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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Cuprate Superconductors parameters

What are the parameters for cuprate superconductors, is it the same with normal superconductors? Because I was wondering if the high temp and low temp makes the difference.
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How does mirror reflection affect laser beam coherence?

I am an engineer that uses 10.6 micon laser beams to damage material. I am not a physicist so be gentle with your answers please. Two adjacent photons with their wave phases locked strike a 45 degree ...
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Is a ray of light, produced by an ordinary light bulb, filtered through a perfect monochromatic filter and 2 (in-line) pinholes, coherent?

A physicist once told me it is not, because even if it is perfectly monochromatic and perfectly collimated (by the two in-line pinholes), each photon has a completely random phase. For a while I ...
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How can valley coherence be defined if the crystal is initially in a mixed state?

In the field of valleytronics, they refer to valley coherence as: "the phase relationship between a particle in a superposition of two different valleys" [S. Vitale et al., Small 1801483 (...
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Incoherence and the bandwidth of a source

It is generally accepted in the literature that the emission bandwidth $\Delta\nu$ of a light source is inversely proportional to its coherence time $\tau_\mathrm{coh}$, i.e.: $$ \Delta\nu \propto 1/\...
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Are hydrogen lamps coherent?

Those hydrogen or mercury tubes should not be coherent, but when looking at them through a grating without using a small aperture in front of the tube, you still see the discrete lines. Or just any ...
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Coherence, Correlation and causality in Quantum Field Theory

I've started to study in details quantum optics and I find difficulties in linking the concepts of coherence and correlation among fields, especially because I'm building right now a background on ...
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How to imagine the superconductive coherence length

the Ginzburg-Landau theory predicts two parameters: the penetration depth of a magnetic field into the superconductor $\lambda$ (which from agrees to London's penetration depth) and the coherence ...
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What has coherence time to do with Energy-time uncertainty?

we know that the coherence time $t=\frac{1}{\Delta f}$can be derived from Fourier transformation. But if we look at the Energy Time Uncertainty which is given by $\Delta E \Delta t ≥ \frac{h}{4\pi}$ ...
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What is the reason two rays originally polarized orthogonally but were rotated to parallel polarization does not visibly interfere even slightly?

The Fresnel–Arago laws by Augustin-Jean Fresnel and François Arago summarise some of the more important properties of interference between light of different states of polarization. The laws are as ...
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In a plain language, what does it mean when one says LASER has a high temporal and spacial coherence?

Does spacial coherence mean that if I took a cross section of the laser beam beam, then I can find a relation between the phase of the electric field between any two points across the cross section ...
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Why do images flip when the sample is raised in Fourier Domain OCT imaging?

Why does raising the sample under a FD OCT machine cause the image to flip at the top? I know that FD OCT is looking at the time delays of backscattered light at every tissue layer which interferes ...
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Measuring coherence length with the Michelson Interferometer

In lab, I've been asked to measure the coherence length of a green-light laser source using a Michelson Interferometer. To do so, I configure the interferometer such that a circular fringe pattern ...
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What defines "minimal coherence" as a condition for the emergence of stationary interference in a chaotic wave field?

Consider the following observations: A superposition of two electromagnetic waves with different frequencies will never produce visible interference patterns. Such waveforms will produce ...
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On the field leakage problem in quantum experiments

In a quantum experiment, does the leakage of the electromagnetic fields lead to the suppression of quantum effects? For example if I have an electron in a box, in some quantum superposition. Can I use ...
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Quantifying coherence with density matrices

I'm aware that the coherence of a statistical ensemble can be measured by looking at the off-diagonal elements of its density matrix, which is computed as the weighted sum of the density matrices of ...
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Chaotic monochromatic light

I am currently reading through the book "The Quantum Theory of Light", by Rodney Loudon, in order to prepare for a science fair project which will involve measuring plant response to ...
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What is a 'good' coherence/correlation function for multimode spectra?

Following up on the question here and this answer in particular, I would like to pose the following question: How to derive a formula for the coherence length of a multispectral source, such as a ...
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"Anti-collimators" for laser beams

I'm a student currently working on a science fair project which will measure the response of plants to coherent vs incoherent light of varying wavelengths. However, the only tunable and narrowband ...
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Magically reappearing fringes in Michelson interferometer for large path length differences?

I've built a simple Michelson interferometer from two mirrors and a beam splitter according to the following schematic: Image source My setup differs from the one in the publication in that mirror M1 ...
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Unsustained Interference Visuals

How does the interference (of coherent EM waves) that is not sustained look like? Kindly provide me with pictures or visual description. I tried searching the web but no avail. People say fluctuations ...
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Does light from incoherent source interfere?

We say that for us to observe interference we use coherent source but even if we use non coherent source light should still interfere, right?
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Interferences between coherent sources facing each other

I don't understand how 2 coherent sources of longitudinal waves (i.e.: sound) facing each other have destructive interferences at certain fixed points between the 2 sources. How come those points aren'...
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Phase shift between coherent longitudinal waves facing each other [closed]

In the following problem: 2 speakers are 6 feets away from each other and facing each other, assuming that they are 2 coherent sources of sound waves (so longitudinal waves), what is the phase shift ...
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How does the interferogram in SD-OCT contain all the depth layer information?

I am reviewing Spectral-Domain Optical Coherence Tomography (SD-OCT) and I came across the figure which describes the principle of SD-OCT: In Time-Domain OCT, the reference mirror has to move to ...
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Molecules are made up of numerous subatomic particles, so don't they constantly interact? How can we achieve quantum coherence? ($\rm C_{60}$)

Since $\rm C_{60}$ is a molecule made up of numerous subatomic particles, no matter how separated from the environment, the interaction between $\rm C_{60}$'s subatomic particles inevitably causes ...
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What is the difference between coherence and entanglement? [duplicate]

I am confused to the two terms, my question is what is the difference between coherence and entanglement?
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Squeezed vacuum state

From: Loudon, Rodney. The quantum theory of light. OUP Oxford, 2000. Consider the single-mode quadrature-squeezed vacuum state defined by $ | \zeta \rangle = \hat{S} (\zeta) | 0 \rangle $ where the ...
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Is this an example of a spatially coherent wave?

My ultimate goal is to understand why the spatial coherence of a wave increases with distance from the wave source. From what I have read though, there seems to be conflicting definitions of spatial ...
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How does lasers emit photons of constant phase and frequency

In my alevel physics book it says that the electrond in the atoms of the laser get excited and de-excited releasing photons of constant frequency. How is this possible if the photons have energy ...
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How does coherence of a light affect how we perceive a sample in a microscope?

First of all, does coherence of a light, which is used for illumination in a microscope, affect the sample, or the way we see/perceive it? I want to know what optical elements do I need to use if I ...
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What does it imply when we say that the waves are perfectly correlated?

I am having a hard time understanding difference between correlation and coherence. I got a nice answer for coherence here- Are two waves being in phase is the same as saying that the two waves are ...
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Will quantum events ever occur on a macro-scale rather than a vacuum? Michio kaku says there's a chance we'll wake up on Mars tomorrow

https://www.theatlantic.com/science/archive/2018/10/beyond-weird-decoherence-quantum-weirdness-schrodingers-cat/573448/ In this post, it is shown that quantum decoherence in the macro world occurs ...
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What is the eponym associated with the relationship between phase variance and expected magnitude?

I'm looking for the eponym (e.g., Stigler's law) associated with the following relationship: \begin{equation} \left|\langle e^{-i\phi} \rangle\right| = e^{-\langle\phi^2\rangle/2} \end{equation} which ...
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In real life, for a tennis ball to go through a wall, does it have to completely prevent the particles from interacting? (decoherence)

In real life, for a tennis ball to go through a wall, does it have to completely prevent the particles from interacting? What would happen if we tried infinitely in the real world, where the ...
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Do things and people in the macro world maintain a quantum decoherence? Or do you repeat quantum coherence and quantum decoherence every moment? [duplicate]

Does quantum decoherence remain uninterrupted for things and people in the macro world? Does the interaction of particles occur permanently without interruption in the macro world? Is that why our ...
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Why aren't macroscopic objects—or really the entire universe—coherent?

From what I understand, when quantum particles interact with the environment, they get entangled with it and the entanglement rapidly spreads until it's dispersed into the environment. So wouldn't ...
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Coherence and superposition principle - equivalent properties?

I'd like to revisit a question I posted earlier. While I now know what coherence means (and how it can be defined) I still struggle to give an intuitive explanation that goes along with the word "...
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Coherent and incoherent electron diffraction

I am learning about electron diffraction in a transmission electron microscope and was wondering about following topic: A single crystalline material will exhibit a diffraction pattern with discrete ...
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What is the meaning of this statement in Optics, Born-&-Wolf regarding coherence length?

In their treatise "Principles of Optics", Max Born and Emil Wolf state in the section on coherence length (page 317, para 1) that: ...... as the difference of optical path is increased, the ...
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Calculating Coherence Length and spectral width given an interferogram

I'm currently doing a lab in which we use a Michelson-Morley interferometer to analyse different light source. One of the mirrors in the interferometer is moved by a stepper motor. One of the light ...
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Long temporal coherence sunlight

What is the reason that sunlight have short temporal coherence? I know everybody says that coherence length is inversely proportional to bandwidth. Does it mean that if sunlight passes through a very ...
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How to scale Poissonian light?

In quantum optics, coherent light with constant frequency, phase, and amplitude shows poissonian photon number statistics: $$P(n) = \frac{\bar{n}^{n}}{n!}e^{-\bar{n}}.$$ A well-known result for ...
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Measuring unit of Spatial Coherence

Usually, the temporal coherence of light is described with the coherence length. This quantity can be measured conveniently with an interferometer and is directly related to the coherence time and the ...
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What does "coherent evolution" of an $N$-body quantum system mean?

In classical physics we know of coherence of waves and in quantum physics we identify coherent states. While those are clearly defined concepts/terms, in literature we regularly encouter also that a $...
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Gaining Quantum information without destroying the coherence

I've read about new optical interference among several telescopes all around the globe. It is supposed to work by combining the quantum states of a photon A arriving at once in every telescope of the ...
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What does the coherence time signifies?

I was reading a book named "Laser Physics And Applications by LV Tarasov". In page 19, It tells that The degree of non-monochromaticity and the time interval $\tau$ consistent with the ...
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Degree of first-order coherence doesn't imply always 100% visibility?

In classic books of quantum optics visibility of interference fringes (for example in Michelson interferometer) is equal to the modulus of the degree of first order coherence $g^{(1)}$, when the ...
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How does the double slit experiment ensure phase coherence?

I am quite unsure of how phase coherence is ensured in the double slit experiment. The most typical answer that I have found is that the path length difference between the lights going in either ...
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Relationship between Purity and Coherence of a quantum state

I know that there is an important relationship between purity and coherence. Loss of purity is often used as a basis-independent sign of decoherence. I'm not completely sold on this. I would have ...
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