Experimental realization of an intrinsically error-protected superconducting qubit

TL;DR

This paper reports the experimental realization of a superconducting $0-ppa$ qubit with intrinsically protected states, showing promising coherence times for fault-tolerant quantum computing.

Contribution

The authors experimentally implement a $0-ppa$ superconducting qubit with protected states, demonstrating its potential for robust quantum information processing.

Findings

Relaxation time of 1.6 ms

Dephasing time of 25 μs

Energy levels match a two-mode Hamiltonian

Abstract

Encoding a qubit in logical quantum states with wavefunctions characterized by disjoint support and robust energies can offer simultaneous protection against relaxation and pure dephasing. Using a circuit-quantum-electrodynamics architecture, we experimentally realize a superconducting $0-\pi$ qubit, which hosts protected states suitable for quantum-information processing. Multi-tone spectroscopy measurements reveal the energy level structure of the system, which can be precisely described by a simple two-mode Hamiltonian. We find that the parity symmetry of the qubit results in charge-insensitive levels connecting the protected states, allowing for logical operations. The measured relaxation (1.6 ms) and dephasing times (25 $\mu$s) demonstrate that our implementation of the $0-\pi$ circuit not only broadens the family of superconducting qubits, but also represents a promising candidate for the building block of a fault-tolerant quantum processor.