Two-qubit logic and teleportation with mobile spin qubits in silicon | Nature

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Subjects

- Quantum information

- Qubits

Abstract

The scalability and power of quantum computing architectures depend critically on high-fidelity operations and robust and flexible qubit connectivity1,2,3. In this respect, mobile qubits are particularly attractive as they enable dynamic and reconfigurable qubit arrays. This approach allows quantum processors to adapt their connectivity patterns during operation, implement different quantum error correction codes on the same hardware and optimize resource use through dedicated functional zones for specific operations such as measurement or entanglement generation4,5,6,7. Such flexibility also relieves architectural constraints, as recently demonstrated in atomic systems based on trapped ions4,5 and neutral atoms manipulated with optical tweezers6,7. In solid-state platforms, highly coherent shuttling of electron spins was recently reported8,9. A key outstanding question is whether it may be possible to perform quantum gates directly on the mobile spins. Here we demonstrate two-qubit operations between two electron spins carried towards each other in separate travelling potential minima in a semiconductor device. We find that the interaction strength is highly tunable by their spatial separation. When we shuttle the two spins towards the centre by 120 nm each for a total displacement of 240 nm, we achieve an average two-qubit gate fidelity of about 99%. Furthermore, we implement conditional post-selected quantum state teleportation between qubits separated by 320 nm with an average gate fidelity of 87%, showcasing the potential of mobile spin qubits for non-local quantum information processing. We expect that operations on mobile qubits will become a universal feature of future large-scale semiconductor quantum processors.

Main

Quantum computing offers the promise to solve complex problems that are intractable for classical computers. As quantum processors scale up, maintaining high connectivity between qubits becomes crucial for implementing effective error correction schemes1,2,3. However, traditional architectures are often restricted to interactions between nearest neighbours, constraining the options for quantum error correction codes and potentially increasing overhead. Mobile qubits offer a promising alternative by enabling flexible connectivity between qubits, thus reducing the overhead associated with error correction schemes4,5,6,7.

Among the various quantum computing platforms, gate-defined semiconductor spin qubits10 have emerged as a promising candidate. These qubits offer a compelling combination of extended coherence times11, high-fidelity operations12,13,14,15,16,17,18,19,20, compatibility with established semiconductor manufacturing techniques21,22,23,24,25 and the potential for high-temperature operation26,27.

Inspired by mobile qubit approaches in atomic systems, in which trapped ions4,5 and neutral atoms6,7 have demonstrated the power of reconfigurable qubit arrays, the question arises whether mobile semiconductor spin qubits offer a route to realize flexible connectivity in a solid-state platform. In recent experiments, a travelling-wave potential, generated by phase-shifted sinusoidal signals applied to successive gate electrodes, transports the spin qubit within a moving quantum dot8,28,29,30. With this so-called conveyor shuttling method, a 99.5% fidelity was achieved when shuttling across an effective 10-μm distance in less than 200 ns (ref. 9).

Building on these advances, we foresee scalable mobile spin qubit architectures based on conveyor-mode shuttling as shown in Fig. 1a, in which qubits can be selectively transported between storage zones and interaction regions are formed by pairs of independent conveyor channels. This approach enables efficient resource sharing and flexible qubit connectivity through shared control lines and sparse storage zones. It may also facilitate uniformly high gate fidelities by performing operations in optimized local electromagnetic environments. The fundamental building block and key challenge for realizing such architectures is the ability to precisely control the interaction between two mobile spin qubits by selectively bringing them together using independent conveyor channels and to achieve high gate fidelities31.

Fig. 1: Mobile spin qubits and shuttling-based architecture.The alternative text for this image may have been generated using AI.Full size image

a, Conceptual architecture for a scalable mobile spin qubit processor based on conveyor-mode shuttling. Qubits can be transported between static storage zones (static dots) and pairs of adjacent conveyor channels that meet at shared interaction zones. Two-qubit operations are performed by simultaneously shuttling two qubits inside the same channel to an interaction zone. This design enables efficient resource sharing. Vertical transport between parallel conveyor channels, passing through vacant storage zones, allows for