraction from entangled SU(2)
coherent states to entangled harmonic oscillator coherent states. Entangled
SU(2) coherent states are discussed in the context of pairs of qubits. We also
introduce the entangled negative binomial states and entangled squeezed states
as examples of entangled SU(1,1) coherent states. A method for generating the
entangled SU(2) and SU(1,1) coherent states is discussed and degrees of
entanglement calculated. Two types of SU(1,1) coherent states are discussed in
each case: Perelomov coherent states and Barut-Girardello coherent states.Comment: 31 pages, no figure
Non-classical properties and algebraic characteristics of negative binomial states in quantized radiation fields
We study the nonclassical properties and algebraic characteristics of the
negative binomial states introduced by Barnett recently. The ladder operator
formalism and displacement operator formalism of the negative binomial states
are found and the algebra involved turns out to be the SU(1,1) Lie algebra via
the generalized Holstein-Primarkoff realization. These states are essentially
Peremolov's SU(1,1) coherent states. We reveal their connection with the
geometric states and find that they are excited geometric states. As
intermediate states, they interpolate between the number states and geometric
states. We also point out that they can be recognized as the nonlinear coherent
states. Their nonclassical properties, such as sub-Poissonian distribution and
squeezing effect are discussed. The quasiprobability distributions in phase
space, namely the Q and Wigner functions, are studied in detail. We also
propose two methods of generation of the negative binomial states.Comment: 17 pages, 5 figures, Accepted in EPJ
Characterization of four-qubit states via Bell inequalities
A set of Bell inequalities classifying the quantum entanglement of four-qubit
states is presented. These inequalities involve only two measurement settings
per observer and can characterize fully separable, bi-separable and
tri-separable quantum states. In addition, a quadratic inequality of the Bell
operators for four-qubit systems is derived
Precise QCD predictions on top quark pair production mediated by massive color octet vector boson at hadron colliders
We present a theoretical framework for systematically calculating
next-to-leading order (NLO) QCD effects to various experimental observables in
models with massive COVB in a model independent way at hadron colliders.
Specifically, we show the numerical results for the NLO QCD corrections to
total cross sections, invariant mass distribution and AFB of top quark pairs
production mediated by a massive COVB in both the fixed scale (top quark mass)
scheme and the dynamical scale (top pair invariant mass) scheme. Our results
show that the NLO QCD calculations in the dynamical scale scheme is more
reasonable than the fixed scheme and the naive estimate of the NLO effects by
simple rescaling of the LO results with the SM NLO K-factor is not appropriate.Comment: 6 pages, 5 figures, 2 tables; version published in EPJ
Secrecy Outage Probability Analysis of Multi-User Multi-Eavesdropper Wireless Systems
In this paper, we explore the physical-layer security of a multi-user
wireless system that consists of multiple users intending to transmit to a base
station (BS), while multiple eavesdroppers attempt to tap the user
transmissions. We examine the employment of multi-user scheduling for improving
the transmission security against eavesdropping and propose a multi-user
scheduling scheme, which only requires the channel state information (CSI) of
BS without the need of the passive eavesdroppers' CSI. We also consider the
round-robin scheduling for comparison purposes. The closed-form secrecy outage
probability expressions of the round-robin scheduling and proposed multi-user
scheduling are derived over Rayleigh fading channels. Numerical results
demonstrate that the proposed multi-user scheduling outperforms the round-robin
scheduling in terms of the secrecy outage probability. As the number of users
increases, the secrecy outage probability of round-robin scheduling keeps
unchanged. By contrast, the secrecy outage performance of the proposed
multi-user scheduling improves significantly with an increasing number of
users.Comment: 5 page
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