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In Deutsch's algorithm, with respect to a given function f, one ends up with the tensor product of two qubits, |f(0)+f(1) mod 2>|[(|0>-|1>)/sqrt(2)] This last step is to "only" measure the first qubit. How, precisely, does one extract the first qubit from a tensor product?

nomadreid
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  • Please consider improving your questions formatting, so it will be easier to understand and answer. http://stackoverflow.com/help/formatting – mcveat Mar 10 '15 at 16:39
  • To restate: let us say I have a process which, mathematically, looks like the tensor product of an unknown bit (that is, a definite qubit) with a known qubit. In order to find out the value of the unknown bit, do I (a) assume that it corresponds to a distinct particle that I can measure separately, (b) put the two-qubit system through a gate that will bring both qubits down to determinate form, or (c) other? – nomadreid Mar 11 '15 at 17:01

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You don't extract anything, your two qubits are two different physical systems, typically they can be two ions. You "simply" measure the ion in which you encoded the first logical qubit.

Loick
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