Three-Qubit Randomized Benchmarking.

Area of Science:

• Quantum Information Science
• Quantum Computing
• Quantum Error Correction

Background:

• Scalable fidelity metrics are essential for advancing quantum computing as quantum circuits grow larger.
• Existing metrics often focus on single- and two-qubit operations, potentially overlooking multiqubit performance.

Purpose of the Study:

• To introduce and investigate three-qubit randomized benchmarking (RB) as a scalable fidelity metric for multiqubit quantum systems.
• To assess the performance of a three-transmon qubit device using three-qubit RB.

Main Methods:

• Implementation of three-qubit randomized benchmarking (RB) on a quantum device with three fixed-frequency transmon qubits.
• Utilizing pairwise microwave-activated interactions (cross-resonance) for gate operations.
• Introduction of simultaneous RB (combining one-, two-, and three-qubit gates) to predict multiqubit errors.

Main Results:

• Measured three-qubit error per Clifford of 0.106 for all-to-all connectivity and 0.207 for linear connectivity.
• Demonstrated that three-qubit errors can be predicted from one- and two-qubit errors using simultaneous RB under certain conditions.
• Showed that introduced coherent errors significantly increased three-qubit error (0.302) in a manner not predicted by simultaneous RB, highlighting limitations of lower-order metrics.

Conclusions:

• Three-qubit RB is a vital metric for accurately evaluating the performance of multiqubit quantum devices.
• The study underscores the necessity of dedicated multiqubit fidelity metrics beyond single- and two-qubit benchmarks.
• Results indicate that specific coherent errors can disproportionately impact three-qubit gate fidelity, necessitating advanced diagnostic tools.