Millisecond lifetimes and coherence times in 2D transmon qubits

Area of Science:

• Quantum computing
• Materials science
• Superconducting circuits

Background:

• Materials improvement is key to reducing loss and decoherence in superconducting qubits for large-scale processors.
• Previous work used tantalum base layers and sapphire substrates, but losses were dominated by surface and bulk dielectrics.
• Addressing both surface and bulk dielectric losses is crucial for advancing qubit performance.

Purpose of the Study:

• To investigate the impact of high-resistivity silicon substrates on superconducting transmon qubit performance.
• To reduce bulk substrate loss by replacing traditional sapphire substrates.
• To achieve significant improvements in qubit quality factors and coherence times.

Main Methods:

• Fabricated 2D transmon qubits using a tantalum base layer on high-resistivity silicon substrates.
• Utilized an improved, low-contamination Josephson junction deposition process.
• Characterized qubit performance, including quality factors (Qavg), lifetimes (T1), and coherence times (T2E).

Main Results:

• Achieved time-averaged quality factors (Qavg) of 9.7 × 10^6 across 45 qubits, with a best qubit Qavg of 1.5 × 10^7.
• Recorded qubit lifetimes (T1) up to 1.68 ms and maximum Q up to 2.5 × 10^7.
• Demonstrated Hahn echo coherence times (T2E) exceeding T1 and single-qubit gate fidelities of 99.994%.

Conclusions:

• Replacing sapphire with high-resistivity silicon significantly reduces bulk substrate loss in superconducting qubits.
• The tantalum-on-silicon platform enables high-quality factor qubits with extended coherence times.
• This materials improvement is architecture-agnostic and readily scalable for large-scale quantum processors.