Benchmarking a High-Fidelity Mixed-Species Entangling Gate

Area of Science:

• Quantum Computing
• Atomic Physics
• Ion Traps

Background:

• Implementing two-qubit logic gates is crucial for scalable quantum computation.
• Using different atomic species (heterospecies) for qubits presents unique challenges and opportunities.
• Efficiently controlling qubits with lasers is a key requirement for quantum algorithms.

Purpose of the Study:

• To demonstrate a high-fidelity two-qubit logic gate between a ^{43}Ca^{+} hyperfine qubit and a ^{88}Sr^{+} Zeeman qubit.
• To utilize a single laser for driving the gate, leveraging the proximity of optical transitions.
• To characterize the performance and fidelity of this heterospecies gate.

Main Methods:

• Implementation of a two-qubit logic gate using ^{43}Ca^{+} and ^{88}Sr^{+} ion qubits.
• Utilizing a single 402 nm laser to drive the gate, exploiting spectral overlap of transitions.
• Characterization via full randomized benchmarking, gate set tomography, and Bell state analysis.

Main Results:

• Successful implementation of a two-qubit logic gate between different ion species.
• Achieved a high gate fidelity of 99.8(1)% using Bell state analysis.
• Demonstrated good spectral isolation and low photon scattering errors with the chosen laser wavelength.

Conclusions:

• Heterospecies ion gates are feasible with high fidelity, comparable to same-species gates.
• A single laser can efficiently drive gates between specific ion species, simplifying experimental setups.
• The achieved fidelity is consistent with known error sources, providing a baseline for future improvements.