Combining n-MOS Charge Sensing with p-MOS Silicon Hole Double Quantum Dots in a CMOS platform*

Silicon hole quantum dots are an interesting complement to conventional electron quantum dots as a way to realise scalable spin qubits. The strong spin-orbit interaction in holes allows all-electric spin control [1]. Recent calculations also suggest it is possible to engineer a “sweet spot” for holes, where environmental decoherence is minimised, while simultaneously allowing rapid spin control [2]. However, the fabrication of p-type devices is not as developed as n-type. As such, disorder and device instability are challenges in p-type devices, and isolation of a single hole in a planar silicon quantum dot was demonstrated only recently [3].

CMOS devices combine both n-type and p-type capabilities within the same chip to offer a route to integrate a high performance, stable electron charge sensor into a hole qubit device. The concept was recently demonstrated using a single electron transistor and a single hole transistor [4] - but a question remains whether a qubit with an ambipolar charge sensor can be fabricated. In this work, we fabricate an n-type charge sensor adjacent to a p-type double quantum dot. We show that this geometry allows sensing of the p-type double quantum dot system down to the last hole. We also demonstrate control of parameters that are essential to qubit operation, including control of the reservoir tunnel rates which can allow latched spin readout [5], as well as control of the interdot coupling rate which is essential for exchange qubit operation. These results show the feasibility of ambipolar CMOS charge sensing qubits.

[1] Crippa et al., Phys. Rev. Lett. (2018)

[2] Liles et al., arXiv. (2021)

[3] Liles et al., Nat. comms. (2018)

[4] Almeida et al., Phys. Rev. B (2020)

[5] Boganet al., Commun. Phys. (2019)