0, 1, superposition

Doh, quantum computers are tristate logic devices?

In classical computer science, bits — or binary digits — hold data encoded as ones and zeros. In quantum computing, data is measured in qubits, or quantum bits. As such, a qubit can have three possible states — one, zero or a “superposition” of one and zero.

I mean technically it is correct, I guess (ignorning mixed states), but doesn’t this make it sound like qubits are just three state classical systems? Or is my nitpicky-meter too high?

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10 Responses to 0, 1, superposition

  1. I was noting this with some friends earlier while we were doing CS homework. This particular mistake is many years old though. I.e., years ago the media was always saying “quantum computers are powerful because they work in trinary.” Now the media is saying “quantum computers are powerful because they solve everything in parallel, so they can solve NP-complete problems in polynomial time.”
    Yeah… :-|.

  2. Aaron Denney says:

    And qutrits will have four states, zero, one, two, and a superposition…

  3. quantum says:

    The article goes on to say that an n-dit has 2^n-1 states: all the basis states, then pairwise superpositions, then superpositions of triples, etc. A quantum computer can compute on all these states in superposition. Therefore n qubits — enough to represent a (2^n)-dit — suffice for checking 2^(2^n) solutions in constant time! And this is without even using all the different mixed states…

  4. I’m always concerned that people will mistake my explanations of what a qubit is, assuming that quantum computers are classical analogue computers. I’ve never worried about people thinking that it was a three level system. Maybe it’s time to start worrying about that!

  5. serafino says:

    If it were so, the Aymara ‘trinary’ language
    would be a sort of quantum language. Or not?

  6. At least it is a step beyond what they used to say, which is that a qubit can be any number between 0 and 1.

  7. I will of course admit to being a total N00B when it comes to quantum computing, but isn’t the categorical explanation here kind of misleading? AFAIK any measurement of a qubit either yields “1” or “0”, so why should those be lumped in with the superposed qubit?

  8. Dave Bacon says:

    Hey Tyler,
    Yep! That’s exactly right. That’s why we’re all mocking the quote! The reason it is technically correct is because a qubit can be in each of these three categories…that is the state can be of the form |0> or |1> or alpha|0>+beta|1>. But the quote reall makes it sound like quantum computing works because there are three different states (tristate logic) which is wrong.

  9. Hey, what do you know, I got it right! Cool.

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