A way to read quantum bits faster and with less hardware
Quantum computers process information in a fundamentally different way from conventional computers, using quantum bits, or qubits, that can exist in multiple states at once. This could allow them to tackle problems beyond the reach of today's machines, from simulating new materials to optimizing complex systems.
But to extract useful results from a quantum processor, researchers must reliably measure the state of each qubit, a task that remains one of the main bottlenecks in the field.
One of the leading approaches to building quantum computers uses superconducting circuits that carry current without resistance at extremely low temperatures.
In superconducting quantum computers, qubits are measured by coupling them to microwave resonators. The problem is that the capacitor connecting the qubit to its microwave resonator also makes the two systems partially mix together. That allows the qubit to be measured, but it also increases the chance that the qubit will lose information or change state during the measurement itself.
Researchers led by Pasquale Scarlino at EPFL have now demonstrated an alternative readout architecture that achieves fast and accurate qubit measurements with fewer additional components. The work, published in PRX Quantum, was carried out in collaboration with the group of Professor Alexander Blais at the University of Sherbrooke, one of the pioneers of superconducting quantum computing.
"This is an important piece of work demonstrating a new, more efficient and faster way of measuring transmon superconducting qubits," says Scarlino, referring to transmons, which are superconducting qubits designed to have reduced sensitivity to charge noise.
The new architecture
Instead of the standard approach of connecting the qubit to its readout resonator using only a capacitor, the team added a Josephson junction alongside the capacitor.
A Josephson junction, named after physicist Brian Josephson, who received the 1973 Nobel Prize in physics, is made by sandwiching a thin layer of a non-superconducting material between two layers of superconducting material. Quantum mechanics allows electrical current to tunnel through this barrier, creating a nonlinear electrical element that is central to many quantum technologies.
In the new quantum computer design, the Josephson junction creates a different type of interaction between the qubit and the resonator, providing built-in protection against one of the main mechanisms that causes qubits to lose information during measurement. This added protection allows the measurement to be performed with a stronger signal, producing a clearer distinction between a logical zero and one and making the measurement easier to identify.
Using this approach, the researchers correctly identified the qubit state 99.4% of the time with an integration time of only 68 nanoseconds. They also achieved a quantum nondemolition fidelity of 98.4%, meaning the measurement itself almost always left the qubit state unchanged.
The experiments closely matched theoretical predictions developed in collaboration with researchers at the University of Sherbrooke, providing a detailed understanding of how the new architecture works.
Simplicity
Beyond performance, one of the main advantages of the design is its simplicity. The scientists were able to make fast and accurate qubit measurements without needing two components commonly used in state-of-the-art superconducting qubit readout systems: Purcell filters and near-quantum-limited amplifiers.
Eliminating these reduces the system's footprint and the number of components that must be fabricated and calibrated while remaining compatible with multiplexed readout, in which many qubits are measured through the same hardware.
The researchers also note that the same architecture is compatible with more conventional linear readout schemes by adjusting the resonator properties, an approach they leave for future device generations.
The new readout architecture combines fast, high-fidelity qubit measurement with a reduced hardware footprint. The authors suggest that these features make the approach a promising alternative for superconducting qubit readout and point out that it is compatible with multiplexed architectures and future implementations.
Publication details
Guillaume Beaulieu et al, Fast, High-Fidelity Transmon Readout with Intrinsic Purcell Protection via Nonperturbative Cross-Kerr Coupling, PRX Quantum (2026). DOI: 10.1103/m348-gy75
Who's behind this story?
BA art history, MA material culture. Former museum editor, paramedic, and transplant coordinator. Editing for Science X since 2021. Full profile →
Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full profile →
Citation: A way to read quantum bits faster and with less hardware (2026, July 28) retrieved 28 July 2026 from https://phys.org/news/2026-07-quantum-bits-faster-hardware.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.