On-chip Thermometry for Quantum Hardware Development

Superconducting qubits’ coherence depends on many factors. One of the known factors to impact coherence is the temperature at which the qubit operates. Though it is typically assumed that the temperature read by the oxide-based thermometers mounted on the coldest plate in the dilution refrigeration (MXC) is the device temperature, many reports in literature suggest that qubit temperature diverges from that of the MXC. While the plate may be at a temperature of ~10mK, other components, and specifically the quantum processor unit chip may be at a higher temperature and thermalize at a different rate. Increasing the size and complexity of future devices will exacerbate this issue, necessitating on-chip thermometry. These thermometers should not impact device performance nor add considerable fabrication complexity. Our on-chip thermometers are based on Dayem bridges, a concept that was shown to work at the 1K range¹, that we have developed further to work at the relevant ranges for superconducting qubits. In this talk, we will describe the ongoing research and development of on chip thermometry at Rigetti, and highlight the advantages of this method for hardware development.

¹ Zgirski et al. Phys. Rev. Applied 10, 044068