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30/10/2024
h 12:00 – Aula Caianiello Dipartimento di Fisica Ettore Pancini
Online: Online participation via MS Teams link
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Prof. Sergey Kubatkin
Chalmers University, Sweden
Learning about decoherence sources in superconducting circuits from the measurements on high-Q superconducting resonators
Abstract
Quantum information technology puts stringent demands on the quality of materials and interfaces in the pursuit of increased device coherence. Yet, little is known about the chemical structure and origins of paramagnetic impurities that produce flux/charge noise causing decoherence of fragile quantum states and impeding the progress towards large-scale quantum computing. Our on-chip electron-spin resonance techniques gave vital clues to the long-standing problem of noise and decoherence in superconducting devices: a technique for on-chip Electron Spin Resonance allowed to identify the chemical species responsible for the flux noise in superconducting circuits. The noise measurements in superconducting resonators point to the link between charge and flux noise in
superconducting circuits: a mild sample treatment has led to tenfold reduction of the surface spins, responsible for the flux noise, as evidenced by ESR, and this treatment has also led to tenfold reduction of the low frequency noise in superconducting resonator, associated with the charge noise. We have developed tunable resonators to evaluate the density of states of decohering defects. Our results demonstrate a previously unexplored decoherence mechanism in the form of a new type of TLS originating from trapped QPs, which can induce qubit relaxation. Control of TLS by a local electric field of scanning gate allows pinpointing positions of TLS. Interaction with quantum liquids helps freezing decoherence sources of solid-state quantum systems, as evidenced by the noise measurements in superconducting resonators.
Short Bio
Sergey Kubatkin is full Professor at Quantum Device Physics, Chalmers.