All Questions
Tagged with photons quantum-optics
165 questions
2
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How do the entangled photons from an SPDC source behave?
As I understand SPDC sources emit entangled photons, but always in the same polarisation. If this source always outputs this certain polarisation are the photons then still in superposition of each ...
- 21
0
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0
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21
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Squeezing degredation via photon loss
Consider a partially reflecting beamsplitter with two input modes $\hat{a}_{in}$ and $\hat{b}_{in}$. It has a transmission coefficient of $\eta$. If the photon in mode $\hat{b}_{in}$ is in the vacuum ...
- 43
0
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1
answer
69
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Is Hadamard gate considered a valid beam splitter when dealing with multiple beam splitters?
I have read that Hadamard gate can be a valid 50:50 beam splitter when dealing with one beam splitter , however when dealing with more than one beam splitter the hadamard gate is no longer valid and ...
- 319
1
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2
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50
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Quantised optical cavities with non zero decay rate
The quantised electric field of an optical cavity can be described as a harmonic oscilator,
$$\hat{H}_{\mathrm{c}}=\hbar\omega_{\mathrm{c}}\hat{a}^{\dagger}\hat{a}.$$
If the cavity mirrors are ...
- 941
4
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1
answer
110
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What happens if obstacles (walls) been put where destructive interference occurs in double slit experiment?
If photon doesn't have probability to be in dark (destructive interference) area, what will be the effect of adding obstacles (walls) in the dark (destructive interference) area for the double slit ...
- 99
0
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1
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32
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Impact of obstacles on Single/ Double split interference pattern
What is the impact of obstacles on the interference pattern if the obstacles are arranged to be located in the destructive interference locations as follow:
According to my understanding to classical ...
- 99
0
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1
answer
51
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If the state is VH+HV how one can prove experimentally that two photons are identical?
From a SPDC source we get two photons in a $|VH\rangle+|HV\rangle$ state. How is to be proven experimentally that they are identical while one would be in $|H\rangle$ and the other in $|V\rangle$ ...
- 679
1
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1
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74
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An optical detector that guarantees single-photons detection
Let's consider a real source emitting a sequence of single-photons (like for example a N-V colour centre pumped with a pulsed laser with highly accurate frequency of the pulses). I want to ...
- 131
1
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0
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38
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What is the total energy of a transform limited pulse?
Something like a holy grail of quantum physics would be, if we could explain why $E=hf$. Einstein, originally meant a finite number of energy quanta, instead of the usual continuous Maxwell equations. ...
- 168
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1
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62
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How non-degenerate photon pair can be entangled?
papers like below describe https://arxiv.org/abs/1305.0986 "A Flexible Source of Non-Degenerate Entangled Photons Based on a Two-Crystal Sagnac Interferometer"
I, somehow, thought that ...
- 17
1
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1
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143
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Why is the second-order correlation function proportional to the population of the excited state?
In this paper (click to open it) A. Beveratos et al., 'Bunching and antibunching from single NV color centers in diamond' the authors write the following equation (page 4, eq. 1.2):
Namely, they ...
- 967
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1
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139
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Why does the following formula stands for photon number conservation?
I'm reading some materials(before eq(129)) about beam splitters while I met the following formula
$$
\hat a_{\mathrm{in}}^{\dagger}\hat a_{\mathrm{in}}+\hat b_{\mathrm{in}}^{\dagger}\hat b_{\mathrm{in}...
- 327
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0
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136
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What is the Hilbert space of a single photon?
I'm trying to understand the second quantization of photons. Following expression (4.3.5) in the lecture note:Second Quantization, a Hilbert space of a indistinguishable multiparticle system in second ...
- 1
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1
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240
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How do beam splitters work?
My main three questions are:
1.) What is the physical phenomenon that occurs in the interaction between a beam of light and a beam splitter that results in two beams of specific proportions of the ...
1
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0
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130
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Photon loss errors versus photon subtraction errors
Cat codes, $|0_L\rangle\approx|\alpha\rangle + |-\alpha\rangle $ and $|1_L\rangle\approx|i\alpha\rangle + |-i\alpha\rangle$, are said correct single-photon loss errors in the literature. Similarly, ...
0
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2
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65
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Are multimode states a product state of single mode states?
Books such as 'Quantum Theory of Light by Rodney Loudon (page 140)' and 'Quantum Optics for Beginners by Ficek and Rizda (page 43)' claim that the multimode state is nothing but a tensor product of ...
2
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2
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318
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How does partially constructive and partial destructive interference work in interferometers?
From what I have gathered, complete constructive or destructive interference results in all light or no light traveling a given path of an interferometer (correct me if this is incorrect). However, ...
1
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0
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Correspondence from classical to quantum light polarization
I understand the classical model of light polarization in terms of two complex numbers, known as Jones vector.
In the quantum case, for example, consider photons sent through two polarizers, the first ...
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25
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9
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6k
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Why does light travel in a straight line if the uncertainty principle is true?
I've asked this on different websites and never gotten an answer that a layperson can understand. Most people just say that light does not have a trajectory and then they do some hand waving. If light ...
- 361
1
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1
answer
76
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What is the state of the light emitted by an esemble of independent single photon emitters?
Upon proper excitation, single molecules (e.g. fluorescent dyes, quantum dots, etc.) spontaneously emit single photons, namely Fock states $|1\rangle$. These states have no statistical uncertainity ...
- 967
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1
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70
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Explanation for few things in this paper about photonic crystals
In this paper two weakly coupled cavities are excited with light. Their frequencies are modulated by a mechanical pulse. I have the following questions:
What is the Hamiltonian of this system ? I don'...
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0
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34
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Mechanism: Instantaneously vary frequency of photons emitted, or passing, by, over a wide range of frequencies, with reliable consistent precision?
For an optical computing application, I need to set frequency of photons emitted or passing by a small mechanism, instantaneously, and it needs to be able to change this frequency from one instance to ...
- 1
1
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0
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112
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What Happens When Three Photons Enter a Non-Polarizing Beam Splitter?
When a single photon enters a non-polarizing beam splitter, in any of the two inputs, it has 50% chance of leaving by each of the two outputs.
When two photons enter this beam splitter, each by one ...
0
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0
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204
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If I split coherent state light in half (by a beam splitter) are the 2 output intensities correlated?
From what I have been told and understand, if I use a simple beamsplitter to split coherent state light, I will obtain 2 coherent states as a result.
Are the intensities of these two output states ...
- 2,281
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1
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315
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Three input/output generalization of 50:50 beamsplitter
A symmetric 50:50 beamsplitter can be represented by a unitary 2x2 matrix acting on a vector of creation operators for the input states:
$$ \begin{pmatrix}
\hat{a}_c^\dagger\\
\hat{a}_d^\...
- 11
1
vote
0
answers
36
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Collision Broadening - Spontaneous emission
I am currently reading Loudon's "The Quantum Theory of Light" and get stuck about the following sentence:
Consider a particular atom radiating light of frequency $w_0$ . A train of
...
- 93
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0
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491
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Approximation for average thermal photon number
I am currently reading the book Introductory Quantum Optics by Gerry and Knight and I am having trouble understanding an approximation they make. In the chapter on thermal fields they derive the ...
- 203
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0
answers
80
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Absorption rate vs. Einstein Absorption Coefficient
I am trying to understand the absorption rate (or absorption probability density), which is defined as
$$p_{ab}=\frac{\sigma c}{V}, $$
where $\sigma$ is absorption (transition) cross section and $V$ ...
- 329
1
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2
answers
149
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Why are photons being identical particles?
Recently, I study quantum optics and deal with quantization of EM field in a cavity. We know we can express/quantize vector potential in terms of $\hat{a},\hat{a}^{\dagger}$ to get a quantized EM ...
- 430
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2
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679
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Why does stimulated emission not contribute to linewidth?
The rough quantum mechanical explanation for linewidth is that the lifetime $\tau$ of an excited level is associated with an uncertainty $\Delta E$ in its energy satisfying $$\Delta E\tau=\hbar$$ and ...
- 2,152
1
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2
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149
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Will a two-photon state be detected at the same spot?
Let us say I excite a particular mode $\omega_l$ of the electromagnetic field by means of parametric downconversion such that both of them are identical in all aspects: polarisation, direction and of ...
- 9,463
1
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1
answer
477
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Beam-splitter 2nd quantization description - distinguishing polarization states
I am studying beam-splitters in 2nd quantization and here is what I got so far
$$
\hat{BS}(\theta) = e^{i\theta(\hat{a}^{\dagger}_1 \otimes \hat{a}_2 + \hat{a}^{\dagger}_2\otimes \hat{a}_1)}
$$
where $...
- 745
2
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3
answers
443
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Quantization of electromagnetic field [closed]
Every quantum optics book starts with quantization of electromagnetic field. Why?
My understanding:
The quantized electric field consist of photon and it helps to derive some properties of photon.
Is ...
- 123
1
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0
answers
62
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Will an entangled photon bouncing off a/penetrating through a mirror "de-tangle" it?
Lets say I create a pair of entangled photons. I then shoot one of the photons through a semi-silvered(semi-reflecting) mirror. one(or both) of the photons are reflected, and (or) one (or both) of the ...
- 75
3
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0
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236
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Why do we get rings in the Spontaneous Parametric Down conversion (SPDC) process?
In the SPDC process, the phase-matching conditions between the o-rays and/or e-rays have to hold for the down-conversion process to take place. Say we have a non-collinear phase-matching at the plane ...
- 195
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2
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329
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What happens if we shoot a single photon to a mirror?
I understand mirrors absorb a small energy portion of the light and reflect most of it. What happens if we shoot a single photon to a mirror? Would it be reflected?
If the answer is Yes, then I would ...
- 1,148
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1
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81
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CHSH Bell measurement, why is there difference between 45 and 135 degree?
Let assume BBO type-2 that simultaneously generates entangled photon pair in forms of horizontal polarization (H) and vertical polarization (V) of photon. One photon is going to Alice and the other is ...
- 43
2
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3
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281
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Can laser light be described by individual photons?
If laser light is described by a coherent state, a macroscopic quantum state, to what extent
does it make sense to speak of individual photons in laser light?
And if the laser is attenuated to be a ...
2
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1
answer
532
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Is photon a wavepacket of electromagnetic field?
Photon is a "particle of light". Light is just a propagating EM field. Therefore photon is (at least intuitively) a localized EM field (i.e. wavepacket).
In quantum optics, the Hamiltonian ...
- 207
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1
answer
236
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Phase/Intensity uncertainty relation
In quantum optic, we have the relationship:
$$\Delta N\Delta \theta>1/2\tag 1$$
But to my knowledge, $\theta\in[0,2\pi[$ so $\Delta\theta$ is finite, then for example if we know perfectly the ...
- 1,748
2
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0
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225
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Is anti-bunched light necessarily sub-Poissonian?
It is well-known that sub-Poissonian photon statistics and light anti-bunching normally occur together, since both effects may be considered as a manifestation of photon streams being 'regular enough'....
- 207
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2
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236
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1:1 Beam-splitter and the Hong-Ou-Mandel effect
We can write the state of two photons in different modes:
$$\tag{1}
\hat{\alpha}^{\dagger} \hat{b}^{\dagger}|0,0\rangle_{a b}=|1,1\rangle_{a b}
$$
According to the Wiki page on the Hong-Ou-Mandel ...
- 261
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1
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112
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About two photon interference in nanophotonics
Within the standard model, photons are point particles, i.e., with no spatial distribution.
On the other hand, classical electromagnetic modes have field distributions.
Suppose there are two different ...
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6
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What is the length of a photon?
Some questions that look kind of similar have been asked before, and I find the answers quite confusing. I intend to ask this question in a way that clearly shows what I'm asking.
Imagine the ...
- 3,086
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1
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263
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How do ladder operators and number states act on multimode states?
The ladder operators for number states, $\alpha_{\ell}^{\dagger}$, and $\alpha_{\ell}$ have the following properties when working on mode $\ell$:
$$\begin{array}{l}
\hat{\alpha}_{\ell}\left|n_{\ell}\...
- 261
1
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1
answer
548
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How to produce and detect Fock or photon number states?
I would like to build, if possible, an intuition of the physical methods on how photon number states $|n\rangle$ are experimentally produced and how are measured. We can focus on single mode.
It would ...
- 896
6
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1
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1k
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How can sub- and super-Poissonian statistics be distinguished from bunching and antibunching?
This is my first post here, so I apologize if there's something wrong.
I am studying quantum optics and I found myself in trouble with the difference between bunching/antibunching and super poissonian/...
- 896
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1
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357
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Coherence and $g^{(2)}$
We talk about how coherent light has a $g^{(2)}(\tau)=1$ and thermal light has $g^{(2)}(0)=2$. However, we can talk about the coherence length of a thermal source if we put it through a very narrow ...
- 128
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1
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355
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Feynman Lecture 26 - Summation of Probability Amplitudes
How does Fig. 26-3 (shown below) correspond to the following paragraph from this Feynman lecture?
Finally, we give a very crude view of what actually happens, how the whole thing really works, from ...
- 149
2
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1
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270
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Does amplitude modulation change a photon's frequency or the number of photons?
In the following, we assume that the polarization is aligned such that the scalar treatment of the electric field is justified.
Furthermore, we limit the discussion to a fixed coordinate $x=0$ to drop ...
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