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I know that macroscopic objects undergo measurements continuously from the environment in which they are placed.
I also know that in a quantum computer one can make a measurement of only a few qubits.
My question is, when a macroscopic object undergoes measurement do all the particles of which it is composed also undergo measurement?

Example:
-If I have a macroscopic system consisting of a lattice of spin 1/2 particles and I measure the magnetic field generated by the object, do all the particles undergo the measurement? If not, how do those that did not undergo the measurement contribute to the field?

Qmechanic
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user361410
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  • You need to model the measurement to describe it - write the Hamiltonian and you will see the answer. (Of course, there are likely many ways to measure a magnetic field.) – Roger V. Mar 10 '23 at 17:05

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A measurement is a type of interaction that allows you to find out the value of a certain property. For example you can measure the momentum of a billiard ball and find out that it is 0 relative to some reference frame. Can you deduce from here that the momentum of any electron/nucleus inside that ball is also 0? Of course not. So, the measurement of a macroscopic quantity is not the same thing as a measurement of all microscopic entities that make up the macroscopic object.

Andrei
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