Measuring and Suppressing Quantum State Leakage in a Superconducting Qubit

Area of Science:

• Quantum Computing
• Quantum Error Correction

Background:

• Quantum systems must remain within their two-level qubit subspace to avoid leakage errors.
• Minimizing leakage errors is essential for the feasibility of quantum error correction.

Purpose of the Study:

• To quantify leakage errors in superconducting qubits.
• To reduce gate errors and leakage rates through optimized control techniques.

Main Methods:

• Utilized randomized benchmarking combined with leakage population measurement.
• Employed derivative reduction by adiabatic gate pulse shaping and pulse detuning.
• Characterized single-qubit gates in a superconducting qubit.

Main Results:

• Achieved single-qubit gate errors consistently below 10^{-3}.
• Reduced leakage rates to the 10^{-5} level.
• Identified incoherent heating as a significant contributor to residual leakage.

Conclusions:

• Optimized control techniques drastically reduce leakage errors in superconducting qubits.
• Incoherent heating is a key factor limiting further error reduction.
• The developed methods are crucial for advancing quantum error correction viability.