Work Package 1: Robust Methods for Quantum Technologies & Photonics


Lead beneficiary:

Foundation of Theoretical and Computational Physics and Astrophysics-University of Sofia (TCPA)



Université de Bourgogne (UBT)
University of Oxford (UOXF)
Technical University of Darmstadt (TUDA)
University of Sussex (UoS)


Many quantum technologies rely on controlling the internal and external states of light and matter with high precision, either at the single-particle level or for ensembles. A simple example is to drive a quantum system from an initial state to an arbitrary target state, in a robust, efficient, i.e. with high fidelity, and fast way. However, we require truly robust methods to cope with imperfections in the experimental parameters. Adiabatic passage techniques provide such robustness. The usual restriction of long interaction times does not apply to parallel adiabatic passage, which uses designed fast adiabatic paths while preserving the robustness. The potential of this unique method developed by UBT has been investigated recently [Phys. Rev. A 80, 043408 (2009); ibid 84, 013423 (2011)], and UOXF / TCPA jointly developed controlled shaping of a single photon produced from atom-cavity systems [New J. Phys. 12, 063024 (2010); ibid 13, 103036 (2011)].

Another robust and accurate tool for quantum state manipulation is the technique of composite pulses developed originally in NMR. It uses a sequence of pulses with suitably chosen phases to control the states of a quantum system in a desired manner. The method greatly enhances the robustness of quantum bit (qubit) manipulations. The adaptation of the method to quantum technology has been pioneered by partner TCPA [Phys. Rev. A 83, 053420(2011)], combined with adiabatic techniques (composite adiabatic passage) in a joint work with partner UBT [Phys. Rev. Lett. 106, 233001 (2011)] and experimentally demonstrated by partner TUDA in a joint work [Phys. Rev. A 88, 063406 (2013)]. TCPA and TUDA recently also developed and implemented universal composite pulses, which compensate unknown errors in any experimental parameter [Phys. Rev. Lett. 113, 043001 (2014)]. Moreover, partner UBT developed robust control by a single-shot shaped field, which speeds up the robust dynamics [Phys. Rev. Lett. 111, 050404 (2013); J. Phys. B 48, 174007 (2015)]. As complementary tools, original methods of optimal control have been developed at UB [B. Bonnard and D. Sugny, AIMS: Applied mathematics 5 (2012)].

We will develop robust and fast strategies for complex quantum control, based on the original combination of composite pulses, shaped pulses and optimal control (UBT, TCPA). These crucial tools will enable technologies for the tasks in WPs 2-4: UOXF, TCPA, UBT will develop theoretical models for coherent light-matter interfaces in CQED and in dense media, for robust trapping of cold atoms, for photonics and for plasmonics at the nanoscale. These concepts will be experimentally implemented in WP2 (UOXF, UoS), in WP3 (TUDA) and in WP4 (UBE, UTT, EPFL) using technologies developed locally and by the industrial partners (QuB, QuT, TP and AU).

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