Criticality, computing, and chaos in open quantum systems
Fabrizio Minganti (EPFL Lausanne)
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 Intermediate-Scale 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 large-scale 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 non-local unitary processes. They are also subject to non-unitary effects from the environment, active measurements, and feedback operations. As such, they can only be modeled within the framework of many-body 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 system-environment 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 steady-state quantum chaos in driven-dissipative 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 second-order dissipative phase transitions in a two-photon 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).