Researchers at Delft University of Technology have demonstrated the operation of two-qubit logic gates using mobile electron spins on a silicon chip. This development, published in Nature, could advance the path toward scalable quantum processors.
The team, led by Lieven Vandersypen at QuTech, utilized a technique called conveyor-mode shuttling. This method applies phase-shifted electrical signals to gate electrodes, creating a traveling-wave potential that carries individual electrons across the chip within moving quantum dots. This approach allows quantum information carriers to be physically transported instead of being fixed in place.
Vandersypen noted, “What if you could make two electron spins interact simply by moving them towards each other, each propagated in a traveling-wave potential minimum?” The researchers achieved an average two-qubit gate fidelity of approximately 99 percent by adjusting the interaction strength based on the spatial separation of the electrons. Furthermore, they implemented quantum state teleportation between spatially separated qubits, achieving an average gate fidelity of 87 percent.
This architecture addresses the challenge of connecting distant qubits without complex wiring. Mobile qubits enable dynamic connectivity and allow different quantum error correction codes to operate on the same hardware. The device was fabricated from isotopically purified silicon-germanium, which is compatible with standard semiconductor manufacturing processes, distinguishing this approach from others that require exotic materials.
The publication coincides with advancements in silicon-based quantum computing. In April, QuTech showcased programmable quantum circuits involving six silicon spin qubits. Additionally, a separate team introduced new spin-qubit readout methods designed to reduce wiring complexity in larger quantum processors.
Vandersypen presented the shuttling paradigm at a Princeton Quantum Colloquium on April 27. The researchers anticipate that operations on mobile qubits will become a universal feature of future large-scale semiconductor quantum processors.
