Cryo-CMOS Dual-Qubit Homodyne Reflectometer Array with Degenerate Parametric Amplification

In quantum computers, the quantum state discrimination of the physical quantum bits (Qubits) occupies ~80% of the quantum error correction (QEC) cycle. The RF reflectometry or dispersive readout determines the Qubit state by monitoring the RF reflection of the attached high-Q resonant tank. Compared to their dc counterparts, the RF reflectometers enjoy a high signal-to-noise ratio (SNR), low drifting, and fast speed. As a result, a high-fidelity, single-shot, scalable reflectometer array based on cryogenic CMOS (Cryo-CMOS) ICs is in demand for the future large-scale Qubit array (10³ ∼ 10⁶ Qubits). However, the classic Cryo-CMOS heterodyne reflectometers, consisting of MOSFET-based LNA, mixer, and baseband blocks, suffer from high noise temperature and dc power. To address these issues, the Cryo-CMOS parametric circuitry based on varactors is explored. In this article, a dual-Qubit homodyne reflectometer array with 2 RX channels and 1 TX channel is demonstrated. In the RX, the degenerate parametric amplifier (DPA) enjoys a Q-enhanced, λ_RF/² differential-mode (DM) resonator for the high-gain parametric amplification. The common mode (CM) RF input of DPA interacts with the DM resonator by a nonreciprocal, dynamic mode coupling (DMC). It eliminates the necessity of a circulator and the potential oscillation of DPA. The scalability challenge of the DPA's noise temperature T_noise versus the environment temperature T_env is also investigated. In the TX, a current-mode logic (CML) divider with interstate locking and a vector modulator (VM) is implemented to achieve fast modulation for the spur and noise rejection. Measured at 4.2 K, the implemented 65 nm Cryo-CMOS chip presents a 4.5∼7 GHz bandwidth, 52 dB peak RF gain, and 78 K noise temperature, and generates a 10 MHz TX pulse train with-22 dBm RF power and 30 dB tunability. It consumes a total dc power of 33 mW.