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 ...

learn more… | top users | synonyms (4)

1
vote
0answers
28 views

Which of Landau's books are suited for undergraduates? [closed]

Seeing how well-received Landau's books are, I want to know if any of them are suited for undergraduates.
3
votes
1answer
94 views

Free space propagator: reconciling two results

In quantum mechanics, the free space propagator $G(q_f=0,q_i=0;\tau)$ can be easily calculated to be $$\sqrt{\frac{m}{2\pi i \hbar \tau}}$$ by inserting an identity operator. However if we use ...
2
votes
1answer
62 views

A question about the uniqueness of Riesz representation theorem

I am sorry this question may be too math related. However, I come from physics background and I would like to ask for an physicist's explanation. As far as I know, the Riesz representation theorem ...
1
vote
2answers
68 views

Hamiltonian of a quantum harmonic oscillator

On page 286-287 of Nielsen Chuang's Quantum Information and Quantum Computation (10th edition) book, the Hamiltonian for a quantum harmonic oscillator is approximated as $H=a^\dagger a.$ What are the ...
1
vote
0answers
36 views

Why is entanglement such a big deal? [duplicate]

I just learned about it to some depth (not very much, just the basics), and I fail to see why is this phenomenon considered strange or unexpected and the like at all. I mean let's consider a bag with ...
5
votes
2answers
83 views

Time reversal symmetry of transverse field Ising model

Is the transverse field Ising model time-reversal invariant? Specifically consider a non-integrable variant: \begin{equation} H = -J \sum_i^{L-1} \sigma_i^z \sigma_{i+1}^z + g \sum_i^L \sigma_i^x + h ...
0
votes
1answer
37 views

Atomic system satisfying a simple level scheme

I have a simple two level system with an allowed dipole transition between the levels. The top level is also allowed to decay to another third level (looks a bit like a lambda system). Could someone ...
7
votes
3answers
728 views

How does the particle in the double slit experiment interacts with the slits?

I have a very normal yet a curious question about the double slit experiment. No one takes much interest in my college to explain the stuff. Instead they are all just busy to complete the syllabus so ...
1
vote
1answer
36 views

1st order perturbation of energy for quantum harmonic oscillator [closed]

I am trying to do part B of Griffiths QM 2nd edition problem 6.2 It asks to find the 1st order correction to the energy for a perturbation of a quantum harmonic oscillator where the new spring ...
1
vote
0answers
35 views

Determine adjoint operator [closed]

I need to determine the adjoint operator to $a_i$: $a_i |n_0, n_1, ... \rangle_S = \sqrt{n_i} |n_0, n_1, ..., n_{i-1}, n_i - 1, n_{i+1}, .. \rangle_S$ where the $S$ should denote the symmetrizer. I ...
0
votes
1answer
43 views

Two fermions with total spin 1 antisymmetric wave function? [closed]

How can I prove, that two fermions with a total spin of 1 must have an antisymmetric wave function?
4
votes
2answers
120 views

Why doesn't gravity mess up the double slit experiment?

So let's say you are doing a double slit experiment. Also, let's use electrons. My question is, won't the gravity of the electron affect the earth, thereby causing it decoherence and its wave ...
0
votes
2answers
39 views

What is the effect of Knowledge in the quantum eraser experiment?

OK, here's a question from a non-physicist about the quantum eraser experiment. If my understanding is correct, photons and their entangled counterparts become a particle and create a ...
0
votes
1answer
58 views

Why doesn't the quantum eraser violate the no-deletion theorem?

In the quantum eraser experiment and its variants, you basically have a double slit experiment, where you detect which slit the photon went through, but then forget this information. My question is, ...
2
votes
2answers
126 views

What patterns could be observed in this quantum entanglement thought experiment?

Please see attached image below. The DEVICE is beaming two streams of entangled particle pairs (B1 and B2) in opposite directions (e.g.: Particle no. 1 (p1) goes left, Particle no. 2 (p2) goes ...
59
votes
7answers
6k views

Does quantum mechanics play a role in the brain?

I'm interested in whether the scale of processes that occur in the brain is small enough to be affected by quantum mechanics. For instance, we ignore quantum mechanics when we analyze a game of tennis ...
1
vote
1answer
29 views

Magnetocaloric Effect and Quantum Spin Relationship?

I watched few videos and read few articles on Magnetocaloric Effect. Basically, some materials, like Gadolinium, heat up if simply placed in magnetic field. But I can't get the explanation they are ...
0
votes
1answer
49 views

How do we imagine a Hadamard gate acting on the Bloch Sphere? [closed]

We can rewrite the Hadamard gate as $R_x(-\pi/2)R_z(-\pi/2)R_x(-\pi/2)$. I am trying to visualize the effect of applying the Hadamard gate to $|+\rangle$ on the Bloch sphere. The X gate takes ...
2
votes
0answers
58 views

Relation between the reduced Green's function and the full Green's function

Let us assume that we have some Hamiltonian and we know its spectrum $$H_0 \psi_n = E_n \psi_n .$$ We define the Green's function in as $$ G(x,y,E) =\sum_m \frac{\psi_m^*(x)\psi_m(y)}{E-E_m}, $$ and ...
0
votes
1answer
30 views

Heisenberg picture transition amplitudes

I want to calculate the transition amplitude for a particle to start at position $q_1$ at time $t_1$ to position $q_2$ at time $t_2$ in the Heisenberg picture. As we are in the Heisenberg picture, ...
2
votes
1answer
72 views

What is spin in QFT, non-relativistic QM, and classical physics? When can we ignore spin? [closed]

In section 4.1.1 of quantum field theory book by M. Schwartz, the author wants to calculate electron scattering by photons and writes the following interaction: $$ V= \frac{1}{2}e\int dx ...
2
votes
2answers
79 views

Can Quantum Measurement Be Detected After The Fact?

My question is simple and has a crude drawing associated with it. I was watching some videos of the quantum erasure experiments and being a computer scientist have researched quantum encryption ...
1
vote
0answers
27 views

Just a question about starting places for quantum mechanics [closed]

So I'm 14 years old. I don't know if anyone would agree with what I'm doing but I'm really interested in learning quantum mechanics. The school I go to doesn't really have any sort of programs to help ...
1
vote
1answer
44 views

Can we measure the energy of one of several identical particles?

Suppose we have a many-particle system described via a many-particle wavefunction that involves single-particle states $\lvert\lambda_{a}\rangle$, $\lvert\lambda_{b}\rangle$, ...
0
votes
0answers
41 views

How do quantum effects scale to a 4 dimensional being?

I just finished High School a couple of weeks ago (Brazilian schedule) and my grandfather gave me a couple of books on quantum mechanics as a gift. I was reading on Heisenberg's Uncertainty ...
0
votes
0answers
39 views

Uncertainty Relation as obtained in Cohen

It starts considering $$\left|\rho\right\rangle = (Q + i\lambda P)\left|\psi\right\rangle$$ where $\lambda$ is an arbitrary real parameter. Then the norm is obtained: ...
0
votes
0answers
36 views

Scattering phases for the Yukawa potential

Assuming a weak Yukawa potential, I need to find the scattering phase shifts in terms of Legendre functions of the second kind $Q_l(x)$. The weak potential allows me to say that $e^{iδ_l}sin(δ_l) ...
3
votes
0answers
39 views

Can the occupation of Floquet bands be calculated from the Keldysh Green's function?

A periodically driven band structure can be semiclassically described by Floquet theory, resulting in photon-dressed Floquet bands (non-equilibrium steady states). Usually, for non-equilibrium ...
-1
votes
2answers
93 views

Double Slit Experiment doubts

Well, I've been reading about this experiment and watched some videos, I'm not a Physicist, and also don't know much about this kind of stuff. But that experiment made me very curious. For what I ...
1
vote
2answers
76 views

Quantum Mechanics/Physics Textbook

This is a reasonably common question however most threads seemed to be focused on introduction to the subject only. I am looking for a textbook in quantum mechanics/physics so that I can revise ...
1
vote
1answer
45 views

Why is the angular momentum added for two independent electron system? (no problem)

There is no problem now. But somebody may be confused by the same analysis when studying QM or Group theory. (actually my motivation for asking this question comes from the SU(5) Grand Unification ...
1
vote
0answers
41 views

Why does the preservation of transition probabilities imply the preservation of all quantum probabilities?

I have a question about symmetries in quantum mechanics. Let $H$ be a Hilbert space, and $\mathbb{P}H$ the corresponding projective Hilbert (ray) space. In quantum mechanics, a symmetry is usually ...
0
votes
0answers
42 views

A New Approach to Quantum Entanglement Communication [duplicate]

I've read other posts on the feasibility of quantum entanglement as a means of communication so I'll save repeating what's already been said. Typically it seems to be shut down as an option because ...
1
vote
2answers
66 views

Negative powers of operators

This may sound like a strange question, but just to be sure: Suppose I have a general Hermitian operator in Hilbert space whose action on an eigenvector is given by $R|r\rangle = r|r\rangle$. Then, I ...
0
votes
0answers
37 views

Why drop the kinetic energy operator in Griffiths QM 2nd edition Example 6.1?

In Griffiths Quantum Mechanics Example 6.1 on page 252, the problem is just a simple square well where the potential floor is raised from zero to $V_0$. Thus he states that the Hamiltonian for this ...
1
vote
2answers
59 views

Why are the allowed energies a continuum in the region $V_{\_} < E < V_{+}$?

I'm studying quantum mechanics and I don't quite understand why there's an energy continuum in the region $V_{\_} < E < V_{+}$ in the following example: It was explained that because of the ...
1
vote
0answers
34 views

Why is there a longer time lag if light behaves as a wave?

In this problem: According to a model based on the electromagnetic theory of light, the electron absorbs all the energy that is incident on the surface within a distance of $5.0\times 10^{-11}\ ...
1
vote
1answer
59 views

how can we reduce the temperature below -60 degree celsius? [closed]

To reduce the temperature below -60 degree celsius. we have to do a project based on this subject.
1
vote
3answers
91 views

Double slit experiment without observer

If we used an instrument to record the double slit experiment but never looked at the footage so to speak, what would the mathematics show us?
1
vote
1answer
53 views

Is spin angular momentum conserved?

According to the Noether theorem, we only have the conserved quantity $$J+S,$$ where $J$ is the orbital angular momentum and $S$ is the spin angular momentum. But I am always impressed that the spin ...
3
votes
2answers
146 views

Confusion about quantum probabilities depending on how coarsely grained the measurement apparatus is

I'm struggling to understand a confusing feature of the Born rule in quantum mechanics, which is that the probability of an outcome appears to depend on how coarsely grained our measurements are. ...
1
vote
1answer
113 views

Hydrogen atom in superposition of energy eigenstates

Suppose a single hydrogen atom is in a superposition of energy eigenstates: $$ \psi = \frac{1}{\sqrt{2}}\psi_{100} + \frac{1}{\sqrt{2}}\psi_{200} \,.$$ Then energy will be $E = ...
1
vote
1answer
35 views

Minimum Power Required to Maintain a Population Inversion

According to many sources, the minimum power required to maintain a population N in the upper level of a two level laser system is $$P_{min}=fA_{21}Nh\nu$$ where $f$ accounts for the lack of 100% ...
3
votes
0answers
29 views

Can different Floquet replicas be distinguished (within Floquet's theorem)?

According to Floquet's theorem, two quasi-energies separated by $n\hbar \omega$ represent the same state. According to this, I would think different replicas are indistinguishable experimentally. ...
0
votes
1answer
91 views

Bigger Galaxies = Faster Clocks [closed]

There are in all about 100 known galaxies with blueshifts out of the billions of galaxies in the observable universe. We have Blue-shifted galaxies are in our own local group, and are all bound to ...
0
votes
1answer
48 views

Can an electron in say, hydrogen ever be in a superposition of atomic orbitals?

So, I understand that quantum systems can be in superpositions of eigenstates. Why is it that we talk about electrons in hydrogen either being in the 1s orbital, or the 2s, or the 2p, etc.? Could I ...
6
votes
0answers
94 views

How do proteins perform their function? [closed]

Let's, for example, take a ribosome. It is an enzyme that is in turn just a molecule that must follow the laws of physics. Correct me if I'm wrong, but it can be looked upon as a molecular machine ...
2
votes
1answer
36 views

Quantum circuit and Witness preserving amplification for QMA

My question is about the witness preserving amplification scheme for QMA proposed by Marriott and Watrous in 2005 (see http://arxiv.org/abs/cs/0506068 and ...
0
votes
0answers
33 views

Kitaev chain for an odd number of electrons

Kitaev shows in "Unpaired Majorana fermions in quantum wires" how unpaired Majorana fermions arise at both ends of a chain of $N$ electrons, where $N$ is even. After a quick literature search, I ...
4
votes
2answers
93 views

Radial quantum number for infinite circular well

For completeness, I will sketch the solution of a particle in an infinite circular well first and then get to my question. I apologize in advance since the introduction is standard undergraduate ...