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Question is: How is the set of states $Q$ logically replaced by a Hilbert space if a classical Turing machine is described by a 7-tuple $M=\langle Q,\Gamma, b,\Sigma, \delta, q_ {0},F\rangle$?

I read here that the set of states Q is replaced by a Hilbert space.
But I want to understand how Hilbert Space is represented in quantum electronics, using Quantum gate circuits

I don't know if this is a physical question but I think that is important to understand what way we need to use if we want represent with (quantum) logical circuits this 'Hilbert space'.

I try to read also here but is not very clear how a Hilbert space is manipulated as a quantum logical circuit https://en.wikipedia.org/wiki/Quantum_finite_automaton

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But I want to understand how Hilbert Space is represented in quantum electronics, using Quantum gate circuits

Quantum gate circuit

Here is a picture of a quantum gate circuit. Those input states --- $ |\psi\rangle , |0\rangle$ --- are elements of the Hilbert space that the computation takes place in.

How is the set of states Q logically replaced by a Hilbert space

This is harder to answer completely in short form. All I can say is that there is some function which takes as an input an element of $Q$ and maps it to an element of Hilbert space. For example, a trivial map would take any element of $Q$ and map it onto $|0\rangle$. That's not very useful, but it's the kind of thing you're asking about. More complicated maps exist.

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  • $\begingroup$ Thank you for your answer. When you say "elements" of the "Hilbert space" you say they are some numbers of some matrix representation that we can call 'vectors' and 'Hilbert space'? I ask this because logically representation of same concept is not easy to figure out. $\endgroup$
    – Jack Rock
    Commented Dec 8, 2020 at 20:48
  • $\begingroup$ Maybe you're familiar with Cartesian space. There are many ways to represent elements of that space: "origin", "(0,0)", even a picture will do. If you want to get crazy, you can even bijectively map the 1D real number line onto Cartesian space. Then "0" would be a representation of the origin. This is called representation theory. Representations are not unique. For Hilbert spaces in QM, bras and kets are typical representations, as are square matrices. Note that the term 'vector' is being used here in a much more general way than what you learned pre-calc. $\endgroup$
    – psitae
    Commented Dec 8, 2020 at 21:20
  • $\begingroup$ ok, I remember that bras and kets are typical representations for Hilbert space. But, electronically speking, how bras and kets are realized with digital/quantum (gate) circuits? Do they use Controlled NOT gate, Hadamard (H) gate? I take a look here now to understand better en.wikipedia.org/wiki/Quantum_logic_gate#Hadamard_(H)_gate $\endgroup$
    – Jack Rock
    Commented Dec 8, 2020 at 21:39
  • $\begingroup$ There's a correspondence between kets and vectors. $|0\rangle$ is [1,0] and $|1\rangle$ is [0,1]. From there, you can use matrix representation of the gates to calculate the result of the computation. $\endgroup$
    – psitae
    Commented Dec 8, 2020 at 21:41
  • $\begingroup$ Thank you. I read here. Maybe I want to find inverse point of view, "How to interpret a matrix as a quantum circuit?" because I prefer represent mathematical structures with quantum logical gates instead to represent quantum gates with matrices. $\endgroup$
    – Jack Rock
    Commented Dec 9, 2020 at 11:57

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