Extending the lifetime of a quantum bit with error correction in superconducting circuits

Area of Science:

• Quantum Computing
• Quantum Error Correction
• Superconducting Circuits

Background:

• Quantum error correction (QEC) is crucial for building fault-tolerant quantum computers.
• Previous QEC demonstrations focused on code properties rather than qubit lifetime.
• The 'break-even' point, where a logical qubit outlasts its physical components, remained elusive.

Purpose of the Study:

• To demonstrate a quantum error correction system that achieves the break-even point.
• To suppress energy loss errors in a logically encoded qubit.
• To advance experimental QEC from concept validation to performance metrics.

Main Methods:

• A qubit was logically encoded in superpositions of Schrödinger-cat states of a superconducting resonator.
• A full QEC protocol was implemented using real-time feedback for encoding, error monitoring, decoding, and correction.
• Full process tomography was used to measure the logical qubit lifetime.

Main Results:

• The corrected logical qubit achieved a lifetime of 320 microseconds, surpassing individual component lifetimes.
• This represents a 20x improvement over the transmon, 2.2x over the uncorrected logical encoding, and 1.1x over the best physical qubit.
• The system demonstrated the effectiveness of hardware-efficient qubit encodings.

Conclusions:

• The study successfully reached the quantum error correction break-even point.
• This work highlights the potential of hardware-efficient encodings for practical quantum computing.
• The results pave the way for exploring fault-tolerant system design and performance optimization.