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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What is the propagator?

What is the propagator? According to Each path is allowed. So it is possible Particle velocity faster than the speed of light?
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34 views

Expected value of $xp$ in harmonic oscillator

I wanna find out the expected value of the $xp$ operator for the $n$-th excited state of the harmonic oscillator, i.e. calculate the value $\langle n|xp|n \rangle$. I express the position and momentum ...
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26 views

connection between entanglement and squeezing [on hold]

I am looking for a good resources in the topic of squeezed quantum states and entanglement. I want to know what is the relation between squeezing and entanglement, firstly electromagnetic radiation, ...
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0answers
27 views

Is time depending on the observer in string theory?

I heard that in the theory of relativity the time of an action is depending on the observer. But in string theory, is the time also depending on the observer? Are strings acting according to the ...
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2answers
33 views

Magnetic quantum numbers - axes correspondence

We know that the magnetic quantum number describes the space orientation of an orbital within an atom. For the $p$-orbital, the magnetic quantum numbers can be -1,0,1 (one for every axis). We have ...
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2answers
76 views

Why are the quantum numbers $n$ and $\ell$ denoted with those letters?

We have 4 quantum numbers: principal, azimuthal, magnetic and spin (denoted $n$, $\ell$, $m$ and $s$ respectively). I assume $m$ and $s$ are simply the initials of 'magnetic' and 'spin'. Is there any ...
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59 views

The fine structure constant - can it genuinely be a random variable?

The question Does it make sense, and are there physical reasons to think about the fine structure constant as a (very concentrated) probability distribution rather than a single real number? ...
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1answer
71 views

QEC and QED with unlimited computational power - how precise they are going to be?

My question is about quantum algorithms for QED (quantum electrodynamics) computations related to the fine structure constants. Such computations (as explained to me) amounts to computing Taylor-like ...
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18 views

Lindblad equation derivation

I'm reading A simple derivation of the Lindblad equation. It introduces a Hamiltonian for a system consisting of a principal system $S$, a heat bath $B$ and an interaction term: ...
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38 views

Path integral method for harmonic oscillator [on hold]

Use the path integral method to calculate the transition $\langle x(f),t(f) \rvert x(i),t(i) \rangle$ for a harmonic oscillator.
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14 views

Landau levels. Gauge symmetry

If we try to find wave function for different vector potential, we will get wave functions, that do not have the same probability at any point( $|\psi_{E,p_y,p_z}|^2 \neq |\psi_{E,p_x,p_z}|^2)$ For ...
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56 views

$e^{\mp i \pi \hbar S_z } S_{ \pm} e^{ \pm i \pi \hbar S_z} = -S_{\pm}.$ [on hold]

I am supposed to show that $$e^{\mp i \pi \hbar S_z } S_{ \pm} e^{ \pm i \pi \hbar S_z} = -S_{\pm}.$$ I tried things like the Hadamard equation, but did not really get close to this equation. Does ...
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29 views

Resource cost and noise effects in quantum teleportation of multible (entangled) qbits

Suppose you have n qubits that are in an unknown state (may be entangled, etc). Can you teleport this state by teleporting each qubit individually (using a Bell state and a classical channel)? If ...
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1answer
27 views

How to determine whether an eigenstate of total spin is symmetric or antisymmetric?

Here we have two identical paticles with spin $I$, integer or half-integer, and there are $(2I+1)^2$ states. Each one of them can be uniquely determined by total spin and its orientation, we can use ...
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2answers
62 views

Proving (instead of discovering) the laws of quantum mechanics

A single toss of a fair coin cannot be predicted. But if we observe a large number of tosses, we can prove mathematically the law that roughly half of them will show up heads. The movements of ...
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2answers
64 views

What's the true reason behind thermal expansion?

Thermal expansion is a normal concept everyday. There are 2 explanations: 1, thermal expansion result in stress, then result in deformation 2, thermal expansion result in deformation, then result in ...
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3answers
102 views

Do electrons pop into and out of existence around the nucleus of an atom?

What surrounds the nucleus is the probability wave. But are the electrons constantly popping in and out of existence around the nucleus in the cloud?
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1answer
46 views

What is the energy of a Gaussian wave packet?

Suppose we have a potential barrier situation, that is $V(x)$ is zero everywhere except on the interval $[-a,a]$, where it is equal to some $V_0 > 0$. Introduce some Gaussian shaped wave packet to ...
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1answer
45 views

What does vector space and bra/ket space mean? [on hold]

I wonder What are the similarities and dissimilarities between a vector space and bra/ket space?
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31 views

Determining Parity of Decaying Quantum System

Show that a particle of spin $1$ cannot decay into two identical particles of spin $0$. The $\rho$-meson has spin $1$ and can decay into two spinless (spin-$0$) $\pi$-mesons, or pions, with ...
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6answers
475 views

On the foundations of quantum physics

Quantum physics has to be validated by experiments. But experiments are to be interpreted in the context of quantum physics. Isn'it like a snake biting its own tail? For example, using a scanning ...
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3answers
266 views

Entanglement and simultaneity

According to the special theory of relativity, distant simultaneity depends on the observer's reference frame. And, according to the quantum theory, in the case of two entangled particles, a measure ...
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58 views

A problem with the Gamow state

Consider a form of potential $U(r)$ as follows $$ U(r)=\begin{cases}0 & 0<r\leq a \\ U_0 & a<r\leq b \\ 0 &r>b\end{cases} $$ In this problem $r$ is the distance from the origin, ...
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1answer
19 views

In what order will the magnetic quantum number be filled

For example, the electron configuration for Cu(II) ion is [Ar]3d9. So only the 3d shell matters to the total orbital angular momentum of the ion. For 3d shell there are 5 possible values of $m_l : ...
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1answer
44 views

Does a static electric field act continuously?

Electromagnetic radiation is emitted and absorbed in discrete units, photons. One photon's energy is described by the well known $E = hf$ formula. Now, if you a have static electric field that ...
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Are there any proposed alternatives to quantum mechanics as there are alternatives to general relativity?

There are a lot of alternatives to general relativity and one of the motivations is attempting to formulate a working theory of quantum gravity. In some limit they reduce to general relativity. But ...
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Show that a barrier which is forbidden for a classical particle can have a finite probability for a quantum particle [on hold]

Show that a barrier which is forbidden for a classical particle can have a finite probability for a quantum particle.
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1answer
108 views

Should the differential of a wavefunction have a time partial derivative?

In chapter 1 of Griffths' QM text, he shows that $\frac{\mathrm{d}}{\mathrm{d}t}\int_{-\infty}^{\infty}|\Psi|^2\,\mathrm{d}x=0$ by noting $$\begin{align} ...
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34 views

How does observer affects the wave-particle nature ? (and related questions: part 2)

Following comments I split my question in to two parts which are independent. The questions are about double slit experiment with an observer(s). Suppose electrons are being used in the experiment ...
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1answer
70 views

Degrees of freedom in Quantum Mechanics

If we look at a particle in classical mechanics, the degrees of freedom increase as its size decreases like the degrees of freedom of an atom is more than that of molecule, and subsequently, the ...
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49 views

How does an observer affect the wave-particle nature? [on hold]

I have heard about the double slit experiment and the effect the observer has on the outcome, mostly in documentaries. I have few questions about what they mean by an observer. I will assume the ...
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27 views

The energy of an electron in a time-dependent electric field

Is energy of an electron in a time-dependent electric field any different from the one in a static field? Why did D.Griffith state in his "Intro to QM"( when he discussed the perturbation of EM waves ...
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38 views

What is the form of the Hamiltonian for periodic boundary conditions? [on hold]

What would the potential term be for a system with periodic boundary conditions? I know the simple harmonic Hamiltonian, but what about a general system such as a wire? I'm trying to solve the ...
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1answer
93 views
+500

Wave/particle-duality as result of taking different limits of a QFT

There is an account on dualities in quantum field theories and string theories by Polchinski from last week http://arxiv.org/abs/1412.5704 At the end of page 4, he writes the wave/particle ...
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Sufficient criterion for su(2) invariant spin-1*spin_s bipartite density matrix

SU(2) invariant spin-1 and spin-S bipartite density matrix is given by $\rho ^{1,S}=\frac1{3*(2S+1)}[1+\alpha {S^A_i\times S^B_i}+\beta S^A_{ij}\times S^B_{ij}]$, i j varies from ...
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2answers
82 views

How can the electron be a wave? [duplicate]

I read about Rutherford's failed attempt to describe the atomic model. Then I read about Bohr's model and his postulates. Ok, that was fine. But then I read in my book a statement that shocked me: ...
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4answers
167 views

Difference between spin and polarization of a photon

I understand how one associates the spin of a quantum particle, e.g. of a photon, with intrinsic angular momentum. And in electromagnetism I have always understood the polarization of an EM wave as ...
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1answer
41 views

Quantum cloning of orthonormal states

If I understand correctly, for two orthonormal states $\left|\psi_1\right\rangle$ and $\left|\psi_2\right\rangle$ in the Hilbert space H, there must exist a unitary transformation $U$, such that: ...
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1answer
116 views

Are wave functions real physical objects? [duplicate]

Are wave functions (ex. electron waves) real physical objects or just mathematical tools?. Some researchers say that they have proof that they are real objects. Here's [the link] ...
3
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1answer
54 views

What topics do I need to study electromagnetism on the quantum scale? [on hold]

What topics do I need to study (in order) so that I can study electromagnetics on the quantum scale? What is the name of the discipline studying electromagnetism on the quantum scale? Do I need to ...
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59 views

What does the relation between mass and energy of a free particle mean?

What does the Hamiltonian for a free particle mean? Does it mean that the kinetic energy of the particle is in reverse relation with mass? $H$ or $E=\hbar^{2}k^{2}/2m$. Or better to ask: what's the ...
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4answers
531 views

Exploring beyond event horizons

In the expanding universe the velocity of separation between galaxies depends upon how far they are. If they are much far away will they have relative velocity of separation greater than speed of ...
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2answers
270 views

Wave function in quantum mechanics

I was wondering about something while studying quantum mechanics. If the wave function collapses when measuring a particle and assumes a single position, how do we know that it was a wave in the first ...
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1answer
41 views

Why two-particle wavefunctions are separable and their corresponding particles are indistiguishable at the same time?

If the wavefunction $\psi(r_1,r_2)$ doesn't represents an entangled state, it is separable: $$\psi(r_1,r_2)=\psi_a(r_1)\psi_b(r_2)$$ In this treatment, we ignore the interaction between two particles ...
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18 views

Energy eigen value for a perturbed free particle system

Suppose we have a one-dimensional free particle system and we introduce a perturbation like $V(x)=V_{0} \cos(Gx)$, where $G$ is the reciprocal lattice vector (it's a periodic perturbation, I think) ...
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14 views

How come plasmon resonances of metals are capable of being tuned to different wavelengths?

I read in this article that plasmon resonances though being a pre-determined property of a metal are capable of being tuned to other wavelengths when these same metals are made into tiny ...
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61 views

Quantum Simple Harmonic Oscillator Interpretation

I am just wondering what does the SHO system from quantum mechanics actually physically represent? Is it just a SHO of a quantum particle, seems a little too obvious for quantum theory? I'm from a ...
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51 views

What collapsed the wave function of organic molecules for life to form? [closed]

The wave function only collapses when it is measured by an observer. So, before life came into the universe, I'm guessing that everything existed in superposition. We are told life was formed as a ...
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1answer
64 views

Is nature quantized?

I was reading Planck's postulate the other day on Wikipedia and couldn't help but noticing the sentence: "...is the postulate that the energy of oscillators in a black body is quantized..." ...
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In MWI, how to make sense of the nonuniqueness of decomposing mixed states into pure states?

It's well known that in quantum mechanics, a generic mixed state can be decomposed into pure states in infinitely many different ways. While this property is kind of understandable if quantum states ...