A cryogenic pulse shaper for spin qubit control utilizing 1ns-time-resolution ADCs on an active silicon interposer operating at sub-100 mK temperatures

Spin quantum bits (qubits) in semiconductor silicon quantum dots are one of the most promising candidates for large-scale quantum processor units, since they potentially have higher scalability through advanced semiconductor integration technologies. However, spin qubits require many control signals such as bias voltages, pulses and high-frequency microwaves, which is a major barrier to scale-up of qubits. In current small-scale quantum computer setup, the spin qubits inside the 100 mK cold finger of dilution refrigerator have been controlled by external room temperature instruments via long cables as shown in the left image of Fig. 1. This setup, consisting of fully analog signal transmission between qubits and external instruments, degrades the signal integrity and causes heat injection via cables, making it unsuitable for scalable qubits. Thus, cryogenic CMOS controller solutions have been widely developed to control the qubits from inside the refrigerator by installing the signal generation circuits on 4 K plate as depicted in the middle image of Fig. 1 [1]. This allows for the connection from the external devices to the refrigerator to be made with only digital wirings, which reduces number of cables and heat inflow. However, the distance between the 4 K plate and the 100 mK cold finger is still more than 2 m, degrading the integrity of wideband signals such as pulses.