 |
 |
Sandu Popescu | |
|---|---|
 Popescu at the Royal Society admissions day in London, July 2017 | |
| Born | 1956 (age 67–68) Oradea, Romania |
| Known for | |
| Awards |
|
| Scientific career | |
| Fields | Physics |
| Institutions | University of Bristol |
| Doctoral advisor | Yakir Aharonov [ citation needed ] |
| Website | sandupopescu |
Sandu Popescu FRS [3] (born 1956 in Oradea, Romania [ citation needed ]) is a Romanian-British physicist working in the foundations of quantum mechanics and quantum information. [4]
He studied with Yakir Aharonov, followed by postdoctoral research positions with François Englert, and then with Abner Shimony and Bahaa Saleh.[ citation needed ] From 1996 to 1999 he was Reader at the Isaac Newton Institute, University of Cambridge.[ citation needed ]
Popescu has been Professor of Physics at the University of Bristol since 1999.[ citation needed ]
Popescu is co-editor and co-author of the first textbook on quantum information and computation. [5]
In 2015, Popescu appeared on Science Channel's Through the Wormhole with Morgan Freeman.
His most important contributions are in the area of quantum nonlocality.[ citation needed ] In collaboration with Daniel Rohrlich, simultaneously and independently from Nicolas Gisin, Popescu showed that non-locality is a generic property of nature: every entangled pure quantum state (i. e. almost every pure state) has nonlocal properties. [6] In collaboration with Charles Bennett, Herbert Bernstein, and Benjamin Schumacher, he established the quantitative theory of entanglement by the discovery of entanglement concentration [7] and dilution, and together with Bennett, Schumacher, Gilles Brassard, John Smolin, and William Wootters a method of entanglement purification (distillation). [8] These works introduced the idea of entanglement manipulation by local operations and classical communication (LOCC), and introduced the notions of entanglement of distillation and entanglement of formation. He also proved that there is a unique measure of entanglement for pure bi-partite quantum states [9] (the von Neumann entropy of the reduced density matrix).
With Daniel Rohrlich, Popescu showed that nonlocal correlations stronger than those allowed by quantum mechanics could exist without violating Einstein's principle of no superluminal signalling. [10] These correlations are now known as Popescu-Rohrlich correlations (PR boxes). This work started the intensive research program taking place at the moment to find new principles of nature that would limit nonlocality to only quantum correlations, and in this way recover quantum mechanics from general principles.
In 1997, he was one of the first researchers to implement quantum teleportation, [11] one of the landmark experiments in quantum information.
Another of Popescu's interests is the foundations of statistical mechanics. In collaboration with Noah Linden, Anthony J. Short and Andreas Winter he proved that virtually any quantum system interacting with a larger system (the "bath") reaches equilibrium. [12] Crucially, this is the first demonstration of equilibration – the most important aspect of statistical mechanics – directly from first principles, without any additional assumptions. The result holds even in situations in which the standard assumptions of statistical mechanics do not apply, such as systems with strong long-range, non-screened interactions where temperature cannot even be defined. In an earlier work with Short and Winter he showed that the so-called equal a priori probability postulate, one of the basic postulates of statistical mechanics, is redundant, and is simply a consequence of typicality. [13] (A similar proof is due to Goldstein et al. [14] )
With Yakir Aharonov and his group, Popescu discovered a number of quantum paradoxes, such as the quantum Cheshire cat, [15] [16] and the quantum pigeonhole principle. [17] [18] They also introduced the idea of superposition of time evolutions. [19]
Together with Serge Massar, Popescu pioneered the study of optimal measurements and proved that in general they require collective (i.e. entangled) measurements on all of the particles in a finite statistical ensemble. [20] Among the counter-intuitive consequences of quantum theory is his discovery with Nicolas Gisin that two antiparallel spins contain more information about their direction than parallel spins. [21]
More recently Popescu's interest is in the thermodynamics of quantum systems. In collaboration with Noah Linden and Paul Skrzypczyk, he described the smallest possible refrigerator, [22] and together with Skrzypczyk and Anthony J. Short, extended the laws of thermodynamics to individual quantum systems. [23]
Popescu has won numerous awards and honours including:
Quantum entanglement is the phenomenon of a group of particles being generated, interacting, or sharing spatial proximity in such a way that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical and quantum physics: entanglement is a primary feature of quantum mechanics not present in classical mechanics.
The Aharonov–Bohm effect, sometimes called the Ehrenberg–Siday–Aharonov–Bohm effect, is a quantum-mechanical phenomenon in which an electrically charged particle is affected by an electromagnetic potential, despite being confined to a region in which both the magnetic field and electric field are zero. The underlying mechanism is the coupling of the electromagnetic potential with the complex phase of a charged particle's wave function, and the Aharonov–Bohm effect is accordingly illustrated by interference experiments.
A Bell test, also known as Bell inequality test or Bell experiment, is a real-world physics experiment designed to test the theory of quantum mechanics in relation to Albert Einstein's concept of local realism. Named for John Stewart Bell, the experiments test whether or not the real world satisfies local realism, which requires the presence of some additional local variables to explain the behavior of particles like photons and electrons. As of 2015, all Bell tests have found that the hypothesis of local hidden variables is inconsistent with the way that physical systems behave.
In the interpretation of quantum mechanics, a local hidden-variable theory is a hidden-variable theory that satisfies the principle of locality. These models attempt to account for the probabilistic features of quantum mechanics via the mechanism of underlying, but inaccessible variables, with the additional requirement that distant events be statistically independent.
Pieter Kok is a Dutch physicist and one of the co-developers of quantum interferometric optical lithography.
Artur Konrad Ekert is a British-Polish professor of quantum physics at the Mathematical Institute, University of Oxford, professorial fellow in quantum physics and cryptography at Merton College, Oxford, Lee Kong Chian Centennial Professor at the National University of Singapore and the founding director of the Centre for Quantum Technologies (CQT). His research interests extend over most aspects of information processing in quantum-mechanical systems, with a focus on quantum communication and quantum computation. He is best known as one of the pioneers of quantum cryptography.
An optical parametric oscillator (OPO) is a parametric oscillator that oscillates at optical frequencies. It converts an input laser wave with frequency into two output waves of lower frequency by means of second-order nonlinear optical interaction. The sum of the output waves' frequencies is equal to the input wave frequency: . For historical reasons, the two output waves are called "signal" and "idler", where the output wave with higher frequency is the "signal". A special case is the degenerate OPO, when the output frequency is one-half the pump frequency, , which can result in half-harmonic generation when signal and idler have the same polarization.
In quantum mechanics, separable states are multipartite quantum states that can be written as a convex combination of product states. Product states are multipartite quantum states that can be written as a tensor product of states in each space. The physical intuition behind these definitions is that product states have no correlation between the different degrees of freedom, while separable states might have correlations, but all such correlations can be explained as due to a classical random variable, as opposed as being due to entanglement.
In physics, interaction-free measurement is a type of measurement in quantum mechanics that detects the position, presence, or state of an object without an interaction occurring between it and the measuring device. Examples include the Renninger negative-result experiment, the Elitzur–Vaidman bomb-testing problem, and certain double-cavity optical systems, such as Hardy's paradox.
In theoretical physics, quantum nonlocality refers to the phenomenon by which the measurement statistics of a multipartite quantum system do not allow an interpretation with local realism. Quantum nonlocality has been experimentally verified under a variety of physical assumptions. Any physical theory that aims at superseding or replacing quantum theory should account for such experiments and therefore cannot fulfill local realism; quantum nonlocality is a property of the universe that is independent of our description of nature.
In quantum information and quantum computing, a cluster state is a type of highly entangled state of multiple qubits. Cluster states are generated in lattices of qubits with Ising type interactions. A cluster C is a connected subset of a d-dimensional lattice, and a cluster state is a pure state of the qubits located on C. They are different from other types of entangled states such as GHZ states or W states in that it is more difficult to eliminate quantum entanglement in the case of cluster states. Another way of thinking of cluster states is as a particular instance of graph states, where the underlying graph is a connected subset of a d-dimensional lattice. Cluster states are especially useful in the context of the one-way quantum computer. For a comprehensible introduction to the topic see.
Jens Eisert is a German physicist, ERC fellow, and professor at the Free University of Berlin. He is also affiliated with the Helmholtz Association and the Fraunhofer Society.
Hardy's paradox is a thought experiment in quantum mechanics devised by Lucien Hardy in 1992–1993 in which a particle and its antiparticle may interact without annihilating each other.
In quantum information theory, quantum discord is a measure of nonclassical correlations between two subsystems of a quantum system. It includes correlations that are due to quantum physical effects but do not necessarily involve quantum entanglement.
The Aharonov–Casher effect is a quantum mechanical phenomenon predicted in 1984 by Yakir Aharonov and Aharon Casher, in which a traveling magnetic dipole is affected by an electric field. It is dual to the Aharonov–Bohm effect, in which the quantum phase of a charged particle depends upon which side of a magnetic flux tube it comes through. In the Aharonov–Casher effect, the particle has a magnetic moment and the tubes are charged instead. It was observed in a gravitational neutron interferometer in 1989 and later by fluxon interference of magnetic vortices in Josephson junctions. It has also been seen with electrons and atoms.
The two-state vector formalism (TSVF) is a description of quantum mechanics in terms of a causal relation in which the present is caused by quantum states of the past and of the future taken in combination.
Continuous-variable (CV) quantum information is the area of quantum information science that makes use of physical observables, like the strength of an electromagnetic field, whose numerical values belong to continuous intervals. One primary application is quantum computing. In a sense, continuous-variable quantum computation is "analog", while quantum computation using qubits is "digital." In more technical terms, the former makes use of Hilbert spaces that are infinite-dimensional, while the Hilbert spaces for systems comprising collections of qubits are finite-dimensional. One motivation for studying continuous-variable quantum computation is to understand what resources are necessary to make quantum computers more powerful than classical ones.
Quantum foundations is a discipline of science that seeks to understand the most counter-intuitive aspects of quantum theory, reformulate it and even propose new generalizations thereof. Contrary to other physical theories, such as general relativity, the defining axioms of quantum theory are quite ad hoc, with no obvious physical intuition. While they lead to the right experimental predictions, they do not come with a mental picture of the world where they fit.
Giacomo Mauro D'Ariano is an Italian quantum physicist. He is a professor of theoretical physics at the University of Pavia, where he is the leader of the QUIT group. He is a member of the Center of Photonic Communication and Computing at Northwestern University; a member of the Istituto Lombardo Accademia di Scienze e Lettere; and a member of the Foundational Questions Institute (FQXi).
Bound entanglement is a weak form of quantum entanglement, from which no singlets can be distilled with local operations and classical communication (LOCC).
| International | |
|---|---|
| National | |
| Academics | |
| Other | |
