Decoupling a Cooper-pair box to enhance the lifetime to 0.2 ms

Area of Science:

• Quantum Electrodynamics (QED)
• Superconducting circuits
• Quantum computing hardware

Background:

• Superconducting qubits are promising for quantum computation.
• Improving qubit coherence times is crucial for scalable quantum computers.
• Circuit QED architectures offer control over qubit-resonator interactions.

Purpose of the Study:

• To investigate the relationship between qubit lifetime and coupling strength in a circuit QED system.
• To achieve significantly longer coherence times for superconducting charge qubits.
• To determine material loss parameters in Josephson junction barriers.

Main Methods:

• Utilized a circuit QED experiment with a quasilumped element superconducting microwave resonator.
• Employed a separate transmission line to address an Aluminum/Aluminum oxide/Aluminum (Al/AlO(x)/Al) Cooper-pair box charge qubit.
• Measured qubit lifetime (T₁) as a function of coupling strength to the transmission line.

Main Results:

• Observed a strong correlation between qubit lifetime and the inverse of the qubit-transmission line coupling.
• Achieved a maximum qubit lifetime of T₁=200 μs at the lowest measured coupling.
• This represents a twentyfold improvement compared to previous Cooper-pair box results.
• Inferred a loss tangent in the AlO(x) junction barrier below 4×10⁻⁸ at 4.5 GHz.

Conclusions:

• Reduced coupling in circuit QED systems can significantly enhance superconducting qubit lifetimes.
• The achieved coherence times suggest extremely low loss tangents in the Josephson junction barrier material.
• These findings are critical for advancing the development of fault-tolerant quantum computers.