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111 | 2012
Annuaire du Collège de France 2010-2011
Résumé des cours et travaux 111e année
Conférenciers invités

Entanglement, Decoherence and Quantum Metrology

Luiz Davidovich
p. 879-880

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1Since the seminal paper published by Albert Einstein, Boris Podolski and Nathan Rosen in 1935, and the famous series of papers published by Erwin Schrödinger in the years 1935 and 1936, entanglement has occupied a central position in quantum physics. This peculiar phenomenon has posed formidable challenges to several generations of physicists. In fact, it took about 30 years since the 1935 papers for the first mathematical consequence of this property to be demonstrated by John S. Bell and about 30 years more for entanglement to be recognized as a possible resource for quantum communication and quantum computation.

2Evolving from a daunting concept to a useful resource, entanglement is at the heart of many suggested applications, involving the efficient transmission of information through dense coding or teleportation, the security of transmitted data through quantum cryptography, the efficient solution of the factorization problem, a speedier data search protocol, efficient measurement of parameters in quantum metrology, and quantum simulations of problems with exponential demand of resources in classical computers.

3Motivated by these suggested applications and also by the fundamental role played by entanglement in quantum mechanics, important experimental results have been obtained in the last few years, concerning the generation and analysis of multiparty entangled states, the transfer of entanglement between two systems, macroscopic signatures of entanglement, and the dynamics of entangled states under the action of the environment.

4And yet many fundamental problems remain unsolved. Among them, the characterization of entanglement for multiparticle systems, the role of entanglement in quantum metrology under decoherence, the dynamics of entanglement for a system in contact with its environment. This last problem is directly related to a practical question: the assessment of the robustness of the applications mentioned above. It also concerns a fundamental problem in physics: the subtle relation between the classical and the quantum world.

5One knows nowadays that decoherence plays a fundamental role in the emergence of the classical world from quantum physics. Theoretical and experimental work have demonstrated that a coherent superposition of two macroscopically distinguishable states decays to a mixture of the same states with a characteristic time that is inversely proportional to some macroscopicity parameter. The decay law is, within a very good approximation, exponential.

6For multiparty entangled states, the environment may affect local properties, like the excitation and the coherences of each part, and also global properties, like the entanglement of the state. The above-mentioned studies on decoherence lead to natural questions regarding the dynamics of entanglement: What is the decay law? Is it possible to introduce a decay rate, in this case? How does the decay of entanglement scale with the number of entangled parts? How robust is the entanglement of different classes of entangled states? How does the dynamics of entanglement under the influence of the environment affect applications like teleportation and quantum metrology?

7These are some of the questions discussed in the series of lectures. The organization of the four lectures is as follows:

Lecture 1: Review of the concept of entanglement. Characterization of entanglement. Quantification of entanglement. Methods for increasing the amount of entanglement; filtering, distillation. Bound entanglement.

Lecture 2: Open system dynamics, quantum channels, and filtering operations. Dynamics of entanglement for two-qubit systems: theoretical and experimental results.

Lecture 3: Dynamics of entanglement for multipartite systems. Introduction to quantum metrology: Cramér-Rao bound, Fisher information, distinguishability of states, role of entanglement in quantum-enhanced metrology.

Lecture 4: Noisy quantum-enhanced metrology: General framework for evaluating the ultimate precision limit in the estimation of parameters. Application to optical interferometers and atomic spectroscopy.

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Cours et travaux du Collège de France. Annuaire 111e année, Collège de France, Paris, avril 2012, p. 879-880. ISBN 978-2-7226-0156-7

Référence électronique

Luiz Davidovich, « Entanglement, Decoherence and Quantum Metrology », L’annuaire du Collège de France [En ligne], 111 | 2012, mis en ligne le 22 novembre 2013, consulté le 20 février 2018. URL :

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Luiz Davidovich

Instituto de Física, Universidade Federal do Rio de Janeiro (Brésil)

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Droits d’auteur

Collège de France

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