3/Hot Silicon Qubits

We aim to achieve high temperature operation qubits (hot silicon qubits) using silicon qubit systems. The high temperature here refers to about 1 Kelvin (-272°C), which is higher than the tens of milli-Kelvin at which solid-state qubits normally operate. If qubits that operate at higher temperatures than usual can be realized, it is expected that the allowable circuit power consumption (heat generation) will dramatically increase due to the cooling capability, and it will be possible to place cryogenic control circuits in the vicinity of the qubits. This is expected to contribute to the realization of large-scale integrated silicon quantum computers. One of the known challenges in achieving hot silicon qubits is the decrease in quantum information retention time as temperature rises. To break this common sense, we are challenging to find the sweet spot where the quantum information retention time reaches its maximum value, based on the deep exploration and clarification of unexplored physics. To achieve this, we are working on the development of advanced control techniques and precise characterization in strong collaboration with other R&D themes.

R&D Challenge

• 6. High temperature operation of silicon qubits

  The operating temperature of silicon qubits could, in principle, be higher than that of superconducting quantum computers, which means that the cooling capacity of a significantly larger refrigerator could be used, which is very advantageous in overcoming thermal problems. We will first conduct experiments using a "small-scale experimental circuit" with a portion of the qubit array structure to identify issues related to improving the fidelity of qubit manipulation for our 5-year goal (qubit operations). Next, we will evaluate and verify 1K temperature operation of silicon qubits; at 1K, the cooling capacity is 1000 times higher than the lowest temperature part of a dilution refrigerator. This allows us to reduce the effects of heat generation and other factors on the control and readout circuits. Next, we will challenge 1.5K operation and provide feedback to the power design of a large-scale integrated silicon quantum computer. 1.5K refrigeration does not require expensive He3 gas and does not require a structure to dilute He3/He4, which allows for a larger refrigeration system at a lower cost. In addition, the refrigeration system can be manufactured by domestic refrigeration equipment manufacturers, and further improvement in cooling capacity can be expected. In addition, we will conduct research and development of silicon hole spin qubits, which can be advantageous in terms of integration, high-speed operation, and heat generation. In terms of coherence and stable device operation, the electron spin system is currently advantageous, and we will compare the two and identify issues. Finally, we will benchmark the electron spin system and the hole spin system in terms of stability, coherence, integration, high-speed operation, and heat generation.

• List of research results " Hot Silicon Qubits "