Alberto Ferraris

Multiplexed local charge storage, close to quantum processors at cryogenic temperatures could generate a multitude of control signals, for electronics or qubits, in an efficient manner. Such cryogenic electronics require generating quasi-static control signals with small area footprint, low noise, high stability, low power dissipation and, ideally, in a multiplexed fashion to reduce the number of input/outputs. In this work, we integrate capacitors with cryogenic high-electron mobility transistor (HEMT) arrays and demonstrate quasi-static bias generation using gate pulses controlled in time and frequency domains. Multi-channel bias generation is also demonstrated. Operation at 4 K exhibits improved bias signal variability and greatly reduced subthreshold swing, reaching values of ~6 mV/decade. Due to the very low threshold voltage of 80 mV at 4 K and the steep subthreshold swing, these circuits can provide an advantage over the silicon-based complementary metal-oxide-semiconductor equivalents by allowing operation at significantly reduced drive bias in the low output voltage regime <1 V. Together with their high-speed operation, this makes HEMTs an attractive platform for future cryogenic signal generation electronics in quantum computers.

The recent developments in quantum computing architectures have caused an increasing interest in cryogenic low-noise amplifiers (LNAs) due to their role in the qubit readout chain. Advanced quantum computers with many qubits will require cryogenic integration of thousands of LNAs. Minimizing LNA power dissipation while maintaining low noise will be of key importance due to the limited available cooling power in cryostats. In addition, self-heating (SH) and heat dissipation of cryogenic LNAs represent limiting factors in the device’s performance and integration. While SH is predicted to increase in transistor channels at cryogenic temperatures, large-scale thermal spreading outside of active devices due to SH is not well understood. Here, the 2-D heat flow due to the SH of InGaAs/InP high electron mobility transistors (HEMTs) is experimentally studied. We realize a matrix of Schottky diode thermal sensors close to the active device, which allows us to obtain a full 2-D temperature mapping with respect to the power dissipated by the HEMT. Measurements are performed in the temperature range of 300–4.2 K. Results indicate that HEMT large-scale thermal spreading due to SH is suppressed at lower ambient temperatures. Below 77 K, the increase of surface temperature at a distance $<$ 12 $\mu$ m from the active area is less than the measurement sensitivity (0.5 K). Therefore, we conclude that the increased SH in the channel at cryogenic conditions does not result in increased surface heating. These results build on our understanding of the opportunities for integrated cryogenic electronics in quantum computers.