# Superconducting circuit protected by two-Cooper-pair tunneling

## TL;DR

This paper introduces a novel superconducting qubit design that leverages two-Cooper-pair tunneling to create a protected quantum state, potentially enhancing qubit coherence by reducing environmental sensitivity.

## Contribution

The work proposes a new superconducting circuit element enabling parity-based qubit encoding with improved protection against decoherence.

## Key findings

- Ground state manifold is nearly degenerate and indexed by Cooper pair parity
- Large capacitance shunting enhances qubit protection
- Potential for increased qubit coherence and stability

## Abstract

We present a protected superconducting qubit based on an effective circuit element that only allows pairs of Cooper pairs to tunnel. These dynamics give rise to a nearly degenerate ground state manifold indexed by the parity of tunneled Cooper pairs. We show that, when the circuit element is shunted by a large capacitance, this manifold can be used as a logical qubit that we expect to be insensitive to multiple relaxation and dephasing mechanisms.