New publication on fault-tolerant code switching

Cologne, September 3, 2025 – neQxt is working on scalable ways to make quantum computers work reliably. By encoding logical information across many physical qubits in a Quantum error correcting code, fragile quantum states are protected against errors that naturally arise in any physical architecture. Implementing a universal set of quantum gate operations on logical qubits remains challenging. Some gates are "easy" to perform fault-tolerantly, while others, like the T-gate, typically require additional costly procedures such as preparing special "magic states".

In our 2024 work, now published in “Quantum”, we analyze an alternative paradigm to realize a universal gate set by transferring an encoded quantum state at will between two types of quantum error correction codes that can, in conjunction, facilitate all required gates easily. Importantly, the code switching scheme relies on transversal gates only, acting on each qubit independently, and is therefore naturally fault-tolerant without extra circuitry. Also, this property allows one to use the scheme for codes of arbitrary distance without increasing the circuit depth. We show through simulations that this method can outperform existing alternatives at realistically attainable physical error rates.

This matters because it offers a path to more practical and scalable fault-tolerant quantum computing. Transversal code switching reduces hardware requirements and could therefore make experimental demonstrations of logical quantum algorithms more accessible in the near future.