- #26

selfAdjoint

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**Bell measurement**(after the late John Bell, a physicist at CERN) is a measurement of a Bell state. It collapses the state.

A

**Bell state**is an entangled quantum state of two particles such that if the state of one particle is measured (Bell measurement) the state of the other can be determined, even though the particles are separated.

**qubit**I think this is what you meant. It's a coined word, made up from "quantum" and "bit". It's pronounced "Q-bit" or cubit, like the Ark measurement.

In quantum mechanics the states of a particle can be superimposed. This does not mean added together, exactly nor does it mean mixed, the closest analogy I can think of is the notes in a chord. The notes are not added or mixed, but you hear them together, as a chord, which is something different from playing the notes one at a time (off topic, Schoenberg never seems to have really go this point). A superimposed state of values for one particle is not the same thing as the entangled state of two particles (Bell state).

So now think of "quantum information. The smallest unit of classical information is the bit. The bit can have one of two state, 0 or 1 (or on or off or many different possibilities). A bit is the amount of information you acquire in answer to a question that can be answered yes or no. For example the sex of a person (ordinarily) is coded in one bit.

Now let the two values or alternative of a bit be superimposed, quantum fashion. This is the minimum unit of quantum information: a qubit.