Tunnel control in a CMOS device with minimal overhead

The tight control of exchange interaction is crucial for the realization of two qubit gates in spin qubit devices. Most device architectures at present rely on dedicated gates to efficiently control the tunnel coupling between neighboring quantum dots. While viable for a few qubits, this method presents scalability issues due to the important overhead and related contact and fan-out difficulties for quantum chips with a large number of qubits. Alternatively, recent proposals of scalable strategies tackle the control of the tunnel coupling by tuning the confinement between the quantum dots.

In this work, we demonstrate the tunability of the tunnel coupling in a foundry-fabricated CMOS device  over one order of magnitude without dedicated tunnel gates. We measure the exchange energy as a function of detuning of an isolated double quantum dot by performing spin-blockade spectroscopy coupled with gate-based reflectometry readout, and fit these results to analytical toy models to estimate the tunnel coupling. Additionally, we realize numerical simulations of exchange in the realistic device structure using the full configuration-interaction method, and obtain a good agreement with experiments. We therefore explore with simulations the viability and limitations of this method of control for the tunnel coupling. These results demonstrate a key component to develop a scalable foundry-fabricated CMOS spin qubit unit cell with minimal overhead.