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Comment by seiferteric | Hacker News Reader

I am out of the loop, are there any "real" quantum computers yet? I was under the impression that no one was really making actual quantum computers yet, but some sort of annealing machine like d-wave. Are these IBM machines finally "real" quantum computers?

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D-Wave is not a "real" quantum computer in the sense that it is not asymptotically faster than a classical computer. Quantum computers with very few Quibits have existed for a while -- I believe the current record is 17 quibits [1]. I believe that to factor an n-bit integer, you need roughly n bits. So right now, we can factor 17 bit integers, which isn't very useful yet. However, I have read that for quantum simulations, it 30 quibit quantum computers might already be useful.

[1] https://en.wikipedia.org/wiki/Timeline_of_quantum_computing

It is worse than that. To factor n bit number you need roughly n "logical" qubits, i.e. qubits that can store information almost indefinitely. The quantum computers that we have contain low quality "physical" qubits that lose their content after a few millisecond. You need to put an error correcting code on top of the physical qubits to encode the logical qubits. You can expect to need 100s or 1000s of physical qubits per logical qubit. I.e. to decode modern public key encryption you need a computer with millions of qubits. Today we have less than 50 in the best research hardware on the planet.

This one I don't get. Isn't "a few milliseconds" more than enough time to gather a guess on integer factorization (and most of the useful problems)? Wouldn't it suffice to run your program again and again over the same short-lived qubits?

Or a good cavity or two.

Yes. Volkswagen has started using Google's 20-qubit quantum computer (or possibly even the 49-qubit one, which will be announced this March):

https://media.vw.com/releases/951

IBM is also giving select customers access to its real 17-qubit quantum computer.

What does a car manufacturer do with a quantum computer?

Quantum computers can be used for some optimization problems.

There are no commerically useful quantum computers yet. Asking whether there are "real" quantum computers is like asking whether 6 noisy transistors wired together in a lab in 1940s were a real (classical) computer.

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