September 25th, 2018 JAN HAASE ANDREA SMIRNE
Universität Ulm

JAN HAASE ’Controllable Non-Markovianity for an Spin Qubit in Diamond’

I will present a flexible scheme to realize non-Markovian dynamics of an electronic spin qubit, using a nitrogen-vacancy center in diamond where the inherent nitrogen spin serves as a regulator of the dynamics. By changing the population of the nitrogen spin, I show that we can smoothly tune the non-Markovianity of the electron spin’s dynamics and will further examine the decoherence induced by the spin bath to exclude other sources of non-Markovianity.

To keep the amount of necessary measurement data at a minimum, Bayesian data analysis can be employed. Furthermore, this allows for a precise quantification of the parameters involved in the description of the dynamics and a prediction of so far unobserved data points. For that, I will develop the probabilistic model applicable to the nitrogen-vacancy center and the available measurement data.

ANDREA SMIRNE ’Quantum Coherence and Non-Classicality: A Multi-Time Approach’

Quantum coherence is a basic trait of quantum mechanics, but the presence of coherences in the quantum description of a certain phenomenon does not rule out by itself an alternative classical description of the same phenomenon. In this talk, I will discuss definite criteria to determine when and to what extent quantum coherence is univocally related with non-classicality, identifying proper conditions under which such connection can be established unambiguously. Starting from the quantum description of a physical system undergoing sequential measurements of one observable, a general property of classical stochastic processes, namely the fulfillment of the Kolmogorov conditions, is exploited to discriminate the resulting multi-time statistics from the statistics of any classical process. In this way, one can prove that a Markovian multi-time statistics obtained from repeated measurements of a nondegenerate observable cannot be accounted for by means of a classical statistics if and only if the dynamics generates coherences (with respect to the measured observable) and subsequently turns them into populations. Here, the effects of the interaction of the measured system with the environment are taken into account, so that the system is treated as an open quantum system, and the notion of Markovianity refers to the fulfillment of the quantum regression theorem. Furthermore, I will show with simple counterexamples that a direct connection between quantum coherence and non-classicality is generally absent if the statistics is non-Markovian.

Seminar, September 25, 2018, 14:30. ICFO’s Seminar Room

Hosted by Prof. Antonio Acín