9,330 research outputs found
Quantum Nonlocality of N-qubit W states
An experimental setup for testing quantum nonlocality of N qubits is
proposed. This method is a generalization of the optical setup proposed by
Banaszek and Wodkiewicz [1]. The quantum nonlocality of N qubits can be
obtained through its violation of N-qubit Bell inequalities. The correlation
function measured in the experiment is described by the Wigner function. The
effect of inefficient detector is also considered.Comment: 5 pages and 2 figures, some errors are corrected in v
Continuous Multipartite Entangled State in Wigner Representation and the Violation of Zukowski-Brukner Inequality
We construct an explicit Wigner function for N-mode squeezed state. Based on
a previous observation that the Wigner function describes correlations in the
joint measurement of the phase-space displaced parity operator, we investigate
the non-locality of multipartite entangled state by the violation of
Zukowski-Brukner N-qubit Bell inequality. We find that quantum predictions for
such squeezed state violate these inequalities by an amount that grows with the
number N.Comment: 5 pages, rewritten version, accepted by Phys. Rev.
Violating Bell Inequalities Maximally for Two -Dimensional Systems
We investigate the maximal violation of Bell inequalities for two
-dimensional systems by using the method of Bell operator. The maximal
violation corresponds to the maximal eigenvalue of the Bell operator matrix.
The eigenvectors corresponding to these eigenvalues are described by asymmetric
entangled states. We estimate the maximum value of the eigenvalue for large
dimension. A family of elegant entangled states that violate
Bell inequality more strongly than the maximally entangled state but are
somewhat close to these eigenvectors is presented. These approximate states can
potentially be useful for quantum cryptography as well as many other important
fields of quantum information.Comment: 6 pages, 1 figure. Revised versio
Bell inequalities for three particles
We present tight Bell inequalities expressed by probabilities for three four-
and five-dimensional systems. The tight structure of Bell inequalities for
three -dimensional systems (qudits) is proposed. Some interesting Bell
inequalities of three qubits reduced from those of three qudits are also
studied.Comment: 8 pages, 3 figures. Accepted for publication in Phys. Rev.
Hardy's Paradox for High-Dimensional Systems: Beyond Hardy's Limit
Hardy's proof is considered the simplest proof of nonlocality. Here we
introduce an equally simple proof that (i) has Hardy's as a particular case,
(ii) shows that the probability of nonlocal events grows with the dimension of
the local systems, and (iii) is always equivalent to the violation of a tight
Bell inequality.Comment: REVTeX4, 5 pages, 1 figure. Typo in Eq. (17) corrected. Ref. [5]
complete
Beyond Gisin's Theorem and its Applications: Violation of Local Realism by Two-Party Einstein-Podolsky-Rosen Steering
We demonstrate here that for a given mixed multi-qubit state if there are at
least two observers for whom mutual Einstein-Podolsky-Rosen steering is
possible, i.e. each observer is able to steer the other qubits into two
different pure states by spontaneous collapses due to von Neumann type
measurements on his/her qubit, then nonexistence of local realistic models is
fully equivalent to quantum entanglement (this is not so without this
condition). This result leads to an enhanced version of Gisin's theorem
(originally: all pure entangled states violate local realism). Local realism is
violated by all mixed states with the above steering property. The new class of
states allows one e.g. to perform three party secret sharing with just pairs of
entangled qubits, instead of three qubit entanglements (which are currently
available with low fidelity). This significantly increases the feasibility of
having high performance versions of such protocols. Finally, we discuss some
possible applications.Comment: 9 pages, 1 figur
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