Measurements and modeling of phonon-mediated quasiparticle poisoning in superconducting qubit arrays
Date of Award
5-11-2025
Date Published
June 2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Physics
Advisor(s)
Britton Plourde
Keywords
Phonons;Quasiparticles;Qubits;Superconducting
Subject Categories
Physical Sciences and Mathematics | Physics | Quantum Physics
Abstract
The realization of a quantum computer that can correct for random errors on its constituent quantum bits, or qubits, is one of the primary goals in the quantum information science community. One of the leading protocols to correct these errors on a quantum processor relies on nearest-neighbor coupling of an array of physical qubits that act collectively as a single logical qubit. Superconducting circuits are a leading implementation of a physical qubit and have been used in some of the first demonstrations of this error correction scheme. A key assumption of this protocol is that errors on the physical qubits are random and uncorrelated. However, high-energy particle impacts from background radiation can deposit large amounts of energy into the device substrates, causing correlated errors in superconducting qubit arrays. In this thesis, we present experimental results where we reduced the sensitivity of a superconducting qubit array to background radiation by adding 10-$\mu$m-thick Cu islands to the back side of the device substrate, which downconverts the energy of athermal phonons, quantized lattice vibrations, via phonon scattering. These structures serve to channel excess energy away from the qubits in the device layer. We then present a detailed Monte Carlo-based simulation of these devices experiencing a particle impact and resolve the spatial and temporal effects on a simulated qubit array. We present an experiment where we intentionally increased the radiation flux by adding a radioactive source outside of the cryostat that houses the qubit chips. Using the resulting data, we can develop a detailed model of the charge dynamics from ionizing impacts within the device substrates. Finally, we present evidence of an additional source of correlated errors with superconducting qubit arrays that likely originate from differential thermal contraction between the thin metal films of the device layer and the insulating substrate. The results presented in this thesis serve to characterize various sources of correlated errors and inform future superconducting qubit device designs that are robust against correlated errors.
Access
Open Access
Recommended Citation
Yelton, Eric, "Measurements and modeling of phonon-mediated quasiparticle poisoning in superconducting qubit arrays" (2025). Dissertations - ALL. 2069.
https://surface.syr.edu/etd/2069
