Coherence Definition and 115 Threads

Recently I've been trying to understand coherence,about waves in general.But its just a little hazy to me.Can someone explain it clearly? Thanks

The coherence I'm asking about is also known as magnitude-squared coherence. Let's say we have input A(t) and we look at the output B(t), the system L is linear but it has damping effect on the signals. In a long time, this damping will literally kill the high frequencies to zero. My...

Hi, I am curious to know if there any passive (or simple active) methods to convert a very coherent signal into an incoherent one? I suppose I would need to find a way to chirp the signal and a non-linear medium might be one method. Any ideas? Thanks narra

What is the best way to calculate the coherence length of a laser?

Hello folks. 2-dimensional spectroscopic techniques have been used to investigate biological systems and found that they transfer energy via coherent pathways. However, some have argued that this has no bearing on how these systems behave in nature, as the sun is not a coherent source and the...

¿ What´s the matter if after decoherence the measured system coherences again with the bath ¿ Is measure erased

Can anyone provide a simple explanation of spatial and temporal. I can't seem to understand the Wikipedia page on Coherence.

Hey people! I'm studying the article "The Quantum Theory of Optical Coherence" by Glauber (see eg. http://prola.aps.org/pdf/PR/v130/i6/p2529_1), and I've a couple of questions. 1. Why are the arguments of E(+) and E(-) in equation 3.6 two different sets of coordinates? We obtained E(-) by...

What is the difference between the two in simple terms ?

My understanding of wave-functions is close to zero, pardon me if the questions don't sound proper. 1. Do we have wave-function usage to describe a) Coherence and b) Entanglement? 2. Has a (mathematical/conceptual) way been developed to show the complementarity between both (a & b) via...

In the ZWM study of 1991 Mandel et al get coherence between the signal photons of two distinct downconversion sources. This is shown with an interference collection between the two possible sources of signal photons (even though they are entangled with the idler). This is achievable because...

I was just curious, sorry if it is already asked, I was going through a book on photonics and came across the relation coherence time, t = λ*λ/Δλ I did not find any proof of this. Can anyone explain me how this relation is found?

Could someone please concisely explain the difference between resonance and coherence?

Why is coherence and entanglement complementary? Lets take the case of a pair of entangled photon. there is very little coherence between the entangled photons. when we try to improve the coherence; the (degree of) entanglement starts to reduce. why does that happen? Does it have...

I would like to have at least a vague idea how coherent is light from an inexpensive 1 mW red semiconductor laser which I have. I tried to find the manufacturer using Google, but I haven't found it. I would like to know the coherence length and the degree of spatial coherence. Is there...

Homework Statement Hi guys, appreciate all the help I can get. This has been bugging me for 24 hours now. I'm starting to think I'm missing something in the question. We are exploring first-order coherence degree. That is, exploring the coherence of two separate signals (wave packets) by...

can coherence be restored [SIZE="1"](after de-coherence)? let's look at single particle (interference) in a double slit experiment: when we try to gain which way ... the ordering of the phase angles between the components of a photon in a quantum superposition is disturbed/changed (?) can...

Quite often one can see descriptions saying that the coherence time of single photons corresponds to the length of the single photon wavepacket (for example Jelezko et al, PRA 67 041802(R) (2003) http://pra.aps.org/abstract/PRA/v67/i4/e041802). I find it hard to come to terms with this picture...

Hi. I'm reading an introductory section on the Bose-Einstein condensation of a non-interacting, spinless boson gas. I'm confused by the claim that the ground state is in a coherent state with eigenvalue sqrt(N0) exp(i theta), where N0 is the expected number of particles in the ground state. The...

(note: I posted this here instead of the Biology forum because the topic involves heavy quantum concepts that mere biologists can't handle) I read PF Mentor Ryan_m_b mentioned elsewhere that "Discussing quantum effects in biology is not a banned topic on this forum, however threads that...

http://www.physorg.com/news192726440.html researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC), Berkeley have recorded the first observation and characterization of a critical physical phenomenon...

I am presently in a Biophysics lab, and am formulating a project wrt transmembrane protein association in lipid bilayers (based on the 4 stage model of membrane protein folding, i.e. partitioning, folding, insertion, association). I was wondering if anyone on here has heard of any decent...

Homework Statement A light source consists of two long thin parallel wires, separated by a distance, W. A current is passed through the wires so that they emit light thermally. A filter is placed in front of the wires to only allow a narrow spectral range, centred at λ to propagate to a...

Hi, In studying about lasers, it was mentioned that lasers are highly focusable, and this was because of the high spatial coherence of lasers. Just want to ask: 1. Why and how does spatial coherence affect focusability? 2. How is a laser typically focused (using a lens?) 3. Why do...

Homework Statement Hi, I am trying to work through exercise 2.1 on page 37 of Microcavities (by alexy kavokin, jeremy baumberg, guillaume malpuech and fabrice laussy) the problem is to prove | g^{(1)}(\tau) | = | cos( \frac{1}{2}(\omega_1 - \omega_2)\tau) ) | where...

It is promised that the quantum coherence will help to improve various measurements. Is it theoretically possible to improve detection of neutrinos with help of quantum coherence?

Hi people :) I want to build an interferometer. In the course of looking for a suitable light source for my instrument I have been advised to check the 'coherence distance' of the sources; it is clear to me that this distance places practical limits on the design of the machine. However...

Hello all, I'm studying classical and quantum coherence in optics and I can't understand what's the physical meaning of second order coherence. I mean, what's the fundamental difference between it and the first order one? I know they are defined differently but I can't see in which case and why...

How could one measure degree of coherence with Fresnel biprism? Hello. I have some questions about the study of partial coherence with a Fresnel biprism. In common text degree of coherence and its relationship to visibility is introduced considering a Young Double Slit experiment. At the...

After erasure (of which-way info) in DCQE or similar experiments, is coherence (constant relative phase) restored?

Does the below sound ok? 1. Interference is caused between coherent waves 2. When we try to find which-way we break the coherence a) When we try to "partially" find which way, we partially break the coherence and hence a "partial" interference pattern 3. DCQE is explained by the fact...

Homework Statement On the wet road / asphalt / there is a oily stain,with refraction coeff 1.4 .Sunlight lights up the grease perpendicular .What colour will be a stain with thickness of d = 250 nm ? The water's refraction coeff is 1.33 Homework Equations Since we are asked what colour...

Hi, I'm confused by subtle differences between the concept. Let's take the example of a Schrodinger Cat. Supposed you could make a box that can isolate anything inside from say gravity, microwave radiation, is in 0 kelvin, etc. or let's just accept (for sake of discussion) that a box can totally...

Homework Statement A filter is used to obtain approximately monochromatic light from a white sources. If the pass band of the filter is 10 nm, what is the coherence length and coherence time of the filtered light? The mean wavelength is 600 nm. Homework Equations c\tau_{0}=l_{c}...

hi does anybody know a derivation of the formula for spatial coherence: a sin(beta) << lambda /2 where a is the length of radiating object and beta is half the opening angle.

When waves are said to be 'coherent', or in-phase, do they always act as a single wave, or do they maintain their individual identities?

Hi Classically, we can interpret the coherence functions (1st order) by using the definition of visibility, i.e., when there is complete coherence, the visibily of a fringe is maximum, and when the is complete incoherence, the visibility of a fringe is minimum. Can one make the same...

I'm not a physicist, and am trying to better understand quantum coherence. I understand that it's defined by the fact that the entire quantum system can be defined by a single wave function. My question is whether, due to wave-particle duality on the quantum level, it is equally valid to speak...

I have a question about quantum coherence phenomena. I understand (basically) how laser light results from light waves that are in sync. I also see how ferromagnetism results from orderly alignment of electron spin amongst iron atoms (though I've posted in another thread asking whether this is a...

Has anyone performed experiments regarding macroscopic quantum coherence (superposition of and macroscopic object)? What about testing if macroscopic objects obey macrorealism, or whether QM prevails? Links to articles or experiments would be apprecited.

I have nothing to add to the question that opens this post.

For any light beam it is normal to characterize the coherence length and time. This is done by measuring the ability light to interfere with itself. Does it make sense to talk about the coherence of a single photon beam, such as the one used in the double slit experiment? Can a single photon...

Hello, I'm a newbie of signal processing, I would like to calculate a frf between two acceleration signals. I have several realizations of each signal. These signals are stationaries and they aren't triggered, so signal arrays doesn't have the same length. I have got these acceleration signal by...

I was just reading up on Bose-einstein condensates and was wondering about something,hopefully you could point me in the right direction. so when you get atoms down to a low enough temperature the pauli exlusion principle gives out and they can sit ontop of each other like bosons,and they...

Hi all I am hoping that somebody here will be able to tell me why that different types of lasers eg He-Ne or Nd:YAG have different coherence lengths and how the coherence of a laser can be improved. I am thinking it is to do with the different gain mediums and the emission process...

I'm trying to understand Newton's rings. So we have a plano-convex lens supported in a plane (please, see image here http://scienceworld.wolfram.com/physics/NewtonsRings.html). The incident light is divided into the light that is reflected at the convex surface and the light that is reflected at...

Hi, 1. I am studying dynamic light scattering in which one experimentally measures intensity correlation i.e., <I(t)I(t+tau)>. Therefore, if the detector looks at a scattering signal from a solution of particles undergoing Brownian motion, under right experimental conditions one can detect the...

I want a clarification in the idea of superposition principle.Perhaps,I should rather say that the distinction of superposition principle in QM and in classical physics. Few weeks back,I was spending time with Gottfried's book. He explains the novelty of superposition principle with the help...

Coherent states are defined as eigenstates of the annihilation (lowering) operator for the quantum harmonic oscillator. So why are these called "coherent"? What does "coherence" generally mean in physics? And what does it have to do with what is known as "quantum de-coherence?" Edit: I...

Homework Statement Monochromatic light (λ = 500 nm) from a particular light source has a frequency bandwidth Δν = 6 x 1011 Hz. (a) What is the coherence length Δx and the coherence time Δt of this light? (b) What is approximately the largest optical path length difference in an...