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.

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Difference between coherent and incoherent energy transfer (e.g. in photosynthesis)?

Several authors distinguish between incoherent and coherent when describing the energy transfer mechanism that forms the basis for photosynthesis. (e.g. Clegg & Sener 2010 and Keren & Paltiel ...
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“Synchronization” Probability of Multiple Waves with Varying Frequencies

Update 1: I've done some digging and I think this is related to signal coherence, namely, that I'm seeing a coherence time of ~3 σ, which is consistent with the definition where Ct=1/Δv where Δv is ...
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Signal coherence/correlation vs quantum coherence

In general, I understand a signal $s(t) \in \mathbb{C}$ is called "coherent" when it has a large autocorrelation function. A pair of different signals $s(t)$, $r(t)$ can also be "coherent" if their ...
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Identify reasons for laser intensity fluctuation

I got a Mitsubishi LPC-826 laser diode (single mode) with laser driver iC-HG. There is no cooling device, but data was captured after 30 mins switching on (which should be temporally stable). The beam ...
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Fiber ring resonators versus microresonators

Fiber ring resonators made of multimode fiber are capable of supporting multiple spatial modes. Even fiber ring resonators made of single mode fiber can, under favorable conditions, support a few ...
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Why does wavelength coherence affect diffusion?

Not to be confused with the relationship between wavelength and photon localization. But, laser light is is able to stay concentrated over a vast distance, much more so than every-day lamp light. ...
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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 ...
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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 ...
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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 ...
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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 ...
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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)?
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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 ...
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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 (...
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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 ...
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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 ...
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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 ...
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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 ...
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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. ...
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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) $$\...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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: ...
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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 ...
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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 ...
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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....
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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 "...
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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?
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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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(...
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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 ...
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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 ...
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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. ...