[Curious Cat (OP)]

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[Eternal Student]

Hi.

  Do Quantum Computers imply the MWI?    I don't think so.   Why would they?

Best Wishes.

[Colin2B]

As @Eternal Student says “why would they”.
Quantum computers will work despite any specific interpretation. Most working physicists just get on with the job without worrying to much about the 20+ interpretations.

[Eternal Student]

Hi again,

What's the point of tags? And, Should I have used Quick Reply?

  Tags appear at the bottom of a post.  I don't find much use for tags but someone might use them to search for a certain thread.
   I don't like the "Quick Reply" feature myself.
   One of the biggest probelms I found when I started using this forum is that you have time limit.  If you spend too long writing a post then you will be logged out and your work could be lost.  Take precautions against this:   The  "back button" on your web browser can sometimes return you to an earlier page and recover all the text you had written but it doesn't work well if you had used the "quick reply" feature.
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So, are U saying that putting a qubit into a (quantum) superposition is just putting it in/between 2 basis states,
which we intend to measure, later on? Nothing more. There is no splitting/recursion, of the world, involved?

     There is a subtle difference between Quantum computing  and  Analogue Computer devices.  A Qubit will only show the value 0 or 1 when it is observed.  It may be in a superposition of states so that there is a certain probability of measuring one value or the other but that is not the same as the Quibit having the value  1/2    or  any other  fraction   you might think of like  1/3.     When measured the Qubit will always show a value of 0 or 1.
     Meanwhile, an analogue computing device does work with continuous (analogue) quantities.  If you take the lid off an analogue computer and put your volt-meter across the right terminals you could see that it was storing a number as a voltage which can be any value from a continuous spectrum.

   So in answer to the last part   "is that all there is to Quantum Computing,  is there no splitting of the worlds   etc?"   I would say it is fundamentally different to analogue computing devices.   There is Quantum Mechanics involved but your interpretation of QM is less important.  It doesn't matter if you think the MWI explains Quantum mechanics or the Copenhagen Interpretation or something else.    All that matters is that the mechanics (the calculations) of Quantum Mechanics can be applied.

Best Wishes.

[evan_au]

Shor's algorithm sounds fantastical, to me.

Publicly described quantum computers have around 50 qubits, and the quantum state decays very quickly (very short "coherence time"). Getting these qubits to work together on a single computation is a real challenge.
- It is thought that to get practical quantum computers, you would need quantum error-correction. This is in its infancy.
- So probably the only practical error correction is to run the algorithm many times, on many quantum computers in parallel, and see if any of them manage to produce a valid answer.
- Fortunately, for applications like this, it is much easier to test if the answer is correct than it is to generate the answer in the first place.

Shor's algorithm is about factoring numbers -  and the the most lucrative application of this would be breaking the Diffie Helman key exchange, which uses typically 1,024 or 2,048 bit keys. So you would need a quantum computer significantly more advanced than the ones publicised by the likes of Google and IBM.

Of course, if such quantum computers existed, in some dark, cold, dungeon, they wouldn't tell us about them!
There are projects going on around the world to produce quantum-resistant encryption codes, and some candidates have been identified.
See: https://en.wikipedia.org/wiki/Post-quantum_cryptography

...is just putting it in/between 2 basis states, which we intend to measure, later on? Nothing more.

There is nothing easy about quantum computers.
- Getting a single qubit into an initial state is fairly easy, but doing it for hundreds or thousands is very difficult
- Measuring a single qubit is fairly easy, but doing it for hundreds or thousands is very difficult
- Getting 2 qubits to interact in the intended way is difficult, but doing it for hundreds or thousands is extremely difficult

The following research found a potential way to synchronise many qubits...

https://newsroom.unsw.edu.au/news/science-tech/missing-jigsaw-piece-engineers-make-critical-advance-quantum-computer-design

[Halc]

NO, I know think it's the quantum entanglement which/that does the splitting/branching.

Despite plenty of pop-articles to the contrary, MWI does not posit any metaphysical splitting/branching into distinct worlds, which would contradict Everett's single premise. A given system has but the one wavefunction that evolves according to the Schrodinger equation.

[yor_on]

Now you got me confused Halc?

https://plato.stanford.edu/entries/qm-manyworlds/

" The Many-Worlds Interpretation (MWI) of quantum mechanics holds that there are many worlds which exist in parallel at the same space and time as our own. The existence of the other worlds makes it possible to remove randomness and action at a distance from quantum theory and thus from all physics. "

the point is that you can't avoid them as I understands it, if you want it to hold.

[yor_on]

And no, quantum computing relies of superpositions, entanglements and in some motto the use of spin.  And then there is those 'probability amplitudes' and interference. It doesn't discuss what happens to those 'unused' outcomes that might had been. Maybe this is closer to what you thought of Halc?