Kavli Affiliate: Irfan Siddiqi
| First 5 Authors: Long B. Nguyen, Long B. Nguyen, , ,
| Summary:
Decoherence errors arising from noisy environments remain a central obstacle
to progress in quantum computation and information processing. Quantum error
correction (QEC) based on the Gottesman-Kitaev-Preskill (GKP) protocol offers a
powerful strategy to overcome this challenge, with successful demonstrations in
trapped ions, superconducting circuits, and photonics. Beyond active QEC, a
compelling alternative is to engineer Hamiltonians that intrinsically enforce
stabilizers, offering passive protection akin to topological models. Inspired
by the GKP encoding scheme, we implement a superconducting qubit whose
eigenstates form protected grid states – long envisioned but not previously
realized – by integrating an effective Cooper-quartet junction with a quantum
phase-slip element embedded in a high-impedance circuit. Spectroscopic
measurements reveal pairs of degenerate states separated by large energy gaps,
in excellent agreement with theoretical predictions. Remarkably, our
observations indicate that the circuit tolerates small disorders and gains
robustness against environmental noise as its parameters approach the ideal
regime, establishing a new framework for exploring superconducting hardware.
These findings also showcase the versatility of the superconducting circuit
toolbox, setting the stage for future exploration of advanced solid-state
devices with emergent properties.
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