@article{Beverland19_JSTAT, doi = {10.1088/1742-5468/ab25de}, url = {https://dx.doi.org/10.1088/1742-5468/ab25de}, year = {2019}, month = {7}, publisher = {IOP Publishing and SISSA}, volume = {2019}, number = {7}, pages = {073404}, author = {Michael E Beverland and Benjamin J Brown and Michael J Kastoryano and Quentin Marolleau}, title = {The role of entropy in topological quantum error correction}, journal = {Journal of Statistical Mechanics: Theory and Experiment}, eprint = {1812.05117}, archiveprefix = {arXiv}, abstract = {The performance of a quantum error-correction process is determined by the likelihood that a random configuration of errors introduced to the system will lead to the corruption of encoded logical information. In this work we compare two different variants of the surface code with a comparable number of qubits: the surface code defined on a square lattice and the same model on a lattice that is rotated by $\pi/4$. This seemingly innocuous change increases the distance of the code by a factor of $\sqrt{2}$. However, as we show, this gain can come at the expense of significantly increasing the number of different failure mechanisms that are likely to occur. We use a number of different methods to explore this tradeoff over a large range of parameter space under an independent and identically distributed noise model. We rigorously analyze the leading order performance for low error rates, where the larger distance code performs best for all system sizes. Using an analytical model and Monte Carlo sampling, we find that this improvement persists for fixed sub-threshold error rates and large system sizes, but that the improvement vanishes close to threshold. Remarkably, intensive numerics uncover a region of system sizes and sub-threshold error rates where the square lattice surface code marginally outperforms the rotated model.} } @article{Bland20_JPhysB, doi = {10.1088/1361-6455/ab81e9}, url = {https://dx.doi.org/10.1088/1361-6455/ab81e9}, pdf = {https://iopscience.iop.org/article/10.1088/1361-6455/ab81e9/pdf}, year = {2020}, month = {5}, publisher = {IOP Publishing}, volume = {53}, number = {11}, pages = {115301}, author = {T Bland and Q Marolleau and P Comaron and B A Malomed and N P Proukakis}, title = {Persistent current formation in double-ring geometries}, journal = {Journal of Physics B: Atomic, Molecular and Optical Physics}, eprint = {1911.12802}, archiveprefix = {arXiv}, abstract = {Quenching an ultracold bosonic gas in a ring across the Bose–Einstein condensation phase transition is known, and has been experimentally observed, to lead to the spontaneous emergence of persistent currents. The present work examines how these phenomena generalize to a system of two experimentally accessible explicitly two-dimensional co-planar rings with a common interface, or to the related lemniscate geometry, and demonstrates an emerging independence of winding numbers across the rings, which can exhibit flow both in the same and in opposite directions. The observed persistence of such findings in the presence of dissipative coupled evolution due to the local character of the domain formation across the phase transition and topological protection of the randomly emerging winding numbers should be within current experimental reach.} } @article{Marolleau24_PRA, title = {Sub-shot-noise interferometry with two-mode quantum states}, author = {Marolleau, Quentin and Leprince, Charlie and Gondret, Victor and Boiron, Denis and Westbrook, Christoph I.}, journal = {Phys. Rev. A}, volume = {109}, issue = {2}, pages = {023701}, numpages = {5}, year = {2024}, month = {2}, publisher = {American Physical Society}, doi = {10.1103/PhysRevA.109.023701}, url = {https://link.aps.org/doi/10.1103/PhysRevA.109.023701}, eprint = {2307.16479}, archiveprefix = {arXiv}, abstract = {We study the feasibility of sub-shot-noise interferometry with imperfect detectors, starting from twin-Fock states and two mode squeezed vacuum states. We derive analytical expressions for the corresponding phase uncertainty. We find that one can achieve phase shift measurements below the standard quantum limit, as long as the losses are smaller than a given threshold, and that the measured phase is close enough to an optimal value. We provide our analytical formulae in a Python package, accessible online.}, } @phdthesis{Marolleau22_PhD, TITLE = {{Quantum atom optics with metastable helium atoms}}, AUTHOR = {Marolleau, Quentin}, URL = {https://pastel.hal.science/tel-04059502}, NUMBER = {2022UPASP166}, SCHOOL = {{Universit{\'e} Paris-Saclay --- Institut d’Optique Graduate School, Laboratoire Charles Fabry}}, YEAR = {2022}, MONTH = {12}, KEYWORDS = {Quantum mechanics ; Nonlocality ; Metastable helium ; Atom interferometry ; Bell inequalities ; Ultra-Cold atoms ; Non localit{\'e} ; Atomes ultra-Froids ; M{\'e}canique quantique ; In{\'e}galit{\'e}s de Bell ; Interf{\'e}rom{\'e}trie atomique ; Helium m{\'e}tastable}, TYPE = {PhD thesis}, PDF = {https://pastel.hal.science/tel-04059502/file/117284_MAROLLEAU_2022_archivage.pdf}, HAL_ID = {tel-04059502}, HAL_VERSION = {v1}, abstract = {Correlation and entanglement properties of multi-particle quantum states have been demonstrated since the 1980s in the context of photonics. Since then, the production and characterisation of non-classical states in various contexts has become a very fruitful research topic, as well as a burning issue for the development of quantum technologies. This thesis presents an experimental platform able to prepare helium atoms in strongly correlated momentum states. The detection technique that has been developed in our group (three-dimensional and resolved to the single atom) allows to efficiently probe these correlation properties, which is in general difficult to achieve for most similar experimental setups. In particular, this manuscript contains a first part of theoretical nature, which deals on the one hand with the generalisation of the Hong-Ou-Mandel effect (in a context where more than two particles are involved); and on the other hand with the implementation of an experiment testing the Bell inequalities for atoms entangled with respect to their velocities. Both experiments could be carried out by our team in the near future. A second experimental part reports on the recent progress made on the platform, as well as the latest experimental results concerning the correlation properties of the atomic source that we have set up.}, } @article{Duverger24_PRApplied, title = {Metrology of microwave fields based on trap-loss spectroscopy with cold Rydberg atoms}, author = {Duverger, Romain and Bonnin, Alexis and Granier, Romain and Marolleau, Quentin and Blanchard, C\'edric and Zahzam, Nassim and Bidel, Yannick and Cadoret, Malo and Bresson, Alexandre and Schwartz, Sylvain}, journal = {Phys. Rev. Appl.}, volume = {22}, issue = {4}, pages = {044039}, numpages = {12}, year = {2024}, month = {10}, publisher = {American Physical Society}, doi = {10.1103/PhysRevApplied.22.044039}, url = {https://link.aps.org/doi/10.1103/PhysRevApplied.22.044039}, eprint = {2404.17445}, archiveprefix = {arXiv}, abstract = {We demonstrate a new approach for the metrology of microwave fields based on the trap-loss-spectroscopy of cold Rydberg atoms in a magneto-optical trap. Compared to state-of-the-art sensors using room-temperature vapors, cold atoms allow longer interaction times, better isolation from the environment and a reduced Doppler effect. Our approach is particularly simple as the detection relies on fluorescence measurements only. Moreover, our signal is well described by a two-level model across a broad measurement range, allowing in principle to reconstruct the amplitude and the frequency of the microwave field simultaneously without the need for an external reference field. We report on a scale factor linearity at the percent level and no noticeable drifts over two hours, paving the way for new applications of cold Rydberg atoms in metrology such as calibrating blackbody shifts in state-of-the-art optical clocks, monitoring the Earth cryosphere from space, measuring the cosmic microwave background or searching for dark matter.}, } @article{Gondret25_PRL, title = {Observation of Entanglement in a Cold Atom Analog of Cosmological Preheating}, author = {Gondret, Victor and Lamirault, Clothilde and Dias, Rui and Camier, L\'ea and Micheli, Amaury and Leprince, Charlie and Marolleau, Quentin and Rullier, Jean-Ren\'e and Robertson, Scott and Boiron, Denis and Westbrook, Christoph I.}, journal = {Phys. Rev. Lett.}, volume = {135}, issue = {24}, pages = {240603}, numpages = {9}, year = {2025}, month = {12}, publisher = {American Physical Society}, doi = {10.1103/h7ws-g9z2}, url = {https://link.aps.org/doi/10.1103/h7ws-g9z2}, eprint = {2506.22024}, archiveprefix = {arXiv}, abstract = {We observe entanglement between collective excitations of a Bose-Einstein condensate in a configuration analogous to particle production during the preheating phase of the early Universe. In our setup, the oscillation of the inflaton field is mimicked by the transverse breathing mode of a cigar-shaped condensate, which parametrically excites longitudinal quasiparticles with opposite momenta. After a short modulation period, we observe entanglement of these pairs that reveals the role played by vacuum fluctuations in seeding the parametric growth, confirming the quantum origin of the excitations. As the system continues to evolve, we observe a decrease in correlations and a disappearance of nonclassical features. These point toward future experimental probes of the late-time nonlinear regime where further analogies can be drawn with reheating, i.e., the thermalization of the postinflationary Universe.}, } @article{Gondret25_CRPhys, title = {Parametric pair production of collective excitations in a Bose–Einstein condensate}, author = {Victor Gondret and Rui Dias and Clothilde Lamirault and L\'ea Camier and Amaury Micheli and Charlie Leprince and Quentin Marolleau and Scott Robertson and Denis Boiron and Christoph I. Westbrook}, journal={Comptes Rendus Physique}, year={2025}, month={12}, doi={10.5802/crphys.266}, url={https://doi.org/10.5802/crphys.266}, pdf={https://comptes-rendus.academie-sciences.fr/physique/item/10.5802/crphys.266.pdf}, eprint={2508.01654}, archiveprefix={arXiv}, abstract = {By exciting the transverse breathing mode of an elongated Bose-Einstein condensate, we parametrically produce longitudinal collective excitations in a pairwise manner. This process also referred to as Faraday wave generation, can be seen as an analog to cosmological particle production. Building upon single particle detection, we investigate the early time dynamics of the exponential growth and compare our observations with a Bogoliubov description. The growth rate we observe experimentally is in very good agreement with theoretical predictions, demonstrating the validity of the Bogoliubov description and thereby confirming the smallness of quasiparticle interactions in such an elongated gas. We also discuss the presence of oscillations in the atom number, which are due to pair correlations and to the rate at which interactions are switched off.}, } @article{Leprince25_PRA, title = {Coherent coupling of momentum states: Selectivity and phase control}, author = {Leprince, Charlie and Gondret, Victor and Lamirault, Clothilde and Dias, Rui and Marolleau, Quentin and Boiron, Denis and Westbrook, Christoph I.}, journal = {Phys. Rev. A}, volume = {111}, issue = {6}, pages = {063304}, numpages = {7}, year = {2025}, month = {6}, publisher = {American Physical Society}, doi = {10.1103/PhysRevA.111.063304}, url = {https://link.aps.org/doi/10.1103/PhysRevA.111.063304}, eprint = {2411.09284}, archiveprefix = {arXiv}, abstract = {We demonstrate the effect of pulse shaping in momentum selective atomic Bragg diffraction. We compare temporal square pulses, which produce sidelobes in momentum space, with other shapes which can produce more nearly square momentum distributions. We produce pulses that simultaneously address two sets of velocity classes and demonstrate that we can control the differential phase imprinted on them in a way that is insensitive to laser phase fluctuations. Our work marks a significant step forward in testing Bell inequalities using massive particles entangled in momentum.}, }