The demonstration of a fundamental building block for a modular quantum-computing architecture - a key step towards viable quantum computers - is reported in a paper published online this week in Nature.

Quantum computers have the potential to solve problems that would considerably tax their classical counterparts. However, building large-scale quantum processors is difficult owing to the errors and noise that are inherent in real-world quantum systems. A modular architecture, in which separate quantum systems are connected within a network, may be the key to scalable quantum computing. However, the development of such an architecture has proven challenging to realize.

Kevin Chou and colleagues have developed an essential component of a modular quantum architecture, demonstrating for the first time a quantum operation across two modules on demand. They present a so-called teleported controlled-NOT logic gate that operates on logically encoded data qubits, a concept proposed in 1999 that has not been demonstrated on demand until now. The teleportation of such quantum gates consists of an operation between two unknown quantum states, without relying on direct interaction between the data qubits.

The realization of a quantum gate can be characterized in terms of its fidelity, which is a measure of the operation’s closeness to its ideal performance. In this case, the authors find the fidelity of the teleported gate to be 79%. By demonstrating that such modular approaches can be successfully realized, this work is a promising step towards the future development of fault-tolerant quantum computers.