[Workshop] Dynamics and control of classical and quantum systems

Tuesday, June 2

14:00-14:45 Registration

14:45-15:00 Introduction

15:00-16:00 Michel Brune (Laboratoire Kastler Brossel, CNRS, Collège de France) – Trapped Circular Rydberg Atoms for Quantum Simulation: Quantum Non-Demolition Detection and Optical Manipulations.

Neutral atoms trapped in optical tweezers and promoted to Rydberg states are one of the most promising platforms for quantum simulation. Due to their exceptional lifetime, circular Rydberg atoms additionally offer an unprecedented potential for being trapped over timescales of tenth of milliseconds at the temperature of 4K as compared to the 100 µs lifetime of the low angular momentum Rydberg levels involved in present neutral-atom-based quantum simulators. We will present a state-selective and non-destructive detection method for single trapped circular atoms of Rubidium in optical tweezer. The method is based on a “dual-Rydberg” architecture combining arrays of circular atoms as computational qubits and of low angular momentum ancilla Rydberg atom for readout. The scheme also allows for optically addressing individual circular atoms. We will also present another circular-atom-based quantum simulator using strontium atoms with the advantage of potential optical manipulation of the second valence electron once the first one is promoted to a circular state.

16:00-16:30 Coffee break

16:30 – 17:30 Nicolas Petit (Mines Paris – PSL, Centre Automatique et Systèmes) – Real-time estimation of kinematic variables for advanced mechanical systems

This presentation will highlight innovative uses of miniature sensors for estimating kinematic variables. The work presented applies to both rigid and flexible bodies, and is implemented in closed-loop control for several autonomous or semi-autonomous systems in robotics, urban mobility, and aerodynamics.

The talk will specifically address fundamental questions regarding the synthesis of asymptotic observers for reconstructing the attitudes of multi-articulated bodies, as well as velocity estimation for high-speed symmetric aerodynamic bodies.

17:30 – 18:30 Mazyar Mirrahimi (Inria, Quantic Team) – Biased-noise qubits for fault-tolerant quantum computation

The theory of quantum error correction and fault-tolerant computation provides a route towards handling the noise in quantum processors but comes at the expense of  significantly  increased complexity in their physical implementation. One promising approach towards such hardware-efficient fault-tolerant processors is to take advantage of the noise bias that is either naturally present in some physical platforms or is engineered through a built-in protection against one type of noise. After an introduction to such biased-noise qubits, I will review various approaches to operate them and benefit from this noise-bias to reduce the complexity of error correction. 

19:00-21:00 Welcome cocktail

Wednesday, June 3

9:00-10:00 Philippe Campagne-Ibarcq (Inria, Quantic Team) – Challenges and progress toward dynamical stabilization of advanced bosonic qubits

Over the past decade, dynamical stabilization of bosonic qubits has emerged as a promising approach for hardware-efficient protection of quantum information. However, applying these techniques to more complex encodings than the Schrodinger cat code requires exquisite control of high-order wave mixing processes in order to enable specific multiphotonic dissipation channels while avoiding unintended non-linear interactions.In this talk I will present how methods originally designed for two-component cat qubits can be extended to stabilize multi-component cat states and GKP states. I will then detail pitfalls and recent progress toward the experimental implementation of these ideas.

10:00-10:30 Coffee break

10:30-11:30  John Gough (Aberystwyth University) – Quantum Feedback Networks: Markovian and Non-Markovian Features

We review the theory of quantum feedback networks and show how it gives a framework for a system theoretic description applicable to quantum engineering. The network rules are presented along with an overview of feedback based control. We will also discuss recent advances in modelling non-Markovian behaviour (joint work with N. Amini, H. Ding, and G. Zhang).

11:30-12:30 Audrey Bienfait (École Normale Supérieure de Lyon, CNRS) – Electronic spins for quantum memories

Among platforms for storing quantum states in the microwave domain, solid state spin ensembles addressed via superconducting circuits stand out for their multimodal storage capability and the second-long coherence time when operated at clock transitions.Successful implementation of a practical memory scheme requires several keys features, such as the ability to tune on-demand the frequency and the bandwidth of the resonator. In this talk, we will present a superconducting circuit architecture accomplishing both, allowing strong coupling to an ensemble of bismuth dopants in silicon. We also explore strategies for reaching the near unity cooperativity regime that is key for high-storage efficiency.

12:30-14:00 Lunch

14:00-15:00 Karine Beauchard  (École Normale Supérieure de Rennes) – Small time control of the bilinear Schrödinger equation.

We consider Schrödinger PDEs, posed on a boundaryless Riemannian manifold M, with bilinear control. We propose a new method to prove the global approximate controllability. Contrarily to previous ones, it works in arbitrarily small time and does not require a discrete spectrum. This approach consists in controlling separately the radial part and the angular part of the wavefunction thanks to the control of the group of diffeomorphisms of M and the control of phases. Surprisingly, the control of phase implies the control of diffeomorphisms. The proofs rely on Lie bracket techniques. We develop this approach on two examples of Schrödinger equations, posed on the d-dimensional torus or Euclidian space.

15:00-16:00  Zaki Leghtas (Mines Paris PSL, Quantic Team) – Encoding Quantum information in Dynamical Superconducting Circuits

Superconducting circuits are macroscopic arrangements of pieces of superconducting material, assembled in the form of metallic wires and plates. Their state is described by collective degrees of freedom such as voltages and currents, that behave quantum mechanically. On the other hand, the area of mathematics known as “dynamical systems”, studies the time evolution and stability of driven systems. In this talk, I will show how we encode quantum information in driven superconducting circuits, and the benefits of this technique for the emergence of quantum technologies.

16:00-16:30 Coffee break

16:30-17:30 Bernhard Maschke (Université Claude Bernard Lyon 1) – Port-Hamiltonian formulations of open quantum systems

Port-Hamiltonian systems are a formulation the dynamics of open physical systems using an extension of Hamiltonian systems obtained by augmenting the state space with pairs of conjugated external variables, called port-variables and defining its dynamics with respect to a Dirac structure extending their Poisson bracket. It has been instrumental for the derivation of energy-aware nonlinear control of multi-physical systems. In this talk, we shall present some preliminary work on their application to open quantum systems. We shall first consider quantum circuits and show how their dynamics may be formulated on Poisson structure and Dirac structure derived from the topology of the circuits and how port-variables may be introduced. Second, we shall present a recent extension of port-Hamiltonian systems to dissipative systems which are defined with respect to a 4-contravariant bracket which  extends Poisson bracket in such a way to encompass the entropy balance. And we shall investigate how this may be applied to the Lindblad equations and relate it to their metriplectic formulation.

Thursday, June 4th

9:00-10:00 Patrice Bertet (CEA iramis) – Quantum control of individual spins in solids

Spins in solids are interesting qubit candidates for quantum technologies, owing to their long coherence times. These applications require novel methods to detect and address them coherently. I will describe methods developed recently in our laboratory to measure and control individual electron and nuclear spins in solids at 10mK. Individual electron spins are coupled to a superconducting microwave resonator to enhance their radiative relaxation. The spontaneously emitted microwave photons are detected by a microwave photon counter based on a superconducting transmon qubit. Individual nuclear spins are readout and driven via their hyperfine coupling to the electron spin.

10:00-10:30 Coffee break

10:30-11:30 Michel H. Devoret (Google Quantum AI, University of California, Santa Barbara) – Introduction to quantum superconducting circuits control questions

Forty years ago, a fundamental inquiry into the possible quantum-ness of macroscopic variables—currents and voltages—launched the field of quantum superconducting circuits. The foundational experiments at Berkeley that first uncovered macroscopic quantum tunneling and energy quantization led progressively to the current era of “artificial atoms.” Unlike natural atoms, these engineered systems allow the tailoring of energy levels and matrix elements by adjustments of dimensional fabrication parameters. The ground and first excited states of these circuits are now utilized as qubits in processors exceeding 100 qubits, capable of executing quantum algorithms that challenge classical computation. Adaptative calibration and error correction of large-scale quantum superconducting circuits pose pressing questions to the theory of quantum control.

11:30-12:30 Christiane Koch (Freie Universität Berlin) – Quantum control and engineering with two-body interactions

Quantum control protocols often rely on multi-body interactions that must be engineered through sequences of two-body couplings. This overhead can lead to significant hardware complexity or, in the worst case, undermine a protocol’s viability. In this talk, I will illustrate these challenges using examples from dissipative state preparation [1,2] and parity measurements in continuous quantum error correction [3]. Conversely, physical qubits are typically embedded in multi-level systems, and  recent developments have begun to leverage these larger structures as a resource, notably in the construction of erasure qubits and bosonic codes. Taken together, these observations suggest a need to rethink what constitutes a “free” physical resource versus an “added” cost, thereby redefining the optimization problem of implementing practical quantum computing.

[1] Langbehn et al. PRX Quantum 5, 030301 (2024)

[2] Langbehn, Mouloudakis et al. arXiv:2506.11964

[3] Halaski & Koch, arXiv:2603.02106

12:30-14:00 Lunch

14:00-15:00 Madalin Guta (University of Nottingham) – Optimal estimation of quantum Markov chains using coherent output post processing and displaced-null measurements

In this presentation I will discuss the problem of estimating dynamical parameters of a quantum Markov chain, in particular how to achieve the quantum Cramer-Rao bound using sequential measurements and computationally efficient estimators. The key tool will be the use of a coherent quantum absorber which transforms the problem into a simpler one pertaining to a system with a pure stationary state at a reference parameter value. Motivated by the proposal in [1] I will consider counting output measurements and show how the statistics of the counts can be used to compute a simple, asymptotically optimal estimator of the unknown parameter. For this, I will introduce translationally invariant modes (TIMs) of the output and show that these modes are Gaussian in the limit of large times and capture the entire quantum Fisher information of the output. Moreover, the counting measurement provides an effective joint measurement of the TIMs number operators. The unknown parameter is estimated using a two stage estimation procedure. A rough estimator is first computed using a simple measurement, and is used to set the absorber parameter. Due to non-identifiability issues of the counting measurement the reference parameter needs to be shifted away from the initial rough estimator, as shown in the displaced-null measurements theory [2]. Finally, an optimal estimator is computed in terms of the total number of excitations of the TIMs, avoiding the need for expensive estimation procedures. Details can be found in [3].

[1] D. Yang, S. F. Huelga, and M. B. Plenio PRX Quantum 13, 031012 (2023)

[2] F. Girotti, A. Godley and M. Guta, J. Phys. A 57 245304 (2024)

[3] F. Girotti, A. Godley and M. Guta, Quantum 9, 1835 (2025)

15:00-16:00  Jean-Michel Coron (Sorbonne Université, laboratoire Jacques-Louis Lions) – Control and stabilization of partial differential equations systems with essential quadratic terms

Our focus is on exploring the controllability and asymptotic stabilization of nonlinear partial differential equations in which the quadratic term plays a crucial role. In these cases, both controllability and asymptotic stabilization are not achievable without these quadratic terms. This includes Schrödinger equations, the viscous Burgers equation, Korteweg-de Vries equations and a Saint-Venant (shallow-water) equation. Regarding controllability, we demonstrate that controlling such systems may require more time than anticipated based on the speed of propagation. For the stabilization aspect, we introduce methodologies for designing stabilizing feedback laws. Additionally, we present unsolved challenges in these two domains.

16:00-16:30 Coffee break

16:30-17:30 Jérémie Guillaud (Alice&Bob) – Fault-tolerant quantum computing with dissipative cat qubits: recent theoretical and experimental progress.

Dissipative cat qubits, stabilised in a superconducting circuit architecture by engineered two-photon dissipation, exhibit a very large noise bias (up to several orders of magnitude between bit-flip and phase-flip error rates). I this talk, I will review recent theoretical work that proposes to leverage this noise bias to design efficient phase-flip error correcting codes, or magic state distillation factories. I will then present some results on recent experimental progress towards building a logical (error corrected) qubit using dissipative cat qubits.

18:30-21:00 Cocktail dinner

Friday, June 5

9:00-10:00 Rémi Robin (Mines Paris PSL, Quantic Team) – Structure-Preserving Numerical Methods for the Lindblad Master Equation

This talk focuses on the numerical simulation of open quantum systems described by the Gorini–Kossakowski–Sudarshan–Lindblad (GKSL) master equation, with an emphasis on systems composed of a few bosonic modes. We analyze the errors introduced by the discretization of the infinite-dimensional Hilbert space, specifically when using the truncated Fock basis, and examine the effects of time discretization, revealing a CFL-like stability condition that limits the time step relative to the spatial truncation. To circumvent this constraint, we introduce novel integration schemes that preserve the structure of the quantum channel evolution while avoiding the CFL restriction. We also propose new algorithms for steady-state and low-lying spectrum computation, which yield substantial computational gains for large bosonic systems. Part of this work is in collaboration with G. Beugnot, P.-L. Etienney, P. Gregory, P. Rouchon, L.-A. Sellem and A. Tilloy.

10:00-10:30 Coffee break

10:30-11:30 Alain Sarlette  (Inria, Quantic Team) – Solving k-SAT problems on quantum machines with Zeno dragging

The k-SAT is a prototypical NP-complete problem. For these, standard quantum computing promises just a quadratic improvement on the exponential runtime of naive exploration. Quantum annealing can also look for a solution, with runtime

depending on a not-too-well-characterized, but exponentially small, spectral gap. We will first revise these notions, including earlier improvements which go further than naive exploration, thanks to a kind of feedback action. We will then present an alternative approach which uses Zeno dragging. Its open-loop performance (Lindblad type equaton) seems related to quantum annealing, but with a more straightforward bound involving the spectral gap. Including feedback improves the runtime and, unlike in other schemes, should also allow to correct online a particular type of quantum hardware errors. This is joint work with the group of Birgitta Whaley at U.Berkeley.

11:30-12:30 Samuel Deléglise (Laboratoire Kastler Brossel) – Probing the quantum motion of a MHz mechanical resonator with a resonant rf-fluxonium

MHz-frequency mechanical resonators are powerful platforms for quantum technologies and tests of fundamental physics, yet efficient control remains challenging due to their low energy scales and the difficulty of coupling them to well-controlled quantum systems at matching frequencies. Here we demonstrate high-fidelity, repeated interactions between a 4-MHz suspended silicon nitride membrane resonator and a resonant superconducting fluxonium qubit. Over the membrane’s 6-ms lifetime, the two systems coherently interact more than 300 times. Using the qubit as a stroboscopic spectrometer, we reconstruct the membrane’s position-noise spectrum, revealing its thermal occupation, qubit-induced back-action, and the characteristic emission–absorption imbalance. This asymmetry directly reflects the non-commutation of phonon ladder operators, demonstrating the quantum character of the long-lived, massive mode. Because the predicted Diósi–Penrose collapse time is comparable to the membrane’s decoherence time, our platform operates in a regime suitable for future interferometric tests of gravity-induced wavefunction collapse.

12:30-14:00 Farewell lunch