Qubits made on 300mm CMOS process for first time

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CEA affiliates Leti and Inac, working with the University of Grenoble Alpes, have demonstrated a quantum-dot-based spin qubit fabricated on a 300mm CMOS line.

The device comprises a two-gate, p-type transistor with an undoped channel. At low temperatures, the first gate defines a quantum dot encoding a hole spin qubit, while the second defines a quantum dot used for the qubit readout. All electrical, two-axis control of the spin qubit is said to be achieved by applying phase-tunable microwave modulation to the first gate.

According to Leti, while the semiconductor spin qubits reported so far have been made in academic labs, its development relies on FD-SOI based FETs. The standard single-gate transistor layout is modified in order to accommodate a second closely spaced gate, which serves for the qubit readout.

The approach also uses a p-type transistor, which means the qubit is encoded by the spin of a hole, rather than the spin of an electron. This, say the partners, allows the qubit to be controlled electrically, with no additional components required for manipulation.

“Our one qubit demonstrator brings CMOS technology closer to the emerging field of quantum spintronics,” said Silvano De Franceschi, pictured, Inac’s senior scientist.

Maud Vinet, Leti’s advanced CMOS manager, added: “This proof-of-concept result, obtained using a CMOS fab line, is driving a lot of interest from our semiconductor industrial partners as it represents an opportunity to extend the impact of Si CMOS technology and infrastructure beyond the end of Moore’s Law.”

Because the thin-film FD-SOI process has a back-gate, this can be used to tune the quantum dot’s electrical state or the dot-to-dot coupling. That, Leti adds, avoids the need for an overlapping top gate and the need to deal with the crosstalk.

The next steps for the project will be to demonstrate ‘a few’ coupled qubits and to develop a strategy for their long range coupling.