Description

2010/12/13, Prof. Daniel Braun (Universite Paul Sabatier Toulouse)

Place:  Sala de Seminarios del Departamento de Física Teórica e Historia de la Ciencia
Time: 11:30h.
Title: Decoherence enhanced measurements

Abstract
The major goal of Quantum Enhanced Measurements is to achieve the Heisenberg limit (HL)- a scaling of the sensitivity as 1/N with the number N of quantum resources.  This would represent a major improvement over the standard quantum limit (SQL), in which the sensitivity scales as the inverse square root of N.  However, despite about 30 years of efforts, the SQL has been surpassed only by very few experiments so far and only for small values of N, as the required highly non-classical states are typically very prone to decoherence.

In this talk I show that under certain conditions, decoherence itself can be used as a signal that allows to achieve the HL by using only an initial product state.  After exploring the effect at the example of the measurement of the length of a cavity containing two optical lattices, I put these new type of "decoherence enhanced measurements" into a broader context of
"quantum enhanced interaction measurements".  I will show in particular that the 1/N scaling does not contradict the theorem stating that the SQL cannot be beaten with a product state, and present a general theory that shows the feasibility of a much larger class of precision measurements that use only a product state and achieve the HL, even in the presence of individual decoherence of all subsystems.