October 31 2012

21.-22.11.2012 Sabrina Maniscalco (Edinburgh) visits us

21.-22.11.2012 Sabrina Maniscalco (Edinburgh) visits us and will give a talk in the Ctrl-Q Seminar on Wednesday 21.11.2012 at 09.15 in E.04. Further information can be found here.

Non-Markovianity as a quantum probe for complex systems and quantum simulators


Quantum probes interacting with complex system can be used, under
certain conditions, to extract information on the system they are
interacting with, ideally in a nondestructive way.
In an open quantum system approach, the interaction of the qubit probe
with the complex environment gives rise to decoherence phenomena
affecting the qubit dynamics. Due to the nontrivial structure of the
environment, the qubit time evolution is usually characterised by
partial information backflow, i.e. non-Markovianity [1]. It has been
shown that non-Markovianity of a qubit probe is a useful
characterisation of the complex system dynamics in the context of
ultracold gases [2].

In the first part of the talk I will introduce a non-Markovianity
measure and, focussing on purely dephasing environments, I will
present a necessary and sufficient condition linking information
backflow with the form of the spectrum of the environment [3].

I will then use this result in the second part of the talk to discuss
two examples of non-Markovianity as a quantum probe. In the case of an
Ising model in a transverse filed coupled to a central spin
(Heppman-Coleman model), I will show that the non-Markovianity measure
vanishes exactly only at criticality, for any value of the number of
spins in the chain [3]. For the case of an ion crystal undergoing a
second order phase transition from a linear to a zigzag structure, I
will show that the non-Markovianity measure decreases monotonically as
we move towards the critical value of the trap frequency.

[1] J. Piilo, S. Maniscalco, K. Härkönen, and K. -A. Suominen, Phys.
Rev. Lett. 100, 180402 (2008); H.-P. Breuer, E.-M. Laine, and J.
Piilo, Phys. Rev. Lett. 103, 210401 (2009).

[2] P. Haikka, S. McEndoo, G. De Chiara, G. M. Palma and S.
Maniscalco, Phys. Rev. A 84, 031602 (R) (2011).

[3] P. Haikka, T. H. Johnson, and S. Maniscalco, ?Time Invariant
Discord and Non-Markovianity? arXiv:1203.6469v2.

[4] P. Haikka, J. Goold, S. McEndoo, F. Plastina, and S. Maniscalco,
Phys. Rev. A 85, 060101 (R) (2012).

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