Quantum control of a cat-qubit with bit-flip times exceeding ten seconds

TL;DR

This paper demonstrates a superconducting circuit implementation of a cat-qubit with bit-flip times exceeding ten seconds, showing that quantum control can be achieved without compromising inherent error protection, a significant step for quantum computing.

Contribution

The authors experimentally realize a cat-qubit with unprecedented long bit-flip times and show controlled quantum manipulations that preserve error protection, advancing the practical use of protected qubits.

Findings

Bit-flip times exceed 10 seconds, four orders of magnitude longer than previous implementations.

Phase-flip times above 490 nanoseconds.

Quantum control does not break the inherent bit-flip protection.

Abstract

Quantum bits (qubits) are prone to several types of errors due to uncontrolled interactions with their environment. Common strategies to correct these errors are based on architectures of qubits involving daunting hardware overheads. A hopeful path forward is to build qubits that are inherently protected against certain types of errors, so that the overhead required to correct remaining ones is significantly reduced. However, the foreseen benefit rests on a severe condition: quantum manipulations of the qubit must not break the protection that has been so carefully engineered. A recent qubit - the cat-qubit - is encoded in the manifold of metastable states of a quantum dynamical system, thereby acquiring continuous and autonomous protection against bit-flips. Here, in a superconducting circuit experiment, we implement a cat-qubit with bit-flip times exceeding 10 seconds. This is a four order of magnitude improvement over previous cat-qubit implementations. We prepare and image quantum superposition states, and measure phase-flip times above 490 nanoseconds. Most importantly, we control the phase of these quantum superpositions without breaking bit-flip protection. This experiment demonstrates the compatibility of quantum control and inherent bit-flip protection at an unprecedented level, showing the viability of these dynamical qubits for future quantum technologies.