Optimal control of complex quantum systems

Friday 6th of May
Versione stampabile

Venue: Room A204, Polo Scientifico e Tecnologico Fabio Ferrari - (Povo 1) Via Sommarive,5

At: 14.30

  • Dott. Tommaso Calarco - Institute for Complex Quantum Systems University of Ulm, Germany

"Optimal control of complex quantum systems”


The control of quantum states is essential both for fundamental investigations and for technological applications of quantum physics. In quantum few-body systems, decoherence arising from interaction with the environment hinders the realization of desired processes. In quantum many-body systems, complexity of their dynamics further makes state preparation via external manipulation highly non-trivial. An effective strategy to counter these effects is offered by quantum optimal control theory, exploiting quantum coherence to dynamically reach a desired goal with high accuracy even under limitations on resources such as time, bandwidth, and precision. In this talk I will:
- introduce the quantum optimal control method we developed to this aim, the CRAB (Chopped Random Basis) algorithm, which is to date the only method that allows to perform optimal control of quantum many-body systems;
- present experimental results obtained via its application to various physical systems, from quantum logical operations in solid-state quantum optics to quantum criticality in ultra-cold atoms, both in open-loop and in closed-loop feedback scenarios, with applications ranging from quantum interferometry with Bose-Einstein condensates on atom chips to magnetic field sensing in diamond NV centers and to the preparation of optical-lattice quantum registers for quantum simulation;
- use these examples to illustrate the quantum speed limit, i.e. the maximum speed achievable for a given quantum transformation, and describe related effects of nonlinearity due to inter-particle interactions and more in general to dynamical complexity;
- propose a way to characterise the latter in an information-theoretical fashion by the bandwidth of the optimized control pulses, as well as a conjecture about using this method for discrimination between different levels of complexity in quantum many-body systems.

Tommaso Calarco is since September 2007 a Full Professor for Quantum Information Processing at the University of Ulm, Germany. He became Institute Director in June 2011 and since October 2014, after the institute was renamed, he holds the position of Director at the Institute for Complex Quantum Systems. Since January 2014 he is Director of IQST (Center for Complex Quantum Science and Technology). He is the Chairman of the European Quantum Technologies Scientific Advisory Board and one of the authors of the "Quantum Manifesto” (qurope.eu/manifesto).