15,148 research outputs found
Entanglement Criteria - Quantum and Topological
This paper gives a criterion for detecting the entanglement of a quantum
state, and uses it to study the relationship between topological and quantum
entanglement. It is fundamental to view topological entanglements such as
braids as entanglement operators and to associate to them unitary operators
that are capable of creating quantum entanglement. The entanglement criterion
is used to explore this connection. The paper discusses non-locality in the
light of this criterion.Comment: 8 pages, LaTeX, to appear in proceedings of Spie Conference, Orlando,
Fla, April 200
Method for universal detection of two-photon polarization entanglement
Detecting and quantifying quantum entanglement of a given unknown state poses
problems that are fundamentally important for quantum information processing.
Surprisingly, no direct (i.e., without quantum tomography) universal
experimental implementation of a necessary and sufficient test of entanglement
has been designed even for a general two-qubit state. Here we propose an
experimental method for detecting a collective universal witness, which is a
necessary and sufficient test of two-photon polarization entanglement. It
allows us to detect entanglement for any two-qubit mixed state and to establish
tight upper and lower bounds on its amount. A different element of this method
is the sequential character of its main components, which allows us to obtain
relatively complicated information about quantum correlations with the help of
simple linear-optical elements. As such, this proposal realizes a universal
two-qubit entanglement test within the present state of the art of quantum
optics. We show the optimality of our setup with respect to the minimal number
of measured quantities.Comment: 7 pages, 5 figure
Inequalities Detecting Quantum Entanglement for Systems
We present a set of inequalities for detecting quantum entanglement of
quantum states. For and systems, the
inequalities give rise to sufficient and necessary separability conditions for
both pure and mixed states. For the case of , these inequalities are
necessary conditions for separability, which detect all entangled states that
are not positive under partial transposition and even some entangled states
with positive partial transposition. These inequalities are given by mean
values of local observables and present an experimental way of detecting the
quantum entanglement of quantum states and even multi-qubit pure
states.Comment: 6 page
Computing quantum discord is NP-complete
We study the computational complexity of quantum discord (a measure of
quantum correlation beyond entanglement), and prove that computing quantum
discord is NP-complete. Therefore, quantum discord is computationally
intractable: the running time of any algorithm for computing quantum discord is
believed to grow exponentially with the dimension of the Hilbert space so that
computing quantum discord in a quantum system of moderate size is not possible
in practice. As by-products, some entanglement measures (namely entanglement
cost, entanglement of formation, relative entropy of entanglement, squashed
entanglement, classical squashed entanglement, conditional entanglement of
mutual information, and broadcast regularization of mutual information) and
constrained Holevo capacity are NP-hard/NP-complete to compute. These
complexity-theoretic results are directly applicable in common randomness
distillation, quantum state merging, entanglement distillation, superdense
coding, and quantum teleportation; they may offer significant insights into
quantum information processing. Moreover, we prove the NP-completeness of two
typical problems: linear optimization over classical states and detecting
classical states in a convex set, providing evidence that working with
classical states is generically computationally intractable.Comment: The (published) journal version
http://iopscience.iop.org/1367-2630/16/3/033027/article is more updated than
the arXiv versions, and is accompanied with a general scientific summary for
non-specialists in computational complexit
A sufficient Entanglement Criterion Based On Quantum Fisher Information and Variance
We derive criterion in the form of inequality based on quantum Fisher
information and quantum variance to detect multipartite entanglement. It can be
regarded as complementary of the well-established PPT criterion in the sense
that it can also detect bound entangled states. The inequality is motivated by
Y.Akbari-Kourbolagh [Phys. Rev A. 99, 012304 (2019)] which introduced
a multipartite entanglement criterion based on quantum Fisher information. Our
criterion is experimentally measurable for detecting any -qudit pure state
mixed with white noisy. We take several examples to illustrate that our
criterion has good performance for detecting certain entangled states.Comment: 11 pages, 1 figur
Macroscopic Observables Detecting Genuine Multipartite Entanglement and Partial Inseparability in Many-Body Systems
We show a general approach for detecting genuine multipartite entanglement
(GME) and partial inseparability in many-body-systems by means of macroscopic
observables (such as the energy) only. We show that the obtained criteria, the
"GME gap" and "the k-entanglement gap", detect large areas of genuine
multipartite entanglement and partial entanglement in typical many body states,
which are not detected by other criteria. As genuine multipartite entanglement
is a necessary property for several quantum information theoretic applications
such as e.g. secret sharing or certain kinds of quantum computation, our
methods can be used to select or design appropriate condensed matter systems.Comment: 4 pages, 3 figures, published version, title extende
Quantum Fisher information-based detection of genuine tripartite entanglement
Genuine multipartite entanglement plays important roles in quantum
information processing. The detection of genuine multipartite entanglement has
been long time a challenging problem in the theory of quantum entanglement. We
propose a criterion for detecting genuine tripartite entanglement of arbitrary
dimensional tripartite states based on quantum Fisher information. We show that
this criterion is more effective for some states in detecting genuine
tripartite entanglement by detailed example.Comment: 12 pages, 2 figure
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