Second-order perturbation theory for dissipative cat qubits
le mercredi 20 mars 2024 à 11:00
Séminaire interne LPMMC
Personne à contacter : Vincent Rossetto ()
Lieu : G421
Résumé : Dissipative cat qubits have attracted a lot of interest in the
recent years. Their main feature is that their unperturbed dynamics is described by a Lindbladian, not a Hamiltonian. This complicates the analysis of the noise effects on them. In this paper we develop perturbation theory on top of the dissipative cat qubit Lindbladian and evaluate the qubit relaxation rate due to the single photon loss up to the second-order in the perturbation strength. We analytically show that the second-order contribution to the slowest decay rate can become parametrically larger than the first-order contribution. Also, we analyze the detuning perturbation up to the second-order using the same procedure.
Liens :
Daniel Rodan-Legrain (Massachussetts Institute of Technology)
Superconductivity and strong correlations in graphene quantum devices
le mardi 26 mars 2024 à 14:00
Séminaire nano-électronique quantique
Personne à contacter :
Lieu : Salle Rémy Lemaire, Institut Néel
Résumé : Graphene possesses exceptional properties that, since its discovery, have attracted wide attention from the scientific and engineering communities. In this talk, I will present a series of experiments via two different approaches, i.e., proximity effect and twist angle design, to induce superconductivity and strong correlations in graphene-based systems—two phenomena that do not intrinsically occur in this material.
In the first part of my talk, graphene is flanked by two superconductors and inherits their superconducting properties by proximity effect. A superconductor-graphene-superconductor junction is coupled to a superconducting circuit to create and manipulate the first graphene-based transmon qubit.
In the second part of my talk, the electronic properties of graphene-based systems are engineered by controlling the relative twist angle between the atomic planes. In particular, when two graphene sheets are stacked on top of each other near the “magic angle” ≈ 1.1°, nearly flat bands develop, featuring superconductivity and correlated insulating states. I will show that local electrostatic control over the different electronic phases of magic-angle twisted bilayer graphene (MATBG) enables the creation of versatile hyper-tunable quantum devices. I will also present transport, local electronic compressibility, and nano-optics experiments to demonstrate the emergence of exotic electronic phases in MATBG. Last, I will discuss studies of novel 2D moiré systems beyond MATBG.
Influence of Trotterization error on single-particle tunneling
le mercredi 03 avril 2024 à 11:00
Séminaire interne LPMMC
Personne à contacter : Denis Basko ()
Lieu : G421
Résumé : Quantum simulation of the single-particle tunneling problem by means of the Suzuki-Trotter approximation (STA) is analyzed. The target system describes a particle hopping across a chain of sites with position-dependent potential profile. The latter is assumed to be smooth and to posses several local minima separated by a potential barrier, arranging a tunneling problem between the localized states in different minima. The conducted analysis confirms the naive criteria of applicability max{T,P} ≪ 1/δt (with T, P being the typical scales of kinetic and potential terms, respectively), while also revealing the structure of error and its actual behavior with system parameters. Notably, in certain cases we find an exponential acceleration of tunneling, while other configurations lead to a complete suppression of the latter. Analysis of the case of large Trotter step is also performed, with the main result being the reconstruction of the low-energy spectrum due to coupling between states with energy difference close to 2π/δt. The connection of the obtained results with the rigorous upper error bounds on the STA error is discussed, with particular emphasis on the reasons for the fact that these rigorous bounds are not always saturated. We also point out that the proposed problem can be directly implemented on existing quantum devices arXiv:2012.00921. The talk is based on the recent paper arXiv:2312.04735.
Amorphous quantum magnets in a two-dimensional Rydberg atom array
le vendredi 12 avril 2024 à 11:00
Séminaire théorie
Personne à contacter : Adolfo Grushin ()
Lieu : G421
Résumé : Amorphous solids, i.e., systems which feature well-defined short-range properties but lack long-range order, constitute an important research topic in condensed matter. While their microscopic structure is known to differ from their crystalline counterpart, there are still many open questions concerning the emergent collective behavior in amorphous materials. This is particularly the case in the quantum regime, where the numerical simulations are extremely challenging. In this talk, we instead propose to explore amorphous quantum magnets with an analog quantum simulator. To this end, we first present an algorithm to generate amorphous quantum magnets, suitable for Rydberg simulators of the Ising model. Subsequently, we use semiclassical approaches to get a preliminary insight of the physics of the model. In particular, we calculate mean-field phase diagrams, and use the linear-spin-wave theory to study localization properties and dynamical structure factors of the excitations. Finally, we outline an experimental proposal based on Rydberg atoms in programmable tweezer arrays, thus opening the road towards the study of amorphous quantum magnets in regimes difficult to simulate classically.