Scalable modular architecture for universal quantum computation

TL;DR

This paper presents a scalable modular architecture for universal quantum computation, demonstrating that connecting controllable qubit arrays with a single entangling gate yields a larger controllable system, enabling resource-efficient quantum processors.

Contribution

It introduces a method to build large controllable quantum systems from smaller controllable modules using minimal entangling gates, reducing control complexity.

Findings

Controllable qubit arrays can be combined with a single entangling gate to form larger controllable systems.

The approach is demonstrated with examples of 10 and 127 qubits inspired by IBM processors.

The modular design reduces the number of local controls and couplings needed for controllability.

Abstract

Universal quantum computing requires the ability to perform every unitary operation, i.e., evolution operator controllability. In view of developing resource-efficient quantum processing units (QPUs), it is important to determine how many local controls and qubit-qubit couplings are required for controllability. Unfortunately, assessing the controllability of large qubit arrays is a difficult task, due to the exponential scaling of Hilbert space dimension. Here we show that it is sufficient to connect two qubit arrays that are evolution operator controllable by a single entangling two-qubit gate in order to obtain a composite qubit array that is evolution operator controllable. The proof provides a template to build up modular QPUs from smaller building blocks with reduced numbers of local controls and couplings. We illustrate the approach with two examples, consisting of 10, respectively 127 qubits, inspired by IBM quantum processors.