Code Division Multiplexing Based Readout Scheme for Spin Qubits

Scaling up the number of qubits in fault-tolerant quantum computing calls for scalable multiplexed control and schemes. This paper introduces a novel digital code multiplexing approach for charge readout in quantum computing. Based on digital control and demodulation, the proposed scheme eliminates the need for sinusoidal or more complex waveform generation. Unlike conventional reflectometry, where the number of qubits dictates the number of physical resonant circuits, the proposed method only depends on digital clock frequency and target readout time, enabling a more compact and scalable implementation. This work demonstrates the proposed scheme by modulating two single-electron transistors (SETs) through a transimpedance amplifier (TIA)-based readout chain operating at 4.2 K. Experimental results show that the proposed method reliably distinguishes SET conductivity states under multiplexing, achieving a bit-error rate (BER) below 10−3 within an integration time of 4.55 µs.