Two-Qubit Logic and Teleportation with Mobile Spin Qubits in Silicon

Why It Matters

Mobile spin qubits provide reconfigurable connectivity and high‑speed gates, addressing a key bottleneck for error‑corrected silicon quantum processors.

Key Takeaways

• Conveyor‑shuttling moves spin qubits 10 µm in <200 ns with 99.5 % fidelity
• Exchange coupling tuned up to ~90 MHz via barrier voltage and shuttle distance
• CZ gate fidelity reaches 98.9 % using shuttling‑based interaction
• Post‑selected teleportation of a spin state achieved with 86.7 % process fidelity
• Motional averaging extends T₂* during transport, reducing charge‑noise impact

Pulse Analysis

The breakthrough hinges on a conveyor‑shuttling technique that physically transports electron spins across a silicon quantum‑well while preserving coherence. Prior work showed static spin qubits could reach >99 % single‑gate fidelity, but nearest‑neighbour coupling limited circuit depth. By applying phase‑shifted sinusoidal voltages to a series of gate electrodes, the team moved qubits 10 µm in under 200 ns, achieving 99.5 % shuttling fidelity and exploiting motional averaging to extend T₂* beyond static values. This dynamic approach unlocks flexible qubit layouts without sacrificing the ultra‑low error rates essential for fault‑tolerant computing.

Tuning the exchange interaction between two mobile spins proved critical. Adjusting the central barrier voltage and the number of conveyor cycles allowed the exchange coupling J to be swept from a few megahertz up to ~90 MHz, with a sweet spot around 33 MHz that balanced speed and coherence. In this regime, the researchers implemented a conditional‑Z (CZ) gate with a 58‑ns duration and measured a fidelity of 98.86 %, rivaling the best static‑dot gates reported to date. The ability to modulate J on‑the‑fly suggests that larger, reconfigurable quantum circuits could be programmed in real time, simplifying the routing of entanglement across a processor.

Beyond gate operations, the platform demonstrated quantum‑state teleportation by generating an entangled Bell pair of mobile spins, performing a Bell‑state measurement, and reconstructing the teleported state with 86.7 % fidelity. This proof‑of‑concept validates that mobile qubits can not only execute high‑speed two‑qubit gates but also serve as carriers of quantum information across a chip. As silicon manufacturing scales to billions of transistors, integrating conveyor‑shuttling with existing CMOS processes could accelerate the deployment of error‑corrected quantum processors, positioning silicon spin qubits as a leading contender in the race for practical quantum advantage.