Academic year 2025/2026
19/03/2026
h 16:00 Room 0M04 – Physics Department
Online: Online participation via MS Teams link
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Speaker: Matteo Carrega (CNR, SPIN, Genova)
Nonreciprocal Superconducting Transport in Hybrid Josephson junctions
Abstract
The development of quantum technologies relies on our ability to coherently control quantum systems, engineer their interactions, and understand the fundamental limits imposed by quantum mechanics. In this perspective, quantum thermodynamics provides a framework to describe energy exchange, dissipation, and nonequilibrium effects in mesoscopic devices, while quantum circuit theory offers powerful tools to model and design complex superconducting architectures.
In this talk, we will first present an overview of our theoretical works at the interface between quantum thermodynamics and superconducting quantum circuits, focusing on energy transport, dissipation, and quantum coherence phenomena.
In the second part, we will discuss a close theoretical–experimental collaboration on hybrid Josephson junctions based on high-quality InSb nanoflags. Owing to their strong spin–orbit coupling and ballistic transport, these systems constitute a versatile platform to explore nonreciprocal superconducting transport. We demonstrate supercurrent rectification — the dissipationless analog of the conventional diode — arising from the interplay of spin–orbit interaction and magnetic fields. Under microwave irradiation, the observation of half-integer Shapiro steps reveals nonequilibrium dynamics linked to a skewed current–phase relation. To directly probe this key quantity, we realized SQUID interferometers based on InSb nanoflag junctions, whose interference patterns highlight significant higher-harmonic contributions.
These results illustrate how combining theoretical insight with advanced nanofabrication enables controlled engineering of hybrid superconducting devices, paving the way toward novel functionalities for future quantum technologies.
REFERENCES
[1] B. Turini et al., Nano Letters 22, 8502 (2022).
[2] A. Lombardi et al., Commun. Materials 6, 272 (2025).
[3] A. Iorio et al., Phys. Rev. Res. 5, 033015 (2023).
[4] A. Chieppa et al., NanoLetters 39, 14412 (2025).
20/03/2026
h 11:30 Room 0M03 – Physics Department
Online: Online participation via MS Teams link
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Speaker: Niccolò Traverso Ziani (Universita` di Genova)
Quantum critical quantum batteries
Abstract
Qualitatively speaking, quantum batteries are quantum systems engineered to store and release energy on demand [1]. One‑dimensional arrays of qubits are particularly insightful in this context because they map naturally onto quantum spin chains out of equilibrium. This connection allows one to analyze their charging dynamics using concepts developed for quantum quenches [2] in a context where the quantum battery is naturally many-body.
In this talk, I will discuss how quantum phase transitions and integrability shape the performance of spin‑chain quantum batteries. I will show that in (Jordan-Wigner) integrable systems the quantum phase diagram strongly affects the stored energy at long charging times [3,4]. In contrast, when integrability is broken, even the charging power displays clear signatures of quantum criticality, exhibiting a strong enhancement around the phase transition [5].
[1] F. Campaioli, S. Gherardini, J. Q. Quach, M. Polini, and G. M. Andolina, Colloquium: Quantum batteries, Rev. Mod. Phys. 96, 031001 (2024).
[2] A. Mitra, Quantum Quench Dynamics, Annual Review of Condensed Matter Physics, Vol. 9:245-259 (2018).
[3] R. Grazi, D. Sacco Shaikh, M. Sassetti, N. Traverso Ziani, and D. Ferraro, Controlling energy storage crossing quantum phase transitions in an integrable spin quantum battery, Phys. Rev. Lett. 133, 197001 (2024).
[4] R. Grazi, F. Cavaliere, M. Sassetti, D. Ferraro, and N. T. Ziani, Charging free fermion quantum batteries, Chaos, Solitons & Fractals 196, 116383 (2025).
[5] D. Farina, M. Sassetti, V. Cataudella, D. Ferraro, and N. Traverso Ziani, Charging power enhancement at the phase transition of a non-integrable quantum battery, arXiv:2603.02819.
Past seminars
9/12/2025
h 14:00 Room 0M03 – Physics Department
Online: Online participation via MS Teams link
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Speaker: Olivier Buisson (CNRS, Neel Institute, Grenoble, France)
High fiedlity and suppression of measurement-induced state transitions in cosφ-coupling transmon readout
Abstract
The field of superconducting qubits is constantly evolving with new types of circuit and designs but, when it comes to qubit readout, the use of simple transverse linear coupling is overwhelmingly prevalent. This type of coupling intrinsically limits the readout mode’s dispersive shift and is known to cause Purcell effect. We propose here to overcome these limitations by engineering a non-linear cosϕ-coupling between the transmon qubit and a dedicated readout mode. This is based upon previous published work [1] on qubit readout with a non-perturbative cross-Kerr coupling engineered by a transmon molecule circuit. A new sample with optimized design and parameters shows a readout fidelity of 99.21% measured using a parametric amplifier and a high Quantum Non- Demolition (QND) fidelity of 97% [2]. Interestingly, these results have been achieved with 89 photons in the readout mode. In addition, we have observed suppression of measurement-induced state transitions (MIST) up to high photon counts above 300 [3]. This effect can be explained by the symmetry of the coupling, which is tunable with a magnetic field. All of these measurements were corroborated by a theoretical study, a numerical analysis of the spectra associated with the nonlinearly coupled circuit, and simulations of the corresponding classical dynamics[3].
[1] R. Dassonneville, et al., “Fast high-fidelity quantum nondemolition qubit readout via a nonperturbative cross-Kerr coupling”, Phys. Rev. X 10, 011045 (2020).
[2] C. Mori, et al., “High-power readout of a transmon qubit using a nonlinear coupling”, arXiv 2507.03642 (2025).
[3] C. Mori, et al., “Suppression of measurement-induced state transitions in cos-coupling transmon readout”, arXiv 2509.05126 (2025).
Short Bio: Olivier Buisson is a senior CNRS researcher (Directeur de Recherche) and the director of the LANEF consortium in Grenoble. His main research areas concern mesoscopic physics and superconducting qubits. Coordinator of The ANR Projet Octaves (2021-2025). In 1999, he initiated quantum dynamics in superconducting qubits and proposed Quantum ElectroDynamics experiments using superconducting qubits. He experimentally studies a large variety of superconducting qubits since then. In 1990, he was contracted to the CRTBT-CNRS lab in Grenoble and studied plasma modes in thin superconducting films. Post-doctoral research in Rio de Janeiro with Prof. Paulo Costa Ribiero and Mauro Doria on biophysics and modelization of anisotropic superconductors. PhD (1990) at the Joseph Fourier University (Grenoble) on superconducting mesoscopic disks and superconducting networks under the supervision of Bernard Pannetier.
Website: https://sqc.cnrs.fr/members