August 19, 2024 | Alexander Anfroev,1,2, Shannon P. Harvey,3,4 Fanghui Wan,3,4 Jonathan Simon,3,5 and David I. Schuster3,4,†
This paper presents the development and characterization of superconducting qubits operating at frequencies up to 24 GHz and temperatures above 200 mK. The researchers used low-loss niobium trilayer junctions, which have a higher superconducting transition temperature compared to aluminum junctions, to fabricate transmons with improved thermal resilience. The qubits exhibit decoherence and dephasing times of about 1 μs, corresponding to average qubit quality factors of approximately 10^6. The study found that decoherence is unaffected by quasiparticles up to 1 K, and the qubits can operate up to approximately 250 mK while maintaining similar performance. This thermal resilience opens new possibilities for scaling up quantum processors, enabling hybrid quantum experiments with high heat dissipation budgets, and introducing a material platform for higher-frequency qubits. The key elements of the fabrication process, including the use of low-temperature plasma-enhanced chemical vapor deposition (PECVD) and residue removal techniques, are detailed, along with the characterization methods used to measure qubit properties. The results highlight the importance of increased frequency and temperature in improving qubit performance and coherence.This paper presents the development and characterization of superconducting qubits operating at frequencies up to 24 GHz and temperatures above 200 mK. The researchers used low-loss niobium trilayer junctions, which have a higher superconducting transition temperature compared to aluminum junctions, to fabricate transmons with improved thermal resilience. The qubits exhibit decoherence and dephasing times of about 1 μs, corresponding to average qubit quality factors of approximately 10^6. The study found that decoherence is unaffected by quasiparticles up to 1 K, and the qubits can operate up to approximately 250 mK while maintaining similar performance. This thermal resilience opens new possibilities for scaling up quantum processors, enabling hybrid quantum experiments with high heat dissipation budgets, and introducing a material platform for higher-frequency qubits. The key elements of the fabrication process, including the use of low-temperature plasma-enhanced chemical vapor deposition (PECVD) and residue removal techniques, are detailed, along with the characterization methods used to measure qubit properties. The results highlight the importance of increased frequency and temperature in improving qubit performance and coherence.