arXiv subjects

Maxime Allemand

Publications and source records attributed to Maxime Allemand.

5 recordsLinked to original sources

arXiv2026

Universal scaling of fluctuations and correlations across the superfluid transition

The critical behavior of a system near a continuous phase transition is commonly characterized by power laws and a set of universal critical exponents. Yet universality at phase transitions has even more fundamental manifestations. It dictates that all observables follow universal scaling functions, which may extend beyond simple power laws. Furthermore, microscopic details are captured entirely by only two system-specific scale factors, that rescale any measured quantity onto its universal form. In this work, we report the experimental validation of this prediction in ultracold lattice Bose gases undergoing the superfluid transition. We extract the scale factors by collapsing the order-parameter cumulants measured at varying entropies. We show that these factors specify scaling functions governing both the order-parameter distribution and two-point correlations. By measuring these scaling functions, we also determine three critical exponents $\beta$, $\gamma$ and $\nu$. Our results provide an experimental demonstration that universal scaling is simultaneously obeyed by multiple observables in a quantum many-body system.

cond-mat.quant-gas↗

arXiv2025

Observation of universal non-Gaussian statistics of the order parameter across a continuous phase transition

Second-order phase transitions are characterised by critical scaling and universality. The singular behaviour of thermodynamic quantities at the transition, in particular, is determined by critical exponents of the universality class of the transition. However, critical properties are also characterised by the probability distribution of the order parameter across the transition, where non-Gaussian statistics are expected, but remain largely unexplored. Here, making use of single-atom-resolved detection in momentum space, we measure the full probability distribution of the order-parameter amplitude across a continuous phase transition in an interacting lattice Bose gas. We find that fluctuations are captured by an effective potential -- reconstructed from the measured probability distribution by analogy with Landau theory -- displaying a non-trivial minimum in the superfluid (ordered) phase, which vanishes at the transition point. Additionally, we observe non-Gaussian statistics of the order parameter near the transition, distinguished by non-zero high-order cumulants undergoing abrupt sign changes. We show numerically that these sign changes of the cumulants obey critical scaling in homogeneous systems, and that their experimental behaviour is not reproduced by classical models, whereas it is captured by a low-temperature quantum model. Our results underscore the crucial role of order parameter statistics in probing critical phenomena and universality.

cond-mat.quant-gas↗

arXiv2024

Tomography of a single-atom-resolved detector in the presence of shot-to-shot number fluctuations

Tomography of single-particle-resolved detectors is of primary importance for characterizing particle correlations with applications in quantum metrology, quantum simulation and quantum computing. However, it is a non-trivial task in practice due to the unavoidable presence of noise that affects the measurement but does not originate from the detector. In this work, we address this problem for a three-dimensional single-atom-resolved detector where shot-to-shot atom number fluctuations are a central issue to perform a quantum detector tomography. We overcome this difficulty by exploiting the parallel measurement of counting statistics in sub-volumes of the detector, from which we evaluate the effect of shot-to-shot fluctuations and perform a local tomography of the detector. In addition, we illustrate the validity of our method from applying it to Gaussian quantum states with different number statistics. Finally, we show that the response of Micro-Channel Plate detectors is well-described from using a binomial distribution with the detection efficiency as a single parameter.

cond-mat.quant-gas↗

arXiv2024

Suppression of Bogoliubov momentum pairing and emergence of non-Gaussian correlations in ultracold interacting Bose gases

Strongly correlated quantum matter -- such as interacting electron systems or interacting quantum fluids -- possesses properties that cannot be understood in terms of linear fluctuations and free quasi-particles. Quantum fluctuations in these systems are indeed large and generically exhibit non-Gaussian statistics -- a property captured only by inspecting high-order correlations, whose quantitative reconstruction poses a formidable challenge to both experiments and theory alike. A prime example of correlated quantum matter is the strongly interacting Bose fluid, realized by superfluid Helium and, more recently, ultra-cold atoms. Here, we experimentally study interacting Bose gases from the weakly to the strongly interacting regime through single-atom-resolved correlations in momentum space. We observe that the Bogoliubov pairing among modes of opposite momenta, emblematic of the weakly interacting regime, is suppressed as interactions become stronger. This departure from the predictions of Bogoliubov theory signals the onset of the strongly correlated regime, as confirmed by numerical simulations that highlight the role of non-linear quantum fluctuations in our system. Additionally, our measurements unveil a non-zero four-operator cumulant at even stronger interactions, which is a direct signature of non-Gaussian correlations. These results shed light on the emergence and physical origin of non-Gaussian correlations in ensembles of interacting bosons.

cond-mat.quant-gas↗

arXiv2022

A Rydberg hydrogen beam for studies of stimulated deexcitation

We present a Rydberg hydrogen beamline developed to commission techniques of stimulated deexcitation for application in antihydrogen experiments at CERN's Antiproton Decelerator. The stimulation of spontaneous decay is a key technology to enhance the number of ground-state anti-atoms available in a beam toward precision spectroscopy and gravity measurements.

physics.atom-ph↗