Lattice Patch Structure for Fixed-Frequency Transmon Quantum Computer with High-Fidelity CNOT Gates

Area of Science:

• Quantum Computing
• Superconducting Circuits
• Quantum Error Correction

Background:

• Superconducting transmon processors are key for quantum computing but face scaling challenges like frequency crowding.
• Conventional qubit-coupler-qubit (QCQ) architectures hinder scalability and efficient surface code implementation.
• Existing architectures are susceptible to external flux noise, impacting operational stability.

Purpose of the Study:

• To introduce a novel lattice-patch architecture for superconducting quantum processors.
• To enhance qubit connectivity and simplify surface code mapping.
• To improve the robustness and scalability of quantum computing hardware.

Main Methods:

• Proposed a novel lattice-patch architecture coupling four fixed-frequency transmons to a single fixed-frequency coupler.
• Utilized multi-level numerical simulations to evaluate gate fidelities and identify parasitic effects.
• Investigated the direct mapping of the architecture onto the surface-code lattice unit (plaquette).

Main Results:

• Achieved CNOT gate fidelities exceeding 0.98 across all six connectivity directions within the patch.
• Demonstrated enhanced qubit connectivity and direct mapping to the surface code lattice.
• Identified residual phase accumulation requiring calibration via virtual Rz gates.

Conclusions:

• The lattice-patch architecture overcomes limitations of conventional QCQ designs.
• This fixed-frequency approach provides inherent robustness against flux noise.
• The proposed architecture is a promising building block for scalable, fault-tolerant quantum computers.