We’ve had a few discussions during class about whether or not quantum computational systems have clearly demonstrated superiority to their classical counterparts. Google is widely acknowledged to have achieved “quantum advantage” in 2019 with its 53 qubit system called Sycamore. There is still some debate about it because IBM claimed to be able to perform the same computation over a period of a few days on its most powerful supercomputer. Nature has a nice piece on this:
https://www.nature.com/articles/d41586-019-03213-z
A little over a year ago a group in China built a photonics-based system that carried out a type of quantum computation (called boson sampling) in 200 seconds. Classical algorithms are much slower, clocking in at 2.5 billion years. Nevertheless, there are some caveats, the most important being is that the photonics system is especially suited to the task of boson sampling and is not a basis for general quantum computing. Furthermore, boson sampling itself is not known to have any useful applications other than allowing quantum computer systems to demonstrate “quantum advantage” over classical systems. Despite these somewhat deflationary notes, I think it’s an impressive feat!
More recently, a researchers were able to construct a programmable photonics chip. The idea behind such an approach is that photons can be used as quantum information carriers. My understanding (which is limited!) is that there have been problems with controlling and scaling up such systems, but that this recent work marks an important step forward in developing this approach. You can take a look at the “News and Views” article about this work in Nature:
https://www.nature.com/articles/d41586-021-00488-z
There’s also a nice description of this in Ars Technica:
I’m not an expert in these matters, but it seems like the progress has been amazing.