Randomized Benchmarking of a Remote cnot Gate Via a Meter-Scale Microwave Link

Area of Science:

• Quantum Computing
• Superconducting Circuits
• Quantum Interconnects

Background:

• Scaling quantum processors requires reliable interconnects between modules.
• Previous methods struggled to differentiate state preparation and measurement (SPAM) errors from transfer errors.
• Randomized benchmarking offers a method to separate these errors.

Purpose of the Study:

• To develop and benchmark a module-to-module microwave interconnect for superconducting quantum processors.
• To achieve high-fidelity remote state transfer and CNOT gates.
• To implement SPAM-error-tolerant benchmarking.

Main Methods:

• Utilized tunable-coupling qubits for module interconnects.
• Employed a frame-tracking technique for SPAM-error-tolerant benchmarking.
• Implemented a superadiabatic transitionless driving method for state transfer.
• Constructed a remote CNOT gate using local CZ gates and remote state transfers.

Main Results:

• Achieved 98.8% remote state transfer fidelity over a 60 cm coplanar waveguide.
• Reported 93.3% CNOT gate fidelity using randomized benchmarking.
• Demonstrated a method to suppress intermediate excitation in the coplanar waveguide.

Conclusions:

• The developed interconnects are crucial for building larger quantum systems.
• The SPAM-error-tolerant benchmarking method allows for accurate characterization of quantum links.
• Standardized fidelity reporting for module-to-module operations is now possible.