Quantum bath suppression in a superconducting circuit by immersion cooling

Area of Science:

• Quantum Computing
• Superconducting Circuits
• Low-Temperature Physics

Background:

• Superconducting devices exhibit temperature-dependent environmental interactions.
• Properties like qubit coherence plateau around 50 mK due to thermal constraints.
• Factors include thermal qubit populations, quasiparticles, and surface spin polarization.

Purpose of the Study:

• To overcome the thermal limitations in superconducting quantum circuits.
• To demonstrate efficient cooling of the decohering environment below 50 mK.
• To explore the impact of sub-millikelvin operation on quantum circuit properties.

Main Methods:

• Operating a superconducting circuit immersed in liquid helium-3 (³He).
• Utilizing ³He as a heat sink to suppress the quantum bath.
• Measuring physical quantities of the circuit at sub-millikelvin temperatures.

Main Results:

• Achieved continuous changes in physical quantities down to sub-mK temperatures.
• Demonstrated a thousand-fold increase in energy relaxation rate of the quantum bath.
• Observed no additional circuit losses or noise from the suppressed bath.

Conclusions:

• Liquid ³He immersion effectively removes thermal constraints in superconducting circuits.
• Quantum bath suppression via ³He enhances coherence and thermal management.
• This technique opens new avenues for improving quantum processor performance.