Pokemon: Protected Logic Qubit Derived from the 0-$\pi$ Qubit

TL;DR

The paper introduces the pokemon protected qubit, derived from the 0-$\\pi$ qubit, with enhanced protection and coherence due to its localized wave functions and potential for implementation with nonlinear inductors.

Contribution

It presents a novel protected superconducting qubit called pokemon, with improved localization and relaxation properties, and discusses its potential for higher coherence in quantum computing.

Findings

Exponential reduction in relaxation due to wave function localization.

Enhanced protection compared to 0-$\pi$ qubit.

Feasibility of using nonlinear inductors for implementation.

Abstract

We propose a new protected logic qubit called pokemon, which is derived from the 0-$\pi$ qubit by harnessing one capacitively shunted inductor and two capacitively shunted Josephson junctions embedded in a superconducting loop. Similar to the 0-$\pi$ qubit, the two basis states of the proposed qubit are separated by a high barrier, but their wave functions are highly localized along both axis directions of the two-dimensional parameter space, instead of the highly localized wave functions along only one axis direction in the 0-$\pi$ qubit. This makes the pokemon qubit more protected. For instance, the relaxation of the pokemon qubit is exponentially reduced by two equally important factors, while the relaxation of the 0-$\pi$ qubit is exponentially reduced by only one factor. Moreover, we show that the inductor in the pokemon can be replaced by a nonlinear inductor using, e.g., a pair or two pairs of Josephson junctions. This offers an experimentally promising way to implement next-generation superconducting qubits with even higher quantum coherence.