While the leading solid-state-based approach today for treating quantum information uses superconducting qubits, there are several potential alternatives. These include semiconductor spin qubits, historically demonstrated in III-V materials, but with limited “lifetime” due to coupling between the electron spin and the nuclear spins of the III-V elements.
Only in recent years has the prospect of using nuclear spin-free, isotopically purified silicon-28, the most-common isotope, made silicon an especially attractive candidate for hosting electron spin qubits with a long quantum coherence time. The main challenge now is defining an elementary cell compatible with circuit upscaling to hundreds of qubits and more.
Leti and its long-time research partner Inac, a fundamental research division of CEA, are investigating a silicon-on-insulator (SOI) technology for quantum computing with proven scalability, since it was originally developed for CMOS VLSI circuits. In this approach, quantum dots are created beneath the gates of n-type (respectively p-type) field effect transistors, which are designed to operate in the “few-electron” (respectively “few-hole”) regime at cryogenic temperatures (below 0.1 K).
Leti and Inac have developed a process for mastering control of the operation of both types of devices using Leti’s SOI nanowire FET technology. Their teams have demonstrated the co-integration and successful operation of quantum objects with conventional CMOS control electronics (standard ring oscillators) on 300mm SOI substrates.
“This technology has acquired a certain degree of robustness, and we aim at using it with very minor modifications to demonstrate qubits co-integrated with their control electronics,” said Louis Hutin, scientific staff. “This co-integration success represents a critical asset for the eventual design of a quantum computer.”