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 ...

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6 views

3D isotropic oscillator and angular momentum algebra

In our QM class, the prof said: "We are ready to begin constructing the individual states of the 3D isotropic harmonic oscillator system. The key property is that the states must organize ...
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1answer
34 views

How to physically prepare a qubit in a certain state?

I earlier asked the question about definition of a qubit. From it I understood that its the experimental setup that actually defines the qubit. But I don't get it's physical realization. How a qubit ...
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2answers
34 views

Correct vector space of eigenkets of angular momentum

When we say an particle is in the state: \begin{equation} |l,m\rangle, \end{equation} what is the underlying state space, as a vector space? Is it a tensor product vector space, of dimension: ...
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1answer
36 views

Algebraic solution of Dirac equation for Coulomb potential

The Runge-Lenz operator enables an algebraic solution of Coulomb potential energy levels without a solution of a differential equation. What is the analog for the solution of the Dirac equation in a ...
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0answers
15 views

Modeling simple laser induced population transfer via adiabatic passage in python [migrated]

I'm trying to model adiabatic passage between two levels in a three-level atom interacting with two laser fields using Scipy and Numpy.. I'm not sure if my model is wrong due to my incorrectly ...
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3answers
57 views

Simultaneity and quantum indeterminism

How can Relativity talk about simultaneity planes when the events are actually quantum in nature so they are indetermined ? How can you say that if you walk on the street with 1m/s you are ...
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2answers
93 views

How to mathematically describe a spin-0 particle

That simple. I can't buy anything; I am only 15. I don't know all the technical things like Eigenstates. I want to know, mathematically written out for beginners, how to make a quantum field theory of ...
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1answer
39 views

Quantum Physics - What is the probability of it being in specific state (Stuck on question) [on hold]

The normalised wavefunction for an electron in an infinite 1D potential well of length 65 pm can be written: $$\psi=(0.038 \psi_{n=1})+(-0.227\ i \psi_{n=10})+(g \psi_{n=5}).$$ If the state is ...
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0answers
16 views

Non-pertubative renormalization and correctness of a theory

Even if I start to understand why perturbative renormalization is necessary, I'm not exactly sure why non perturbative renormalization is. After asking the question to several theorists, what I think ...
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1answer
45 views

Treating matter waves as light waves?

Is it valid to treat a matter wave as a light wave with wavelength equal to the de Broglie wavelength of the matter wave? Either way please can you explain why?
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1answer
43 views

Anything special about the internal structure of Carbon-12?

In trying to understand the various structures carbon forms, I'm wondering what, if anything, is so special about having 6 neutrons and 6 protons in the nucleus. I'm aware there are permutations ...
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0answers
18 views

Materials Si and SiO2 [on hold]

I have just designed a structure with a little quantum point of Si on the substrate of SiO2. What special qualities can be expected for it?
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1answer
37 views

Question regarding entanglement

Could the paradoxical nature of entanglement be the result of a change in the nature of quantum properties, or an incomplete understanding of such, instead of non-locality?
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1answer
56 views

Question about the double slit experiment

If we measure a particle before it passes through the slit, would we see the particle or the interference pattern on the screen after the slits?
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0answers
25 views

Variational principle perturbation

I am trying to learn 2D SHO and free particle variational principles. However, I came across a perturbation like so: $Ax^2y^2$. The particle is simple harmonic in $x$ and a free particle in $y$? I'm ...
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1answer
38 views

Quantum Harmonic Oscillators

I'm having trouble with quantum harmonic oscillators and I'm not sure how to approach these questions: . I'd really like to get my head around these concepts but I'm struggling to understand fully. ...
2
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0answers
66 views

Quantum mechanical monopole [duplicate]

Recently in physics news, scientists have experimentally discovered the so-called quantum mechanical monopole. It seems that a quantum mechanical monopole is different from a magnetic monopole. So my ...
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0answers
54 views

my car is overheating after I just fixed the water pump? [on hold]

Steam coming out the Cool lit jug.. my engine shaking. Also my exhaust pipe throwing Water vapor out. I just changed the water pump..
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0answers
45 views

Are there any event-based interpretations of quantum physics? [on hold]

Are there any interpretations of quantum physics where we have a combination of probabilities and objective realizations of these probabilities on a very low level. The first part of my question is ...
2
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0answers
35 views

Understanding quantum coherence in biological processes (Magnetoreception)

Moved my questions to the top. Context below. Why is the strength of the electric field and the coupling constant being compared to the inverse coherence time? What is the inverse coherence time? Is ...
2
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0answers
28 views

Toric Code and the String-Net Model

What, exactly, makes the toric code a quantum error-correcting code as opposed to any other string-net model? What makes it special? The way I understand it, it's a normal string-net model on a torus, ...
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0answers
11 views

Second-order correction in Quantum-Confined Stark effect

In the wikipedia article, there is a second-order correction in the Quantum-Confined Stark Effect. I could not understand how it was solved. I did not understand the meaning of 2(0) and 1(0) and how I ...
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0answers
19 views

Isotropic 3D oscillator excitation levels in different eigenket basis

An isotropic 3D oscillator's excitations can be represented by combinations of raising operators $\hat{a}_i^{\dagger}$ acting on the vacuum $|0,0,0\rangle=|0\rangle$ in the $x,y,z$ basis, but also ...
2
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2answers
43 views

How do you find the projection operator onto an eigenspace if you don't know the eigenvector?

I was working on exercise 2.60 of Nielsen-Chuang which is as follows: Show that $\vec{v}\cdot\vec{\sigma}$ has eigenvalues $\pm 1$, and that the projectors onto the corresponding eigenspaces are ...
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0answers
21 views

Quantum Monte Carlo for harmonic oscillator

I'm trying to calculate harmonic oscillator using quantum monte carlo (path integral and metropolis algorithm). It's one particle in harmonic potential. I know the theory. One divides the partition ...
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0answers
31 views

Why don't wavefunctions for electrons in neighbouring molecules overlap?

I've come across this picture of two linked molecules. The intramolecular distances look similar to the intermolecular distances and it seems like that will be the case however you draw it because of ...
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1answer
36 views

Normalizing a wave function in a mixed well

So I got this potential and want to solve for the even wavefunctions http://imgur.com/GKAy4nD Since it's symmetric around the origin I need only to look at the interval [0,b] and solve for the ...
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1answer
49 views

Can I Weyl-order the following Hamiltonian?

I am trying to perform a path integral but I am having trouble with the Weyl ordering of my Hamiltonian. The Lagrangian of the system in question is $$L~=~\frac{1}{2}f(q)\dot{q}^2,$$ where $f(q)$ ...
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63 views

Why isn't everthing in a superposition state? [duplicate]

I know that a superposition is a state in which there are 50% and 50% (other % also) chances of two things to happen so why am I not in a superposition state? Example, I am at rest and i now choose to ...
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2answers
54 views

Why can't a classical bit behave like a qubit?

For example i have a 2 qubits which can have 4 possibilities i.e. 00, 01, 10, 11 so this shows that the 2 qubits can contain four bits of information as they are superpositioned but i think 2 ...
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0answers
77 views

Symmetries and quantum numbers $n$, $l$, $m$, $s$ [on hold]

I would like to better understand the symmetries and groups underpinning the quantum numbers $n,l,m,s$ for a bound electron. My understanding is that: $n$ is the principal quantum number, and is ...
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0answers
45 views

When trying to see what symmetries an operator generates, how do you “decide” what coordinate to apply it to?

Suppose I have $\hat{O}_{1}=-i\hbar\partial_{x}$ then \begin{eqnarray} e^{-i\gamma\hat{O}_{1}/\hbar}x\,e^{i\gamma\hat{O}_{1}/\hbar}=x+\gamma \end{eqnarray} and \begin{eqnarray} ...
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0answers
34 views

Role of Hilbert Space in physics [duplicate]

Why in quantum mechanics do we require that the state space be a Hilbert space rather than just an inner product? Does the completeness of the norm have any clear physical role?
2
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1answer
32 views

Notation of angular momentum operators vs numbers

I'm reading about finding the mass of quarks in mesons. In the lecture notes, it says We need to find $\langle\boldsymbol{s}_q\cdot\boldsymbol{s}_\bar{q}\rangle$. Since $L=0$, then ...
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25 views

Why doesn't the electron fall into the nucleus? [duplicate]

Electrons move around the nucleus, which contain protons and neutrons. I know that quantum mechanics tells us that the nucleus is made up of fundamental particles, but why (quantum mechanically ...
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0answers
26 views

What is a state vector? [on hold]

Please can someone give me an intuitive expansion of a state vector? For example, what are they, functions? What does one state vector represent? One does it mean to add two state vectors? etc. I have ...
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1answer
22 views

Multiply creation operator by a phase factor

A basic question, but I'm not completely confident what I'm doing is legit. I can multiply a creation operator by an arbitrary phase factor and it doesn't change any physics. True? I have a ...
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2answers
70 views

Meaning of the Angular Momentum in Quantum Mechanics

There was a discussion about the angular momentum in QM in an online course that I am attending now. The discussion and the answers did not satisfy me so I wanted to ask it on Physics SE. In the ...
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1answer
23 views

Is post selection a quantum effect?

Suppose I have two bits $x$ and $y$ and a map $M:x,y \to x \veebar y,x \veebar y$ where $x,y$ $\in \{0,1\}$ and $\veebar$ stands for bit xor. If I post-select the case where the output is $x^{'}=0 , ...
2
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1answer
61 views

Entanglement and the uncertainty principle

Suppose you have two maximally entangled particles. You measure the spin about the x axis of the first and the spin about the y axis of the second. But both spins cannot be known simultaneously, so ...
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1answer
40 views

Angular Momentum Expectation Values in Spherical Coordinates

I have a homework problem that asks: Using the spherical harmonics calculate $\langle J_x \rangle$, $\langle J_y \rangle$, $\langle J_z \rangle$ in the state $|l,m\rangle$. Use the derivative ...
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1answer
44 views

Compatible Observables and Measurement

Suppose $A$ and $B$ are compatible observables (i.e. $[A,B] = 0$). We take the eigenkets of $A$ to be $|a_1 \rangle \ldots |a_N \rangle$. Further, we suppose that the first $k$ eignekets of $A$ are ...
2
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2answers
65 views

Transition from 4-potential to E and B [on hold]

In my lecture notes there is a step that i cannot follow: $$\frac{i}{2}[\gamma^{\mu},\gamma^{\nu}] (\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu})=: \sigma^{\mu\nu}F_{\mu\nu}=i\vec{\alpha} ...
-1
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0answers
16 views

why does the spaceship stand still in the bubble while movement is taking place outside? [on hold]

The question concerns travel faster then the speed of light.Another quesion conecerning the colour in the front being bler och the colour in back being redder. How it possible just these two colours ...
3
votes
1answer
69 views

Time Evolution of Position Operator

I am trying to understand why $$e^{-it\triangle}xe^{it\triangle}=x-2it\nabla$$ where $x$ is just multiplication operator by $x$. In particular, the text says this can be seen by differentiating with ...
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0answers
27 views

What is the reason for 2 qubits no longer being entangled after interaction with a causality violating qubit?

Background : I was reading the following paper on closed timelike curves ( CTC ) : Quantum Mechanics Near Closed Timelike Curves. The Deutsch consistency equation for CTC is $$\rho_{CTC}=Tr_{CR}( U ...
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0answers
24 views

p-adic and quantum mechanics [duplicate]

In physics we call integer based quantity as “quantization”, so you have energy, momentum etc taking quantized values. But in math, this kind of situation is really the age old problem of number ...
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1answer
37 views

Derivation of Pauli Hamiltonian

In my lecture notes there is a step that i cannot follow: $$\frac{i}{2}\epsilon_{ijk}\sigma_k [\pi_i,\pi_j] = -e\epsilon_{ijk}\partial_iA_j\sigma_k$$ with $\vec{\pi}=\vec{p}-e\vec{A}(x)$ When I ...
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1answer
40 views

What are the units of the creation and annihilation operators?

The creation and annihilation operators - also known as ladder operators are; $ \hat{a}^\dagger$ and $\hat{a}$ respectively. Using the equation $\hat{H} = \hbarω\left(\hat{a}^\dagger \hat{a} + ...
3
votes
2answers
180 views

What exactly implies the need of quantum mechanics for self-adjoint and not only symmetric operators? [duplicate]

We know that quantum mechanics requires self-adjoint operators, not only symmetric. Can we say that this follows ONLY from the two following axioms of quantum mechanics, namely that each observable ...