1,650 research outputs found
Method of convex rigid frames and applications in studies of multipartite quNit pure-states
In this Letter we suggest a method of convex rigid frames in the studies of
the multipartite quNit pure-states. We illustrate what are the convex rigid
frames and what is the method of convex rigid frames. As the applications we
use this method to solve some basic problems and give some new results (three
theorems): The problem of the partial separability of the multipartite quNit
pure-states and its geometric explanation; The problem of the classification of
the multipartite quNit pure-states, and give a perfect explanation of the local
unitary transformations; Thirdly, we discuss the invariants of classes and give
a possible physical explanation.Comment: 6 pages, no figur
Nonadditive measure and quantum entanglement in a class of mixed states of N^n-system
Through the generalization of Khinchin's classical axiomatic foundation, a
basis is developed for nonadditive information theory. The classical
nonadditive conditional entropy indexed by the positive parameter q is
introduced and then translated into quantum information. This quantity is
nonnegative for classically correlated states but can take negative values for
entangled mixed states. This property is used to study quantum entanglement in
the parametrized Werner-Popescu-like state of an N^n-system, that is, an
n-partite N-level system. It is shown how the strongest limitation on validity
of local realism (i.e., separability of the state) can be obtained in a novel
manner
Study of the effects of high intensity sound on turbulent incompressible flow
The effects of propagating a sonic disturbance without reflection in a direction parallel but contrary to flow, over the entire flow, were experimentally studied in a 10-cm by 10-cm square duct with a fluid velocity of 6.8 meters per second, or pipe Reynolds number of 4.7 X 10(4). The effect was investigated over a range of sound frequencies of 300 to 1800 cps and sound pressure levels of 85 to 140 db re 0.0002 microbars. Sonic excitation reduced the low frequency components (below 300 cps) of the incoming turbulence. The turbulence reduction was greatest for a sound of frequency 700 cps and increased with increasing SPL. This reduction of incoming turbulence appears to retard transition to turbulence by reducing the amount of turbulence in air entering the duct thereby altering the turbulence profile without apparently changing the velocity profile.http://www.archive.org/details/studyofeffectsof00carlLieutenant, United States NavyApproved for public release; distribution is unlimited
Probabilistic Quantum Memories
Typical address-oriented computer memories cannot recognize incomplete or
noisy information. Associative (content-addressable) memories solve this
problem but suffer from severe capacity shortages. I propose a model of a
quantum memory that solves both problems. The storage capacity is exponential
in the number of qbits and thus optimal. The retrieval mechanism for incomplete
or noisy inputs is probabilistic, with postselection of the measurement result.
The output is determined by a probability distribution on the memory which is
peaked around the stored patterns closest in Hamming distance to the input.Comment: Revised version to appear in Phys. Rev. Let
The Role of Stress in the Pathogenesis and Maintenance of Obsessive-Compulsive Disorder
Individuals with obsessive-compulsive disorder often identify psychosocial stress as a factor that exacerbates their symptoms, and many trace the onset of symptoms to a stressful period of life or a discrete traumatic incident. However, the pathophysiological relationship between stress and obsessive-compulsive disorder remains poorly characterized: it is unclear whether trauma or stress is an independent cause of obsessive-compulsive disorder symptoms, a triggering factor that interacts with a preexisting diathesis, or simply a nonspecific factor that can exacerbate obsessive-compulsive disorder along with other aspects of psychiatric symptomatology. Nonetheless, preclinical research has demonstrated that stress has conspicuous effects on corticostriatal and limbic circuitry. Specifically, stress can lead to neuronal atrophy in frontal cortices (particularly the medial prefrontal cortex), the dorsomedial striatum (caudate), and the hippocampus. Stress can also result in neuronal hypertrophy in the dorsolateral striatum (putamen) and amygdala. These neurobiological effects mirror reported neural abnormalities in obsessive-compulsive disorder and may contribute to an imbalance between goal-directed and habitual behavior, an imbalance that is implicated in the pathogenesis and expression of obsessive-compulsive disorder symptomatology. The modulation of corticostriatal and limbic circuits by stress and the resultant imbalance between habit and goal-directed learning and behavior offers a framework for investigating how stress may exacerbate or trigger obsessive-compulsive disorder symptomatology
Separability and Fourier representations of density matrices
Using the finite Fourier transform, we introduce a generalization of
Pauli-spin matrices for -dimensional spaces, and the resulting set of
unitary matrices is a basis for matrices. If and H^{[ N]}=\bigotimes H^{% [ d_{k}]}, we give a
sufficient condition for separability of a density matrix relative to
the in terms of the norm of the spin coefficients of
Since the spin representation depends on the form of the tensor
product, the theory applies to both full and partial separability on a given
space % . It follows from this result that for a prescribed form of
separability, there is always a neighborhood of the normalized identity in
which every density matrix is separable. We also show that for every prime
and the generalized Werner density matrix is fully
separable if and only if
Frontier between separability and quantum entanglement in a many spin system
We discuss the critical point separating the quantum entangled and
separable states in two series of N spins S in the simple mixed state
characterized by the matrix operator where , , is the
unity matrix and is a special entangled
state. The cases x=0 and x=1 correspond respectively to fully random spins and
to a fully entangled state. In the first of these series we consider special
states invariant under charge conjugation, that generalizes
the N=2 spin S=1/2 Einstein-Podolsky-Rosen state, and in the second one we
consider generalizations of the Weber density matrices. The evaluation of the
critical point was done through bounds coming from the partial
transposition method of Peres and the conditional nonextensive entropy
criterion. Our results suggest the conjecture that whenever the bounds coming
from both methods coincide the result of is the exact one. The results we
present are relevant for the discussion of quantum computing, teleportation and
cryptography.Comment: 4 pages in RevTeX forma
Generalized reduction criterion for separability of quantum states
A new necessary separability criterion that relates the structures of the
total density matrix and its reductions is given. The method used is based on
the realignment method [K. Chen and L.A. Wu, Quant. Inf. Comput. 3, 193
(2003)]. The new separability criterion naturally generalizes the reduction
separability criterion introduced independently in previous work of [M.
Horodecki and P. Horodecki, Phys. Rev. A 59, 4206 (1999)] and [N.J. Cerf, C.
Adami and R.M. Gingrich, Phys. Rev. A 60, 898 (1999)]. In special cases, it
recovers the previous reduction criterion and the recent generalized partial
transposition criterion [K. Chen and L.A. Wu, Phys. Lett. A 306, 14 (2002)].
The criterion involves only simple matrix manipulations and can therefore be
easily applied.Comment: 17 pages, 2 figure
Optimal Lewenstein-Sanpera Decomposition for some Biparatite Systems
It is shown that for a given bipartite density matrix and by choosing a
suitable separable set (instead of product set) on the separable-entangled
boundary, optimal Lewenstein-Sanpera (L-S) decomposition can be obtained via
optimization for a generic entangled density matrix. Based on this, We obtain
optimal L-S decomposition for some bipartite systems such as and
Bell decomposable states, generic two qubit state in Wootters
basis, iso-concurrence decomposable states, states obtained from BD states via
one parameter and three parameters local operations and classical
communications (LOCC), Werner and isotropic states, and a one
parameter state. We also obtain the optimal decomposition for
multi partite isotropic state. It is shown that in all systems
considered here the average concurrence of the decomposition is equal to the
concurrence. We also show that for some Bell decomposable states
the average concurrence of the decomposition is equal to the lower bound of the
concurrence of state presented recently in [Buchleitner et al,
quant-ph/0302144], so an exact expression for concurrence of these states is
obtained. It is also shown that for isotropic state where
decomposition leads to a separable and an entangled pure state, the average
I-concurrence of the decomposition is equal to the I-concurrence of the state.
Keywords: Quantum entanglement, Optimal Lewenstein-Sanpera decomposition,
Concurrence, Bell decomposable states, LOCC}
PACS Index: 03.65.UdComment: 31 pages, Late
- …