Fast, High-Fidelity Addressed Single-Qubit Gates Using Efficient Composite Pulse Sequences

Area of Science:

• Quantum Computing
• Atomic Physics
• Quantum Control

Background:

• High-fidelity quantum operations are essential for building scalable quantum computers.
• ^{43}Ca^{+} hyperfine qubits offer potential for atomic clock applications and quantum information processing.
• Controlling individual qubits in a multi-qubit system presents significant challenges.

Purpose of the Study:

• To implement high-speed, high-fidelity addressed single- and multi-qubit gates.
• To benchmark the gate fidelity and error rates for ^{43}Ca^{+} qubits in a surface trap.
• To investigate the scalability of microwave control for quantum registers.

Main Methods:

• Utilized electronic microwave control for addressed single-qubit gates.
• Employed a spatial microwave field gradient for independent control of two qubits in close proximity.
• Implemented an efficient four-pulse scheme for two-qubit operations.
• Performed parallel randomized benchmarking to quantify gate errors.

Main Results:

• Achieved a single-qubit Clifford gate error rate of 1.5×10^{-6} using 600 ns π/2 pulses.
• Demonstrated independent addressed two-qubit gates with an average error rate of 3.4×10^{-5} per addressed π/2 gate.
• Showcased the feasibility of controlling qubits with 5 μm separation.

Conclusions:

• Microwave control provides a fast and high-fidelity method for operating ^{43}Ca^{+} atomic clock qubits.
• The demonstrated spatial addressing technique is scalable to larger numbers of qubits in a single register.
• This work contributes to the development of robust quantum computing architectures.