Wednesday, October 24, 2018

Scalable materials for quantum information

There is no question that the explosive spread of electronics and optoelectronic technology in the 20th century has its foundation in the growth and preparation of high quality materials - silicon with purity better than parts per billion, single crystals cut and polished to near-atomic flatness, with exquisite control of impurity concentrations; III-V compound semiconductors for high speed transistors, LEDs, and lasers; even ultrapure SiO2 for millions of km of ultralow loss optical fiber.

Any new electronics-based technology intended to supplant or supplement now-traditional electronic materials at scale is going to need a material platform that can credibly reach similar quality.  Many of the 2d materials have a long way to go in that regard.  However, there have been recent advances in a couple of specific systems targeted for particular forms of quantum information devices.  

arXiv:1810.09350 - Nelz et al., Towards wafer-scale diamond nano- and quantum technologies
It is possible to grow single-crystal diamond films on the 100 mm wafer scale, starting with Si substrates coated with iridium/yttria-stabilized zirconia.  There are dislocations and stacking faults, but it's getting there.  If the native defect density can be controlled and eliminated to a very fine level, and ion implantation can be used to create well-defined defects (NV centers and the like), that would be a big boost to hopes of wide-spread use and mass fabrication of quantum devices based on these systems.

arXiv:1810.06521 - Sabbagh et al., Wafer-scale silicon for quantum computing
Those who want to use electron spins in Si as quantum bits need to worry about whether nuclear spins from naturally abundant 29Si.  It has now been shown that it is possible to use isotopically enriched silane made from 28Si to grow epitaxial layers of material almost devoid of 29Si, and that MOS devices made from this stuff can be of high quality.  It's worth noting:  Isotope separation of different Si isotopic variants of silane by centrifuge is easier than trying the same thing with, e.g, uranium hexafluoride to enrich 235U, because the percentage mass difference is considerably higher in the Si case.

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