Questions tagged [quantum-mechanics]

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.

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Spontaneous emission and coherence

Assume I prepare a linear superposition $\frac{1}{\sqrt{2}}(|g \rangle+|e\rangle)$ between a ground and excited level for a large number of "atoms" (it can by any multilevel system, not ...
1 vote
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Probability for error correction of phase flip error

I study by myself with books about error correction. I read about 'three qubits error correction', and I try to think about the change in the probability to get error. Let's say that the probability ...
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Are there proofs by contradiction in physical theories? [closed]

I am interested in whether there is such a thing as a proof by contradiction in physics, especially fundamental physical theories like QM or GR. I am just being curious, and I haven't been able to ...
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Quantum interference : an instantaneous consequence of superposition? [closed]

Is quantum interference a process that takes place over time, or an instantaneous consequence of superposition?
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Momentum Eigenvalues for Particle in a Box

A question from my college exams is as follows: Find out the eigenfunctions and eigenvalues of the momentum of a particle of mass $m$ moving inside an infinite one-dimensional potential well of width ...
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Using Galilean covariance to find conditions on physical observables

Let's suppose that coordinates have to transform accoring to the Inhomogenous Galilean Group. Then $$x' = x + a + v(t+b)$$ $$t' = t + b$$ Let's use a funtion $\psi(x,t)$ of $x$ and $t$ as the ...
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What's wrong with my solution? Infinite wall and delta barrier scattering [closed]

We have the potential $$V(x)=\begin{cases}\infty & ,x \le 0 \\ V_0\delta(x-a) & ,x>0\end{cases}$$ The problem is to find the amplitude of scattered wave and to analize the phase shift ...
1 vote
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How to deal with explicit time dependence in the Heisenberg picture?

I am studying for my test in Quantum Mechanics, and there is something I don't quite understand about the Heisenberg picture and Heisenberg's equation of motion. In the lecture, we derived Heisenberg'...
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How can one "encode" momentum into the wave-equation of a QM harmonic oscillator? [duplicate]

I am learning about Quantum Mechanics using Griffiths book and after reading the section about the quantum harmonic oscillator, I was left wondering how one can construct a solution to the Schrodinger ...
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How to propagate the wavefunction of a photon in single slit diffraction?

During my undergrad, I remember writing a simulation in which the diffraction patterns which emerge from light passing through a single slit were calculated. This was done, basically, by calculating ...
1 vote
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Understanding the measurement of '"evil" using the GHZ effect

I was reading this interesting article originally published by Quanta Magazine, which tries to explain the GHZ effect in simple terms. The GHZ effect is, in the physicist Sidney Coleman’s words, “...
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In what sense are the eigenfunctions of a Hermitian operator complete? [closed]

I understand that most physicists believe that the eigenfunctions of any Hermitian operator form a complete basis of the Hilbert space. That's why we can use the perturbation method to expand a wave ...
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Constructing a gapped family of Hamiltonians in the trivial paramagnet

Consider the trivial paramagnet, which has the Hamiltonian $$H = - \sum_i \sigma^x_i$$ Now let's say I have two different Hamiltonians $$H_0 = H + 2\sigma^x_{i_0} \qquad H_1 = H + 2\sigma^x_{i_1}$$ ...
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Ccoding for a hamiltonian, ladder operators of a quantum harmonic oscillator [closed]

How do I represent $$a_k ∣n_1 n_2 n_3 ,,,,n_n⟩ = √nk-1 ∣n_1 n_2 n_3 ,,,,n_n⟩$$ and $$a_k^\dagger ∣n_1 n_2 n_3 ,,,,n_n⟩= √nk-1 ∣n_1 n_2 n_3 ,,,,n_n⟩$$ in python(qutip or qiskit preferably) and where ...
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How does the simple description of spin relate to the Dirac equation?

Coming from a chemistry background, spin (the spin 1/2 case at least) is usually introduced in QM by saying there are abstract $\alpha$ and $\beta$ states together with rules for how operators act on ...
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Can many-worlds approach testability, if considered in a naively realistic physical context? [closed]

This is more of a philosophical question although it may be acceptable in the context of physics. It concerns Hugh Everett's many worlds interpretation of quantum mechanics. Many popular physicists, ...
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