# QUANTUM FEEDBACK CONTROL FOR CONTINUOUS-VARIABLE QUANTUM SYSTEMS

Topic: quantum systems | All

Séance du jeudi 16 avril 2015, Salle L 218, 14h.

Marco Genomi, University College London

I will review some recent results obtained by applying quantum feedback control protocols to continuous variable (CV) quantum systems. I will start by showing the Gaussian formalism able to describe continuous quantum filtering (monitoring), via general-dyne detection for CV quantum systems described by quadratic Hamiltonians and linearly coupled to a Markovian environment. Then I will present the ultimate bounds on quantum squeezing and entanglement, the paradigmatic resources for CV quantum information, achievable via quantum filtering and feedback strategies, given a certain dissipative dynamics [1]. The usefulness of these bounds will be shown with some examples, in particular for the case of a quantum oscillator interacting with a non-zero temperature Markovian bath [2,3].

Next, I will present some applications of continuous-monitoring and feedback to quantum opto-mechanical systems. I will start by showing the usefulness of quantum filtering for steady-state cooling and squeezing generation of a levitated dielectric nanosphere trapped in an optical cavity [4].

Finally I will move to a hybrid setup, where a mechanical oscillator interacts with a two-level system (qubit): I will show how repeated measurements (at discrete time steps) and feedback operations on the qubit can induce a dynamics that prepares the mechanical oscillator in a squeezed steady state [5].

Marco Genomi, University College London

I will review some recent results obtained by applying quantum feedback control protocols to continuous variable (CV) quantum systems. I will start by showing the Gaussian formalism able to describe continuous quantum filtering (monitoring), via general-dyne detection for CV quantum systems described by quadratic Hamiltonians and linearly coupled to a Markovian environment. Then I will present the ultimate bounds on quantum squeezing and entanglement, the paradigmatic resources for CV quantum information, achievable via quantum filtering and feedback strategies, given a certain dissipative dynamics [1]. The usefulness of these bounds will be shown with some examples, in particular for the case of a quantum oscillator interacting with a non-zero temperature Markovian bath [2,3].

Next, I will present some applications of continuous-monitoring and feedback to quantum opto-mechanical systems. I will start by showing the usefulness of quantum filtering for steady-state cooling and squeezing generation of a levitated dielectric nanosphere trapped in an optical cavity [4].

Finally I will move to a hybrid setup, where a mechanical oscillator interacts with a two-level system (qubit): I will show how repeated measurements (at discrete time steps) and feedback operations on the qubit can induce a dynamics that prepares the mechanical oscillator in a squeezed steady state [5].