A Cryo-CMOS 4.57GHz Dual-Qubit Homodyne Reflectometer Array with High Q Degenerate Parametric Amplifier Through Dynamic Mode Coupling

Error-corrected quantum computing does not only require large-scale (10⁶-10⁹) physical Qubit arrays but also relies on high-fidelity, scalable quantum-to-classic interface electronics. Quantum control and readout systems based on cryogenic CMOS integrated circuits mitigate the error of Qubit manipulation, reduce the cabling complexity, and facilitate the quantum feedback, which pave the way towards practical quantum error correction (QEC) and logic quantum gates. RF reflectometry is widely adopted for qubit states readout. Reflectometry conducts Qubit states discrimination (collapsed to '0' or '1') by detecting the resonant frequency through RF reflection of a high-Q LC tank associated with the sensor Qubit (Fig. 1). The quantum states are encoded in either the amplitude or the phase of the reflected RF signal. Compared with its DC counterpart, the reflectometry achieves unprecedented charge sensitivity, reduces the integration time, and avoids long-term drifting. However, conventional heterodyne reflectometer schemes [1][4][5] adopt sophisticated up/down mixers, ADC, DAC, and PLL for the Qubit excitation and down-mixing, respectively. They suffer from poor TX-RX isolation, inter-modulation, and high DC power, which deteriorate the scalability and readout fidelity. To address these challenges, a highly scalable dual-Qubit homodyne reflectometer array is proposed in this paper. It drives the LC tank by a single PLL and detects the reflection by a high-gain degenerate parametric amplifier (DPA). Along with fast modulation and lock-in detection, it mitigates the interference, complex cabling, and high DC power of conventional heterodyne reflectometers.