Quantum

Protecting bosonic codes from ancilla-induced errors with continuous-variable flags

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Briefings

A new continuous-variable flag protocol protects bosonic quantum codes from ancilla-induced errors by using an auxiliary oscillator to encode and correct phase-space errors. The scheme requires no new hardware components, utilizing existing dispersive couplings and rotations to drive the flag. Simulations using realistic circuit-QED parameters predict over three orders of magnitude fewer logical errors for a four-component cat code compared to standard parity measurements, with a finite-energy GKP logical lifetime approaching the noiseless-ancilla bound.

Key points

• The continuous-variable flag protocol uses an auxiliary oscillator coupled via dispersive interactions to encode and correct phase-space errors from ancilla decay in bosonic codes.
• Simulations with realistic circuit-QED parameters predict over three orders of magnitude fewer logical errors for a four-component cat code using the flag compared to standard parity measurements.

Context and limitations

Results are based on simulations with realistic circuit-QED parameters; the protocol's performance under different noise conditions remains to be verified experimentally.

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