IBM unveils 433 qubit quantum computer

There is no known polynomial time algorithm for TSP. AFAIK there are quantum algorithms for TSP with quadratic speedup in comparison to the brute force method (still exponential though).

The one thing quantum computers are (currently and theoretically) able to solve efficiently is the factorization problem, but are very much limited by low qubit number, i.e. engineering problems.

seasox2• 4 years ago

There was a time when people used to say these things about conventional computers, remember the 50s?

bvrmn• 4 years ago

Does it calculate generic Shore?

credit_guy• 4 years ago

Do you mean Shor's algorithm [1]? Most likely no, or IBM would have made sure you'll hear about that.

But let's say it can, and somehow IBM forgot to mention.

Shor's algorithm reduces to a quantum Fourier circuit, with 2N qubit inputs and 2N qubit outputs, where N is the number of digits of the number to be factored. That's 4N qubits only for inputs and outputs.

So, in the best case scenario, this computer would be able to factor a 108-binary digit number.

My computer (2020 Intel-based iMac) can do that in one minute.

Here's the code if you want to try it on your computer:

  import sympy
  n_digits = 54
  p = sympy.randprime(2**(n_digits-1), 2**n_digits)
  q = sympy.randprime(2**(n_digits-1), 2**n_digits)
  sympy.factorint(N)

Output: {53882560694857690729: 1, 44658549937294814041: 1}

[1] https://en.wikipedia.org/wiki/Shor%27s_algorithm

nemoniac• 4 years ago

Before the last line you need

    N = p * q

hdjjhhvvhga• 4 years ago

There's something unsettling about them calling these "quantum computers." There's too much noise for them to be actually usable. It's as if someone constructed one half of an abacus and started calling it "abacus." It just doesn't feel right.

And when we actually build a quantum computer (which, I hope, happens by the end of this century), everybody will be too bored about it.

aliswe• 4 years ago

How do we reconcile between these kinds of news and that Quantum Physicist who says that Quantum computers never will amount to anything? I'm confused ...

e63f67dd-065b• 4 years ago

The claim that quantum computers will never amount to anything is more nuanced than that. There is multiple parts to that claim:

- Shor's algorithm is about the only productive thing we've figured out where a quantum computer has an advantage

- IBM unveils 433 qbit computer, to factor 4096 RSA we're gonna need 8192 logical qbits

- Those 433 qbits are physical qbits, and there's (to the best of my knowledge) no literature on their measurement fidelity, coherence timelines, etc. These are purely experimental machines, it's not like you can plug your laptop into their giant cryogenic machines and run quantum algorithms without a giant team of literal quantum physicists standing by the thing and monitoring it

- How those 433 qbits actually translate into any amount of meaningful computation is up in the air

- The best we figured out was 5 logical qbits running a specialised Shor's algorithm on the 127qbit computer they unveiled a few years back to factor 21=3*7

- Nobody has, to the best of my knowledge, actually run the full Shor's algorithm on anything of note, even on these systems

Not a quantum physicist; I only have vague memories from a quantum computing seminar I took long ago. Feel free to correct if any of the above is incorrect.

desro• 4 years ago

Why such cynicism in the comments? This is a pretty cool achievement, even if it's incremental or lacks present application (I'm not qualified to say either way).

I'm cheering them on!

6nf2• 4 years ago

Can it do anything faster than a traditional supercomputer yet?

derekmcloughlin• 4 years ago

Sabine Hossenfelder has a good summary of the state of Quantum Computing so far:

https://youtu.be/CBLVtCYHVO8

IBM unveils 433 qubit quantum computer

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