Nonequilibrium Quasiparticles in Superconducting Quantum Bits

by Chuan-Hong Liu (LBNL)

Thursday 16 Oct 2025, 16:00 → 17:00 US/Pacific

Abstract: The ideal superconductor offers a pristine host for the fragile quantum states of a superconducting quantum computer. With an energy gap protecting against low-energy excitations, qubits should, in principle, be isolated from unwanted modes that cause irreversible decay of quantum information. In practice, however, a significant density of excitations persists above the superconducting ground state, even at ultralow temperatures. These excitations, known as quasiparticles, can drain energy from the qubit mode and induce dephasing, thereby degrading quantum computer’s performance. In this talk, we will discuss two dominant mechanisms of quasiparticle generation: resonant millimeter-wave absorption and impacts from high-energy particles. We further show that careful device design, combined with a well-shielded operating environment, provides effective strategies to mitigate quasiparticle poisoning. A deeper understanding of these processes will be essential for realizing the next generation of superconducting quantum computers that are resilient against quasiparticle-induced errors.

Zoom:

https://lbnl.zoom.us/j/98854322464?pwd=K2tKUm1VZjRlV1J5RHE3cXdHQzRxdz09

Meeting ID: 988 5432 2464

Passcode: 142239