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Quantum mechanics describes the microscopic properties of nature in a regime where classical mechanics no longer applies. It explains phenomena such as the wave-particle duality, quantization of energy, and the uncertainty principle and is generally used in single-body systems. Use the quantum-field-theory tag for the theory of many-body quantum-mechanical systems.

31 votes
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Evolution operator for time-dependent Hamiltonian

Yes, you are on the right track. The series you have there is called Dyson's series. First note that the $n$'th term looks like $$ U_n = \left(-\frac{i}{\hbar}\right)^n\int_0^t dt_1 \cdots\int_0^{t_{n …
Olaf's user avatar
  • 3,102
23 votes

Quantum mechanics on a manifold

As far as I understand it there are essentially two ways in which you can study quantum mechanics on a manifold with some curvature. Classically speaking these two ways lead to the same physics but in …
Olaf's user avatar
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10 votes
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Equation of motion for the reduced density matrix

There are a number of schemes that have been developed over the years to describe the dynamics of the reduced density matrix. The problem that you encounter is that you have to make a choice between c …
Olaf's user avatar
  • 3,102
5 votes
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Expectation value of time-dependent Hamiltonian

My approach would be: first determine the time evolution of $\hat{x}(t)$ and $\hat{p}(t)$. For $\hat{x}$ you have $$ \frac{d}{dt}\hat{x}_H(t) = i[H_H,\hat{x}_H(t)] = \frac{i}{2m} [\hat{p}_H(t)^2,\hat{ …
Olaf's user avatar
  • 3,102
3 votes

Can the Heisenberg interpretation or path integrals apply to open quantum systems?

Yes, it can. An example is Brownian motion, in which you are interested in the dynamics of a particle in contact with some external reservoir without being interested in the dynamics of said reservo …
Olaf's user avatar
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2 votes
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Isn't it incorrect for the minimal gauge coupling and related calculations in Prof. Ezawa's ...

I have done this calculation some time ago. My convention was: $$ X = x - \frac{P_y}{m \omega_c}\quad Y = y + \frac{P_x}{m \omega_c} $$ and $$P_i = p_i +\frac{e}{c} A_i$$ And the magnetic field is …
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0 votes

Special relativity version of Feynman's "Space-Time Approach to Non-Relativistic Quantum Mec...

The method introduced here by Feynman is the Path Integral approach to quantum mechanics. When trying to include special relativity, you also need to move from quantum mechanics to quantum field theor …
Olaf's user avatar
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