Quantum computers, devices that process information leveraging quantum mechanical effects, could tackle some tasks that are difficult or impossible to solve using classical computers. These systems represent data as qubits, units of information that can exist in multiple states at once, unlike the bits used by classical computers that represent data using binary values ("0" or "1").
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Some of the quantum computers developed in recent years store quantum information in the spin (i.e., intrinsic angular momentum) of electrons or nuclei that are trapped in small semiconductor-based structures, known as quantum dots. For these devices to operate reliably, however, engineers need to be able to precisely measure the quantum states of the spin qubits they rely on, a process that is known as qubit readout. It would also be advantageous for these states to be precisely measured in a way that is architecturally compact, or in other words, using space-efficient hardware as opposed to numerous bulkier components.
Researchers at Quantum Motion and University College London (UCL) recently introduced a new approach to clearly read out the states of spin qubits leveraging high-frequency electrical signals. This method, introduced in a paper published in Nature Electronics, was developed by Jacob F. Chittock-Wood and his colleagues while he was completing his Ph.D. at UCL.
"Initially, our aim was to characterize a new generation of quantum devices made using industrial chip technology," said Jacob F. Chittock-Wood, lead author of the paper and now a post-doctoral researcher at RIKEN in Japan, told Phys.org. "During our measurements, however, we came across an unexpected signal that led us to uncover a new way of reading out spin qubits. We then used this technique to measure the exchange interaction between two electron spins, which is the key interaction behind two-qubit operations in spin-based quantum computers."
Amplifying weak signals with a radio-frequency cascade
The new approach to measure spin qubit states introduced by Chittock-Wood and his colleagues is called radio-frequency electron-cascade readout. This method leverages radio-frequency signals to move electrical charge back and forth within semiconductor-based quantum dot devices.
"This motion is coupled to a reservoir, where it creates a much stronger response and effectively amplifies a signal that would otherwise be very weak," explained Chittock-Wood. "What is unique is that this process repeats continuously with the radio-frequency drive, rather than happening as a single cascade event. We demonstrated the effect experimentally in a planar silicon MOS spin-qubit device."
As part of their study, the researchers implemented their approach on a prototype quantum processor and assessed its ability to distinguish between different spin states. They found that their method yielded much clearer signals, improving the signal-to-noise ratio by over 35 dB.
Notably, Chittock-Wood and his colleagues could reliably read out two-electron spin states in about 7.6 microseconds. Moreover, using their approach, they achieved the coherent control over spin qubits necessary to perform quantum logic operations.
"At the end of a quantum computation, qubits must be measured to determine the result," said Chittock-Wood. "In semiconductor spin qubits, that is usually done using a nearby charge sensor, but those sensors add complexity and take up valuable space on the chip. Our radio-frequency electron-cascade readout offers a compact alternative by strongly amplifying a signal that is normally quite weak. In our planar silicon MOS devices, this made dispersive readout hundreds of times faster than previous approaches on the same platform, while maintaining similar performance."
A further step towards scalable quantum computing
The spin qubit readout method devised by this research team could soon be improved further and applied to larger quantum processors. In the future, it could also enable the readout of qubit states from afar, which would allow multiple qubits to share a common readout infrastructure.
The improvements in measurement clarity and speed reported in this recent paper could soon inspire other researchers to devise similar radio-frequency-based spin readout methods. Eventually, these methods could contribute to the advancement of quantum computers, potentially facilitating their shift from small laboratory systems to larger and fully functioning processors that can be deployed in the real world.
"The main attraction of this approach is that, in principle, it could allow multiple qubits to be measured in parallel while sharing the same readout infrastructure," added Chittock-Wood. "The next step is to extend the method to larger arrays and demonstrate that kind of distant, multiplexed readout. If successful, it could reduce the number of sensors and wiring lines needed to scale up quantum chips."
Written for you by our author Ingrid Fadelli,edited by Gaby Clark, and fact-checked and reviewed by Robert Egan—thisarticle is the result of careful human work. We rely on readers like you to keep independent science journalism alive.If this reporting matters to you,please consider a donation (especially monthly).
More information: Jacob F. Chittock-Wood et al, Radiofrequency cascade readout of coupled spin qubits, Nature Electronics (2026). DOI: 10.1038/s41928-026-01582-8.
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This story was originally published on Phys.org.
