Towards laser control of open quantum systems: memory effects

ABSTRACT

Laser control of open quantum systems (OQS) is a challenging issue as compared to its counterpart in isolated small size molecules, basically due to very large numbers of degrees of freedom to be accounted for. Such a control aims at appropriately optimising decoherence processes of a central two-level system (a given vibrational mode, for instance) towards its environmental bath (including, for instance, all other normal modes). A variety of applications could potentially be envisioned, either to preserve the central system from decaying (long duration molecular alignment or orientation, qubit decoherence protection) or, to speed up the information flow towards the bath (efficient charge or proton transfers in long chain organic compounds). Achieving such controls requires some quantitative measures of decoherence in relation with memory effects in the bath response, actually given by the degree of non-Markovianity. Characteristic decoherence rates of a Spin-Boson model are calculated using a Nakajima–Zwanzig type master equation with converged hierarchical equations of motion expansion for the memory kernel. It is shown that, by adequately tuning the two-level transition frequency through a controlled Stark shift produced by an external laser field, non-Markovianity can be enhanced in a continuous way leading to a first attempt towards the control of OQS.

KEYWORDS:

• Open quantum systems
• measure of non-Markovianity
• coherence
• Spin-Boson model
• laser control

PACS CLASSIFICATION:

• 33.80.-b
• 03.65.Yz
• 42.50.Hz

Acknowledgments

We acknowledge Prof. Christiane Koch, Prof. Christoph Meier, Prof. Arne Keller and Prof. Eric Charron for fruitful discussions. O. Atabek thanks the organisers of the Molecules and Laser Fields Symposium in honour of Andre Bandrauk, in Orford (QC), Canada, 4–7 May 2016, where part of the control scheme has been discussed. We acknowledge support from the ANR-DFG, under Grant No. ANR-15-CE30-0023-01. This work has been performed with the support of the Technische Universität München Institute for Advanced Study, funded by the German Excellence Initiative and the European Union Seventh Framework Programme under Grant Agreement No. 291763.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

ANR-DFG [grant number ANR-15-CE30-0023-01]; Technische Universität München Institute for Advanced Study, funded by the German Excellence Initiative; Deutsche Forschungsgemeinschaft [grant number ANR-15-CE30-0023-01]; European Union Seventh Framework Programme [grant number 291763].