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If two separated observers are supplied with entanglement, in the form of n pairs of particles in identical partly-entangled pure states, one member of each pair being given to each observer; they can, by local actions of each observer, concentrate this entangle-ment into a smaller number of maximally-entangled pairs of particles, for example… (More)

- David Deutsch, Artur Ekert, Chiara Macchiavello, Sandu Popescu, Anna Sanpera
- 1998

Existing quantum cryptographic schemes are not, as they stand, operable in the presence of noise on the quantum communication channel. Although they become operable if they are supplemented by classical privacy-amplification techniques, the resulting schemes are difficult to analyse and have not been proved secure. We introduce the concept of quantum… (More)

- Daniel Collins, Nicolas Gisin, Noah Linden, Serge Massar, Sandu Popescu
- 2001

Bell inequalities, local realism, quantum foundations, quantum information, quantum non-locality, non-locality We develop a novel approach to Bell inequalities based on a constraint that the correlations exhibited by local variable theories must satisfy. This is used to construct a family of Bell inequalities for bipartite quantum systems of arbitrarily… (More)

- Sandu Popescu, Daniel Rohrlich
- 1997

Quantum mechanics permits nonlocality—both nonlocal correlations and nonlocal equations of motion—while respecting relativistic causality. Is quantum mechanics the unique theory that reconciles nonlocality and causality? We consider two models, going beyond quantum mechanics, of nonlocality: " superquantum " correlations, and nonlocal " jamming " of… (More)

entanglement, quantum theory, quantum information, quantum computation, foundations of quantum mechanics Previous investigations of entanglement manipulations have focused on the average properties of the outcomes and little is known about the actual probability distribution. Here we go beyond the average properties. We show that, for a pure entangled state… (More)

- N Linden, Sandu Popescu, A Sudbery
- 1998

quantum mechanics, quantum information, quantum non-locality, quantum entanglement As far as entanglement is concerned, two density matrices of n particles are equivalent if they are on the same orbit of the group of local unitary transformations, U (d1) % ??? % U (dn) (where the Hilbert space of particle r has dimension dr). We show that for n greater than… (More)

by 1964, an old but still troubling story. The fact that identical measurements of identically prepared systems can yield different outcomes seems to challenge a basic tenet of science and philosophy. Frustration with the indeterminacy intrinsic to quantum mechanics was famously expressed in Albert Einstein's assertion that " God doesn't play dice. " By… (More)

Entanglement bits or " ebits " have been proposed as a quantitative measure of a fundamental resource in quantum information processing. For such an interpretation to be valid, it is important to show that the same number of ebits in different forms or concentrations are inter-convertible in the asymp-totic limit. Here we draw attention to a very important… (More)

- Daniel Rohrlich, Sandu Popescu
- 1996

Quantum mechanics and relativistic causality together imply nonlocality: nonlo-cal correlations (that violate the CHSH inequality) and nonlocal equations of motion (the Aharonov-Bohm effect). Can we invert the logical order? We consider a conjecture that nonlocality and relativistic causality together imply quantum mechanics. We show that correlations… (More)