Abstract: Superconducting circuits are an attractive system for forming qubits in a quantum computer because of the natural energy gap to excitations in the superconductor. However, experimentally it is observed that superconducting qubits have excitations above the superconducting ground state, known as quasiparticles, at a density that is many orders of magnitude above the expected equilibrium level. These quasiparticles are dissipative and can directly impact qubit coherence; in some cases, quasiparticle poisoning bursts can lead to correlated errors between qubits across an array, a process that is fatal to quantum error correction schemes. Quasiparticles can be generated by a range of energy-deposition sources, including photons from the qubit environment with energy above the superconducting gap, or the impact of high-energy particles from background radioactivity or cosmic ray muons. Following an overview of these various quasiparticle poisoning mechanisms, I will describe two recent experiments: one studying absorption of millimeter-wave photons by spurious antenna modes of qubit structures, the other measuring correlated phonon-mediated quasiparticle poisoning in multiqubit chips in the aftermath of high-energy particle impacts. I will discuss strategies for protecting qubits from these poisoning effects for the implementation of future fault-tolerant quantum processors.
JQI Seminars are held on Mondays during Fall and Spring semesters at 11:00 a.m. Eastern Time in Room 2400 of the Atlantic Building. University of Maryland affiliates may participate using Zoom. The seminars are also livestreamed on the JQI YouTube channel (https://www.youtube.com/user/JQInews), which supports audience participation in the chat interface.
You will need to bring your cell phone, so you can sign in. For Zoom, please submit a chat saying hello with your first and last name, so you can receive lunch. Lunch will be served after the seminar only to the individuals that have attended.
At 4pm, there will be a tea in ATL 2117 for our speaker and students - this is a chance for students to ask questions directly to our speaker. Refreshments will be served.