Oct 9, 2024: Adam Shaw & David Long [Stanford University]

David Long's talk title: Autonomous Stabilization of a Floquet System Using Static Dissipation
Abstract:
David Merrick Long: Engineered quantum systems typically decohere on long time scales, settling into a rarely-useful steady state. Periodic (Floquet) modulation of the system parameters can produce useful short-time effects, but also tends to drive the system to a mixed steady state. In this talk, I will show that incorporating an auxiliary system with static coupling and simple static dissipation can circumvent this problem. The final steady state of the system becomes a useful periodically varying state, with a high overlap with a single quasienergy state of the isolated evolution. This effect has recently been observed experimentally in the adiabatic (slow modulation) regime using a transmon qubit coupled to a superconducting resonator, and theoretical analysis shows that the effect extends well outside the adiabatic regime. These results show that Floquet systems can support state purification and cooling processes without the need for complicated time-dependent dissipation or feedback.
Research interest keywords: condensed matter, quantum dynamics, localization, thermalization, topology
Adam Shaw's talk title: Measuring entanglement and learning noise with emergent randomness
Adam Shaw: Randomness has long been employed to characterize quantum computers with techniques like randomized benchmarking and random circuit sampling, but it is not clear how such ideas apply to the more general setting of analog quantum simulators. Here we discover time-independent Hamiltonian dynamics are far more random than they first appear by uncovering the emergence of random state ensembles hidden in the time-evolution or partial measurement of generic quantum systems. Using these findings, we import techniques for fidelity estimation from random circuit sampling for systems of up to 60 atoms with a Rydberg analog quantum simulator, reaching a regime that challenges state-of-the-art classical computers. As concrete applications of these techniques, we estimate the actual experimental mixed state entanglement entropy, and show how to learn nearly-arbitrary noise models affecting quantum systems. In total, our results reveal the hidden similarities between quantum simulators and computers, and uncover concrete means of improving near- and far-term controlled quantum systems.
Research interests:
Rydberg atom arrays, characterizing quantum systems, combining quantum metrology with quantum information science