Guéry-Odelin group
Université Toulouse III – Paul Sabatier, Toulouse, France
- Tracked papers
- 36 (2009–2026)
Topics
The most frequent field-map topics among the PI' tracked papers.
Recent papers
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Cooperative control and geometric amplification in dissipative quantum systems
Abstract
In the control of dissipative quantum systems, the slow relaxation modes usually set the ultimate manipulation timescale. Here we show that this apparent bottleneck can be bypassed: dissipation itself becomes a control resource when fast relaxation channels are deliberately exploited. We demonstrate this mechanism for a qubit subject to non-unital and anisotropic Bloch relaxation. A short coherent pulse first reorients the Bloch vector onto a fast dissipative eigendirection; the subsequent free relaxation then carries the state close to the target, with at most one final corrective pulse. The resulting bang-drift-bang strategy is cooperative: coherent control selects the dissipative channel, while the bath performs most of the transfer. For axial targets, we obtain a closed-form speedup over passive relaxation by a factor of order $κ=T_1/T_2\gg1$. For out-of-equilibrium non-axial targets, an additional off-axis interception mechanism provides a further geometric amplification, allowing the hitting-time speedup, still normalized to the axial passive-reset time, to exceed the axial $κξ$ benchmark by an extra factor of four to five. The mechanism therefore directly connects to standard Bloch-vector qubit platforms, including magnetic-resonance spins, nitrogen-vacancy centers, and superconducting circuits, with potential relevance for quantum-control and fast-reset protocols.
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Fast quantum-state transfer in Su-Schrieffer-Heeger chains beyond the noninteracting regime
Abstract
Shortcuts to adiabaticity have made topological edge-state transfer fast in the single-particle regime, but their extension to interacting systems is obstructed by nonlinear phase accumulation. We show that this obstruction can be removed in Su-Schrieffer-Heeger chains by making the next-nearest-neighbor shortcut hopping phase tunable. In the mean-field regime, this yields an exact nonlinear shortcut: one hopping quadrature keeps the state on the instantaneous dark-state trajectory, while the orthogonal quadrature cancels the interaction-induced self-phase modulation. The resulting protocol is nonperturbative in the mean-field interaction strength. When applied to the full Bose-Hubbard dynamics, the mean-field shortcut remains beneficial but saturates below unit fidelity, exposing genuinely many-body corrections beyond the product-state picture. We then optimize the transfer directly in the many-body Hilbert space and find that complex, phase-tunable next-nearest-neighbor hoppings recover near-perfect fidelity. Our results show that hopping phases are not merely a technical refinement, but a key control resource for fast and high-fidelity transport in interacting topological systems.
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Quantum Geometric Limits for Non-Abelian Holonomies
Abstract
Stokes' theorem turns Abelian Berry phases into curvature fluxes, whereas path ordering precludes such a simple formula for non-Abelian holonomies. We show that a quantitative form of this intuition survives: arbitrary Wilczek--Zee holonomies obey a universal quantum geometric limit~(QGL), in which the holonomy magnitude is bounded by a surface integral of the non-Abelian curvature norm. Recasting holonomic evolution as an effective Stokes--Schrödinger dynamics driven by transported curvature, we identify the QGL as the geometric counterpart of conventional quantum speed limits, with a time-integrated generator norm replaced by a surface-integrated curvature cost. The induced contour--surface variational problem is governed by a non-Abelian Lorentz force, which we address with a brachistochrone ansatz of curvature-weighted geodesics. Applied to an SU(2) tripod dark subspace, near-optimal protocols spontaneously align the transported curvature along a single Lie-algebra direction, effectively taming non-Abelianity.
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Floquet engineering of tight-binding Hamiltonians in momentum space lattices
Abstract
Quantum simulation with ultracold atoms provides a versatile platform to emulate condensed-matter models. In particular, momentum-space lattices enable the realization of programmable tight-binding Hamiltonians. Here, we generalize this approach by exploiting quantum resonances of a periodically driven (shaken) rotor within the Floquet framework. Using first-order time-dependent perturbation theory, we derive analytical relations between the lattice modulation and the effective tight-binding parameters, and identify explicit solutions for several resonances. We further apply optimal-control techniques to enhance the multi-period Floquet fidelity and extend the accessible parameter regimes. Experimentally, we implement this scheme with a Bose-Einstein condensate of rubidium-87 atoms in a dynamically modulated optical lattice. We demonstrate the simulation of the Rice-Mele model, including band-structure measurements and topological edge states, as well as momentum Bloch oscillations, and superlattice configurations with controlled periodicity. Our results establish quantum resonances as a powerful resource for Floquet engineering of tight-binding models in momentum space.
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Time-optimal force sensing with ultracold atoms
Abstract
We develop a time-optimal approach to force sensing using a Bose-Einstein condensate in a shaken optical lattice. Optimal control protocols are derived from a Fisher information framework and yield optimal dynamics that spontaneously organize in intereferometer-like structures, where multiple interferences combine to maximize sensitivity. We analyse how measurement precision scales with control time and how the finite momentum dispersion of the condensate changes the optimal dynamics, observing an abrupt change of conformation from single- to double-folded interference structures for robust controls. The protocols are implemented experimentally for cold atoms subjected to inertial and magnetic forces, demonstrating high sensitivity and robustness. Our approach establishes a general route to time-optimal quantum sensing beyond standard interferometric architectures, applcable across all quantum platforms.
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Optimal control over the full counting statistics in a non-adiabatic pump
Abstract
We introduce a systematic procedure based on optimal control theory to address the full counting statistics of particle transport in a stochastic system. Our approach enhances the performance of a Thouless pump in the non-adiabatic regime by simultaneously optimizing the average pumping rate while minimizing noise. We demonstrate our optimization procedure on a paradigmatic model for the electronic transport through a quantum dot, both in the limit of vanishing Coulomb interaction and in the interacting regime. Our method enables independent control of the moments associated with charge and spin transfer, allowing for the enhancement of spin current with minimal charge current or the independent tuning of spin and charge fluctuations. These results underscore the versatility of our approach, which can be applied to a broad class of stochastic systems.
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Unitary Transformations using Robust Optimal Control on a Cold Atom Qudit
Abstract
In this paper, we design and experimentally implement various robust quantum unitary transformations (gates) acting on $d$-dimensional vectors (qudits) by tuning a single control parameter using optimal control theory. The quantum state is represented by the momentum components of a Bose-Einstein condensate (BEC) placed in an optical lattice, with the lattice position varying over a fixed duration serving as the control parameter. To evaluate the quality of these transformations, we employ standard quantum process tomography. In addition, we show how controlled unitary transformations can be used to extend state stabilization to global stabilization within a controlled vector subspace. Finally, we apply them to state tomography, showing how the information about the relative phase between distant momentum components can be extracted by inducing an interference process.
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Approaching the Quantum Speed Limit in Quantum Gates with Geometric Control
Abstract
We present a geometric optimization method for implementing quantum gates by optimally controlling the Hamiltonian parameters, with the goal of approaching the Mandelstam-Tamm Quantum Speed Limit (MT-QSL). Achieving this bound requires satisfying precise geometric conditions that govern the evolution of quantum states. We extend this geometric framework to quantum unitary operators in arbitrary dimensions and analyze the conditions necessary for saturation of the bound. Additionally, we show that the quantum brachistochrone, when generalized to operators, does not, in general, saturate the MT-QSL bound. Finally, we propose a systematic optimal control strategy based on geometric principles to approach the quantum speed limit for unitary driving. We illustrate this optimization method on a set of four well-known two-qubit quantum gates. Our procedure significantly reduces the deviation from the optimal quantum speed limit while preserving high quantum fidelity.
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Optimal control of a Bose-Eintein Condensate in an optical lattice: The non-linear and two-dimensional cases
Abstract
We numerically study the optimal control of an atomic Bose-Einstein condensate in an optical lattice. We present two generalizations of the gradient-based algorithm, GRAPE, in the non-linear case and for a two-dimensional lattice. We show how to construct such algorithms from Pontryagin's maximum principle. A wide variety of target states can be achieved with high precision by varying only the laser phases setting the lattice position. We discuss the physical relevance of the different results and the future directions of this work.
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Optimal Floquet Engineering for Large Scale Atom Interferometers
Abstract
The effective control of atomic coherence with cold atoms has made atom interferometry an essential tool for quantum sensors and precision measurements. The performance of these interferometers is closely related to the operation of large wave packet separations. We present here a novel approach for atomic beam splitters based on the stroboscopic stabilization of quantum states in an accelerated optical lattice. The corresponding Floquet state is generated by optimal control protocols. In this way, we demonstrate an unprecedented Large Momentum Transfer (LMT) interferometer, with a momentum separation of 600 photon recoils ($600\hbar k$) between its two arms. Each LMT beam splitter is realized in a remarkably short time (2 ms) and is highly robust against the initial velocity dispersion of the wave packet and lattice depth fluctuations. Our study shows that Floquet engineering is a promising tool for exploring new frontiers in quantum physics at large scales, with applications in quantum sensing and testing fundamental physics.