Disentangling the facts from the hype of quantum computing

Re:Disentangling the facts from the hype of quantum computing by krastanov on Tuesday September 20, 2022 @11:11PM (#32920439)

Your second paragraph does not make much sense to me. Pretty much any quantum error correcting code being pursued today deals both with phase-flips and bit-flips. The comment about "pure" state also does not make much sense to me: a qubit afflicted by phase noise would not be in a pure state. I think you might be using the word "pure" in a way that is not the typical way it is used in the field.

Maybe you are trying to say that the more toy-like codes that have been demonstrated today, like the repetition code, do not protect against phase flips. That is true, these "easy" codes that are small enough for demonstrations on today's immature hardware indeed do not protect against all types of errors.

But codes like the toric code or qLDPC codes do protect both against phases errors and bit-flip errors. They are just too expensive to implement on today's immature hardware.

Lastly, no, Dwave's annealing approach is not particularly promising compared to others. Annealing does not provide real-world performance boost compared to classical computers unless you have error-corrected qubits.

[ Parent | on HN ]

Re:Disentangling the facts from the hype of quantum computing by mikewarot on Tuesday September 20, 2022 @11:30PM (#32920543)

I'm not talking about phase flips, but actual accumulated phase rotation due to noise, error, cross-talk, etc. Quantum error correction is geared towards keeping a Qubit in alignment with some axis through the Bloch sphere, at the two poles where it intersects the Bloch sphere. In order for the QFT to work, you have to be able to rotate around at least one axis, not near its poles.

[ Parent | on HN ]

Re:Disentangling the facts from the hype of quantum computing by krastanov on Tuesday September 20, 2022 @11:32PM (#32920561)

I still do not understand. Quantum error correction does not require the qubit to be in a particular orientation on the Bloch sphere: any point on the Bloch sphere is equally protected. Are you saying that certain gates are simply difficult to perform precisely, e.g. that they will always have some systematic over-rotation? That also seems to be fixable with what is called randomized compiling.

[ Parent | on HN ]

Re:Disentangling the facts from the hype of quantum computing by mikewarot on Wednesday September 21, 2022 @12:13AM (#32920748)

Any point on the Bloch sphere can be protected... any discrete point, or set of points... but QFT and the rotations it depends upon are analog operations, not discrete.

[ Parent | on HN ]

Re:Disentangling the facts from the hype of quantum computing by krastanov on Wednesday September 21, 2022 @12:35AM (#32920836)

No, all points are protected, not just some set. And no, you do not need infinite precision gates. The only reasonable interpretation of your argument that I can think of is that you are saying that systematic coherent errors add up in a way that error correction can not fix. That is a fascinating problem but it seems to be fixed by turning these errors into incoherent ones through "twirling" and "randomized compilation".

[ Parent | on HN ]

Re:Disentangling the facts from the hype of quantum computing by mikewarot on Wednesday September 21, 2022 @12:55AM (#32920937)

I hope you're right, it would be nice for QC to work out.

[ Parent | on HN ]

Re:Disentangling the facts from the hype of quantum computing by shuuv4678igt on Wednesday September 21, 2022 @08:03AM (#32923814)

do you work on actual feasible implementation or just theoretical circuits for perfect mature qc?

[ Parent | on HN ]

Re:Disentangling the facts from the hype of quantum computing by krastanov on Wednesday September 21, 2022 @09:47AM (#32925098)

I do basically zero work on "algorithms" or circuits for perfect quantum computers. The majority of my work is "here we have this noisy physical system, what can we do to it to make it look more like the abstract idea of a perfect quantum computer". I guess the classical equivalent would be "I am designing the internals of vacuum tubes".

[ Parent | on HN ]