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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1answer
21 views

Why Quantum Information was defined? [on hold]

Quantum Information Theory is a very much discussed term in Theoretical Physics, Information Science and Mathematics. Till now nearly 50 years after first definitions we have no usage in Computer ...
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2answers
32 views

Explain why quantum behavior is not observed in daily life

People always ask: How come we don't see any "Wave" attached to a classical object such as a car? You always see the object in the same place without any uncertainty. I am sure there are answers, ...
0
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0answers
4 views

Difference between thin film interference and Bragg diffraction of electron

Thin film interference is given by: $2dsin\theta=n\frac{\lambda}{n_i}$, where $d$ is the thickness of film, $\theta$ is the angle between incident light and tangent to the surface, $n$ is an integer, ...
0
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1answer
18 views

Post mortem measurement of particle-wave duality

I was wondering what the outcome of this experiment would be: You shoot single photons at a double slit. On their way there you preform a momentum measurement (so not to disturb the spacial wave ...
0
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0answers
5 views

Mach-Zehnder interferometry wave functions

Consider the set up below: I have read that in the apparatus the wavefunction is given by: $$|\psi \rangle=e^{i\theta}|c \rangle +i |b \rangle$$ where $\theta$ is the phase added by the phase ...
0
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0answers
46 views

Addition of states of two different Hilbert spaces

I am having difficulty in understanding the following. Let us say, I have two mutually exclusive Hilbert spaces $H_1$ and $H_2$. Let these have the basis states $\lbrace|\psi_1\rangle\rbrace$ and ...
-6
votes
0answers
23 views

Is Arc reactor really possible?? and do the findings fit onto it? [on hold]

Since this is a fictitious device, and it has no "official" scientific explanation in the Iron Man canon that I'm aware of, I'm going to make something up. I'm mixing real science and fake science ...
-1
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0answers
23 views

Using the spin lowering and spin raising operator on a two-particle wave function, how do I do it?

You have two spin 1/2 particles in the ground state of the harmonic oscillator potential, they do not interact with each other, and the Sz projection was measured to be zero. I am supposed to use the ...
0
votes
1answer
27 views

Angular momentum and the Units

I'm just curious about why many physical identities build relationship with the same units as angular momentum like the action, Lagrangian$\cdot$time, Hamiltonian$\cdot$time, phase space area etc?
0
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1answer
32 views

The minimum possible energy for five noniteracting spin $\frac{1}{2}$ particles

Question What is the minimum possible energy for five (noniteracting) spin $\frac{1}{2}$ particles of mass $m$ in a one-dimensional box of length $L$? Answer: $$ 2 \times ...
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1answer
40 views

Do photons have/contribute to mass?

Do electrons gain mass by absorbing photons during excitation and releasing them by returning to the ground state? Do photons have mass in the form of energy by $E=mc^2$?
-1
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1answer
44 views

Time dependent solution to infinite well

A particle of mass $m$ is confined within an infinite, one-dimensional potential well, $U(x)$, of width $a$. $$ U\left(x\right) = \left\{ \begin{array}{lr} \infty &\: x \leq ...
2
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1answer
32 views

Sequential Stern-Gerlach Experiments

Suppose a beam of particles is prepared with spin in the $+z$ direction (e.g. by a Stern-Gerlach apparatus). Suppose this beam then enters a Stern-Gerlach apparatus with orientation $\theta$ relative ...
2
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3answers
170 views

What counts as information?

What counts as information? In e.g. the EPR experiment why is one entangled particle knowing instantaneously the state of the other not counted as 'information'.
-3
votes
1answer
50 views

How do I normalize this wavefunction? [on hold]

I need to find the normalisation constant $A$ for the wave function: $$ \psi\left(x\right) = \left\{ \begin{array}{lr} A &\: \frac{-a}{4} \leq x \leq \frac{a}{4}\\ 0 &\: ...
1
vote
3answers
40 views

Calculating the probability of a given energy

Given a normalised wavefunction say $$\psi(x) = A\sin(n\pi x),$$ (where $A$ is a normalisation constant) I can calculate the probability of finding the particle being between a position $x$ and $x + ...
-3
votes
0answers
11 views

What is the energy levels of 1d hydrogen by using WKB? [on hold]

I need to find the energy levels of 1d hydrogen using WKB and $V(x)=-1/x$? can you help me please?
0
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0answers
45 views

Acceleration of uncharged particles

Following on from this comment - do uncharged particles radiate under acceleration? (no offense to the commenter, just clarifying as I've not heard of this before) Why is this? I vaguely recall a ...
0
votes
0answers
39 views

Photograph of Light as Wave and Particle [duplicate]

what is this? actually its the first photo of light as wave and a particle. The bottom "slice" of the image shows the particles, while the top image shows light as a wave. i have questions 1.how ...
0
votes
1answer
21 views

Does the electron confinement energy vary with temperature?

I was introduced the electron confinement energy. At room temperature thermal energy of a particle is about $k_B T$, where $T=298K$, giving about $25meV$. I was told that $E_\text{confinement}=50emV$, ...
0
votes
2answers
55 views

'schrodinger' picture in measurement based topological quantum computation

I am looking at the measurement processes in topological quantum computation (TQC) as mentioned here http://arxiv.org/abs/1210.7929 and in other measurement based TQC papers. Let's say I start with ...
2
votes
4answers
150 views

Physical reason why the derivative of a wavefunction has to be continuous?

Question What is the physical reason (i.e. without any maths) that the derivative of a wavefunction (except with infinite potentials) has to be continuous? Other info I know that in the classical ...
3
votes
4answers
140 views

What really is a particle?

In Classical Mechanics we consider particles as things whose internal structure for the purpose of studying some phenomenon might be neglected. In that setting we associate particles to points and ...
1
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1answer
50 views

How might I show that an operator is, by definition, an 'observable'? [on hold]

Here is my problem: I understand what is meant by 'observable' but don't have a formal definition at hand. How do I 'show' it?
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votes
0answers
30 views

Posibility of time travel/multiple realities/time phase shifting [on hold]

Sounds odd and unlikely, but let me explain the situation. Going on the de ja vue ideal, which we probably have all experienced, I believe things of such a matter are possible. Just today when I ...
0
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1answer
49 views

Getting to spins of arbitrary direction

Let me rephrase this question: Let us assume we know that symmetry transformations always look like this: $$U(s)=e^{iKs} $$ with a hermitian Operator K. This tells us that for very small $s$: ...
6
votes
4answers
148 views

Does quantum mechanics imply that particles have no trajectories?

In Classical Mechanics we describe the evolution of a particle giving its trajectory. This is quite natural because it seems a particle must be somewhere and must have some state of motion. In Quantum ...
1
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0answers
33 views

What is the relationship between coherent states and quantum coherence?

What is the relationship between coherent states and quantum coherence? To me coherent states were only talked about in regard to Quantum Harmonic Oscillator, whereas coherence and decoherence on the ...
2
votes
1answer
57 views

Number of Nodes in energy eigenstates

I have a question from the very basics of Quantum Mechanics.Given this theorem: For the discrete bound-state spectrum of a one-dimensional potential let the allowed energies be $E_1<E_2< ...
0
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0answers
28 views

Why we compare expectations sometimes and sometimes probabilities?

I am reading device independent approach on quantum mechanics from here device independent outlook on quantum mechanics. In here the author introduces local variable theory. Then he give two results. ...
1
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0answers
41 views

Scattering amplitude, link between quantum mechanics and QFT

In quantum mechanics, we can define the scattering amplitude $f_k(\theta)$ for two particles as the magnitude of an outgoing spherical wave. More precisely, the asymptotic behaviour (when ...
3
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2answers
114 views

Why does the magnitude squared of the wave function give us the probability density? [duplicate]

My question doesn't go much beyond the title: Why does $$\left | \psi \left ( x,t \right ) \right |^{2}$$ give us the probability density of something appearing at a certain location? I understand ...
1
vote
2answers
33 views

A binary operator required for observing whether the particle is present in a given spatial region

Consider the wave function $\psi(x)$, I want to define an experiment using quantum mechanical rules. The experiment is to find whether the particle is in the region of space (a,b). The observable is ...
1
vote
1answer
104 views

Difference in partition function of classical and quantum Ideal gas

First, I have read this question:What is meant by the term "single particle state" There is an analysis going on in my book (Mandle F. Statistical Physics) that has brought me in a ...
0
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0answers
56 views

Does EPR permit information to travel faster than light? [duplicate]

This question always throws me: Discuss if the EPR paradox violates special relativity? The information of the state of one particle is instantaneously transmitted to the other particle, but ...
0
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0answers
17 views

Hadron Annihilation - what happens with the constituents

When a Hadron and its antimatter equivalent annihilate, what happens to the QCD "soup" (for lack of an appropriate term) from each? Eg, the valence quarks in a proton - antiproton event, to they pair ...
1
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0answers
18 views

symmetry group of multi-electron atom

Neglecting spin effects, the energy levels of multi-electron atoms are characterized by states of definite total orbital ($L^2$) and spin angular momentum ($S^2$). From this it seems that the ...
6
votes
2answers
109 views

Do bras and kets have dimensions?

I'm trying to understand more intuitively what bras and kets are, but some aspects of them remain a mystery to me. We usually think of $\psi (x)$ as having dimension of $[1/\sqrt{L}]$ so that ...
1
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2answers
75 views

Have two identical quantum mechanical experiments ever been done?

Have two experiments ever been done such that the set up is identically the same, (when I say identically I mean down to the atomic level). Of course the experiment would have to be very simple. If it ...
2
votes
3answers
97 views

What can change a photon's frequency?

I found this question: Is it possible to apply force to a light particle? As it states, gravity can change the frequency of light by changing its momentum. My question regards other phenomena that ...
0
votes
1answer
49 views

Can someone explain what's the difference between all these terms in “Simple Words” with their “applications”? [on hold]

I'm very confused between all these terms. Can someone explain what's the difference between Classical Mechanics, Relativistic Mechanics, Quantum Mechanics, Quantum Field Theory, ...
0
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0answers
40 views

How is a measurement on an electron done?

There are two ways how to change a direction of a qubit - one with Larmor precession, another with a measurement. I am not sure about the measurement one. Let's say I have an electron with spin ...
0
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0answers
15 views

Infinite bare quantities and dressed quantities confusion

I'm getting very confused. Taking the example of the mass of the Z-boson. Constructing the GWS model using gauge symmetry breaking one finds a lagrangian which is a function of the Z-boson mass: ...
1
vote
1answer
46 views

Example for System Given Hilbert Space

What are some concrete examples of physical systems such that their corresponding Hilbert space is given by $\mathbb{C}$? Also, what is the physical difference between a system whose corresponding ...
1
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1answer
41 views

Uncertainty relation and instrumental errors

I was puzzled recently by what I've read in the internets about Heisenberg's uncertainty principle (one probably should never do this). It claimed that in the usual relation $$ ...
0
votes
1answer
42 views

Oberving a photon through double slits

If we send a particle with mass through the double slits we observe a interference pattern. That is of course if we don't observe which slit the particle goes through. If we do then we get two peaks ...
1
vote
1answer
17 views

Franck-Hertz experiment what transition takes place?

For the Franck-Hertz experiment there is a voltage drop at $4.9\rm\,V$. What transition does this represent in the mercury? Looking at the energy levels it seems to be from the ground to the 2nd ...
0
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1answer
31 views

Quantization in Black Body Radiation [duplicate]

Why does energy need to be quantized to explain black body radiation? Wouldn't the approximate normal distribution of the kinetic energy of particles at a certain temperature be sufficient, ie. few ...
1
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0answers
48 views

What's the advantage of using bra-ket notation over inner-product notation? [migrated]

Both notations look pretty similar, and appear similar when undergo algebraic operations. Apart from personal taste (aesthetics) concerning commas (<,>) vs. pipes (<|>), what is (are) the ...
0
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2answers
48 views

derivation qm canonical ensemble

In classical mechanics the canonical ensemble can be derived from the microcanonical ensemble of two systems in weak interaction. Is a similar thing possible in quantum mechanics? Is there any good ...