• Séminaire interne LPMMC
• Personne à contacter : Benoît Vermersch ()
• G 421

Résumé : The quantum Fisher information (QFI) is a fundamental quantity of interest in many areas from quantum metrology to quantum information theory. It can in particular be used as a witness to establish the degree of multi-particle entanglement in quantum many-body-systems. As the QFI is a macroscopic property of the quantum state, it has been a challenge till date to measure it in state-of-art quantum platforms. To address this problem, I will firstly discuss the randomized measurement (RM) toolbox which has emerged as a good candidate to estimate properties associated to the density matrix [Nature Reviews Physics volume 5, (2023)]. This framework motivated us to formulate the QFI in terms of a converging series of lower bounds that can then be estimated using the RM toolbox [Phys. Rev. Lett. 127, 260501, (2021)]. Lastly I will show some preliminary experimental estimations of the QFI on a superconducting device that implement recent error mitigation and post-processing methods.

Liens :LPMMC

• Séminaire théorie
• Personne à contacter :
• G 421

Résumé : The identification of universal properties from minimally processed datasets is one goal of machine learning techniques. Both in supervised or unsupervised settings, “making sense” of hitherto unseen raw data is defined at the outset, byencoding the task (regression, classification, etc.) in an objective function. This turns learning and inference into an optimisation problem. Here, starting from data-sets sampled from classical partition functions and one-dimensional quantum models, we build networks (graphs) by drawing links between the points according to a cutoff distance that is determined by the data structure and the choice of metric. Remarkably, this enables a transfer of methods and concepts from disconnected fields that allow us to tackle in an agnostic way the study of phase transition in several models. We observe how the minimum number of variables needed to accurately describe the important features of a data-set, the intrinsic dimension Id, behaves in the vicinity of phase transitions. We show how the finite-size analysis of the Id allows us to identify critical points with an accuracy comparable to methods that rely on apriori identification of order parameters. We review previous works [Physical ReviewX 11 (1), 011040] and elaborate on the topic with new results in case of ground states of one-dimensional quantum systems.

Liens :

• Séminaire nano-électronique quantique
• Personne à contacter : Jeremie Viennot ()
• Salle Rémy Lemaire K223, Institut Néel et via https://univ-grenoble-alpes-fr.zoom.us/j/91808901596?pwd=UWZ2cml2N1VBOEZBenk0d3RJek9rdz09

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• G 421

Liens :LPMMC

• Séminaire théorie
• Personne à contacter :
• G 421

Résumé : Self-binding in Bose-Bose mixtures has received lots of theoretical [1] and experimental [2] attention in the recent years, and a few studies also discussed Bose-Fermi droplets [3]. Fermi-Fermi mixtures with interspecies attraction, however, are not expected to display self-bound states, since the fermions of one species should overcome a strong Pauli pressure to bind the fermions of the other. This repulsion is, in fact, the fundamental mechanism that provides stability of Fermi mixtures along the BCS-BEC crossover, in which the dimers repel and do not form larger clusters [4]. In our work [5], we find that a 1D Fermi-Fermi mixture with sufficiently large mass imbalance can form a self-bound state in the thermodynamic limit. This result elaborates our previous few-body analyses [6], and is based on a mean-field theory in which the heavy fermions are described within the Thomas-Fermi approximation, which is exact in the limit of large mass ratios. We are also extending our theory towards the 2D case, which is complicated by the same scaling with length of the kinetic energy and of the interaction energy of the system. We now have preliminary evidence of the existence of few-body clusters and of their binding [7]. Our work sets the basis for understanding liquid-like states in fermionic gases.

• [1] D. S. Petrov, Quantum Mechanical Stabilization of a Collapsing Bose-Bose Mixture, Phys. Rev. Lett. 115, 155302 (2015).
• [2] C. R. Cabrera, et al., Quantum liquid droplets in a mixture of Bose-Einstein condensates, Science 359, 301 (2018).
• [3] D. Rakshit, et al., Self-bound Bose–Fermi liquids in lower dimensions, New J. Phys. 21, 073027 (2019); T. Karpiuk, et al., Bistability of Bose–Fermi mixtures, New J. Phys. 22, 103025 (2020).
• [4] D. S. Petrov, C. Salomon, and G. V. Shlyapnikov, Weakly bound dimers of fermionic atoms, Phys. Rev. Lett. 93, 090404 (2004).
• [5] J. Givois, A. Tononi, and D. S. Petrov, Self-binding of one-dimensional fermionic mixtures with zero-range interspecies attraction, arXiv:2207.04742 , accepted for publication on SciPost Physics.
• [6] A. Tononi, J. Givois, and D. S. Petrov, Binding of heavy fermions by a single light atom in one dimension, Phys. Rev. A 106, L011302 (2022).
• [7] J. Givois, A. Tononi and D. S. Petrov, in preparation (2023).

Liens :

• Séminaire nano-électronique quantique
• Personne à contacter : Jeremie Viennot ()
• Salle Rémy Lemaire K223, Institut Néel et via https://univ-grenoble-alpes-fr.zoom.us/j/91808901596?pwd=UWZ2cml2N1VBOEZBenk0d3RJek9rdz09

Résumé : Remarkably, complex assemblies of superconducting wires, electrodes, and Josephson junctions are compactly described by a handful of collective phase degrees of freedom that behave like quantum particles in a potential. Almost all these circuits operate in the regime where quantum phase fluctuations are small—the associated flux is smaller than the superconducting flux quantum—although entering the regime of large fluctuations would have profound implications for metrology and qubit protection. The difficulty arises from the apparent need for circuit impedances vastly exceeding the resistance quantum. Independently, exotic circuit elements that require Cooper pairs to form pairs in order to tunnel have been developed to encode and topologically protect quantum information. In this work, we demonstrate that pairing Cooper pairs magnifies the phase fluctuations of the circuit ground state. In a first experiment, we measure a tenfold suppression of flux sensitivity of the first transition energy only, implying a twofold increase in the vacuum phase fluctuations and showing that the ground state is delocalized over several Josephson wells. In a second experiment, we demonstrate that Cooper-pair pairing mediates high order photon-photon interactions, resulting in some peculiar spectral properties. Ref.: W. C. Smith et al., Phys. Rev. X 12, 021002

Liens :

• Séminaire LPMMC
• Personne à contacter : Vincent Rossetto ()
• G 421

Liens :

• Séminaire nano-électronique quantique
• Personne à contacter : Jeremie Viennot ()
• Salle Rémy Lemaire K223, Institut Néel et via https://univ-grenoble-alpes-fr.zoom.us/j/91808901596?pwd=UWZ2cml2N1VBOEZBenk0d3RJek9rdz09

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• G 421

Liens :LPMMC

• Séminaire QuantAlps
• Personne à contacter : Michele Filippone ()
• TBD

Résumé : TBA

Liens :Atac Imamoglu

• Séminaire nano-électronique quantique
• Personne à contacter : Jeremie Viennot ()
• Salle Rémy Lemaire K223, Institut Néel et via https://univ-grenoble-alpes-fr.zoom.us/j/91808901596?pwd=UWZ2cml2N1VBOEZBenk0d3RJek9rdz09

Liens :

• Séminaire théorie
• Personne à contacter : Adolfo Grushin ()
• G 421

Liens :

• Séminaire nano-électronique quantique
• Personne à contacter :
• Salle Rémy Lemaire K223, Institut Néel et via https://univ-grenoble-alpes-fr.zoom.us/j/91808901596?pwd=UWZ2cml2N1VBOEZBenk0d3RJek9rdz09#success

Résumé : The fractional quantum Hall effect is one of the most intriguing phenomena of condensed matter physics, where electronic interactions in a two-dimension electron gas subjected to a strong magnetic field lead to the emergence of highly exotic states with highly unusual properties. Among these, the existence of neutral edge modes, carrying only energy along the edges of the sample in a direction upstream to that of charge transport, has driven more than three decades of research. Their charge neutral nature has made them singularly challenging to probe, such that they were only first observed in 2010. Since then, many works have addressed the thermal transport properties of neutral modes, in particular whether they exchange energy with their neighboring counterpropagating charged edge modes. Significant progress was recently made on this topic, but an important question remained unanswered: can upstream neutral modes exchange energy and thermalize with integer¬-charged edge modes located up to several hundreds of nanometers away from them? This question is far from trivial, as it can profoundly change our understanding of the quantum Hall effect in terms of independent transport channels, and affect the realization of future experiments seeking to explore and exploit the remarkable properties of fractional quantum Hall states. We present heat transport measurements in quantum Hall states of graphene demonstrating that the integer channels can strongly equilibrate with the fractional ones, leading to markedly different regimes of quantized heat transport that depend on edge electrostatics. Our results allow for a better comprehension of the complex edge physics in the fractional quantum Hall regime. G. Le Breton, R. Delagrange, Y. Hong, M. Garg, K. Watanabe, T. Taniguchi, R. Ribeiro-Palau, P. Roulleau, P. Roche, and F. D. Parmentier, Phys. Rev. Lett. 129, 116803 (2022).

Liens :

• Séminaire QuantAlps
• Personne à contacter : Michele Filippone ()
• Lieu à préciser

Liens :

• Séminaire théorie
• Personne à contacter : Adolfo Grushin ()
• G 421

Liens :