How small can thermal machines be? Towards the smallest possible refrigerator (2009)
Linden, Noah, Popescu, Sandu, Skrzypczyk, Paul
We investigate the fundamental dimensional limits to thermodynamic machines. In particular we show that it is possible to construct self-contained refrigerators (i.e. not requiring external sources...
Closed sets of non-local correlations (2009)
Allcock, Jonathan, Brunner, Nicolas, Linden, Noah, Popescu, Sandu, Skrzypczyk, Paul, Vertesi, Tamas
We introduce a fundamental concept -- closed sets of correlations -- for studying non-local correlations. We argue that sets of correlations corresponding to information-theoretic principles, or more...
On the speed of fluctuations around thermodynamic equilibrium (2009)
Linden, Noah, Popescu, Sandu, Short, Anthony J, Winter, Andreas
We study the speed of fluctuation of a quantum system around its thermodynamic equilibrium state, and show that the speed will be extremely small for almost all times in typical thermodynamic cases....
Quantum mechanics: Why isn't nature more non-local? (2009)
Many predictions and consequences of quantum mechanics defy intuition. New insights into the limits of communication between spatially separated parties could bring us closer to grasping the nature...
Quantum mechanical evolution towards thermal equilibrium (2008)
Linden, Noah, Popescu, Sandu, Short, Anthony J., Winter, Andreas
The circumstances under which a system reaches thermal equilibrium, and how to derive this from basic dynamical laws, has been a major question from the very beginning of thermodynamics and...
Emergence of Quantum Correlations from Non-Locality Swapping (2008)
Skrzypczyk, Paul, Brunner, Nicolas, Popescu, Sandu
By studying generalized non-signalling theories, the hope is to find out what makes quantum mechanics so special. In the present paper, we revisit the paradigmatic model of non-signalling boxes and...
Testing a Bell inequality in multi-pair scenarios (2008)
Bancal, Jean-Daniel, Branciard, Cyril, Brunner, Nicolas, Gisin, Nicolas, Popescu, Sandu, Simon, Christoph
To date, most efforts to demonstrate quantum nonlocality have concentrated on systems of two (or very few) particles. It is however difficult in many experiments to address individual particles,...
Dynamic entanglement in oscillating molecules (2008)
Cai, Jianming, Popescu, Sandu, Briegel, Hans J.
We demonstrate that entanglement can persistently recur in an oscillating two-spin molecule that is coupled to a hot and noisy environment, in which no static entanglement can survive. The system...
Briegel, Hans J., Popescu, Sandu
We discuss the possibility of existence of entanglement in biological systems. Our arguments centre on the fact that biological systems are thermodynamic open driven systems far from equilibrium. In...
Simulation of partial entanglement with nonsignaling resources (2008)
Brunner, Nicolas, Gisin, Nicolas, Popescu, Sandu, Scarani, Valerio
With the goal of gaining a deeper understanding of quantum non-locality, we decompose quantum correlations into more elementary non-local correlations. We show that the correlations of all pure...
Sequential weak measurement (2007)
Mitchison, Graeme, Jozsa, Richard, Popescu, Sandu
The notion of weak measurement provides a formalism for extracting information from a quantum system in the limit of vanishing disturbance to its state. Here we extend this formalism to the...
No quantum advantage for nonlocal computation (2006)
Linden, Noah, Popescu, Sandu, Short, Anthony J., Winter, Andreas
We investigate the problem of "nonlocal" computation, in which separated parties must compute a function with nonlocally encoded inputs and output, such that each party individually learns nothing,...
KLM quantum computation with bosonic atoms (2006)
A Knill-Laflamme-Milburn (KLM) type quantum computation with bosonic neutral atoms or bosonic ions is suggested. Crucially, as opposite to other quantum computation schemes involving atoms (ions), no...
KLM quantum computation as a measurement based computation (2006)
We show that the Knill Laflamme Milburn method of quantum computation with linear optics gates can be interpreted as a one-way, measurement based quantum computation of the type introduced by Briegel...
Oblivious transfer and quantum channels (2006)
Gisin, Nicolas, Popescu, Sandu, Scarani, Valerio, Wolf, Stefan, Wullschleger, Jürg
We show that oblivious transfer can be seen as the classical analogue to a quantum channel in the same sense as non-local boxes are for maximally entangled qubits.
The foundations of statistical mechanics from entanglement: Individual states vs. averages (2005)
Popescu, Sandu, Short, Anthony J., Winter, Andreas
We consider an alternative approach to the foundations of statistical mechanics, in which subjective randomness, ensemble-averaging or time-averaging are not required. Instead, the universe (i.e. the...
Entanglement swapping for generalized non-local correlations (2005)
Short, Tony, Popescu, Sandu, Gisin, Nicolas
We consider an analogue of entanglement-swapping for a set of black boxes with the most general non-local correlations consistent with relativity (including correlations which are stronger than any...
On the entanglement concentration of three-partite states (2005)
Groisman, Berry, Linden, Noah, Popescu, Sandu
We investigate the concentration of multi-party entanglement by focusing on simple family of three-partite pure states, superpositions of Greenberger-Horne-Zeilinger states and singlets. Despite the...
The Entanglement of Superpositions (2005)
Linden, Noah, Popescu, Sandu, Smolin, John A.
Given a bipartite quantum state (in arbitrary dimension) and a decomposition of it as a superposition of two others, we find bounds on the entanglement of the superposition state in terms of the...
The physics of no-bit-commitment : Generalized quantum non-locality versus oblivious transfer (2005)
Short, Tony, Gisin, Nicolas, Popescu, Sandu
We show here that the recent work of Wolf and Wullschleger (quant-ph/0502030) on oblivious transfer apparently opens the possibility that non-local correlations which are stronger than those in...
On the quantum, classical and total amount of correlations in a quantum state (2004)
Groisman, Berry, Popescu, Sandu, Winter, Andreas
We give an operational definition of the quantum, classical and total amount of correlations in a bipartite quantum state. We argue that these quantities can be defined via the amount of work (noise)...
Popescu, Sandu, Groisman, Berry, Massar, Serge
The question of finding a lower bound on the number of Toffoli gates in a classical reversible circuit is addressed. A method based on quantum information concepts is proposed. The method involves...
Non-local correlations as an information theoretic resource (2004)
Barrett, Jonathan, Linden, Noah, Massar, Serge, Pironio, Stefano, Popescu, Sandu, Roberts, David
It is well known that measurements performed on spatially separated entangled quantum systems can give rise to correlations that are non-local, in the sense that a Bell inequality is violated. They...
Frames of Reference and the Intrinsic Directional Information of a Particle With Spin (2004)
Collins, Daniel, Popescu, Sandu
"Information is physical", and here we consider the physical directional information of a particle with spin. We ask whether, in the presence of a classical frame of reference, such a particle...
Energy-time entanglement of quasi-particles in solid-state devices (2003)
Scarani, Valerio, Gisin, Nicolas, Popescu, Sandu
We present a proposal for the experimental observation of energy-time entanglement of quasi-particles in mesoscopic physics. This type of entanglement arises whenever correlated particles are...
Entanglement cost of generalised measurements (2003)
Jozsa, Richard, Koashi, Masato, Linden, Noah, Popescu, Sandu, Presnell, Stuart, Shepherd, Dan, ...
Bipartite entanglement is one of the fundamental quantifiable resources of quantum information theory. We propose a new application of this resource to the theory of quantum measurements. According...
Quantum nonlocality, Bell inequalities and the memory loophole (2002)
Barrett, Jonathan, Collins, Daniel, Hardy, Lucien, Kent, Adrian, Popescu, Sandu
In the analysis of experiments designed to reveal violation of Bell-type inequalities, it is usually assumed that any hidden variables associated with the nth particle pair would be independent of...
Conditions for the confirmation of three-particle non-locality (2002)
Mitchell, Peter, Popescu, Sandu, Roberts, David
The notion of genuine three-particle non-locality introduced by Svetlichny \cite{Svetlichny} is discussed. Svetlichny's inequality which can distinguish between genuine three-particle non-locality...
Bell-type inequalities to detect true n-body non-separability (2002)
Collins, Daniel, Gisin, Nicolas, Popescu, Sandu, Roberts, David, Scarani, Valerio
We analyze the structure of correlations among more than two quantum systems. We introduce a classification of correlations based on the concept of non-separability, which is different {\em a priori}...
Teleportation of Entangled States of a Vacuum-One Photon Qubit (2001)
Lombardi, Egilberto, Sciarrino, Fabio, Popescu, Sandu, De Martini, Francesco
We report the experimental realization of teleporting an entangled qubit. The qubit is physically implemented by a two-dimensional subspace of states of a mode of the electromagnetic field,...
A classical analogue of entanglement (2001)
Collins, Daniel, Popescu, Sandu
We show that quantum entanglement has a very close classical analogue, namely secret classical correlations. The fundamental analogy stems from the behavior of quantum entanglement under local...
Violations of local realism by two entangled quNits (2001)
Collins, Daniel, Popescu, Sandu
Results obtained in two recent papers, \cite{Kaszlikowski} and \cite{Durt}, seem to indicate that the nonlocal character of the correlations between the outcomes of measurements performed on...
Aharonov, Yakir, Botero, Alonso, Popescu, Sandu, Reznik, Benni, Tollaksen, Jeff
Classical-realistic analysis of entangled systems have lead to retrodiction paradoxes, which ordinarily have been dismissed on the grounds of counter-factuality. Instead, we claim that such paradoxes...
The non-local content of quantum operations (2000)
Collins, Daniel, Linden, Noah, Popescu, Sandu
We show that quantum operations on multi-particle systems have a non-local content; this mirrors the non-local content of quantum states. We introduce a general framework for discussing the non-local...
Exact and Asymptotic Measures of Multipartite Pure State Entanglement (1999)
Bennett, Charles H., Popescu, Sandu, Rohrlich, Daniel, Smolin, John A., Thapliyal, Ashish V.
In an effort to simplify the classification of pure entangled states of multi (m) -partite quantum systems, we study exactly and asymptotically (in n) reversible transformations among n'th tensor...
Good dynamics versus bad kinematics. Is entanglement needed for quantum computation? (1999)
We consider quantum computing with pseudo-pure states. This framework arises in certain implementations of quantum computing using NMR. We analyze quantum computational protocols which aim to solve...
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...
The Halting Problem for Quantum Computers (1998)
We argue that the halting problem for quantum computers which was first raised by Myers, is by no means solved, as has been claimed recently. We explicitly demonstrate the difficulties that arise in...
Causality and Nonlocality as Axioms for Quantum Mechanics (1997)
Popescu, Sandu, Rohrlich, Daniel
Quantum mechanics permits nonlocality - both nonlocal correlations and nonlocal equations of motion - while respecting relativistic causality. Is quantum mechanics the unique theory that reconciles...
Concentrating entanglement by local actions---beyond mean values (1997)
Suppose two distant observers Alice and Bob share a pure bipartite quantum state. By applying local operations and communicating with each other using a classical channel, Alice and Bob can...
ACTION AND PASSION AT A DISTANCE An Essay in Honor of Professor Abner Shimony ∗ (1997)
Sandu Popescu, Daniel Rohrlich
Quantum mechanics permits nonlocality—both nonlocal correlations and nonlocal equations of motion—while respecting relativistic causality. Is quan-tum mechanics the unique theory that reconciles...
Revisiting Bell's theorem for a class of down-conversion experiments (1996)
Popescu, Sandu, Hardy, Lucien, Zukowski, Marek
A certain class of parametric down-conversion Bell type experiments has the following features. In the idealized perfect situation it is in only 50% of cases that each observer receives a photon; in...
Thermodynamics and the Measure of Entanglement (1996)
Popescu, Sandu, Rohrlich, Daniel
We point out formal correspondences between thermodynamics and entanglement. By applying them to previous work, we show that entropy of entanglement is the unique measure of entanglement for pure...
Action and Passion at a Distance: An Essay in Honor of Professor Abner Shimony (1996)
Popescu, Sandu, Rohrlich, Daniel
Quantum mechanics permits nonlocality---both nonlocal correlations and nonlocal equations of motion---while respecting relativistic causality. Is quantum mechanics the unique theory that reconciles...
Quantum Privacy Amplification and the Security of Quantum Cryptography Over Noisy Channels (1996)
David Deutsch, Artur Ekert, Richard Jozsa, Chiara Macchiavello, Sandu Popescu, Anna Sanpera
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...
Concentrating Partial Entanglement by Local Operations (1995)
Bennett, Charles H., Bernstein, Herbert J., Popescu, Sandu, Schumacher, Benjamin
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...
Purification of Noisy Entanglement and Faithful Teleportation via Noisy Channels (1995)
Bennett, Charles H., Brassard, Gilles, Popescu, Sandu, Schumacher, Benjamin, Smolin, John A., Wootters, William K.
Two separated observers, by applying local operations to a supply of not-too-impure entangled states ({\em e.g.} singlets shared through a noisy channel), can prepare a smaller number of entangled...
Bell's inequalities and density matrices. Revealing hidden nonlocality. (1995)
As is well known, quantum mechanical behavior cannot, in general, be simulated by a local hidden variables model. Most -if not all- the proofs of this incompatibility refer to the correlations which...
An optical method for teleportation (1995)
A teleportation method using standard present day optical technology is presented.
Negative Kinetic Energy Between Past and Future State Vectors (1994)
Rohrlich, Daniel, Aharonov, Yakir, Popescu, Sandu, Vaidman, Lev
An analysis of errors in measurement yields new insight into classically forbidden quantum processes. In addition to "physical" values, a realistic measurement can yield "unphysical" values; we show...
Causality Constraints on Nonlocal Quantum Measurements (1993)
Consequences of relativistic causality for measurements of nonlocal characteristics of composite quantum systems are investigated. It is proved that verification measurements of entangled states...