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Balances CMOS semiconductor process affinity with stable quantum dot operation
November 24, 2020
Hitachi has successfully developed a prototype for the basic structure of a quantum bit*1 array using silicon semiconductors that will help enable large-scale integration of quantum bits for quantum computers. Until now, producing compact quantum computers has been difficult because large-scale integration entails increasing the amount of signal wiring for operating quantum bits. The prototype array attempted to achieve large-scale integration by arranging quantum bits in a two-dimensional state while limiting the increase in signal wiring by making shared use of signal wires that control multiple quantum bits through the application of CMOS semiconductor circuit technology.*2 Hitachi confirmed the stable formation of quantum dots*3 – which trap electrons during quantum computation – in the desired positions on the array. Going forward, Hitachi will work on testing quantum computation using this array structure and accelerate the development of silicon quantum computers with which large-scale integration is possible.
Two-Dimensional Silicon Quantum Bit Array Structure (Left-Hand Images) and Cross-Section Photos of Prototyped Quantum Bit Array (Right-Hand Images)
These results have already been published as a featured article in the science journal Applied Physics Letters (23 April, 2020; Japan time; 24 April)
Some of the findings were obtained through research conducted in collaboration with the Tokyo Institute of Technology.
Quantum dot is a fundamental structure for realizing a quantum bit. A key issue in achieving large-scale integration is the fact that as the number of quantum bits increases, the amount of signal wiring needed to operate the various quantum bits also increases, making it impossible to develop compact quantum computers. This array uses devices that form multiple quantum bits with signal wiring corresponding to word lines and bit lines*7, which intersect each other in the same manner as semiconductor memory such as SRAM and DRAM*8, and a structure that controls the coupling between quantum bits. Sharing signal wiring in this manner makes large-scale integration of quantum bits possible while limiting the increase in the wiring amount.
This structure makes stable operation of quantum dots possible based on optimization of the structure (gate length of the two types of gate electrode mentioned above, positional relationship, etc.) and the voltage applied to each gate electrode.
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