Since the beginning of the project in December 2020, and despite the pandemic that disrupted lab organisation we have:
1.Built a new lab space at ENS Paris to host the experiments from project Q-feedback and equipped a He3 dilution cryostat with necessary RF and DC electronic devices now intensively used for the experimental tasks of Q-feedback.
2.Hired a team of scientists: We have hired a team 5+2 PhD students and 2+2 postdocs working on various aspects of Q-feedback.
3.Contributed with the control-theoretical methods (WP1) developed in Q-feedback to key experiments: two conducted by Z. Leghtas (doi:
https://doi.org/10.1103/PRXQuantum.4.020350(odnośnik otworzy się w nowym oknie) and
https://arxiv.org/abs/2307.06617(odnośnik otworzy się w nowym oknie)) where the bit-flip time of a cat-qubit is increased by many orders of magnitude; one experiment conducted by B. Huard (
https://doi.org/10.48550/arXiv.2402.05046(odnośnik otworzy się w nowym oknie)) with potential application to quantum error correction protocols on bosonic codes.
4.Published a proposal of a state-of-the-art experimental circuit ensuring autonomous stabilization and generation of GKP-qubits (
https://doi.org/10.1103/PhysRevX.15.011011(odnośnik otworzy się w nowym oknie)). We developed here a novel approach to stabilize these qubits by dissipation engineering (i.e. quantum controller) in high-impedance circuits. French, European and US patents protect this proposal (FR3133467A1, EP4490674A1, US20250181958A1).
5.Published five papers on adiabatic elimination and efficient numerical simulations for composite open quantum systems encountered in bosonic code (
https://doi.org/10.48550/arXiv.2303.04495(odnośnik otworzy się w nowym oknie) https://doi.org/10.1016/j.ifacol.2023.10.1779
https://doi.org/10.48550/arXiv.2303.17308(odnośnik otworzy się w nowym oknie) https://doi.org/10.48550/arXiv.2303.05089
https://doi.org/10.48550/arXiv.2404.01802(odnośnik otworzy się w nowym oknie)). The new numerical scheme is protected by European and US patents (EP4428768A1, US20240303519A1).
6.Published control-theoretical results: on GKP-qubit autonomous stabilisation (doi.org/10.1109/CDC51059.2022.9992722 and doi.org/10.1016/j.ifacol.2023.10.1776); on parameter estimation based on stochastic master equation (https://doi.org/10.1016/j.ifacol.2023.10.110 10.1109/LCSYS.2024.3407608); convergence of bipartite open quantum systems stabilized by reservoir engineering (
https://doi.org/10.1007/s00023-024-01481-8(odnośnik otworzy się w nowym oknie)).
7. Analysed in
https://doi.org/10.48550/arXiv.2410.00975(odnośnik otworzy się w nowym oknie) the flux-pump-induced degradation of 1 for dissipative cat qubits. This article combines time-dependent Schrieffer-Wolff perturbation theory with numerically exact Floquet theory.
8.Published an original numerical method to generate quantum gates for open quantum systems via a monotonic algorithm with time optimization (
https://www.aimsciences.org/article/id/6708e39b2d4d1a4052cb08cf(odnośnik otworzy się w nowym oknie)).
9.Obtained new results submitted for publications:
-on complete-positivity, trace preserving and linear schemes for simulations on classical computers of infinite dimensional open quantum systems including truncation-errors estimation (arXiv:2501.09607 and arXiv:2503.01712).
-on classical parameter estimation of quantum stochastic master equation from standard correlation functions attached to realistic measurement data (arXiv:2410.11955)
-on dynamical models of reduced order for continuously measured quantum systems (arXiv:2503.08296)
-on a prototypical circuit that we designed, fabricated and tested to engineer high-order dissipation channels and investigate sources of residual nonlinearities in the context of Q-feedback (arXiv:2501.05960).
