Work

A Cryo-CMOS Electron- and Nuclear-Spin Controller for Color-Center Quantum Processors

Year: 2026

Type: article

Abstract: Pursuing a scalable quantum processor based on color centers in diamond, this work presents a novel multi-qubit cryo-CMOS system-on-chip (SoC) with a class-DE radio frequency digital-to-analog converter (RFDAC) and a class-D pulse-density modulation (PDM) driver that controls both electron and nuclear spin qubits of a nitrogen-vacancy (NV) center using a shared driving coil. The electron spin driver employs a polar-based architecture with programmable memory for amplitude control and a direct-digital-synthesis (DDS) phase modulation (PM) path for accurate phase and frequency control. The nuclear-spin driver adopts a digital loop filter with resonant feedback to shape quantization noise out of band, while ensuring improved supply rejection thanks to a feedback loop via an analog-to-digital converter (ADC). Fabricated in a 40-nm CMOS process and operating at 6 K, the chip can drive over 80 mA output current with a 52 dB signal-to-noise-ratio (SNR) over 50 MHz bandwidth (BW) at the electron-spin target frequency (2.5 GHz), and 36 mA with SNR > 52 dB over 20 kHz BW and a spurious free dynamic range (SFDR)$= {\mathrm {47~\text {dB}}}$across the target nuclear-spin band (1.9 to 2.1 MHz), allowing for driving operations on multiple nuclear spins with high fidelity. Driving the qubits resulted in a Rabi frequency of 2.31 MHz (1.95 kHz) for the electron (nuclear) spins, while drawing 45 mW (17 mW) from the supply. The single-qubit operation on an electron (and a nuclear) spin, characterized using gate-set tomography (GST), achieves a fidelity of 99.3(1)% (99.5(1)%). These results advance the scalability of distributed quantum processors based on color centers in diamond.

Source: IEEE Journal of Solid-State Circuits

DOI: 10.1109/jssc.2026.3724484