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Dr Xing-Yu Zhu E: [email protected] T: +86 18715110836 W: http://jdxy.ahszu.edu.cn/info/1026/3765.htm Yurchanka Siarhei/Shutterstock.comYurchanka

Building blocks for quantum network architectures

Detail Research Objectives

School of Mechanical and Electronic Engineering Based on a - module, Dr Zhu examines scalable Suzhou University quantum network architecture. Suzhou 234000, P. R. China References Key Laboratory of University of Science and Technology of China Zhu, X.Y., Tu, T., Guo, A.L., Zhou, Z.Q., Guo, G.C. and Li, C.F. Hefei 230026, P. R. China (2020). Spin-photon module for scalable network architecture in quantum dots. Scientific reports, 10(1), 1-9. Available at: Bio https://doi.org/10.1038/s41598-020-61976-2 Dr Xing-Yu Zhu works at the School of Mechanical and Electronic Engineering, Suzhou University. He received his PhD in physics from the University of Science and Personal Response Technology of China in 2020. Dr Zhu has been working on the theoretical research of solid-state spin quantum What are some real-world computing. applications which could benefit from modular network architectures? Funding • National Natural Science Foundation of China The network architectures frequently use small simple (No. 11974336) modules to build large complex systems, and this has many advantages: flexibility, robustness, and scalability. • National Key R&D Program of China In particularly, each module operates individually as (No. 2017YFA0304100) a highly functional node, and nodes connect to each • The Scientific Research Foundation of Suzhou University other through . Thus, the network architectures (No. 2020BS006) are very useful for quantum simulation of interacting quantum many-body systems. Collaborators • Tao Tu (USTC) • Guang-Can Guo (USTC) Xing-Yu Zhu Photo Credit: Physical Sciences ︱ Xing-Yu Zhu at Suzhou University and a his team, they can be divided into two https://www.nature.com/articles/s41598-020-61976-2 broad categories, or ‘architectures’. In the first of these, are arranged in large, orderly arrays, where each will interact directly with its neighbours to process information. Node A Coaxial line Node B Building blocks for Dr Zhu names these systems Resonator ‘monolithic’ architectures.

Alternatively, systems can exploit the enigmatic phenomenon of quantum Spin S-T qubit quantum network in entanglement, where the observed Driving pulse of one particle can b

directly correspond with that of another l 0 ‘entangled’ particle, no matter how far Charge degeneracy architectures apart they are separated. In what Dr regime Zhu’s team call ‘network’ architectures, gy leve c By exploiting the mysterious effects of , Although phenomena such as the effect enables qubits in different networks of interacting quantum bits can offer reliable ways for particle superpositions and quantum parts of a system to become entangled Ener quantum computers to process information. However, many challenges entanglement are still far from being by exchanging a photon, and then, to remain before these systems can be widely applied. Through his properly understood, they are now process information simultaneously. 0 research, Dr Xing-Yu Zhu at Suzhou University in China has developed being used to send, receive, store, an elegant approach to these network architectures, based on modules and process information at far As Dr Zhu explains, both of these d containing semiconductors just a few atoms across. As building blocks greater speeds and efficiencies than architectures face challenges relating for larger systems, these modules could greatly improve the reliability of conventional computers currently to calculation errors – but based on the γ κ quantum computing technologies. allow. Yet despite these exciting results of previous studies, one appears developments, the technology still to win out over the other. “The key faces many difficult challenges before issue of architecture design is to find a uantum computing is among around the world are continually quantum computers can be widely realistic path from the feasible state-of- Δ the most exciting and rapidly developing cutting-edge computation applied in everyday scenarios. art technology to quantum information Qchanging branches of modern techniques, whose capabilities would processing in a fault-tolerant manner”, research. By harnessing quantum have astonished computer scientists Among the most pressing of these he says. “Compared to a monolithic effects to make calculations, researchers just a few years ago. issues is the need to seamlessly architecture, a network architecture integrate the outcomes of real-life may be more achievable for many quantum processes – which play out physical platforms.” within real physical systems on atomic Spin-photon modules for a network architecture. scales – with those of the calculations In their research, Dr Zhu and his initiated by users. In practical settings, colleagues propose new ways to operations must be carried out using achieve reliable quantum information Dr Zhu proposes new ways to achieve large enough numbers of quantum bits, processing using network architectures or ‘qubits’, to improve the capabilities – based on a rapidly growing branch of reliable quantum information of quantum computers over their semiconductor technology. processing using network architectures conventional counterparts. INTRODUCING QUANTUM DOTS – based on a rapidly growing branch of Inevitably, however, such deeply With electrical conductivities falling complex operations will lead to in between those of conductors semiconductor technology. calculation errors, which must then be (such as metals) and insulators (such corrected: a costly and time-consuming as glass or plastic), semiconductors ultraviolet light, causing it to transition of these bands is engrained into the process. To combat this issue, are a crucially important element in from an insulator to a conductor. On a material composition of the quantum researchers need to develop systems many modern technologies. Recently, quantum scale, this involves a single dot. As a result, when the that minimise errors in their calculations it was discovered that when these electron in the dot transitioning from transitions back to the valence band, – but this is no simple task. materials are scaled down to just a few an insulating ‘valence band’ to a it will release a photon with a highly VectorMine/Shutterstock.com nanometres in size, creating structures ‘conductance band’ as it absorbs the specific energy, which perfectly matches MONOLITHS AND NETWORKS named ‘quantum dots’, they can ultraviolet photon. this difference. In recent years, a diverse array of display remarkably similar properties to techniques has emerged to process individual atoms. Just as orbiting have In Dr Zhu’s research, this effect is quantum information with as few errors discrete, or ‘quantised’ energy levels relevant since the quantum states of as possible. Each of them has its unique These properties can be observed characteristic of their atoms, the electrons contained in quantum dots pros and cons, but according to Dr when a quantum dot is illuminated by difference in energy between both can function as qubits, becoming

researchfeatures.com researchfeatures.com Photo Credit: Transfer a purely through manipulations of the Fault-tolerant quantum computation photons coupled to electron spins. https://www.nature.com/articles/s41598-020-61976-2 A 0.8 “This needs to be done in a way that can be extended to systems containing many quantum dots”, Dr Zhu continues. 1 0.7 B “We do this by applying a driving microwave pulse to the system, protocols 0.8 which mediates tuneable interactions 0.6 between the electron spins and 0.6 photons.” This enables operators to https://www.nature.com/articles/s41598-020-61976-2 efficiently generate and absorb photons 0.5 on demand, improving the functionality 0.4 Credit:Photo of the system. Network architectures

0.2 0.4 Finally, within entangled pairs of qubits, it is critically important to ensure 0 that the quantum information held 0.3 within one qubit strongly correlates with that of the other. “The key Physical elements: spin-photon modules challenge here is to establish high- I 0.2 quality remote entanglement in the Network architecture X presence of unavoidable errors”, Dr b Zhu says. “Our approach exemplifies Z 0.1 -iY the feasibility of network architecture Each node includes -iY using currently available experimental several spin-photon Z X techniques.” This is achieved through 0 advanced mathematical procedures, modules I which minimise the influence of

Quantum state transfer between two network nodes. The process matrix of the state transfer in the basis {I, X, − iY, Z} using the quantum process calculation errors.

tomography, and the fidelity reaches Fp = 87.8%. BUILDING BLOCKS FOR photos – in which transverse light waves NETWORK ARCHITECTURES Perhaps the most important feature are aligned along one specific direction. With these measures in place, Dr Before these qubits can be integrated Zhu’s team now present promising of the team’s design is its ability to be into practical network architectures, new routes towards feasible network integrated with many other identical Dr Zhu’s team have identified three architectures. The most significant important challenges, and propose result of these efforts has been a new modules: acting as ‘building blocks’ for measures to overcome them. design for a small, simple ‘spin-photon module’. Containing two quantum more complex systems. The first of these relates to the ability dots, whose electrons can be coupled of network architectures to read and to a photon through spin-charge entangled with other qubits to Yurchanka Siarhei/Shutterstock.com write information onto their qubits, hybridisation, these modules can Inter-node form robust network architectures. using only photons. “This is challenging process quantum information in many error rate Compared with the qubits used in because of the weak influence of a useful ways to produce clear, accurate previous network architectures, such single electron’s spin on its surrounding output signals. as trapped ions and single atoms, this environment, which limits the spin- Intra-node error approach allows for far more reliable photon coupling rates”, explains Dr Perhaps the most important feature rate information processing – significantly Zhu. “We resolve this challenge by of the team’s design is its ability to be reducing calculation errors. For Dr using a method called ‘spin-charge integrated with many other identical

Zhu and his team, these capabilities hybridization’.” This involves coupling modules: acting as ‘building blocks’ for Network architecture towards scalable quantum computation. offer unprecedented opportunities the electric field of a single photon with more complex systems. This enables for developing network architectures the spin of a system comprising two researchers to construct and manipulate suitable for everyday use. entangled quantum dot electrons. As a intricate networks of entanglement, consistent with present technology and can be achieved through far simpler result, system operators can read and suitable for advanced applications in might be achievable in the near future”, architectures than were previously DEVELOPING A NEW MODULE write information onto the qubits far quantum computing. “The spin-photon Dr Zhu concludes. thought possible. Through future The researchers propose that qubits more easily. module we propose constitutes a work to realise their proposal can take the form of quantised ‘spins’ in kind of building block for the network Without the need for further experimentally, Dr Zhu’s team could quantum dot electrons. In this context, The team’s second challenge emerges architecture and all higher functions are technological innovations, this soon bring the widespread use of The research of Dr Zhu brings us one step spin is a purely quantum property, closer to everyday quantum computing. from the need to reliably generate and built upon it. The results of our work approach could ensure that practical everyday quantum computing a step comparable to the polarisation of absorb photons within quantum dots, indicate that the spin-photon network is quantum information processing closer to reality.

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