What's with the (very bad) jokes?
As for diamonds... lol... let's see... we first made a man-made diamond back in 1950.
In the following 10 years (up to 1960's) they could have fully incorporated chip production via man-made diamonds.
And yes, they were viable for such use back then and could have been produced in mass quantities cheaply with good enough quality to be used for computers (this is even more-so possible today)
So effectively, we could have had diamond based computer chips for decades and technology that far surpasses current one in terms of power/efficiency and thermal output.
Actually, it's very likely the technology itself was made, never released into commercial production though.
One of the reasons why man-made diamonds were never put into mass production is due to the single cartel that holds the diamond market in it's proverbial grasp and effectively controls it, giving it means to charge insane prices.
That said, even if they are put in mass production, from a resource/technological/manpower point of view, production is cheap and more than doable in practically record time (has been for some time now), but still, as it's with any new product, it will probably cost A LOT because manufacturers love to overcharge for new technologies, even if they themselves spent a fraction on it.
On top of that, Graphene as a material was placed as public knowledge over 12 years ago.
Had they wanted to implement it in practical use, it would have taken them 2 years tops.
And if they made a combination of graphene/diamond chips... lol...
Seriously folks... consumer based technology is toying in obscurity for decades, but hey, the market is in no hurry to implement new technologies as soon as they are discovered because that would probably put a large dent into profits (merely because people would not be enticed to upgrade anytime soon).
What we have now in circulation is laughably outdated.
But hey... we live in a capitalist world... well-being of mankind is not the goal of such a system because money and profits are (everything else is a proverbial side-effect).
Quantum computers?
They should have been in circulation by now.