All-Microwave Leakage Reduction Units for Quantum Error Correction with Superconducting Transmon Qubits.

Area of Science:

• Quantum Computing
• Superconducting Circuits
• Quantum Information Science

Background:

• Minimizing leakage from computational states is a significant challenge in multi-level quantum systems, such as superconducting qubits.
• Transmon qubits, widely used in circuit Quantum Electrodynamics (cQED), are susceptible to leakage into higher energy states, impacting computational fidelity.

Purpose of the Study:

• To experimentally realize and extend the quantum-hardware-efficient, all-microwave leakage reduction unit (LRU) for transmons.
• To evaluate the efficacy of the LRU in reducing leakage in the second and third excited transmon states.
• To demonstrate the application of simultaneous LRUs in a quantum error correction context.

Main Methods:

• Implementation of an all-microwave leakage reduction unit (LRU) tailored for transmon qubits within a circuit QED architecture.
• Characterization of LRU performance, measuring leakage reduction efficacy and impact on the qubit subspace.
• Integration and testing of multiple simultaneous LRUs in a quantum error correction protocol involving stabilizer measurements.

Main Results:

• Achieved up to 99% leakage reduction efficacy in the second and third excited transmon states within 220 nanoseconds.
• Demonstrated minimal impact of the LRU on the essential qubit subspace (ground and first excited states).
• Showcased suppression of leakage buildup to within 1% in data and ancilla qubits over 50 cycles of a weight-2 stabilizer measurement.

Conclusions:

• The realized LRU provides an effective solution for mitigating leakage errors in superconducting transmon qubits.
• The LRU is compatible with quantum error correction schemes, significantly improving their performance by reducing leakage.
• This work advances the practical implementation of high-fidelity superconducting quantum computing systems.