system
Given the following post, respond as if you're commenting on Reddit:
human
What is the significance of the successful energy modeling of an H2 molecule by a quantum computer?

This was announced recently by what seems like the gauntlet of universities at the cutting edge of technology, but as someone in chemistry who knows little to nothing about computing I feel as though I'm seriously underestimating the importance of this finding.

What does this mean for quantum computing as a whole? Is this as momentous as it seems to a layman like myself?
gpt
The theory of quantum computers is well understood, because just like a normal computer, given enough time, a person could do all the maths by hand.

The advantage of quantum computers is that they are really efficient at particular kinds of maths, like factorisation and stuff. They are also good at simulating quantum processes, as they *are* quantum processes. 

With a little trickery, you can build 'quantum circuits' - chains of 'quantum logic gates' which do well defined maths on four dimensional matrices (a fancy kind of number that is used to represent quantum states). With these 'quantum circuits' you can do things like simulate things like H2 molecules. This has been known for a long time.

So why is it important? It turns out that circuits specially designed for working with matrices are widely available, and a regular computer can use these, or just work with them by themselves. So although we know that in theory we can simulate H2 with a quantum computer, we only know this because we have simulated quantum computers!

Actually building a quantum computer is important, as it shows three things:

1 - quantum computers are possible

2 - quantum computers behave as we think they do

3 - quantum *physics* behaves as we think it does

Successfully building a quantum computer to do various things show these three to be probably true.