610,322 research outputs found
Controlled generation of field squeezing with cold atomic clouds coupled to a superconducting transmission line resonator
We propose an efficient method for controlled generation of field squeezing
with cold atomic clouds trapped close to a superconducting transmission line
resonator. It is shown that, based on the coherent strong magnetic coupling
between the collective atomic spins and microwave fields in the transmission
line resonator, two-mode or single mode field squeezed states can be generated
through coherent control on the dynamics of the system. The degree of squeezing
and preparing time can be directly controlled through tuning the external
classical fields. This protocol may offer a promising platform for implementing
scalable on-chip quantum information processing with continuous variables.Comment: accepted by Phys. Rev.
Method for classifying multiqubit states via the rank of the coefficient matrix and its application to four-qubit states
We construct coefficient matrices of size 2^l by 2^{n-l} associated with pure
n-qubit states and prove the invariance of the ranks of the coefficient
matrices under stochastic local operations and classical communication (SLOCC).
The ranks give rise to a simple way of partitioning pure n-qubit states into
inequivalent families and distinguishing degenerate families from one another
under SLOCC. Moreover, the classification scheme via the ranks of coefficient
matrices can be combined with other schemes to build a more refined
classification scheme. To exemplify we classify the nine families of four
qubits introduced by Verstraete et al. [Phys. Rev. A 65, 052112 (2002)] further
into inequivalent subfamilies via the ranks of coefficient matrices, and as a
result, we find 28 genuinely entangled families and all the degenerate classes
can be distinguished up to permutations of the four qubits. We also discuss the
completeness of the classification of four qubits into nine families
An entanglement measure for n-qubits
Recently, Coffman, Kundu, and Wootters introduced the residual entanglement
for three qubits to quantify the three-qubit entanglement in Phys. Rev. A 61,
052306 (2000). In Phys. Rev. A 65, 032304 (2007), we defined the residual
entanglement for qubits, whose values are between 0 and 1. In this paper,
we want to show that the residual entanglement for qubits is a natural
measure of entanglement by demonstrating the following properties. (1). It is
SL-invariant, especially LU-invariant. (2). It is an entanglement monotone.
(3). It is invariant under permutations of the qubits. (4). It vanishes or is
multiplicative for product states.Comment: 16 pages, no figure
The gravitational field of a global monopole
We present an exact solution to the non-linear equation which describes a
global monopole in the flat space. We re-examine the metric and the geodesics
outside the global monopole. We will see that a global monopole produces a
repulsive gravitational field outside the core in addition to a solid angular
deficit. The lensing property of the global monopole and the global
monopole-antimonopole annihilation mechanism are studied.Comment: 8 pages, no figure
Quantum Doubles from a Class of Noncocommutative Weak Hopf Algebras
The concept of biperfect (noncocommutative) weak Hopf algebras is introduced
and their properties are discussed. A new type of quasi-bicrossed products are
constructed by means of weak Hopf skew-pairs of the weak Hopf algebras which
are generalizations of the Hopf pairs introduced by Takeuchi. As a special
case, the quantum double of a finite dimensional biperfect (noncocommutative)
weak Hopf algebra is built. Examples of quantum doubles from a Clifford monoid
as well as a noncommutative and noncocommutative weak Hopf algebra are given,
generalizing quantum doubles from a group and a noncommutative and
noncocommutative Hopf algebra, respectively. Moreover, some characterisations
of quantum doubles of finite dimensional biperfect weak Hopf algebras are
obtained.Comment: LaTex 18 pages, to appear in J. Math. Phys. (To compile, need
pb-diagram.sty, pb-lams.sty, pb-xy.sty and lamsarrow.sty
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