Quantum dots have taken a significant leap forward in the quest for quantum networks, thanks to a team of researchers who harnessed many-body physics.
By entangling nuclear spins into a ‘dark state,’ they have created a quantum register capable of storing and retrieving quantum information with high fidelity. This breakthrough is a crucial step toward scalable quantum communication and computing.
A New Breakthrough in Quantum Networks
This research, published in Nature Physics, marks an important milestone. The study introduces optically connected qubits, a key advancement required for developing stable and scalable quantum nodes essential for quantum networks.
Quantum dots, nanoscale structures with unique optical and electronic properties, have been used in various technologies. Their ability to emit single photons makes them particularly promising for quantum communication.
“This breakthrough is a testament to the power many-body physics can have in transforming quantum devices.”
Mete Atatüre
However, to build effective quantum networks, stable qubits that can interact with photons and locally store quantum information are necessary. The Cambridge team, in collaboration with the University of Linz, addressed this challenge by leveraging the atomic spins within quantum dots to create a many-body quantum register.
Harnessing Many-Body Physics for Quantum Storage
The researchers successfully stabilized 13,000 nuclear spins into a collective ‘dark state,’ reducing environmental interactions and enhancing coherence and stability. This dark state serves as the logical ‘zero’ state of the quantum register.
A complimentary ‘one’ state, represented by a single nuclear magnon excitation, was introduced. Together, these states enable the writing, storage, retrieval, and reading of quantum information with high fidelity.
The researchers demonstrated these capabilities with a complete operational cycle, achieving a storage fidelity of nearly 69% and a coherence time exceeding 130 microseconds. These results signify a significant advancement for quantum dots as scalable quantum nodes.
Unlocking the Potential of Quantum Dots
Nature Physics highlights the contributions of Mete Atatüre, co-lead author of the study and Professor of Physics at the Cavendish Laboratory. Atatüre emphasizes the potential of quantum dots as multi-qubit nodes and the strides being made toward realizing the promise of quantum technologies.
The study represents a unique combination of semiconductor physics, quantum optics, and quantum information theory. Advanced control techniques were used to polarize nuclear spins in gallium arsenide (GaAs) quantum dots, creating an environment conducive to robust quantum operations.
Overcoming Long-Standing Challenges
Dr. Dorian Gangloff, co-lead author and Associate Professor of Quantum Technology, discussed overcoming the challenges caused by uncontrolled nuclear magnetic interactions. By applying quantum feedback techniques and leveraging the uniformity of GaAs quantum dots, the researchers established quantum dots as operational quantum nodes.
This breakthrough not only enhances quantum dots’ potential but also provides a powerful platform to explore new many-body physics and emergent quantum phenomena.
The Future of Quantum Memory and Networks
The Cambridge team aims to improve their control techniques to extend the quantum register’s storage time to tens of milliseconds. This enhancement will make quantum dots suitable as intermediate quantum memories in quantum repeaters, vital for connecting distant quantum computers.
They are currently focusing on this goal through the QuantERA grant, MEEDGARD, in collaboration with the University of Linz and other European partners. Their research was supported by EPSRC, the European Union, the US Office of Naval Research, and the Royal Society.
As we move toward the International Year of Quantum in 2025, this work highlights the innovative progress being made in quantum technologies. The potential applications for quantum networks in communication and distributed computing are immense.
Reference: “A many-body quantum register for a spin qubit” by Martin Hayhurst Appel, Alexander Ghorbal, Noah Shofer, Leon Zaporski, Santanu Manna, Saimon Filipe Covre da Silva, Urs Haeusler, Claire Le Gall, Armando Rastelli, Dorian A. Gangloff, and Mete Atatüre, 24 January 2025, Nature Physics.
DOI: 10.1038/s41567-024-02746-z
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