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1answer
49 views

Effects of measurement on particle energy

According to quantum mechanics, once you measure a particle's energy, its wave function collapse into some state, an eigenfunction with some eigenvalue (which is the particle energy). But if a ...
1
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1answer
76 views

Annihilation Operator on Entangled State - How Does This Not Break No-Communication Theorem?

If I have the state $$|\psi\rangle=\frac{1}{\sqrt{2}}\left(|2\rangle_{A}|0\rangle_{B}+|0\rangle_{A}|2\rangle_{B}\right)$$ and apply the annihilation operator to B $$a_{B}|\psi\rangle=|\phi\rangle=\...
0
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0answers
40 views

Collapse of quantum state after measurement of degenerated eigenvalue (From textbook Shankar) (Closed)

I want to ask an easy question from Problem 4.2.1, Quantum Mechanics(2nd) by Shankar. Let's say Operators, $L_{x}$, $L_{y}$, $L_{z}$ are $$L_{x}$ = $1/2^{1/2}$ $\begin{pmatrix} 0& 1 &0 \\ ...
1
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1answer
72 views

Why does superposition principle and Copenhagen interpretation not contradict with themselves?

In quantum mechanics, when we say that a particle in a state $|x_1\rangle$, physically the states $|x_1 \rangle $ and $c |x_1\rangle$ (for some $c\not = 0\in \mathbb{C}$) are the same, i.e they ...
2
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1answer
74 views

Does the Hermitian Operator Reduce the Non-eigenstate State to the Self-Eigenstate?

Let's consider $\left| \Psi \right> $ some state of quantum system. Let's also consider some Hermitian Operator $\hat{Q}$, with the discrete specrum: $$ \hat{Q}\left| Q_n \right> = Q_n\left| ...
0
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2answers
91 views

Question regarding the projection postulate of quantum mechanics

In Quantum Mechanics, McIntyre states the projection postulate like so: After a measurement of $A$ that yields the result $a_n$, the quantum system is in a new state that is the normalized ...
1
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1answer
154 views

Is this assertion by Landau and Lifshitz's QM equivalent to the axiom that state spaces are vector spaces?

Many expositions of Quantum Mechanics begin by stating axioms of the following type: "The state of a quantum mechanical system is given by a nonzero vector in a complex vector (or Hilbert space) ...
0
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1answer
103 views

Understanding the Formalism of wave function collapse [duplicate]

For example, a perfect measurement ($\hat A=\hat x$) on position: $$\hat x\psi=x_0\psi$$ The eigenvalue $x_0$ is the result of measurement. The eigenfunction $\psi$ is the wavefunction after ...
0
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1answer
615 views

Calculating the probability of eigenvalues from a superposition of two wave-functions

To calculate the probability of eigenvalues from a superposition of two wave-functions do you normalize the overall wave-funtion or the individual wave-functions. I am aware that one can write $\Psi =...
-1
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2answers
171 views

Does measuring operator $A$ on state $|\psi\rangle$ leave the system in $A |\psi\rangle$?

Given an observable $A$ and a system in the state represented by the vector $|\psi \rangle$, after the measurement is the system in the state $A |\psi \rangle$?
0
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1answer
37 views

Given any two quantum states and the information that the system is in one of these two states

Given any two quantum states and the information that the system is in one of these two states, one cannot reliably devise a single measurement which could determine with certainty which state the ...
-1
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2answers
542 views

Superpositions and expectation values in quantum mechanics

When the wavefunction of a particle is not an eigenfunction of an operator, the property to which the operator corresponds does not have a definite value, Why? Also consider a linear combination of ...
11
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5answers
3k views

Does an electron move from one excitation state to another, or jump?

I'm wondering, when an electron changes state, does it move from one state to another over some (very small) time period? Or does it change from one state to another in no time? If the former, what ...
10
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4answers
1k views

What does it mean to apply an operator to a state?

Let's say I have an operator $\hat{A}$ and a state $|\psi\rangle$. What exactly is the state $\hat{A}|\psi\rangle$? Is it just another different state that I am describing using my $\hat{A}$ and $|\...
4
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3answers
897 views

If I go to the church of the greater Hilbert space, can I have Unitary Collapse?

Actually, unitary pseudo-collapse? Von Neuman said quantum mechanics proceeds by two processes: unitary evolution and nonunitary reduction, also now called projection, collapse and splitting. ...
1
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1answer
61 views

In which way is decoherence not symmetric between the two considered systems?

If a quantum system interacts with a "big" quantum system, you have dephasing. The models of decoherence all have this atog aproach to them, about what is to understood of the interaction of the ...
5
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4answers
3k views

How does a state vector be projected onto an eigenspace after measurement

In http://en.wikipedia.org/wiki/Measurement_in_quantum_mechanics#Degenerate_spectra, it is said that If there are multiple eigenstates with the same eigenvalue (called degeneracies),..., The ...