Cryogenic CMOS LNA based on Resistive-Feedback for RF readout of Spin-Qubits

Abstract

The promise that quantum computing is going to solve intractable computational problems has drawn tremendous interest and motivation in research communities throughout the world. However, operating a large-scale quantum computer requires classical electronics. In the present experimental setups, classical electronics is placed at room temperature rather than at cryogenic environment where qubits operate, hence requiring a huge amount of interconnections. Considering future scaling of qubits, classical electronics for readout and control must be placed close to these qubits. This thesis project explores the readout of spin qubits which are one of the most promising candidates for a large-scale quantum computer. The readout chain is one of the essential component for operating the large-scale quantum computer. Baseband and RF readout techniques for readout of spin qubits were explored in this thesis project. Based on this, the decision was taken to implement amplifier for RF readout as this gives the option for multiplexed readout of multiple qubits over a single wire connecting the quantum processor and the control electronics thus minimizing the number of readout lines from 20mK to the 4K stage where cryogenic electronics is envisioned to be operating. Limited scaling of the transistor drain noise at cryogenic temperatures was explored. Since many qubit channels are to be multiplexed broadband LNA is required. Resistive-Feedback was selected as a suitable topology to be implemented in TSMC 40nm CMOS. This is due to its simplicity in providing input match and robust broadband noise performance. The test chip was fabricated and tested both at the room and cryogenic temperatures. When operating at the room temperature the LNA achieved minimum noise temperature of 27K at 200MHz which increases up to 45K at 1GHz with a power consumption of 67mW. The S11 is greater than -30dB at 200MHz and increases up to -10dB at 800MHz. Preliminary measurement results at 5K show the LNA achieving minimum noise temperature close to 4K at 400MHz which increases to 6K at 1GHz with power consumption of close to 37mW. Low noise temperature of the LNA would enable higher readout bandwidths. Also, broadband low noise temperature enabled by resistive feedback will increase the number of channels to be multiplexed and will result in the reduction in interconnections.