Fully Integrated Cryo-CMOS Spin-to-Digital Readout for Semiconductor Qubits

A fully integrated CMOS readout operating at cryogenic temperature for semiconductor spin qubits is fabricated and characterized. The readout is based on a direct spin-to-digital conversion, consisting of integrating the spin-dependent current from a sensing single-electron transistor and an accurate comparator to provide a 1-bit digital output related to the qubit state. The cryogenic comparator uses floating-gate transistors to obtain a low power, compact, and self-calibrated threshold. The readout can resolve a variation of the sensing current of 250 pA with a submicrosecond time resolution and a fidelity of 99.86% for a total power consumption of 1.2 mW and an occupation area of less than 0.04 mm2. Compared to the most common RF-reflectometry readout techniques, our solution does not require off-chip components and the handling of microwave signals, paving the way for a more compact and reliable readout system.