# Questions tagged [quantum-states]

A quantum state is a mathematical entity (abstract geometrical or specific algebraic function) that provides a probability distribution for the outcomes of each possible measurement on a system.

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### Showing there are infinitely many decompositions of a non-pure state [duplicate]

Consider Problem 2.10 from Ballentine (paraphrased): Show (by constructing an example depending on a continuous parameter) that this can be done in infinitely many ways. I'm not sure how to proceed. ...
• 464
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### Why symmetry transformations change either the state or the operator but not both. Why?

Why is it assumed that the symmetry transformations change either the state $\psi$ or the operator $O$ but not both simultaneously? For example, if you assume $\psi\to T\psi$, you take $O\to O$ and if ...
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### Interpretation of time evolution in Quantum Mechanics

Let a quantum mechanical system, at time $t=0$, be described by: $$|\psi(0)\rangle = c_1(0) |E_1\rangle + c_2(0) |E_2\rangle \;,$$ here $|E_1\rangle$, $|E_2\rangle$ are energy eigenstates. Now, for ...
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### Entanglement Entropy and Entanglement Negativity for pure/mixed separable/entangled state

My question is how is Entanglement Entropy (EE) and Entanglement Negativity (N) related to the combinations of pure/mixed and separable/entangled states? That is for pure separable (PS), pure ...
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### Collapse postulate in the density operator formalism [duplicate]

To the extent that the collapse postulate holds, textbooks will almost invariably restrict the discussion to contexts in which states are represented by normalized kets, so that the collapse postulate ...
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### What is the most general mathematical structure for representing a state in QM?

In quantum mechanics textbooks which are a little more careful it is common to see it noted that a (pure) quantum state is not a vector $|\psi\rangle$ but rather a ray in Hilbert space, $c|\psi\rangle$...
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### If you change the state of one entangled particle will it change the other? [duplicate]

I have seen a bunch of duplicates of this question and I’m sorry if this is a true duplicate, but all the other duplicates have super long and complicated answers that I don’t understand. I just want ...
1 vote
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### Defining initial values of atoms/particles

For a college project I'm simulating the change of magnetization of multiple protons that influence each other. The goal of my project is to provide a good software structure, so my primary focus was ...
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