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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Why do bonds with positive and negative charges not collapse?

I previously believed that the reason positive and negative charges don't constantly attract until they collapse is due to a repulsive strong force at small distances. However, in a textbook by ...
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54 views

Single particle tunneling Hamiltonian

In reference to Problem 9, Chapter 2 in Modern Quantum Mechanics by JJ Sakurai, For a single particle tunneling in a 1D double well potential, with position eigenkets $\mid R\rangle$, $\mid ...
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2answers
116 views

When does the world split in MWI

I've been reading Eliezer Yudkowsky's blog post regarding decoherence and many worlds, and although he is not a physics but a strong proponent of MWI, I can basically see why he feels that MWI is a ...
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58 views

QM sytem with eigenvalues of the form $f(m*n)$ and prime number gap spectrum

Depending on the dimension and the symmetry and form of the potential, the energy eigenvalues of a quantum mechanical system have different functional forms. Eg. The particle in the 1D-box gives rise ...
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3answers
98 views

Precedence and quantum entanglement: The Alain Aspect experiment in spacetime

Recall that the spin components of a spin-entangled pair do not exist until one of the pair undergoes quantum observation, at which time both of the pair immediately obtain quantum random opposing ...
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26 views

Transformation applied to system without symmetry

Imagine we have a central potential which gives us the Hamiltonian of the form: $$\hat H=-\frac{\hbar^2}{2m} \nabla^2 +V(r)$$ In general this is not symmetric under translation. But let us say that I ...
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47 views

Is QC with Superpositioned Quantum Gates any different than normal Quantum Computation?

This might be more appropriate for theoretical CS stackexchange, but it feels sufficiently low level to be relevant here. Consider the following thought experiment: I have a Quantum FPGA, it is a ...
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104 views

Three dimensional isotropic harmonic oscilator Hamiltonian

Let us consider the Hamiltonian for the isotropic three dimensional harmonic oscilator: $$H = \dfrac{\mathbf{P}^2}{2m}+\dfrac{m\omega^2\mathbf{R}^2}{2},$$ where $\mathbf{P}$ and $\mathbf{R}$ are the ...
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22 views

Why does parahydrogen have a lower energy than orthohydrogen?

I found this on the wikipedia page on spin isomers of hydrogen: Parahydrogen is in a lower energy state than is orthohydrogen. It seem almost like it is obvious but I am having trouble reasoning ...
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78 views

Why do shiny surfaces reflect more light than other surfaces?

I'm an A-level student and I love learning new things in physics. A new concept that I learnt says that the reflection is due to the scattering of light by electrons in the material. I've got my ...
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1answer
53 views

Going to the interaction picture in the Jaynes–Cummings model [closed]

In the Jaynes–Cummings model for a two level atom, the Hamiltonian for the atom is defined as (I let $\bar{h}=1$) $$H_a=\omega_a\frac{\sigma_z}{2}$$ and the field Hamiltonian is ...
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1answer
23 views

What determines photoelectric yield

Is there any difference between the photoelectric yield of different metals apart from the threshold wavelength? To be more clear: Will metals with the same work function emit the same amount of ...
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47 views

Position and momentum measurement effects on wave functions

I have a few short questions about an interpretation of what happens with position and momentum wave functions described in literature I am using. Given momentum space wave function and position space ...
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22 views

transition probability and superpositon

suppose that we are dealing with a particle moving in an infinite potential well(a box of length L). Let the wavefunction of the particle be ψ(x,t)=c1ψ1(x,t)+....+cnψn(x,t) suppose that after ...
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15 views

Can energy be organised into elemental form other than hydrogen?if yes,then how?

I wanted to know whether energy can be organised into elemental form easily. If is so then , can antimatter be generated in a similar way other than pointing high intensity laser at some metal foils ...
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49 views

If all the particles of a Bose-Einstein condensate become entangled with each other,does the system still remain a Bose-Einstein condensate?

I know that an entangled system is found in a single entangled state and that when you try to observe the individual state of a particle from an entangled system using a reduced density matrix, you ...
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32 views

Is energy always a diminishing quantity in imaginary time?

If we write Schrodinger equation in imaginary time $\tau = it$, then one can easily show that the energy $E(\tau) = \langle \psi(\tau)| \hat{H} |\psi(\tau)\rangle$ is a diminishing quantity, i.e. ...
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52 views

Can there be a wave function that is physically possible but is non differerentiable (maybe even non-continous)?

The definition of a wave function demands continuity and differentiability so that it can satisfy the Schrödinger Equation. My question is whether this assumption is necessary for reality. Does ...
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48 views

What happens to Boson and Fermi gases at very low temperature?

At low temperatures Fermi gases pile up to the state with the Fermi-energy having one particle in each state and Boson gases form Bose-Einstein condensates. However, the only derivations I have seen ...
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68 views

Why doesn't the expectation of position for a plane wave obey kinematics?

Consider the plane wave: $$\Psi = Ne^{i(\vec{p}\cdot\vec{r} - Et)/\hbar}$$ with N is the normalisation factor. The expectation value of momentum for this wave is: $$\begin{align} ...
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61 views

reduced single particle density matrix (1-RDM) in second quantization

Is it possible to approach one body density matrix without using field operators ? For example for a double well potential, the reduced single particle density matrix is defined as: $$ ...
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49 views

Quantum non-locality with commuting measurements?

We consider the Bell scenario, in which Alice and Bob share an entangled pure quantum state $\mid \Psi \rangle_{AB}$. Alice gets an input in the set $\{1,2\ldots X\}$ and Bob gets an input in the set ...
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39 views

Hartree-Fock orbitals of a periodic crystal -> Bloch waves?

I am wondering how I can see that the Hartree-Fock orbitals of a periodic crystal obey the Bloch theorem? My problem is that the Hartree-Fock Hamiltonian does not have the form $-\frac 1 2 ...
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35 views

Geiger counter in the Schrodinger's cat experiment

Inside the Schrodinger's cat's box, the moment the radiation is detected by the counter, doesn't this mean the system already has a fixed eigenstate (a collapsed wave function, or is decoherent, ...
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37 views

many-body state in second quantization

The ground state of a system of N particles is represented as $$ \mid \Psi \rangle = \frac{1}{\sqrt{2^NN!}}\big( \hat{a}_1^{\dagger} + \hat{a}_2^{\dagger} \big)^{N} \mid 0\rangle $$ or similarly $$ ...
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If I pass one member of an entangled pair through a polarizer, does the other member assume a correlated polarization?

Does that mean I have influenced the measurement result of one member of the entangled pair by acting on the other? Can information be sent this way using entanglement?
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“Randomness” versus “uncertainty”

Highly rated PhysicsSE contributor @CuriousOne regularly makes the following claim about quantum mechanics (e.g. here): There is no randomness in quantum mechanics, there is only uncertainty. I ...
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41 views

Time independent perturbation theoery

Why do we talk of transitions only in time dependent perturbation theory when the eigen states are corrected even in time independent perturbation theory? If we can,for sake of argument,say : eigen ...
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29 views

Estimating “attributes” of a single photoelectric interaction

Disclaimer: I'm a mathematics grad student working on medical imaging. My knowledge of physics and physical intuition is, for the most part, quite poor. Question: I've been reading a lot about the ...
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31 views

Singlet and triplet excited states in He atom

I found the following example for Term symbol usage in my coursebook: There are two electrons in He atom. Let the first one $e_{1}$ be in ground state, with $n_{1}=1$, $l_{1}=0$, $m_{l1}=0$, ...
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37 views

Action of Swap operator

I am trying to understand concept of swap operator, introduced in the article http://arxiv.org/pdf/1001.2335v2.pdf by means of simple example. Swap operator is supposed to act on two identical(?) ...
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5answers
114 views

How Are Quantum Computers Able to Store Any Data at all?

So if qubits can have more than two states, and according to this video, https://www.youtube.com/watch?v=T2DXrs0OpHU you don't know what you get until you actually "open the box", if its all ...
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160 views

Quantum Physics [closed]

The problem statement, all variables and given/known data A beam of ultraviolet light with wavelength of 200 nm is incident on a metal whose work function is 3.0 eV. Note that this metal is applied ...
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Does this length refer to wavelength or length? [closed]

In this question: A He-Ne laser emits red light of the wave length $\lambda = 632.8\ \mathrm{nm}$ with a beam diameter of $2.0\ \mathrm{mm}$ and a power output of $1.0\ \mathrm{mW}$ [...] (d) How ...
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27 views

Photoelectric effect – What is the probability of a photon absorbtion by an electron?

Is it correct that each photon above threshold frequency is absorbed by an electron What is the probability of a photon absorbtion by an electron? Can a quantitative example be given?
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57 views

Instantaneous energy eigenstates for forced harmonic oscillator

I'm interested in applying the adiabatic theorem to the forced harmonic oscillator with time dependent hamiltonian of the form: $$H(t) = \hbar \omega(a^{\dagger}a + \frac{1}{2}) - f(t)a - ...
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11 views

Rotational-Vibrational Energy State Equation Derivation

I am having a mental block at the moment and for some reason I can't seem to derive these two equations: From this initial equation for Rotational-Vibrational Energy equation: I was hoping any ...
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25 views

How can I find out allowed quantum transitions?

My active element is fluorine(F), I have an energy level diagram: So, i must choose the pump's channel and find out what quantum transitions are allowed. How can i do it?
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What is $\langle \phi | H | \psi \rangle$ in QM?

I know that $\langle \phi | \psi \rangle$ is the probability of going from the $\psi$-state to the $\phi$-state, and that $\langle \phi | H | \phi \rangle$ is the expectation value of the energy for ...
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1answer
83 views

Can a system be PERFECTLY simulated by a quantum (and classical) computer? [closed]

This is a thought experiment, and as such will assume some crazy things. Let's say I decide to perfectly simulate my university as it is right now. I use a magic machine to instantly scan the entire ...
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24 views

Choosing the boundary conditions knowing the potential

So I have to apply Numerov's algorithm to solve the Schrödinger equation in spherical coordinates using the potential $V(r)=-A e^{-r/a}$, where $A=32.7MeV$ and $a=2.18fm$. I have already ...
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20 views

Quanta exchange between 2 harmonic oscillators during an Otto cycle

The focus of my current studies lies on the "Quantum Otto cycle" (e.g. presented on the first pages of this paper). The "machine" as well as the "baths" are represented by harmonic oscillators. Both ...
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2answers
66 views

Gaining or Losing Too Many Electrons

So I understand that an atom can gain or lose electrons and still retain it's identity - for example a Carbon atom is still carbon even if it loses 5 of it's 6 electrons because it is the number of ...
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48 views

How does the two slit experiment work?

Whilst going through 'A brief history of time', I faced difficulty in understanding the two slit experiment. How can an individual electron cause fringes on screen? I was unable to understand it? ...
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16 views

Explanation of two slit experiment [duplicate]

Whilst going through 'a brief history of time' ,I faced difficulty in understanding the two slit experiment. How can individual electrons cause fringes?
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25 views

How to see alpha radiation

Hello I am looking to replicate the double-slit experiment using alpha radiation from a sample of Polonium-210. Keep in mind that I would need to put it in a vacuum so cloud chambers would not work. I ...
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1answer
97 views

Quantum mechanics - measuring position

I am watching Susskind's Stanford Lectures on quantum mechanics. The eigenvectors (eigenfunctions) of the position operator are of the form $\delta(x-k)$. But $$\int\delta^{*}(x-k)\delta(x-k)\, ...
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31 views

How to quantify the level of non determinism / randomness in the universe

I recently read a little about the Bell test (I'm not a physicist, but reasonably well educated) and I started wondering if there is a way to express the level of non-determinism as a single number ...
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53 views

Why is a two level laser impossible to make? [duplicate]

I would like to know why it is impossible to have a two level laser ? Indeed if I write the equations (I neglect here the spontaneous emission), I have : $\frac{dN_2}{dt}=W(\omega).B.(N1-N2)$ and ...
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How does the electromagnetic field of an electron and a rotating ball of charge behave in a co-rotating reference frame?

First time poster, hope I'm not breaking any rules. Basically I'm curious about how far the classical analogy of an electron as a rotating ball of charge can be stretched. The situation I'm ...