Quantum

Bias-Preserving Entanglement of Kerr-Cat Qubits with an ATS Coupler

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Briefings

This research introduces an asymmetrically threaded SQUID (ATS) parametric coupler to entangle Kerr-cat qubits with high fidelity. Numerical simulations show a bias-preserving controlled-X (CX) gate achieving 99.69% fidelity in the absence of photon loss, while maintaining a noise bias of 9922 under a 100 kHz single-photon loss rate. This protocol suppresses non-adiabatic leakage and supports concatenated cat-qubit architectures.

Key points

• The ATS coupler enables high-fidelity, bias-preserving entangling gates between Kerr-cat qubits using photon-number asymmetry.
• Simulations demonstrate a 99.69% fidelity bias-preserving CX gate in the absence of photon loss for a 50 ns duration.

Context

Kerr-cat qubits offer a hardware-efficient route to fault-tolerant quantum computing by suppressing bit-flip errors exponentially while phase-flip errors increase linearly with mean photon number. Entangling operations must be bias-preserving to prevent phase-flip errors from propagating into bit-flip errors.

Limitations

Results are based on numerical simulations of the full circuit Hamiltonian. The study does not account for experimental photon loss beyond the specified 100 kHz rate, and the 99.69% fidelity is conditional on the absence of photon loss.

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