Quantum optimal control theory

Building a working quantum computer requires ultra-precise control of quantum dynamics, with errors below the so-called fault-tolerance threshold (a few per mille at most). In a real-world environment, this amounts to overcoming enormous practical challenges, because laboratory systems only allow for imperfect implementation of theoretical schemes. Optimal control theory (OCT) is a set of methods developed to design systems that can achieve a desired behavior with limited resources and the biggest possible probability of success. Its applications cover such diverse fields as aerodynamics and ultrafast laser-assisted chemical reactions.

The basic idea of OCT is illustrated in the picture to the right: when you want to perform a non-trivial process, you can't get it right the first time - but retrying helps improve. Once you know your stuff, you may be able to do pretty amazing things, though.

In the context of QIPC, OCT has already been shown to yield improvements for quantum devices that can take performance beyond the otherwise unattainable fault-tolerance threshold. The first goal of our research is to extend the applicability of OCT to a broader range of physical implementations of QIPC than already demonstrated. Several open questions concern the robustness of the approach in the presence of noise, dissipation and other imperfections. Thus a second goal is the development of techniques to deal with those issues that limit the applicability of the method in several of the physical scenarios currently considered as candidate implementations for quantum information processing.