Measurement Definition and 1000 Threads

Homework Statement The circuit in the attached photo has a one-qubit operation ##U## which is controlled by the first qubit. The box with the meter and arrow denotes a measurement. If ##U=H## what is the probability of finding 0 or 1 in the final measurement of the second qubit? Homework...

Homework Statement (c is a constant) The attempt at a solution -In the first measure we got a1, so the state of the system would be psi1. -In the second measure, there's no information about what eigenvalue we got. Would the state of the system still be psi1? Psi1 is written in terms of B...

The Fundamental Theorem of Quantum Measurements (see page 25 of these PDF notes) is given as follows: Every set of operators ##\{A_n \}_n## where ##n=1,...,N## that satisfies ##\sum_{n}A_{n}A^{\dagger}_{n} = I##, describes a possible measurement on a quantum system, where the measurement has...

I'm panicking right know, and I wonder if someone can answer these questions: 1) Nm^3 is a unit of measurement for Volume or Moles? 2) I have a flow at T=500K and, let's say, it is Q = 100 Nm^3/h When I find the value of the flow at T=500K I do ##Q_{real} = Q* \frac T {273.15K}##. The new Q...

Homework Statement Homework Equations For sine wave RMS/Avg = 1.11 For DC, RMS = Avg = Peak Value The Attempt at a Solution I didn't understand the solution. There is a 24V DC supply. I give it to an AV Voltmeter. The Voltmeter responds to average value. So the voltmeter would give 24V DC. So...

I am interested in defining Krauss operators which allow you to define quantum measurements peaked at some basis state. To this end I am considering the Normal Distribution. Consider a finite set of basis states ##\{ |x \rangle\}_x## and a set of quantum measurement operators of the form $$A_C =...

In scientific experiment, we often have a physical property that can change but have no detectable impact on the measurement. For example, suppose I have a mass of (say) 30 grams attached to a string passing over a pulley. I can add up to another 2 grams and the system doesn't budge. In our...

Hello, Please I don't get how a Magnetometer property measurement system (MPMS) and a Superconductor quantum interference device (SQUİD) are working, can someone explain it ? Thank you very much

I hoped to use a Keithley 2400 source meter to generate a ~120Hz AC signal by outputting a 2-point sweep from 1A to -1A on an infinite trigger. The waveform image is attached below. The end goal is a resistance measurement for bulk semiconductor materials, we prefer AC measurement to avoid...

Hi. I’m a PhD student at University of Toronto, in philosophy of physics. I have a number of questions which are quite fundamental: just trying to get everything clear in my head in the most succinct way possible, so I’m sorry if the questions seem remedial. First question: what is the...

Sorry, me again. In another thread #47 I gave a experimental setup to detect an anisotropy in light speed of the form ##c(\hat{n}) = c_o + \alpha (\hat{n}\cdot\hat{v})##. It was pointed out quite correctly that the error incurred in the long arm to the sensor would cancel the anisotropy making...

Hi, What is people measuring when they measure the speed of light (c) actually? the photons or the waves? or some kind of manifestation of light? I ask because I was reading about photons and that they "might" have a very small mass and therefore are not traveling at c. If photons have a...

Hi,I’ve heard of a technology that enables to measure the distance of a satellite to the ground station by using non-coherent spread spectrum. Can anybody tell me what’s the name of this technology?Senmeis

Hey everybody! as part of a project i need to solve this problem: i have a small closed (50 mm height, 5 mm radius) tank made of PMMA fiiled mostly by salted water and a bit air. the water get a 200 (C) pulse for a very short time of 20 micro-seconds and start to transform into gas (there is a...

The following is a somewhat mathematical question, but I am interested in using the idea to define a set of quantum measurement operators defined as described in the answer to this post. Question: The Poisson Distribution ##Pr(M|\lambda)## is given by $$Pr(M|\lambda) =...

My question is simple, and I'm only asking it because most places talk about more advanced problems than this one: I've measured the radius of a sphere (a very regular one) with a micrometer of 0.01 mm resolution. I took 3 measures (rotating it between each measure), and all of them were...

Can a reasonable observable operator be defined which measures a two-component observable, first component for the approximate coordinate and the second for the approximate momentum (so that the precision of each measurement do not contradict Heisenberg inequality)? I am actually thinking of...

Hello everyone, I understand the hydrostatic fluid pressure in static fluids: static pressure varies linearly with depth and the infinitesimal fluid parcels located at the same depth in the fluid experience the same isotropic hydrostatic pressure. By Pascal principle, the atmospheric pressure...

I am writing an article on Eratosthenes and am having a little trouble on how he actual found the angle of the stick. Because as far as I can gather there was no series solutions for any of the trig defin no calculators. All he knew was the length of the shadow and the height of the stick. I...

Given a wave function $$\Psi(r,\theta,\phi)=f(r)\sin^2(\theta)(2\cos^2(\phi)-1-2i*\sin(\phi)\cos(\phi))$$ we are trying to find what a measurement of angular momentum of a particle in such wave function would yield. Attempts were made using the integral formula for the Expectation Value over a...

Homework Statement Homework Equations in addition to those provided in the questions, I used the following: Tr(B) = sigma<x_j|B|x_j> purity = Tr(rho^2) The Attempt at a Solution [/B] I find calculating trace and purity very confusing. Am I on the right track with question 1? With...

I've read that a particle's position can be measured by firing a photon at it, but how does one actually determine the position of the particle by doing this? What is the maths behind it (is it calculated from momentum conservation)? Furthermore, I've read that increasing the energy of the...

Let's say we do a double slit experiment with the standard laser/two slit setup with a screen to view the pattern. 1. In the first run, we just turn on the laser and observe the screen with our unaided eyes. We see an interference pattern consistent with the wave-like nature of light, correct...

In almost general case, the space-time metrics looks like: \begin{equation} ds^2 = g_{00}(dx^0)^2 + 2g_{0i}dx^0dx^i + g_{ik}dx^idx^k, \end{equation} where ##i,k = 1 \ldots 3## - are spatial indeces. The spatial distance between points (as determined, for example, by the stationary observer)...

This thread is to serve as - a collection of theories that have been falsified by and/or have had new constrained placed on them by the ongoing gravitational wave measurements. - a place to discuss the further constraining/falsifying of still existing models using GW data. I'll start by posting...

Reading about collapse and Born rule it gives strong feeling that there is semantic mess in QM with the word "measurement". Wikipedia describes Born rule in following way: In its simplest form it states that the probability density of finding the particle at a given point is proportional to the...

In Born interpretation of the wave function it notes that the matter itself cannot be measured however the square of its absolute value is measurable. I am lost as to why the product can be measured but not the wave function itself. Can someone provide clarity?

I'm trying to understand the impact of past measurements, and when measurements occur. As I understand it, in the simplest case, you've got a particle emitter in the center of a circle, and a measuring plate around the circle. Here in the ideal case the particle is emitted and has equal...

That's pretty much it. Are physical objects essentially clumps of energy, and that energy is measured as mass? And do objects become more massive as they receive more energy through push?

In the radiation detection, it's of common use pulse-type systems, which have a preamplifier between the detector and the amplifier. I have read that the preamplifier primary function is reduction of attenuation of the signal that exits from the detector by matching the impedance of the detector...

Hello! I've made a lot of research about measurement of high magnetic fields - such us 1T - 2T and I can't find sensors for this range. I'm looking for a hall sensor with which I will be able to measure 1T magnetic field with good accuracy - about 0.1 mT. Do you know about anything like that...

In page 9 of http://www.theory.caltech.edu/people/preskill/ph229/notes/chap4.pdf we can find simple form of Bell inequalities for three binary variables: $$ P(A=B) + P(A=C) + P(B=C) \geq 1 $$ which is kind of obvious: "This is satisfied by any probability distribution for the three coins because...

I've been studying the von Neumann measurement scheme (and understanding the math part) where the system and apparatus are quantum in contrast to the orthodox where the apparatus is classical. I'd like to know the following. 1. Is the von Neumann measurement scheme 100% orthodox and believed by...

What is the difference between average and composite power?

Suppose an observer in the Earth frame set out to measure the length AB by measuring the time interval between the event "B coincides with D" (event BD) and the event "A coincides with D" (event AD), and then multiplying the time with ##v##. This observer argues that an observer in the train...

Finally... this month, Virgo and LIGO look for gravitational waves together (they started yesterday). The Virgo detector is a bit less sensitive than the LIGO detectors at the moment, but it is still a big improvement: It is an independent experiment, on a different continent run by different...

Say that they are not entangled. Assume classical quantum laws still hold but that there are only two particles in this universe with nothing else. How would one of the particles measure the other? Both particle's location and momentum are nonexistent until a measurement occurs by one on the...

Consider the Gaussian position measurement operators $$\hat{A}_y = \int_{-\infty}^{\infty}ae^{\frac{-(x-y)^2}{2c^2}}|x \rangle \langle x|dx$$ where ##|x \rangle## are position eigenstates. I can show that this satisfies the required property of measurement operators...

I have seen similar threads on here but not one with any detailed answer so I felt I would ask myself. I took a short undergrad module in measurement and uncertainty, intended to prepare for the numerous lab sessions and reports that would follow in the proceeding modules. In that particular...

Hello everyone, I'm actually working on developping a phase shift sensor using one phase modulated signal, i know that the title is confusing beaucause the phase shift measurement need two signals , I'm trying to do this with the zero crossing method so if I could found the timestamps of the...

Homework Statement In my experimental setup I have a purpose built small aluminium tube that has a black layer on the inside to mimic a blackbody. The tube is heated so the inside emits as a blackbody. A separate temperature sensor attached to the tube gives the temperature of the tube. I...

I've just read an article (link to the discussed paper at the end) talking about a newly proposed Maxwell's demon where they use a quantum measurement to extract energy from the system, which made me think, isn't energy conserved in QM as well (at least in the average sense)? and seeing that a...

I'm well aware of the common adage and quantum fact that, until a particle is measured by some sort of instrument, it exists in a state of superposition, can interfere with itself, etc. My questions pertains to the definition of "measurement". In order for something to qualify as a measurement...

Something about the theory of quantum measurement/collapse in the case of quantum fields... Suppose I have a field, either a scalar, vector or spinor, that I want to describe as a quantum object. For simplicity let's say that it's a scalar field ##\phi (\mathbf{x})##, where the ##\mathbf{x}## is...

If we consider a measurement of a two level quantum system made by using a probe system followed then by a von Neumann measurement on the probe, how could we determine the unitary operator that must be applied to this system (and probe) to accomplish the given measurement operators.

<Moderator's note: two essentially very similar threads merged.> Hello! I am a bit confused about the idea of measurement in QM. As far as I understand, if you measure the position of a particle, the wavefunction of that particle changes into a delta function, and thus the particle gets...

Suppose, the energy of a particle is measured, say ##E_1##. So now the state vector of the particle is the energy eigenket ##|E_1>##. Then the position of the particle is measured, say ##x##. As the Hamiltonian operator and the position operator are non-commutative, the state vector is changed...

I analyzed uncertainty analysis of 2 port measurement. I referenced 2 book "Transmission Reflection and Short Circuit Line Methods for Measuring Permittivity and Permeability" at pages 31 equation(2.83) "Transmission and Reflection and SCL Permittivity Measurements" at pages 44 equation(2.67)...

Hello! So I'm working to try to understand shor algorithm and I have some doubts. So, after the hadamard gates we apply the unitary gate that construct the function yk mod N. Next we do a measurement in the second register to get some function value. So, when I do this measurement on the...

Description of the situation I have measured the incident number of electrons in a channel electron multiplier at different light polarization angles (a photoelectron angular distribution measurement). The events follow a poisson distribution and as far as I know the number of electron counts in...