Single-electron operations in a foundry-fabricated array of quantum dots

(a) Scanning electron image of one of the Foundry-fabricated quantum dot devices. Four quantum dots can be formed in the silicon (dark grey), using four independent control wires (light grey). These wires are the control knobs that enable the so called quantum gates. (b) Schematic of the two-dimensional array device. Each Qubit (red circle) can interact with its nearest neighbor in the two-dimensional network, and circumvent a Qubit that fails for one reason or other. This setup is what “second dimension” means. Credit: University of Copenhagen

Researchers at the Niels Bohr Institute, University of Copenhagen, in collaboration with the French CEA-Leti, have found industrially-manufactured transistor wafers to be suitable as a qubit platform capable of moving to the second dimension, a significant step for a working quantum computer.

One of the key features of the devices is the two-dimensional array of quantum dots. Or more precisely, a two by two lattice of quantum dots.

Silicon quantum dots are attractive for the implementation of large spin-based quantum processors in part due to prospects of industrial foundry fabrication. However, the large effective mass associated with electrons in silicon traditionally limits single-electron operations to devices fabricated in customized academic clean rooms.

The team demonstrated single-electron occupations in all four quantum dots of a 2 x 2 split-gate silicon device fabricated entirely by 300-mm-wafer foundry processes. By applying gate-voltage pulses while performing high-frequency reflectometry off one gate electrode, they performed single-electron operations within the array that demonstrated single-shot detection of electron tunneling and an overall adjustability of tunneling times by a global top gate electrode.

They also used the two-dimensional aspect of the quantum dot array to exchange two electrons by spatial permutation, which may find applications in permutation-based quantum algorithms.

The result has been published in Nature Communications.