Mid-circuit logic executed in the qubit layer of a quantum processor

TL;DR

This paper demonstrates mid-circuit measurements and feedforward operations within the quantum layer of silicon spin qubits, reducing reliance on classical processing and addressing key engineering challenges for scalable quantum computing.

Contribution

It introduces an in-layer control technique for mid-circuit measurements, enabling feedforward operations without routing information to classical electronics, a novel approach in silicon spin qubits.

Findings

Mid-circuit measurements performed in silicon spin qubits.

Feedforward operations executed within the quantum layer.

Potential to reduce power consumption in future quantum computers.

Abstract

Practical quantum computers need to continuously exchange data between classical and quantum subsystems during a computation. Mid-circuit measurements of a qubits state are transferred to the classical electronics layer, and their outcome can inform feedforward operations that close the loop back to the quantum layer. These operations are crucial for fault-tolerant quantum computers, but the quantum-classical loop must be completed before the qubits decohere, presenting a substantial engineering challenge for full-scale systems comprising millions of qubits. Here we perform the first mid-circuit measurements in a system of silicon spin qubits, and show that feedforward operations can be performed without needing to route information to the classical layer. This in-layer approach leverages a backaction-driven control technique that has previously been considered a source of error. We benchmark our in-layer strategy, together with the standard FPGA-enabled approach, and analyse the performance of both methods using gate set tomography. Our results provide the first step towards moving resource-intensive classical processing into the quantum layer, an advance that could solve key engineering challenges, and drastically reduce the power budget of future quantum computers.