Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [coherence]

Coherence describes properties of correlations among physical quantities of waves, with special emphasis on constant phase differences and frequencies in common. Such collective linkages enable stationary (temporally and spatially constant) interference.

0
votes
0answers
10 views

How would measuring the number of photons on a finite number of pulses break coherence of a weak coherent laser source in COW QKD protocol

I' m trying to understand attacks on Quantum key distribution protocols. In the COW QKD protocol, pulses from Alice are passed through an asymmetric coupler and a fraction 'T' of the photons are sent ...
2
votes
1answer
28 views

What kind of light coherence is required for an image

If 1- Optically speaking, an image point (or pixel) is a light interference pattern 2- interference patterns require phase coherence then 3- the source of the image point must emit coherent light ...
2
votes
3answers
68 views

Why oil films still have color when illuminated by an incoherent source (sun) at oblique incidence

I understand how coherent light can produce interference patterns with a thin oil film. However the sun is a spatially incoherent light source. How can it be that at oblique incidence I still see ...
0
votes
0answers
18 views

Combine coherence tomography with second harmonic generation

I was given the task to combine the OCT procedure with second harmonic generation. Problem is I am completely new to this stuff. Could anyone give me a few proposals which I could use as starting ...
0
votes
0answers
26 views

Why is a point source required for observing perfect double slit interference?

What would happen with a non-point but coherent source (some kind of ideal flashlight which produces perfectly coherent light for example)?
-1
votes
1answer
44 views

Dimensional grid of spatial coherence on earth of Pole Star radiation

One spot on earth receives a constant stream of stellar radiation: this is the North Pole where the Pole star radiation flows constantly. Given that a point source of light is considered to emit a ...
1
vote
1answer
27 views

Loss of beam power over astronomical distances

pardon my choice of words, but English isn't my native language, so I might use the wrong terms at some places. Beside this, I do have a hypothetical situation which might be a bit off reality (...
1
vote
1answer
45 views

Unable to get interference from milk using Time domain OCT (Michelson Morley interferometer) approach

I was able to construct time domain Optical coherence tomography based on Michelson Morley interferometer using a LED. While testing the interferometer, I used glass slide, layers of scotch tape. I ...
0
votes
0answers
23 views

Glauber's theory of coherence. Separating a time dependent Electric Field into positive and Negative parts

I saw this expression of the E- Field in the seminal paper of RJ Glauber on quantum coherence and I don't understand how he came to it. He says that in the absence of a fourier integral representation ...
0
votes
2answers
45 views

Time-of-flight spectroscopy and energy-time uncertainty

I am a bit confused about spectral and temporal filtering of light. I consider a single-photon source of a bandwidth of $1\,$nm at $1550$ nm. That means, that the wavelength of the emitted photons ...
1
vote
1answer
53 views

How often do particles regain quantum coherence after decoherence?

Quantum decoherence is "well known" process. It is simply defined as a loss of quantum coherence. It is often used as a partial explanation for "collapse of the wave funtion" (wave funtion is ...
0
votes
0answers
16 views

Is photoconductive antennas terahertz imaging system coherent?

Currently I am learning THz imaging system. And I find that the light source of PCA THz system is laser beam (?). But what confuses me is that the THz system in this paper is like point source. Well. ...
0
votes
0answers
22 views

Calculating the $g^{(2)}$ correlation function

I want to make sure I am doing this right. I am also lost on how to continue at the end I have to calculate $$g^{(2)}(0) = \frac{G^{(2)}(0)}{|G^{(1)}(0)|^2}$$ for the following states (1) $$\...
2
votes
0answers
21 views

How does thermalisation make incoherent waves into coherent ones?

Thermalisation is the process by which out-of-equilibrium systems reach equilibrium. Coherence refers to the phases of waves being a constant difference apart. While reading a paper on axion stars, I ...
0
votes
1answer
69 views

double-slit experiment showing faster than light information transfer?

In the figure shown below, a laser sends a continuous stream of a large (almost infinite) number of photons per second at a double slit, and the photons are then are displayed on a screen. The upper ...
2
votes
1answer
71 views

can entangled photons produce an interference pattern?

Suppose you have a laser that emits entangled photons in opposite directions towards a double-slit screen setup as shown below. The photons are entangled such that if a photon on the left travels ...
0
votes
1answer
31 views

How could we extend Kuramoto Model to Arbitrary Dimensions?

The generalised version of a theory describing synchronisation in an ensemble shows that coherence arises differently depending on whether the number of dimensions is even or odd. But how could you ...
1
vote
0answers
43 views

Why there is no even order in high-order harmonics generation of noble gas?

As we all know, there is no even-order peaks in HHG of noble gas. I understand this phenomenon by the knowledge here: there will be odd and even peaks in the frequency domain when we do fourier ...
1
vote
0answers
163 views

YDSE - coherence of light from slits and width of slits

In Young's double slit experiment, 2 slits act as coherent sources. Why is coherence lost when the width of the slits is greater than half of the fringe width, i.e, if slit width is greater than the ...
1
vote
0answers
46 views

Can this experiment prove photons are mixed-frequency?

In this SE question, I asserted that mixed-frequency photons exist. Elsewhere I have asserted that a photon can have a finite coherence length. The two assertions are, of course, closely related: ...
4
votes
1answer
124 views

Optical coherence versus quantum coherence

Optical coherence is usually defined to be the measure of statistical correlation (for example if the phase difference is constant) of a pair of waves. Recently I came across the notion of quantum ...
0
votes
0answers
16 views

Is this expression for light coherence length correct?

On the Wikipedia page for coherence length, here, the expression for the coherence length for a Gaussian source is $L = \sqrt{ \frac{2 ln(2)}{n\pi}} \frac{\lambda^2}{\Delta \lambda}.$ In this ...
1
vote
0answers
48 views

mutual coherence

I read Vertex-Frequency Analysis on Graphs (arxiv link) Shuman, David I, et al. “Vertex-Frequency Analysis on Graphs.” Applied and Computational Harmonic Analysis, vol. 40, no. 2, 2016, pp. 260–291....
1
vote
1answer
92 views

Hong Ou Mandel Effect for incoherent photons

I am trying to show that the Hong Ou Mandel effect will not happen if the photons are not coherent. I am not sure where I am going wrong with my maths. I have tried to emulate the coherent case but ...
0
votes
1answer
46 views

Formal Properties of Coherence relations

Suppose that two particles a and b are in a coherent state. Is the coherence relation between a and b satisfy all of the following? (1) Irreflexive: a and b are distinct particles (although they ...
5
votes
1answer
299 views

The term “Coherence” is overloaded!

I have troubles with modern terminology in the field of quantum information technologies. There are a lot of new terms that everyone is using and no-one takes time to explain, even though modern ...
1
vote
1answer
56 views

How long does a particle keeps his quantum state?

Assuming there is one particle in our world but all the fields we know today exist also. Because particles can interact with fields, I guess they can change there quantum state. how long can they be ...
1
vote
1answer
62 views

How does “coherence” contribute to inverting a two-level system?

In laser physics I am told that inverting a two-level system is not possible, since it will become transparent once the inversion reaches 50% and no longer be able to absorb more photons. This makes ...
-3
votes
1answer
70 views

Never ending quantum superposition? [closed]

So I am wondering over the Copenhagen Interpretation how can a decoherence or measurement ever happen. If in the beginning of the universe everything was in a state of coherence being in ...
7
votes
5answers
377 views

Quantum interpretation of light coherence

When I studied interferences, I saw that only coherent sources could interfere. In physics, two wave sources are perfectly coherent if they have a constant phase difference and the same frequency, ...
5
votes
4answers
414 views

Difference between pure quantum states and coherent quantum states

In the post What is coherence in quantum mechanics? and the answer by udrv in this post it seems to imply that a pure quantum state and coherent quantum state are the same thing since any pure state ...
3
votes
2answers
171 views

Coherence as an (incomplete) measure of the number of correlated spins

Consider a system of $N$ spin $1/2$ particles in one dimension. Working in the conventional shared $\hat{\sigma}_i^z$ basis for the system's Hilbert space (spin up/spin down basis), a coherence term ...
1
vote
0answers
42 views

Physical reason for light incoherence

In my physics notes it is stated that the light phase changes every 10^-8 seconds, hence light from 2 light original light sources. I understand how light from incoherent light doesn't allow for ...
0
votes
1answer
1k views

Coherent vs In Phase vs Polarized Light [duplicate]

What are the distinct differences, if any, between Coherent Light, Light that is In Phase, and Polarized Light? Also: I have found conflicting definitions of coherent light, where one definition is "...
0
votes
1answer
105 views

What is meant by quantum coherence in the context of a two-level atomic system?

What is meant by quantum coherence in the context of a two-level atomic system?
0
votes
1answer
76 views

Is it theoretically possible to split a photon into two that are coherent with the original?

Purely theoretically speaking, is there a reason a photon cannot be turned into two lower energy photons with the same polarization as the first?
2
votes
0answers
49 views

What is the difference between complex and real coherneces?

If we have one density matrix $$\rho=\begin{bmatrix}1/2&&1/2\\1/2&&1/2\end{bmatrix}$$ for the state $\lvert\psi\rangle=\frac{1}{\sqrt2}(\lvert g\rangle+\lvert e\rangle)$ and a ...
5
votes
2answers
178 views

Why produces a laser coherent radiation?

Short question: Why is the light emitted by a laser coherent? Respectively, why is stimulated emission coherent? edit: How does a laser emit light in a coherent state? seems to be connected to the ...
3
votes
4answers
2k views

What is superconducting coherence length?

I'm an electronics student, and don't know much about some physics concepts. I was studying superconductivity and came to the London equation, Meissner effect and BCS theory. I kind of understood ...
0
votes
1answer
117 views

Would an incoherrent point source of light have any effect on a coherent

If you had a coherent laser beam that was split between reference and sample beams and the sample beam passes through the emission from a point source, there should be some disturbance right? I know ...
1
vote
1answer
42 views

Principle of Ergodicity in Derivation of Coherence Function

I am a bit confused about the following thing: In the derivation of the coherence function for the electric field at two times $t_1$ and $t_2$, following simplification is made: $$\langle E^*(t_1) E(...
5
votes
1answer
481 views

Density matrices, off-diagonal terms, coherences and correlations

I'm trying to better understand the off-diagonal terms of the density matrix - an often brought up question on this site I realise. Specifically my confusion at the moment concerns the interpretation ...
0
votes
0answers
42 views

Phase front of a laser beam through an imperfect optical element

I'm not sure what to make of the following thought experiment: consider a Rayleigh interferometer, where one arm holds a cuvette with some transparent liquid. The aim is to measure the refractive ...
4
votes
3answers
341 views

Coherence and Interference

Is coherence always necessary for interference? I thought so, but I came across a problem: If you try to measure an x-ray spectrum, you usually do so by using bragg reflection on a crystal, i.e. ...
3
votes
2answers
174 views

Relating Temporal Coherence and Intensity of Interference Pattern

In trying to understand the phenomenon of coherence a bit deeper, I have come to face the following question. Suppose one uses an interferometer (Micheloson-Morley, Mach-Zehnder, etc) to measure the ...
1
vote
1answer
458 views

Expression for quasi monochromatic wave: dependence of the amplitude on time

In Principles of Lasers - O. Svelto (chapter 11) the author gives the following explanation for quasi-monochromatic waves: In most cases of interest to us, the spectral bandwidth of the light ...
2
votes
3answers
192 views

How to interpret the definition of optical autocorrelation function for electric field?

For EM waves the "temporal coherence" can be described quantitively using the autocorrelation function $$\Gamma(\vec{r_1},\tau )=\lim_{T \to \infty }\frac{1}{2T}\int _{{-T }}^{{+T }}E(\vec{r_1},t+\...
2
votes
1answer
261 views

Is the coherence of a quantum state a relative concept?

It is often said that e.g., in describing the collapse of states in Quantum Mechanics (QM), speaking or analyzing in terms of information provides a more solid footing compared to focusing on changes ...
0
votes
1answer
71 views

Why is it difficult to get white light sources that maintain a constant phase difference?

In my text book the explanation for the question is this (Collins Year 1 and AS level physics): It is difficult to get white light sources that maintain a constant phase difference.Light is emitted ...
10
votes
2answers
707 views

How are coherent states in the real world made?

Coherent states are quantum states that are said to act "as classically as possible". You can define coherent states for the harmonic oscillator, or more generally for any collection of harmonic ...