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 [measurements]

The tag has no usage guidance.

11
votes
0answers
271 views

How does one compute the state of a quantum system following imperfect measurement?

Suppose I have a quantum system $S$ ("system") with Hamiltonian $H_S$ and initial density matrix $\rho_S(0)$. I allow $S$ to interact with another system $P$ ("probe"), which has Hamiltonian $H_P$ and ...
9
votes
0answers
235 views

What is actually happening when a magnetoresistive magnetometer degausses itself?

I'm trying to understand if anisotropic magnetoresistive devices themselves (not other passive ferromagnetic components) can become magnetized, and if so, how the application of a DC 1.1 gauss field ...
6
votes
0answers
129 views

Measuring the Dirac field

If the Dirac field $\psi(x)$ is to the electron as the Electromagnetic field is to the photon, why is it that we can measure the Electromagnetic field, whereas the Dirac field we cannot?
6
votes
0answers
118 views

What quantum measurement formalism is easiest to implement physically?

As part of my studies and research, I have learned to work with three different measurement formalism which I define to avoid any ambiguity with the nomenclature: General measurements, which are ...
5
votes
0answers
1k views

projective measurement & POVM

Let us consider the following completely positive map $\mathcal{B}(\mathbb{C}^n)\ni\rho\mapsto L\rho L^\dagger$, where $L\in\mathcal{B}(\mathbb{C}^n)$ is any arbitrary operator (and can have rank $>...
4
votes
0answers
629 views

Calculating statistical significance of peak over background in counting experiment

I histogrammed the invariant masses of particular events in a counting experiment. There is a specific peak which towers over the expected exponential background. How can I give the statistical ...
3
votes
0answers
45 views

Continuous Measurement equations

In a physics text, "Quantum Measurement Theory and it's Applications" by Kurt Jacobs, it describes the idea of a "continuous measurement" (measurement taking place over time $T$): $$dy = x_{true}dt + \...
3
votes
0answers
245 views

How are the melting points of metals measured

How are melting points of metals measured? What are the apparatuses used and how do they "conceive" heat units?
3
votes
0answers
58 views

Limits on the information obtained through optical measurements

Consider a Gedankenexperiment shown in the figure below. There are two lasers $S1$ and $S2$ with exactly the same specifications on paper. In practice, they are of course somewhat different but ...
3
votes
0answers
140 views

What is the shortest controllable time?

I was reading http://en.wikipedia.org/wiki/Planck_time and noticed a reference to: http://phys.org/news192909576.html where it is stated that: 12 attoseconds is the world record for shortest ...
3
votes
0answers
297 views

Measure energy state of quantum harmonic oscillator

When discussing the quantum mechanical harmonic oscillator we are talking about energy eigenstates. How would one actually measure in which state an harmonic oscillator is in? Could you weigh it and ...
3
votes
0answers
34 views

Review of Gas Chromatographs?

Could anyone suggest a recent review article or book on gas chromatography instrumentation? My interest is in the devices themselves, rather than using them for a particular application. This article,...
2
votes
0answers
134 views

Energy cost of the measurement without perturbing the system?

Background Let's say I have a Hamiltonian $\hat H$ (assume the Schrodinger equation) and it be in an arbitrary eigen-energy state: $$ \hat H_{\text{system}} | m \rangle = E_m |m \rangle$$ And I ...
2
votes
0answers
55 views

How does weak measurement affect quantum state?

I'm trying to understand how to describe the quantum state after weak measurement using these two toy examples. Hopefully, these simple examples and your answer will help others who want to learn ...
2
votes
0answers
27 views

Would the voltmeters give different readings in a circuit with induced current?

$\def\vE{{\vec{E}}}$ $\def\vD{{\vec{D}}}$ $\def\vB{{\vec{B}}}$ $\def\vJ{{\vec{J}}}$ $\def\vr{{\vec{r}}}$ $\def\vA{{\vec{A}}}$ $\def\vH{{\vec{H}}}$ $\def\ddt{\frac{d}{dt}}$ $\def\rot{\operatorname{rot}}...
2
votes
0answers
28 views

Resource to learn modelisation of quantum measurement

I need to learn how we do model quantum measurement (for experiments for example). If we study a quantum system X, when we measure it we usually consider a projective measurement (so we use the ...
2
votes
0answers
71 views

Indicator of the acoustic level in near field

Usually in acoustics, it is assumed that what we hear is the acoustic pressure. In far field - when the distance to the source is larger than the size of the source and than the wavelength - one has $...
2
votes
0answers
43 views

Question about statement of uncertainty

I have a doubt about uncertainty of a measurement. I have a sample of a specific material which is my reference material and it is calibrated and NIST traceable. This sentence is in its data-sheet: ...
2
votes
0answers
32 views

Measurement of a real apparatus

Do we know the approximate form of measurement operators for a realistic measuring apparatus? For instance, consider a cloud/bubble/spark chamber. What operator $\hat X$ can be considered to measure ...
2
votes
0answers
377 views

Working principle of a DC clamp-meter

I am trying to understand how a DC clamp meter works and found this image: (Source: http://www.kew-ltd.co.jp/en/support/mame/detail.php?id=60) My first guess of how this works is that somehow Ampere'...
2
votes
0answers
398 views

Measuring Stiffness & Spring Damping Coefficient of Hard Rigid Material Objects

I have a set of objects made out of mostly stiff materials and what I want to do is to find out the stiffness and spring damping coefficients of those objects. I need to find out the values ...
2
votes
0answers
89 views

Anomalous oxygen in aluminium sample SEM EDS

I have a sample of aluminium which I'm interested in finding the rough composition of. The sample is a part of a large number of samples which I sanded down and polished with a polishing table. I ...
2
votes
0answers
217 views

How can we measure light quality, quantity and duration in the field?

I am interested in measuring the light availability for coffee plants under a range of different adaptation practices (shade, cover crops etc). We want to ensure that the measurement can be automated (...
2
votes
0answers
307 views

17 MeV Anomaly in Beryllium Nuclear Decays - is it just a bump in sensitivity?

edit: @annav has noted an informative blog post summarizing the theoretical (but not experimental error) issues related to this measurement. There is some excitement about a bump in an electron-...
2
votes
0answers
134 views

Is an interaction-free measurement an irreversible process?

From what I've understood from reading different online sources including PSE*, measurements in quantum mechanics are generally argued to be irreversible (at least, when a macroscopic measuring device ...
2
votes
0answers
66 views

How precisely do we know the van der Waals radius of hydrogen?

I've found several sources that say the van der Waals radius of hydrogen is $120 pm$. How precisely do we know this number? What order of magnitude is the error on this measurement?
2
votes
0answers
268 views

Simultaneous measurement of non-commuting observables without uncertainty

A pair of non-commuting Observables $\hat{X}$ and $\hat{P}$ does not have a common set of eigenfunctions, i.e., it can not be measured simultaneously. Let us for the sake of simplicity assume that $[\...
2
votes
0answers
171 views

Can a Bell state measurement be described in the von Neumann measurement scheme?

I have been reading and studying this article recently about non-local weak measurements and quantum erasure. Usually the weak measurement formalism is described using the von Neumann scheme for ...
2
votes
0answers
1k views

Molecular structure correction factor in Mass Flow Controller

This question concerns device called Mass Flow Controller (or Mass Flow Meter). For a video explaining the principle: see https://www.youtube.com/watch?v=G62ma2IFh9o These devices are factory ...
2
votes
0answers
503 views

A method/device for measuring angles, as an experiment?

What's the best device for measuring angles, as an experiment for a fundamental physics lab at the university level? The first experiment in our fundamental physics lab is "Measuring & Measurement ...
2
votes
0answers
55 views

Are there limits to human/devices perception?

As far as i know, measurement devices present measurements based on something that affects the device's particles, for instance, forces, heat, tension, voltage... My question is, given that every ...
2
votes
0answers
75 views

Maximum error of number of observations within several certain intervals – Accuracy of variable is known

I have carried out a series of measurements of different thermal comfort parameters from which I have calculated another variable called PMV. My data set consists of hourly measurements (and ...
2
votes
0answers
89 views

sensitive scale & resistance of analog current meter

Does the resistance of an analog current meter increase or decrease when it is set to a more sensitive scale (lower range)?
2
votes
0answers
65 views

What is weak coupling of photon polarization to a pointer?

This question is refered to those who are familiar with the concept of weak measurement. In short: How can the polarization of a photon be coupled to the position of a pointer state? What is the ...
2
votes
0answers
71 views

How to formulate collapse in polarization subspace of a photon?

I am wondering how to describe the collapse of a photon state when it is measured in the polarization degree of freedom (say by a filter which let pass just one particular polarisation). Let the free ...
2
votes
0answers
69 views

need data-point: count rate of APD (avalanche photo-diode) for specific aperture and stellar magnitude

I hope lab / experimental physics is fair game for this web-site. If not, sorry! I'm designing a sensor system to perform specialized [astronomy and space-sciences] experiments, and need a "reality ...
2
votes
0answers
56 views

If the measurement of the proton size is correct and it is lower that it was expected than what are the theoretical implications?

In the press release of the recent measurement of the proton structure, they barely mention various theoretical explanations for the effect. What is the most likely (not assuming now that the ...
2
votes
0answers
412 views

How do I do error calculus right using gnuplot as an example?

Given is a set of measurements with their respective errors for example an energy spectrum. In gnuplot one is to fit a function $ f(x;\{p_i\})$ depending on a variable $x$ and on fit parameters $p_i$. ...
2
votes
0answers
290 views

Galaxies and projected radius vs arcmins

I have two sets of data (globular clusters), one for the Andromeda Galaxy and one for the Milky Way. I want to compare the distribution of globular clusters between the two galaxies according to ...
1
vote
0answers
25 views

Is there a way to argue that the appearance of the dependence of past states is stochastic behavior?

Suppose in a particular set of observations that you observe what appears to be a correlation of future results based on past results. Is there a way to be certain that such a phenomena isn't just the ...
1
vote
0answers
33 views

How to measure a Bell inequality violation in IBM Q? (Or analytically)

I made some circuit to prepare a 2 qubit state, but I am having trouble understanding how to measure Bell's inequality. I know the inequality is of the form $$|E(a,b)-E(a,b')+E(a',b)+E(a',b')| \leq 2$...
1
vote
0answers
10 views

How to Measure Electric-Field Probe Sensitivity?

I am doing some reading on current methods for detecting electric fields. A figure of merit for the systems is, naturally, the minimum strength of field that can be measured, in units of Volts per ...
1
vote
0answers
22 views

Uncertanty in Chi-squared measurements, spectra-like

Let's say I have some observational data. For example: in a certain wavelength interval I measure the flux, 10 000 points, and I have the uncertainty for each one of them. For example: ...
1
vote
0answers
30 views

Subtractive cancellation errors in the lab

I am quite familiar with the problem associated with loss of significance in numerical analysis. This problem seems to be an even bigger problem in the science lab, where subtracting one physical ...
1
vote
0answers
80 views

How do we quantify and measure the net entropy of today's universe?

We know that the Universe evolved from a very low entropy state in the early universe to very high entropy state of today's universe. What is the quantitative definition of the net entropy of the ...
1
vote
0answers
12 views

Calculating Uncertainty with Mean Absolute Deviation

I'm taking an Introductory Physics course and, when learning about approximating uncertainty, I was wondering if a more quantitative method would be to calculate the Mean Absolute Deviation using the ...
1
vote
0answers
56 views

Attempting to calculate the mobility from SCLC measurement (space charge limited current)

I performed an SCLC measurement on a p-type material (hole transport layer) for a solar cell. Referring to the wikipedia page:https://en.wikipedia.org/wiki/Space_charge The relationship between $J$ ...
1
vote
0answers
42 views

Can time be described as a distance?

Can we do away with time in the coordinate system? When I picture the x,y and z planes and plot positions, the idea of adding a time element seems redundant. The time element adds a reference to an ...
1
vote
0answers
22 views

Can we track phonon's path similarly to how we track electron's path in a bubble chamber?

An answer to a recent question argues that Standard Model's particles like electron are "real" because we can see their tracks in e.g. bubble chamber. So now I wonder: can we track quasiparticles ...
1
vote
0answers
45 views

Observables in Relativistic QM

I am thinking about observables in relativistic quantum mechanics (RQM). The position operator (X) is considered to be an observable in QM vs time, which seems to be just a parameter. What about RQM? ...