Abstract
Superfluid helium's low-loss dielectric properties, excellent thermal conductivity, and unique collective excitations make it an attractive candidate to incorporate into superconducting qubit systems. We controllably immerse a three-dimensional superconducting transmon qubit in superfluid He4 and measure the spectroscopic and coherence properties of the system. We find that the cavity, the qubit, and their coupling are all modified by the superfluid, which we analyze within the framework of circuit quantum electrodynamics. At temperatures relevant to quantum computing experiments, the energy relaxation time of the qubit is not significantly changed by the presence of the superfluid, while the pure dephasing time modestly increases, which we attribute to improved thermalization of the microwave environment via the superfluid.
| Original language | English |
|---|---|
| Article number | 012336 |
| Journal | Physical Review A |
| Volume | 101 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jan 22 2020 |
| Externally published | Yes |
Funding
We are grateful to R. McDermott, D. I. Schuster, P. M. Harrington, M. I. Dykman, N. O. Birge, G. Koolstra, J. Kitzman, and S. Hemmerle for fruitful discussions. We thank J. P. Davis and G. G. Popowich for technical assistance with proper superfluid thermalization. We also thank R. Loloee and B. Bi for technical assistance and use of the W. M. Keck Microfabrication Facility at MSU. The Michigan State portion of this work was supported by the Cowen Family Endowment and by the NSF (Grant No. DMR-1708331). The Washington University portion of this work was also supported by the NSF (Grants No. PHY-1607156 and No. PHY-1752844, CAREER).