Of course, as you’re aware, this is the million-dollar question, and in fact, one of the quantum hardware companies, Rigetti, has literally put a million-dollar bounty on — if you run quantum advantage demonstration or hardware, we’ll give you a million dollars. In fact, that’s probably an underpayment, because it would be such a big milestone, but we have some views on this.
Knowing that this is also an educational podcast, I might take a side step here to note that one of the things that I’m really excited about that has happened in the development of quantum algorithms is the invention of something called a variational algorithm. In particular, it used to be that back in the ’90s, the quantum algorithms were envisioned where you run it once and you get your answer. Instead, there’s this new breed of algorithms that are more adaptive and variational in nature, so you don’t just run it once. You run it dozens of times — in fact, probably millions of times.
It gives a lot of error resilience, and If I can give an analogy here, I started thinking of it as, imagine your thermostat at home for heating and cooling is broken in such a way that it still works when you turn it right, it gets warmer, and when you turn it left, it gets colder, but the actual knob is mistuned. It says that it’s 80 degrees Fahrenheit, and it’s actually a comfortable 72. That’s something that I consider very annoying, but it’s not like the end of the world. You can still recalibrate your expectations so that if you want it to be very cold, then it ends up showing, say, 70, which would seem comfortable, but actually, it’s colder, and vice versa. So, that’s the kind of resilience that a variational algorithm gives: The quantum computer itself can be miscalibrated, but it doesn’t really matter at the end of the day, because as long as you can turn the knob, and left is left and right is right, you just rebalance to a new point.
Bringing us back to your question of quantum advantage, I think that with this variational algorithm paradigm, there’s now a hope for having quantum advantage. Before, we have, as people may have heard, these error-corrected qubits. So, in one path, where we need error correction, that’s going to take millions of qubits to get to quantum advantage, and that path will almost certainly happen, in my opinion, but I think it’s 10-plus years away. I do think that sometime in the next five years or so, if error rates keep on plummeting the way they are for current quantum systems, we can get away with not having perfect error-corrected quantum machines if we adopt these approaches, like these variational algorithms.
Obviously, predictions are hard to make, but I would venture, yes, that it’s very feasible in five years, with continuing hardware improvements and continuing code design improvements with the software, that there will be an inflection point where it’s more cost effective to run a problem on a quantum computer than on a classical computer.