New approaches to control open quantum systems

New approaches to control open quantum systems

Date limite de candidature : 21/06/2023
Date de début : 01/10/2023
Date de fin : 01/10/2024

Pôle : Automatique et systèmes
Type de poste : Post-Doc ou ATER
Contact : Nina Amini (

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New approaches to control open quantum systems

This proposal will focus on problems in control and observation for quantum systems. The
project is within the project ANRQ-COAST (estimation and control of open quantum systems).
In the last three decades, the growing interest in quantum technology initiated the development
of a decent quantum control theory. Measuring and controlling quantum systems are experimen-
tally feasible as it has been proven lately in the pioneering work [15]. Automatic control designs
turn out to be promising for quantum computation. The main focus is to apply quantum feed-
back control in order to manipulate the performance of open quantum systems interacting with
an environment with subsequent loss of information. Classical control theory is not immediately
applicable to quantum systems. Several open problems regarding optimality, robustness, and
best design methods for dealing with generic quantum models can be addressed combined with a
concrete implementation.
The main axes of future research are summarized as follows.
PDE approach: A useful approach to describe concrete physical evolution is provided
by the theory of partial differential equations (PDEs), for instance stochastic Schrödinger
equation [2]. For such systems, continuous observed outputs might be feasible leading to
the question of output feedback control and stabilization. Such designs have appeared
for instance in [3] but for the finite-dimensional realization of such systems. However,
taking the continuum limit of the model, we obtain PDEs not depending on the number
of states leading to scalability and a uniform approach. A PDE approach would lead to
more scalable controllers as the high dimensionality of such systems complicates the design.
Single and interconnected PDE models of quantum systems require the construction of
a physically meaningful theory for efficient and robust control and estimation strategies.
Generic strategies based on Lyapunov theory for interconnected PDEs have appeared for
instance in [7, 8, 9]. It is required to adapt similar approaches in the context of stochastic
PDEs describing the evolution of quantum systems taking into account the specificities
and limitations occurring in such systems. Such methodologies have not been sufficiently
explored yet.
Mean-field games in quantum control: Mean-field games [11] have physical realizations
in quantum systems, see e.g. [10, 4] for the propagation of chaos. Classical mean-field games
are characterized by the Hamilton-Jacobi-Bellman equation (for the value function u of each
player) combined with the Fokker-Planck equation (for the density function p of the players).
Nevertheless, it becomes nontrivial to describe the distribution of the quantum particles as
it is supported on the set of density matrices Sd which is Lebesgue negligible. Therefore, we
need to identify its support and find a suitable reference measure on its support to establish
the corresponding Fokker-Planck equation. Inspired by [18], we start by considering the
mean-field qubit system, where we may write explicitly the dynamics of each component.
For this system, we aim to show the well-posedness of the Hamilton-Jacobi-Bellman and
Fokker-Planck equations and to derive the propagation of chaos. Furthermore, it is mean-
ingful to investigate state reconstruction problems in the context of inverse problems for
PDEs, we may reconstruct the unknown dynamics of the aggregate distribution of the par-
ticles (Fokker-Planck equation) by observing the optimal control problem of an individual
(Hamilton-Jacobi-Bellman equation).

Nonlinear systems: Quantum feedback control when the controller is a quantum system is
treated for linear systems, see [14]. There still remains an optimal design. There are various
problems that should be addressed for quantum feedback control including robust stability
and feedback control design for nonlinear quantum systems (see e.g., [5, 12, 13]), which
capture better the dynamics of such systems. Most of the previous works study the case
when the controller is a classical controller and the controller depends on the measurements
which perturb the quantum system dynamics. For the latter case, we will study the model
reduction strategies to make a classical controller realistic in practice. For the quantum
controller, theories as well as constructive algorithmic realizations for both control and
observer problems of high-dimensional nonlinear systems will be established preserving also
the so-called physical relizability conditions. A classical Luenberger approach was extended
for instance to linear quantum systems. It would be of interest to investigate such extension
to nonlinear systems.
Contact: Nina Amini, Gaoyue Guo, Paolo Mason.
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stochastic differential master equation describing a monitored qubit, Journal of Mathematical
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