Abstract
A promising building block for a fault-tolerant quantum processor is demonstrated: Exponential protection against relaxation and first-order protection against dephasing is achieved in a superconducting qubit.
Highlights
Preserving the coherence of quantum superpositions over prolonged times is key for large-scale quantuminformation processing [1,2,3]
We first introduce the general features of the 0–π circuit proposed by Brooks et al [12], and we describe the experimentally achievable “soft” regime, where the ground state degeneracy is lifted, the qubit states are exponentially protected against relaxation and charge-noise-induced dephasing and first order protected against flux noise
The 0–π circuit has a unique position among superconducting qubits as it promises simultaneous protection against energy relaxation and pure dephasing, a feature that none of the previously developed superconducting devices have
Summary
Preserving the coherence of quantum superpositions over prolonged times is key for large-scale quantuminformation processing [1,2,3]. Unlike single-mode qubits, such as the transmon, superconducting circuits with more degrees of freedom featuring wave functions in a multidimensional configuration space can be simultaneously protected against energy relaxation and pure dephasing. One such example is the intrinsic protection of the twomode 0–π qubit [11,12], where the combination of one delocalized flux mode (light-fluxonium-like) and one delocalized charge mode (transmonlike) supports the realization of states that are characterized by disjoint support as well as charge insensitivity and flux insensitivity. We provide details about the fabrication, numerical calculations, modeling, and the motivation for the parameter choice in the appendixes
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