- #1
DrClaude said:You don't start the problem correctly. The ##|S_z = + \hbar/2 \rangle## state is not an eigenstate of the Hamiltonian, so after a time ##T_2##, the state of the system is not ##e^{-i E T_2 / \hbar} |S_z = + \hbar/2 \rangle##.
In which direction is the magnetic field?BREAD said:H=-(e/mc)S * B , Sz and H differ just by a multiplicative constant, so they commute. The Sz eigenstates are also energy eigenstates.
In the problem, megnetic field is Bx direction.DrClaude said:In which direction is the magnetic field?
So how can you rewrite ##\mathbf{S} \cdot \mathbf{B}##?BREAD said:In the problem, megnetic field is Bx direction.
Sx * BDrClaude said:So how can you rewrite ##\mathbf{S} \cdot \mathbf{B}##?
DrClaude said:You have to express the initial state in terms of the eigenstates of the Hamiltonian.
Don't forget the normalization factor.BREAD said:Sx and H have same eigenstates, so the initial state l+> is lSx+> + lSx->
DrClaude said:Don't forget the normalization factor.
But now that the state is expressed in terms of the eigenstates of the Hamiltonian, it should be easy to calculate the time evolution.
Why? This is a very standard problem in QM and illustrates nicely the concept of precession.BREAD said:I think the answer is weird
I replied the answer that i triedDrClaude said:Why? This is a very standard problem in QM and illustrates nicely the concept of precession.
Ok, I had replied before you posted the solution.BREAD said:I replied the answer that i tried
I got it, then how can i approach problem(b) i think the result of first measurement is same with (a)DrClaude said:Ok, I had replied before you posted the solution.
There is a problem, as you can clearly see that the prbability you get ranges from 0 to 2. Check again how you calculate the absolute value squared.
The probability of measuring Sz = +ħ/2 is indeed given by the same equation, replacing T2 by T1. But you already know the measurement result, so you need to figure out what you get at T2.BREAD said:I got it, then how can i approach problem(b) i think the result of first measurement is same with (a)
DrClaude said:The probability of measuring Sz = +ħ/2 is indeed given by the same equation, replacing T2 by T1. But you already know the measurement result, so you need to figure out what you get at T2.
By the way, you can simplify the result you get using explicit values for E1 and E2.
Time dependent expectation value problems are mathematical equations used to describe the behavior of a quantum mechanical system over time. They involve calculating the expected value of a physical quantity, such as position or momentum, at different points in time.
Time dependent expectation value problems are typically solved using the Schrödinger equation, which describes the evolution of a quantum system over time. This equation involves using mathematical techniques, such as integration and differential equations, to find the time-dependent solutions.
Solving time dependent expectation value problems allows us to understand and predict the behavior of quantum systems over time. This is important in many fields, including physics, chemistry, and engineering, as it helps us to design and develop new technologies and materials.
Yes, time dependent expectation value problems have many practical applications. For example, they can be used to model the behavior of atoms and molecules in chemical reactions, or the movement of electrons in electronic devices.
One limitation is that time dependent expectation value problems are based on the assumption that a quantum system is in a pure state. In reality, many systems are in a mixed state, which can make the calculations more complex. Additionally, these problems may not accurately predict the behavior of systems at the quantum level, as quantum mechanics is still a developing field of study.