Thoughts on Quantum Computing - from a Physicist
New post, now with screenshot.
My background: PhD student in Physics, working on quantum information on the theory side. I do know many friends that work on the experimental side, though.
As much as I appreciate the interest in my field over the last year or so, I personally think it's best to keep expectations realistic. Especially with some DD posts I have seen posting incomplete information, and even blatantly false statements (in Physics). I want to clear those up and some personal thoughts on some quantum computing startups.
Quantum communication doesn't allow for faster-than-light propagation of information
I have seen a DD post that says IonQ achieved faster than light communication via networked entanglement of particles. VERY common misconception about entanglement. Affecting one particle in a pair of entangled particles does not affect the other, it will just break the entanglement. It is proven to be impossible via the no-communication theorem.
Breaking Cryptography, more like breaking your portfolio as you baghold for 10-20 years
Yes, Shor's algorithm is real. No, it won't be possible to break encryption until we get a quantum computer with at least 2000 qubits. The most optimal implementations of Shor's algorithm requires around 2n qubits to factor an n-bit number.
As an example for RSA-1024, you'll need more than 2000 LOGICAL qubits. Factoring in error correction, which requires multiple PHYSICAL qubits to represent one single logical qubit, you'll most likely need upwards of 100k physical qubits before we can actually break real-world encryption. I personally see that taking at least 20 years, but some more optimistic estimates place it at 10 years.
IonQ
There's many DD touting IonQ's lower error rates, longer lifetimes, and all-to-all connectivity. While all of these are true, they often forget to mention one drawback: the gate speeds.
It takes around a thousand times longer to execute an operation on trapped ion platforms compared to superconducting platforms (which Google, IBM uses). While finance/techbros that have never touched a quantum mechanics textbook will point to the fact that the lifetime of the qubit is at most on the order of 100 seconds, and think that quantum algorithms won't require more than that time anyways, so this shouldn't be an issue.
However, keep in mind that the algorithms that are most likely to see real-world use are optimization algorithms like VQE and QAOA. These algorithms need to repeat the quantum circuit many, many times as they gradually change the parameters in the circuit to find the optimal set of solutions.
Furthermore, if your circuit output is some continuous variable that's encoded into the probability of measuring one of the states, then you need to repeat the circuit upwards of thousands of time to get a good estimate of that probability.
As a conservative estimate for a simple optimization algorithm, let's say that you need 1000 repetitions of the circuit, each one taking 1000 repetitions to get the output, and each run of the circuit takes 1 second on a trapped ion computer. That takes 11 and a half days on a trapped ion computer, as compared to 17 minutes on a superconducting one. If we use a pay-by-the-minute model in the future for quantum computers, then IonQ likely has to charge less per minute, since you need more time to run an algorithm on their platform. Sure, they can charge a premium for the lower error rates, but if they charge the same amount per minute as superconducting platforms, then customers are likely to simplify the algorithm they want to run (to be more tolerant of errors) to get a solution at a thousandth of the price.
Rigetti
Honestly, looking at their spec sheets for their platforms, and comparing it to Google's and IBM's, I don't see them pulling ahead at any point. Their board also literally kicked out the original founder for (allegedly) being a prick in general.
QUBT
Literally never seen any substantial work from them.
Positions:
Disclaimer
This is not financial advice. I've literally got my portfolio tied up in RKLB and LUNR because I don't know anything about space outside of Kerbal Space Program. I don't invest in quantum because I know quantum. I invest in space because I don't know space. Someone please make a similar post about space to convince me that space is bad too so I'll finally put my money into VOO and QQQ.