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 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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3answers
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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0answers
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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0answers
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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1answer
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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0answers
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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1answer
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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1answer
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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1answer
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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0answers
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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1answer
46 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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1answer
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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0answers
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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1answer
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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1answer
61 views

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?
3
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4answers
122 views

“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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1answer
40 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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0answers
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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0answers
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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0answers
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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0answers
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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1answer
98 views

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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1answer
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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1answer
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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0answers
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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0answers
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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2answers
204 views

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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0answers
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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0answers
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
64 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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0answers
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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0answers
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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0answers
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 ...
3
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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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1answer
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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0answers
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 ...
3
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0answers
22 views

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 ...
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0answers
12 views

Problem in resonant tunneling diode (RTD)

What happen if the two barrier width in RTD are not same? How the transmission coefficient change for this? How the dips are formed in the transmission coefficient graph?
20
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4answers
377 views

Heisenberg's uncertainty principle for mean deviation?

The Heisenberg uncertainty principle states that $$\sigma_x \sigma_p \ge \frac{\hbar}{2}$$ However, this is only for the standard deviation. What is the inequality if the mean deviation, defined as ...
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0answers
13 views

range of validity of gravitional field in describing quantum interference experiments

There has been some interest in looking at quantum interference experiments using neutrons falling due in the Earth's gravity (see for example Abele and Leeb, New Journal of Physics 14 (2012)). In ...
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0answers
35 views

Calculating Clebsch-Gordan coefficients through Racah's formula

So Clebsch-Gordan coefficients are found in tables, but I need to calculate them using Racah's formula, which reads as following: $c_+ (J,M) f_{m_1}^{M+1}=c_+(j_1,m_1-1) f_{m_1-1}^M + c_+(j_2,M-m_1) ...
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1answer
40 views

Correlating two definitions of bound states in quantum mechanics

In Griffiths, he defines a bound state to be that stationary state for which the total energy E is such that $E<V(\pm\infty)$. Let $\psi(x)$ is a stationary state satisfying $E<V(\pm\infty)$ and ...
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0answers
36 views

Sufficient condition for square integrability [duplicate]

The necessary condition for $\int\limits_{-\infty}^{+\infty}|\psi(x)|^2dx$ to be integrable is that $\psi(x)\rightarrow 0$ as $x\rightarrow\pm\infty$. But this is not the sufficient condition. For ...
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0answers
45 views

How to manipulate higher spin systems (higher than spin 1/2) using a given operator?

I’ve been reading ¨Halzen, F., and A. D. Martin. Quarks and Leptons. New York: Wiley Text Books, January 1984. ISBN: 9780471887416¨, and I’d like some clarification of a concept, please: I’m ...
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0answers
32 views

How would a BEC respond to the gravitional force of a small mass so sensitively?

Recently I watched a BBC programme on anti-gravity, most of which was wishful thinking by NASA and BAe Systems 20 years ago. At the end of the program through, they did show what appeared to be a ...
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2answers
48 views

Observer in the double slit experiment with photons

In the double slit experiment with photons, the interacting observer is an instrument, detector… If you replace the detector with a piece of metal with the same mass as the mass of the detector, the ...