This is exciting! But keep in mind that the PR materials can be confusing. If you look at the specs https://www.rigetti.com/qpu you can see their quantum processors have on the order of 10 qubits, and after less than ~10 logical gates the state of the system will be completely scrambled due to the imperfections of the gates. It is a great milestone, and it should be celebrated, but we need something much bigger and way less sensitive to noise to be able to call it "quantum computer".
It should be noted that while quantum computers in this regime don’t outperform classical computers, they still can do sensible calculations. Aside from the toy calculations like producing a Bell state, it seems that the “Hello World” of quantum computing is becoming calculating energies of simple molecular configurations, like dihydrogen.
Given that it’s computing something via a bonafide programming language, I don’t think it’s unfair to call it a “quantum computer”.
The advantage of scalable digital quantum computers when/if they get built is that they can do certain very specific mathematical operations in polynomial time (instead of exponential for classical computers). This is a fairly imprecise statement (but gives good intuition). It is conjectured without yet being proven (still, there are many clues to it being true). It applies only to very specific problems, so there are "classically easy" problems which we will just continue solving with classical computers, and there are many problems that are infeasibly difficult for both classical and quantum computers.
An example of where quantum computers will excel is simulating large organic molecules (which is impossible today) ushering a new era of drug discovery and material science.
While there are toy applications of small computers, you probably need hundreds or thousands logical qubits. Given the low quality of the hardware and the environmental noise it is expected that you will need to use error correction codes where you encode a single logical qubit on top of hundreds or thousands of physical qubits.
In other words, once we have a machine with 10000 physical qubits that can all be well controlled and entangled with each other, with gate fidelities of 0.99 nobody (almost nobody) will be able to argue that it is not a quantum computer.
This device here has 20ish qubits with gate fidelities of 0.8 to 0.98.
From what I've read so far they give you both: a VM that simulates qbits for local development, but then you can schedule a real run a physical quantum device (that's the cloud side).
As someone who understands nothing about quantum computing, what are some good resources to begin learning? Hopefully with examples/code that I can run.
Yanofsky and Manucci's "Quantum Computing for Computer Scientists" is a smooth intro if you come from a CS background.
Nielsen and Chuang's "Quantum Computation and Quantum Information" is more thorough and advanced from a mathematical point of view. But it contains a primer on the linear algebra required.
I'm currently taking a class of QC and we're following the book "Quantum Computation and Quantum Information" by Michael Nielsen and Isaac Chuang: I find it very clear and it doesn't assume prior experience/knowledge of the topic.
I suggest you to give a look.
Aaronson’s “Quantum Computing Since Democritus” is quite good. For hands-on examples, pull down the Microsoft quantum development kit, which includes the Q# programming language and the ability to run programs on a simulated quantum computer or submit to quantum runtimes like IBM’s.
Does anyone know where this system stands performance wise vs classical computers? Are there types of problems where this is known to be faster now? Or are we still waiting for more qubits for that to happen? Thanks!
> Are there types of problems where this is known to be faster now?
Not yet. This is commonly called "quantum advantage" or "quantum supremacy", i.e. proof that on a certain (even artificial and with no practical applications) problem a quantum computer can perform better than classical state-of-the-art. So far even for the task of simulating quantum circuits (which quantum computer should definitely be better at!) we don't have enough cubits to have a go at quantum advantage.
Depending on connectivity (full connectivity like on ionQ vs planar connectivity like IBM / Rigetti), we need between 100-200 and thousands of qubits to show quantum advantage (denser connectivity -> lower qubit number requirement). And that's just for a synthetic problem with no applications.
No Quantum computer has been shown to do anything useful faster than a normal computer. Everything you can do on any existing quantum computer you can do faster on a normal computer.
If you want to play with quantum algorithms your best shot is simulating a quantum computer.
Don't get me wrong: Scientists should do research on Quantum computers. They may or may not be useful in the future. But selling QC as a (useful) service? It's decades away.
