Measurement-free, scalable and fault-tolerant universal quantum computing

TL;DR

This paper introduces a measurement-free, scalable, and fault-tolerant approach to universal quantum computing by combining code switching and concatenation techniques, eliminating the need for measurements during computation.

Contribution

It develops new measurement-free protocols for transferring encoded information between color codes and extends these methods to higher-distance codes, enhancing practicality and scalability.

Findings

Protocols outperform measurement-based approaches in realistic regimes

Successful transfer of encoded information between 2D and 3D color codes

Scalable pathway for universal quantum computing on current quantum processors

Abstract

Reliable execution of large-scale quantum algorithms requires robust underlying operations and this challenge is addressed by quantum error correction (QEC). Most modern QEC protocols rely on measurements and feed-forward operations, which are experimentally demanding, and often slow and prone to high error rates. Additionally, no single error-correcting code intrinsically supports the full set of logical operations required for universal quantum computing, resulting in an increased operational overhead. In this work, we present a complete toolbox for fault-tolerant universal quantum computing without the need for measurements during algorithm execution by combining the strategies of code switching and concatenation. To this end, we develop new fault-tolerant, measurement-free protocols to transfer encoded information between 2D and 3D color codes, which offer complementary and in combination universal sets of robust logical gates. We identify experimentally realistic regimes where these protocols surpass state-of-the-art measurement-based approaches. Moreover, we extend the scheme to higher-distance codes by concatenating the 2D color code with itself and by integrating code switching for operations that lack a natively fault-tolerant implementation. Our measurement-free approach thereby provides a practical and scalable pathway for universal quantum computing on state-of-the-art quantum processors.