High-fidelity parametric beamsplitting with a parity-protected converter

Area of Science:

• Quantum Information Science
• Superconducting Circuits
• Quantum Computation and Simulation

Background:

• Fast, high-fidelity operations between microwave resonators are crucial for bosonic quantum computation and simulation.
• Coupling resonators via nonlinear converters and parametric processes is a promising approach.
• Achieving both speed and fidelity is challenging due to parasitic processes and decoherence.

Purpose of the Study:

• To demonstrate a method for achieving fast and high-fidelity operations in superconducting circuits.
• To suppress unwanted nonlinear interactions and prevent converter-induced decoherence.
• To engineer a highly-coherent beamsplitter and fast swaps between microwave cavities.

Main Methods:

• Utilized a differentially-driven DC-SQUID as a nonlinear converter coupled to two high-Q microwave cavities.
• Leveraged inbuilt symmetries of the converter Hamiltonian to suppress unwanted nonlinear interactions.
• Carefully managed drive frequencies and environmental noise spectrum.
• Characterized the beamsplitter in the cavities' joint single-photon subspace.
• Detected and post-selected photon loss events.

Main Results:

• Engineered a highly-coherent beamsplitter and fast (~100 ns) cavity swaps.
• Operations were primarily limited by the intrinsic single-photon loss of the cavities.
• Achieved a beamsplitter gate fidelity exceeding 99.98% through post-selection.

Conclusions:

• Leveraging converter Hamiltonian symmetries is effective in preventing converter-induced decoherence.
• The demonstrated approach significantly surpasses the current state-of-the-art in beamsplitter gate fidelity.
• This work provides a pathway for robust and efficient quantum operations in superconducting circuits.