Dual-rail encoding with superconducting cavities.

Area of Science:

• Quantum Computing
• Quantum Error Correction
• Superconducting Circuits

Background:

• Quantum error correction (QEC) is crucial for reliable quantum computation.
• Minimizing and mitigating errors in quantum hardware is essential for advancing QEC.
• Existing quantum hardware faces challenges with dominant error sources like photon loss.

Purpose of the Study:

• To introduce a novel quantum hardware design, the circuit-Quantum Electrodynamics (QED) dual-rail qubit.
• To demonstrate a method for converting dominant photon loss errors into correctable erasure errors.
• To enable universal quantum operations using a gate-based approach with minimal ancilla overhead.

Main Methods:

• Encoding a physical qubit in the single-photon subspace of two superconducting microwave cavities.
• Utilizing a transmon ancilla for gate operations, state preparation, and readout.
• Implementing error detection and conversion mechanisms to transform hardware errors into erasure errors.

Main Results:

• The circuit-QED dual-rail qubit effectively converts photon loss errors into erasure errors.
• A gate-based set of universal quantum operations (state preparation, readout, single/two-qubit gates) is achievable with one transmon ancilla per qubit.
• First-order hardware errors are converted to erasure errors, leaving significantly smaller background Pauli errors.

Conclusions:

• The dual-rail cavity qubit demonstrates a favorable hierarchy of error rates.
• This qubit design is expected to perform effectively below relevant QEC thresholds with current coherence times.
• The proposed circuit-QED implementation offers unique advantages over linear optics approaches for QEC.