Centre de Physique Théorique


Mercredi 14 juin 2017

15h30 – 16h30, Amphi 5 du CPT

Quantum reference frames, quantum asymmetry, and quantum information

Robert W. Spekkens (Perimeter Institute for Theoretical Physics)

The asymmetry properties of a quantum state specify how and to what extent a given symmetry is broken by the state. If implementing symmetric dynamics is easy while implementing dynamics that break the symmetry is hard or impossible, then asymmetry becomes a resource (analogous to the resource of entanglement). It is the key resource in the field of quantum metrology because correlating reference frames (i.e., synchronizing clocks, aligning gyroscopes, etcetera) is a problem of distributing information about a group and the measure of how well a state can achieve such an alignment is a measure of its asymmetry. It is also significant for understanding the consequences of symmetric dynamics : measures of the asymmetry of a state provide new constraints on the possible state evolutions, constraints that supplement those imposed by Noether’s theorem. Formalizing the notion of asymmetry also provides perspective on some conceptual puzzles, such as an apparent failure of Curie’s principle in the quantum realm. A pervading theme of the talk will be the invasion of physics by information theory.