Séminaires du LPTMC

Alessio Lerose (University of Oxford)
24.04.2024 10:45  11:45SéminairesSynthetic quantum matter out of equilibrium: A few recent advances from theory to simulation

Manuel Pino (Nanotechnology Group, Universidad de Salamanca)
25.03.2024 10:45  11:45SéminairesCorrelated volumes for metallic wavefunctions on a randomregular graph
We study the metallic phase of the Anderson model in a randomregular graph, specifically the
degree of ergodicity of the highenergy wavefunctions. We use the multifractal formalism to analyze numerical data for unprecedented large system sizes, obtaining a set of correlated volumes which control finitesize effects. Those volumes grow very fast with disorder strength but show no tendency to diverge, at least in an intermediate metallic regime. Close to the Anderson transitions, we characterize the crossover to system sizes much smaller than the first correlated volume. Once this crossover has taken place, we obtain evidence of a scaling in which the derivative of the first fractal dimension behaves critically with an exponent ν = 1.The talk is based on the following works:
 Correlated volumes for extended wavefunctions on a randomregular graph.
M Pino, JE Roman arXiv preprint. ArXiv:2311.07690 (2023)
 Scaling up the Anderson transition in randomregular graphs.
M Pino. Physical Review Research 2 (4), 042031 (2020)
 From ergodic to nonergodic chaos in Rosenzweig–Porter model.
M Pino, J Tabanera, P Serna Journal of Physics A: Mathematical and Theoretical 52 (47), 475101 (2019)

Laurens Vanderstraeten (University of Gent)
19.03.2024 10:45  11:45SéminairesQuantum spin liquids and tensor networks
Quantum spin liquids are stronglycorrelated systems of spins that do not order at zero temperature. As a result, they exhibit exciting collective manybody effects such as topological order, quantum criticality and quasiparticle fractionalization. In this talk, I will explain how we can model these systems naturally using the language of tensor networks. I will show that this gives us insight into the nature of a spin liquid wavefunction, and allows us to perform numerical simulations of candidate models for realizing spin liquid physics.

Fabrizio Minganti (EPFL)
18.03.2024 10:45  11:45SéminairesCriticality, computing, and chaos in open quantum systems.
Quantum technologies represent a frontier of both fundamental and applied research, with global efforts aimed at developing quantum computers and simulation platforms that address practical challenges. However, the current era, known as the Noisy IntermediateScale Quantum (NISQ) era [1], presents a unique set of challenges. In NISQ systems, quantum devices are open, interacting with their environment and experiencing dissipation. This dissipation poses a significant obstacle to the largescale fabrication of quantum hardware, potentially limiting quantum advantages by degrading crucial properties like entanglement.
NISQ devices consist of numerous interacting particles undergoing both local and nonlocal unitary processes. They are also subject to nonunitary effects from the environment, active measurements, and feedback operations. As such, they can only be modeled within the framework of manybody open quantum systems. In these systems, the interplay between dissipative and Hamiltonian evolution leads to states and phenomena distinct from those observed in equilibrium condensed matter physics. In this presentation, I will delve into the understanding and investigation of these emergent properties in open quantum systems. The focus will particularly be on critical phenomena like phase transitions [2] and chaos [3], highlighting their unique features. I will also showcase the recent experimental demonstrations of our theoretical predictions [4,5].
While in many applications dissipation is a barrier to overcome, given appropriate engineering of the systemenvironment coupling, dissipation can be a resource. Indeed, dissipative processes can be used to steer the dynamics of NISQ systems, bypassing the hardware limitation determined by design and fabrication, such as energy, couplings, connectivity, etc. I will discuss how leveraging the distinctive features of open quantum systems and its emergent phenomena significantly boost the performance of quantum hardware, with a specific focus on their applications in quantum information encoding [6] and precision metrology [7].
[1] J. Preskill, Quantum Computing in the NISQ era and beyond, Quantum 2, 79 (2018).
[2] FM, A. Biella, N. Bartolo, and C. Ciuti, Spectral theory of Liouvillians for dissipative phase transitions, Phys. Rev. A 98, 042118 (2018).
[3] F. Ferrari, L. Gravina, D. Eeltink, P. Scarlino, V. Savona, and FM, Transient and steadystate quantum chaos in drivendissipative bosonic systems, arXiv 2305.15479 (2023).
[4] G. Beaulieu, FM, S. Frasca, V. Savona, S. Felicetti, R. D. Candia, and P. Scarlino, Observation of first and secondorder dissipative phase transitions in a twophoton driven Kerr resonator, arXiv 2310.13636 (2023).
[5] L. P. Peyruchat, F. Ferrari, FM, and P. Scarlino, Signature of dissipative quantum chaos in coupled nonlinear driven resonators, in preparation.
[6] L. Gravina, FM, and V. Savona, Critical Schrödinger Cat Qubit, PRX Quantum 4, 020337 (2023).
[7] R. Di Candia, FM, K. V. Petrovnin, G. S. Paraoanu, and S. Felicetti, Critical parametric quantum sensing, npj Quantum Information 9, 23 (2023). 
Eleanor CRANE (MIT)
13.03.2024 14:00  15:00SéminairesAdvantages of Digital QubitBoson Hardware for Quantum Simulation
Finding a straightforward, scalable and universal framework for quantum simulation of strongly correlated fermions and bosons is important from material science to highenergy physics. Here, we develop hybrid qubitoscillator operations for microwave cavities coupled to transmon qubits required for implementing dynamics of bosonic matter, fermionic matter, and Abelian gauge fields in (2+1)D. We then expand the method to ground state preparation and propose measurement of various longrange correlation functions required for the study of phase transitions. We implement numerical proof of principle experiments for a (1+1)D Z2 Bose Hubbard (BH) gauge theory and the U(1) Schwinger model. We include the main sources of hardware noise, which we mitigate through postselection based on Gauss' law. This new approach motivates us to uncover the phase diagram of the Z2 BH model, relevant to the Higgs sector. We discover a new phase of matter which exhibits strong density fluctuations which we dub the `clump' phase. Finally, we perform a complexity analysis and find that for one Trotter step of these example models, qubit systems require higher gate counts than our proposal by three orders of magnitude. Our correspondingly higher circuit fidelities may help us to successfully capture the essential physics of these theories in the nearterm.

Paul Robin (Institute of Science and Technology Austria)
11.03.2024 10:45  11:45SéminairesIon transport at the nanoscale: from ionelectron coupling to artificial ion channels
The transport of charged species is key to many processes in cellular biology, from sensory detection to osmoregulation and neurotransmission. Despite its apparent simplicity, the dynamics of ions in very confined spaces (biological ion channels, carbon nanotubes, atomicsize pores...) still holds many mysteries. In all these cases, nonlinear and dynamical effects occur when ions cross a nanometric channel. There is therefore a need for a better understanding of the dynamics of ion transport at the molecular scale. In this talk, I will present how progess in nanofluidics has enabled to build new types of channels, with dynamical properties that resemble that of biological pores (voltage gating, memory effects, etc.). In particular, I will focus on types of atomically small channels where fluctuations of water and ions can be coupled to the electronic properties of the walls. I will show how this coupling can be harnessed to develop ‘iontronic’ devices, where one can control flows of ions to carry out computations. In turn, I will also show how a better understanding of fluctuations in nanoscale charge transport can allow to decypher some properties of biological and artificial pores, a longstanding problem.

Bo Han (Weizmann Institute)
07.03.2024 14:00  15:00SéminairesEntanglement: Cornerstone of Quantum Phases and Transitions (par zoom)
Entanglement is the unique property that sharply distinguishes quantum from classical physics. Quantum entanglement is the hallmark of quantum phases and transitions without symmetry breaking. Beyond the conceptual level, quantum entanglement is essential in quantum computing devices. By instilling entanglement into unentangled product states, physicists have realized topologically ordered phases with anyons and noisy intermediatescale quantum (NISQ) devices in experiments. In this talk, I discuss two examples exhibiting an inseparable connection between entanglement and phases of matter. The first is the topologically ordered time crystal phase, which has been realized experimentally on quantum processors; the second is spin ladders with specific discrete symmetries, emulating 2D spinful bosons with longrange entanglement. I conclude with an outlook on how quantum entanglement reshapes science and technology in manybody physics.
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