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## Physics Colloquium: Quantum Metrology in Open Quantum Systems, 8 May 2013

Start:
May 08, 2013 04:00 PM

End:
May 08, 2013 06:00 PM

Location: Harrie Massey LT

#### Prof. Susana Huelga (University of Ulm)

#### Physics Colloquium: Quantum Metrology in Open Quantum Systems

#### Date:

Weds 8 May 2013

#### Time:

4.00pm, followed by a drinks reception.

#### Location:

The Harrie Massey Lecture Theatre (UCL)

#### Abstract

How small can error bars become? Quantum mechanics sets a lower bound to the ultimate resolution in a parameter estimation problem. This so called Heisenberg limit can be achieved when genuinely quantum properties (entanglement) are exploited for state preparation and measurement. Quantum correlations, though, are easily degradable in the presence of environmental noise. We will discuss the problem of phase estimation, of direct relevance in precision spectroscopy, in an open system formulation. We will show that in the presence of purely Markovian noise, the advantage of using maximally entangled states is lost and standard scaling, as set by the central limit theorem, is restored. However, when the noise displays memory effects the situation is very different. Using an exactly solvable model of a physically realistic finite band-width dephasing environment, we demonstrate that the ensuing non-Markovian dynamics enables quantum correlated states to outperform metrological strategies based on uncorrelated states using otherwise identical resources. We show that this conclusion is a direct result of the coherent dynamics of the global state of the system and environment and therefore the obtained scaling with the number of particles, which surpasses the standard quantum limit but does not achieve Heisenberg resolution, possesses general validity that goes beyond specific models.

#### Biography:

Professor Susana Huelga

University of Ulm, Institute of Theoretical Physics

Susana Huelga joined the Institute of Theoretical Physics of Ulm University in October 2009 after more than 13 years working in England, where she led the Quantum Information group at the University of Hertfordshire following postdoctoral appointments at Oxford and Imperial College London. She has experience in theoretical quantum optics and quantum information, her research focusing in analysing the interplay between coherent and dissipative interactions and the persistence of quantum effects in noisy environments. She has contributed towards the development of quantum metrology and has recently pioneered work in the newly developed field of quantum biology.