Reviewed by Louis CastelJan 29 2025
Scientists at the University of Cambridge's Cavendish Laboratory have used the atoms inside a semiconductor quantum dot to create a functional quantum register in a revolutionary development for quantum technologies. The study was published in Nature Physics.
The study shows how to create a new kind of optically connected qubits, which is a significant step forward for the creation of quantum networks, where stable, scalable, and adaptable quantum nodes are crucial.
The distinctive optical and electrical characteristics of quantum dots, which are nanoscale objects, result from quantum mechanical effects. These systems have already found application in medical imaging and display screens, and their ability to function as bright single-photon sources has largely led to their adoption in quantum communication.
Effective quantum networks, however, require stable qubits that can interact with the photons and locally store quantum information in addition to single-photon emission. By using the atoms' natural spins to create quantum dots, the study creates a working many-body quantum register that can store data for long periods.
A group of interacting particles, in this case, the nuclear spins inside the quantum dot, whose collective behavior results in new, emergent properties not found in individual components, is referred to as a many-body system. The researchers developed a scalable and resilient quantum register by utilizing these collective states.
The Cambridge team successfully prepared 13,000 nuclear spins into a collective, entangled state of spins called a "dark state," working closely with colleagues at the University of Linz. This dark state, which is the logical "zero" state of the quantum register, improves coherence and stability by reducing interaction with its surroundings.
To illustrate a coherent wave-like excitation involving a single nuclear spin flip propagating through the nuclear ensemble, they introduced a complementary “one” state as a single nuclear magnon excitation. When combined, these states allow for the high-fidelity writing, storing, retrieval, and reading out quantum information.
By attaining a coherence time of more than 130 microseconds and a storage fidelity of almost 69% over the course of an operational cycle, the researchers proved this. As scalable quantum nodes, this represents a significant advancement for quantum dots.
This breakthrough is a testament to the power many-body physics can have in transforming quantum devices. By overcoming long-standing limitations, we’ve shown how quantum dots can serve as multi-qubit nodes, paving the way for quantum networks with applications in communication and distributed computing. In the 2025 International Year of Quantum, this work also highlights the innovative strides being made at the Cavendish Laboratory toward realizing the promise of quantum technologies.
Mete Atatüre, Study Co-Lead Author and Professor, Physics, Cavendish Laboratory, University of Cambridge
Quantum information theory, quantum optics, and semiconductor physics are combined in this research. Gallium arsenide (GaAs) quantum dots' nuclear spins were polarized by the researchers using sophisticated control techniques, which produced a low-noise environment for reliable quantum operations.
By applying quantum feedback techniques and leveraging the remarkable uniformity of GaAs quantum dots, we’ve overcome long-standing challenges caused by uncontrolled nuclear magnetic interactions. This breakthrough not only establishes quantum dots as operational quantum nodes but also unlocks a powerful platform to explore new many-body physics and emergent quantum phenomena.
Dorian Gangloff, Study Co-Lead Author and Associate Professor, Quantum Technology, University of Cambridge
In the future, the Cambridge team hopes to improve the control methods and increase the amount of time their quantum register can store information to tens of milliseconds. Due to these advancements, quantum dots could be used as intermediary quantum memories in quantum repeaters, which are an essential part of connecting distant quantum computers.
To achieve this ambitious goal, they have partnered with Linz and other European partners to advance quantum memory technologies using quantum dots through their new QuantERA grant, MEEDGARD. The Royal Society, EPSRC, the European Union, and the US Office of Naval Research funded this study.
Journal Reference:
Ghorbal, A., et al. (2025) A many-body quantum register for a spin qubit. Nature Physics. doi.org/10.1038/s41567-024-02746-z