Efficient measurement of quantum gate error by interleaved randomized benchmarking (1203.4550v2)

Abstract: We describe a scalable experimental protocol for obtaining estimates of the error rate of individual quantum computational gates. This protocol, in which random Clifford gates are interleaved between a gate of interest, provides a bounded estimate of the average error of the gate under test so long as the average variation of the noise affecting the full set of Clifford gates is small. This technique takes into account both state preparation and measurement errors and is scalable in the number of qubits. We apply this protocol to a superconducting qubit system and find gate errors that compare favorably with the gate errors extracted via quantum process tomography.

• The paper proposes a novel protocol that uses interleaved randomized benchmarking to efficiently measure the error of individual quantum gates.
• It integrates randomized gate sequences with inserted target gates to isolate error rates and provide robust theoretical bounds.
• The method shows improved precision over quantum process tomography, advancing the development of fault-tolerant quantum computing.

Overview of Efficient Measurement of Quantum Gate Error by Interleaved Randomized Benchmarking

The paper "Efficient Measurement of Quantum Gate Error by Interleaved Randomized Benchmarking" details a significant step forward in the measurement of quantum gate errors. Authored by Magesan et al., the paper introduces an experimental protocol that is scalable for estimating the average error of individual quantum computational gates, utilizing a method known as interleaved randomized benchmarking (IRB). This essay offers a concise overview of the paper’s objectives, methodologies, key results, and implications for quantum computing.

The haLLMark of this protocol is its efficiency in estimating quantum gate errors, leveraging the randomized benchmarking (RB) technique — a method known for its scalability and capability to deliver noise characterization that is relatively independent of state-preparation and measurement (SPAM) errors. The paper stems from the need to overcome limitations posed by quantum process tomography (QPT), an existing technique hindered by scalability issues and SPAM error dependencies. Instead of requiring exhaustive information about the quantum process, this protocol emphasizes partial characterization — focusing specifically on individual gates within the Clifford group.

Methodology

The protocol is rooted in:

1. Standard Randomized Benchmarking: Implementing sequences of random gates is employed to reveal, through fidelity decay, the average error rates across the gate set.
2. Interleaved Benchmarking: Inserting the gate of interest between random sequences of Clifford gates to ascertain its individual error rate. The paper presents a robust analysis, providing theoretical bounds on the estimated error for the designated gate.

Key Results

Applied to a superconducting qubit system, the protocol successfully measured the average error of single-qubit gates, $X_{\pi/2}$ and $Y_{\pi/2}$. The experimental demonstration revealed an impressively bounded average error of $0.003 \left[0,0.016\right]$. These results notably outperform those acquired via QPT, showcasing the protocol’s promising precision and reliability.

Implications and Future Directions

Practically, the findings of this paper facilitate improved error characterization in quantum processors, crucial to advancing fault-tolerant quantum computation. The ability to efficiently and accurately quantify gate errors can lead to the refinement of quantum algorithms and potentially expedite the development of robust quantum computing systems.

Theoretically, the protocol’s independence from SPAM errors and its scalability across an increasing number of qubits offer substantial methodological advancements in quantum error correction metrics. The approach aligns with the quantum industry's drive towards achieving computational fidelity that supports real-world applications.

Looking to the future, this research paves the way for further exploration into quantum gate benchmarking extensions, possibly involving other types of gates or different configurations within quantum systems. It poses an interesting avenue for assessing the dynamics of quantum gate operations in both simpler and more complex quantum architectures. Ultimately, this work contributes importantly to the foundation of scalable, high-fidelity quantum computation, a crucial step toward fully operational quantum computers.