Quantum Information Processing with Cat Qubits

Quantum information processing with cat qubits harnesses superpositions of coherent states in bosonic modes to encode and manipulate quantum information. In contrast to two-level qubits, cat qubits reside in an oscillator’s large Hilbert space, where engineered dissipation or multi-photon drives stabilise superpositions of opposite-phase coherent states. This architecture offers an intrinsic bias against certain error channels, notably exponential suppression of bit-flip errors while tolerating more frequent phase-flip events. By exploiting symmetry-protected manifolds and bias-preserving operations, cat qubits enable hardware-efficient fault tolerance, high-fidelity logical gates and innovative approaches to quantum annealing and error correction. The global significance of this paradigm lies in its capacity to reduce error-correction overheads and to deliver scalable platforms for universal quantum computation, quantum simulation and optimisation tasks.

Research from Nature Portfolio

Recent studies have demonstrated fast, high-fidelity operations between microwave resonators used to host cat qubits. By coupling two high-Q cavities via a parity-protected nonlinear converter and actuating parametric drives, researchers engineered beamsplitter gates with durations on the order of 100 ns and achieved gate fidelities exceeding 99.98%. Leveraging Hamiltonian symmetries suppresses unwanted nonlinear interactions and minimises converter-induced decoherence.

Work on holistic control strategies has realised a universal set of logical gates on a qubit encoded in a superconducting cavity resonator using four-component cat states. Accurate characterisation of the coupled oscillator–transmon system Hamiltonian allowed the implementation of arbitrary single- and two-qubit operations with inferred fidelities above 98%. This approach illustrates the power of numerical pulse optimisation in the large Hilbert space of bosonic modes.

Another line of investigation employs networks of two-photon-driven Kerr-nonlinear resonators to implement quantum annealing. Each resonator encodes an Ising spin in a degenerate cat-state manifold, and local four-body interactions map optimisation problems onto the oscillator network. Numerical simulations indicate that this platform exhibits strong resilience to photon loss, yielding high success probabilities in combinatorial optimisation while offering a realistic roadmap for circuit QED implementations.

Quantum Information Processing with Cat Qubits publication trend

The graph below shows the total number of articles in quantum information processing with cat qubits across all publications each year (not limited to Nature Index journals).

Technical terms

Schrödinger cat state: A quantum superposition of two coherent states with opposite phases in a bosonic mode, used to encode quantum information with noise-bias properties.

Bosonic mode: A quantised electromagnetic or vibrational mode that supports an infinite-dimensional Hilbert space, enabling encoding of logical qubits in superpositions of photon number states.

Two-photon driven-dissipative process: A stabilisation mechanism that uses a coherent two-photon drive and engineered loss to confine a bosonic mode to a cat-state manifold, protecting against single-photon errors.

Bias-preserving operation: A gate or measurement that maintains the intrinsic error-rate asymmetry of a biased qubit, ensuring that suppressed error channels remain exponentially unlikely.

Logical qubit: An error-protected qubit encoded in multiple physical states or modes, whose design allows detection and correction of dominant error types without compromising protected operations.

References

1. High-fidelity parametric beamsplitting with a parity-protected converter. Nature Communications (2023).
2. Implementing a universal gate set on a logical qubit encoded in an oscillator. Nature Communications (2017).
3. Quantum annealing with all-to-all connected nonlinear oscillators. Nature Communications (2017).
4. Autonomous quantum error correction and fault-tolerant quantum computation with squeezed cat qubits. npj Quantum Information (2023).
5. Building a Fault-Tolerant Quantum Computer Using Concatenated Cat Codes. PRX Quantum (2022).
6. Repetition Cat Qubits for Fault-Tolerant Quantum Computation. Physical Review X (2019).