Measurements Definition and 397 Threads

I recently came across the following paper on QFT and Quantum Measurements. https://arxiv.org/abs/1311.0205 I have read it, but it may not be legit as it seems to accept the idea of virtual particles, which I find somewhat problematic, as discussed before. Before reaching any conclusions, I...

Hi guys, I have a problem with point 2 of this exercise: The electron of a hydrogen atom is initially found in the state: having considered the quantum numbers n,l,m and epsilon related to the operators H, L^2, Lz and Sz. I am asked: determine the possible outcomes of a measurement of J^2...

Hi Pfs, I would like to know if it would be possible for our known theories to derive conservation laws if space time was really granular. I think that entanglement is the only process which would succeed.

I have read that if one measures the Hamiltonian and receives a value of h2, then the quantum state will be in ##|h2\rangle##. Finding the probability of a1 is done by projecting ##|a1\rangle## upon ##|h2\rangle## divided by ##\langle h2|h2\rangle##. In other words: $$\frac{|\langle...

TL;DR Summary: I have a Force Table Lab and am not sure if the "percent error" is the correct way to express errors. I also need some help on sig figs for my results. Hello, I am working with the usual undergrad force tables apparatus. I would like to know how to express the results of...

To be more precise: can we put two objects together so there will be a space with width of one (or some number below 10) atom's diameter(s) between them?

Scolnic et al have put out a new preprint with an updated value for the Hubble constant as measured from the Tip of the Red Giant Branch: https://arxiv.org/abs/2304.06693

In quantum mechanics if I repeat a measurement of the same observable in succession I get the same quantum state if it is not a degenerate state. If I make the system under consideration interact with another quantum system and meanwhile keep measuring it what happens? Does the system not...

I was imagining trying to construct a rectangle of area ##A = xy## If we give a symmetric error to each dimension ##\epsilon_x, \epsilon_y## $$ A + \Delta A = ( x \pm \epsilon_x )( y \pm \epsilon_y )$$ Expanding the RHS and dividing through by ##A## $$ \frac{\Delta A}{ A} = \pm...

For the background of the discussion see my Insight artice ''Quantum Physics via Quantum Tomography'' and the posts #405 and later of the thread ''Nature Physics on quantum foundations''. Trying to translate your statements into precise formulas, and using ##\Pi## in place of ##E## (which to me...

TL;DR Summary: Finding the probability with one measurement and multiple measurements on separate days. Question: Hypokalemia is diagnosed when blood potassium levels are low, below 3.5 mmol/L. Let’s assume we know a patient whose measured potassium levels vary daily according to N(µ = 3.8...

I found out about this interesting paper through a Tweet by Steven Thomson. https://arxiv.org/abs/2108.05169 https://www.nature.com/articles/s41467-022-31608-6 Relativistic Bohmian trajectories of photons via weak measurements Joshua Foo, Estelle Asmodelle, Austin P. Lund, Timothy C. Ralph...

I have a VNA with an SMA connector for measuring reflection. If I connect only the center conductor of the SMA to a piece of metal, I get a spectrum. My question is, what should I be doing with the outer connector? I am trying to learn EE by reading and doing. I don't have a lot of intuition...

Hi All, I received good insight from a previous post, https://www.physicsforums.com/threads/pulling-a-heavy-load.1015640/#post-6637181, now that I'm at the point of expanding the drawer support on the ceiling, I ran into the following. How is it that my level says it's leveled but the tape...

I am measuring the volumetric flow rate of a diesel fuel using "Turbines" flow meter, both in the supply and return fuel lines of an industrial diesel engine (https://www.cat.com/en_US/products/new/power-systems/industrial/industrial-diesel-engines/18398034.html – coupled with a generator for...

Hello! Is there any measurement (can be from different papers/experiments) of a diatomic molecular isotopic chain (i.e. at least 3 isotopes of a given nucleus) where the ground state is ##^{2}\Sigma##?

The idea is to have 2 clocks at position A and B. The clocks are synchronized by sending a light pulse from position S over 2 equal distances x. The receiver is at position R at a distance y rectangular to the direction AB and exactly in the middle between A and B and right below S. for proofing...

Hi Pfs I read this answer in https://quantumcomputing.stackexchange.com/questions/136/if-all-quantum-gates-must-be-unitary-what-about-measurement Quantum measurements are special cases of quantum channels (CPTP cards). Stinespring dilation states that any quantum channel is realized by...

Howdie! We have been playing around with melting and molding HDPE pellets recently. After that, we measured their diameter and thickiness 5 times each to get an uncertainty. In our experiments we put one pellet between gamma-source and detector and measure its attenuation. After that we place...

I was wondering, if we have a measurement of, say, spin of an electron, which can yield spin-up and spin-down in the context of MWI, then the electron gets entangled with the measurement device, yielding the wave function ##|Measurement_{spin-up}, Value_{spin-up} \rangle +...

I made an experiment in the lab. I took some measurements with the CsI(Tl) detector by placing the cobalt at a distance of 5 cm. I have attached the measurement result. I need to find the count for the peak energies. How can I do it? Any idea?

This situation is really confusing me. First of all, does accounting compressibility affect the measurements for CL? If yes, how does CL change as a function of the increasing mach number? Back to the problem, above is the "in-flight" lift curve for a plane traveling at high speeds, so the CLs...

While physics is generally believed to be CPT symmetric, there are processes for which such symmetry is being questioned - especially the measurement. One of examples of (allegedly?) going out of QM unitary evolution is atom deexcitation - we can save its reversibility by remembering about...

Hello, All measurement instruments have a finite accuracy. For example, a thermometer may provide a temperature measurement that is +-2F from the "actual" and true temp value. For example, if the reported measurement is 70F, the actual temperature may be between 72F and 68F. That said, let's...

If you measure the light transmission over time of the human thumb you can get the heart rate. Is there another thing you can get by using light transmission ? like the Heart rate? can you find bacteria in water using light transmission ?is light transmission measurement even the right word ?

Hello! I have some points in the plane, with errors on both x and y coordinates. The goal of the experiment is to check if the points are consistent with a straight line or not i.e. if they can be described by a function of the form ##y = f(x)=a+bx## or if there is some nonlinearity involved...

Hi. I'm new to the forum and and I am currently studying quantum mechanics. According Sakurai, page 24, "When the measurement is performed, the system is" thrown into" one of eigenstates of observable". This raised some questions for me: Is possible two measurements simultaneous of one...

I had never heard of Schwinger's Quantum Mechanics: Symbolism of Atomic Measurements until very recently. I wonder what you people think about that QM textbook. Is it a good introduction to QM? A reference? Or, possibly an outdated and bad book? At first glance, it seems a masterpiece to me...

Would using gravitational waves to measure (it's obviously a gedankenexperiment!) position and momentum of, say, an electron in a specific state, disprove HUP since the quantum of energy of grav. waves does not exist? Would it be possibile to have an arbitrarily small uncertainty in position...

Hello! I see that the experiments looking for electric dipole moment (EDM) of fundamental particles (especially for the electron) are able to place constraints on new BSM particles with masses of around 10 TeV or even more, in a model independent way i.e. we just need to measure a non-zero...

Is this correct? "The systematic error in a measuring instrument due to non-uniform or wrongly marked graduation due to which a measurement may be less or greater than actual measurement is called zero error of the measuring instrument". Another one: The measuring instruments are combination...

Just few questions based on experimental presentation of results: In (semi-)inclusive measurements (say, p + p -> Y + X), producing some well defined state Y and the rest, X, summed over, is there typically a minimum cut made on the p_t of the state Y? If so why? What is the reason of...

Hi, I have measured a set of V-I values, and I have to provide the value of the resistance. I have used ac and dc current. The circuit was quite simple: power supply -> ammeter -> resistance -> [power supply] wave generator -> ammeter -> resistance -> [wave generator] Voltage was measured...

I have a question about statistics or measurement technology. Let be ##K## and ##N## natural numbers. We measure a variable ##x_{kn}## where ##k\in\{1,K\}## and ##n\in\{1,N\}##. Let us say that you have ##K## measurement series to measure ##N## values ##x_{kn}## No matter how big ##N## is...

We're working on a project that plots flux density of a light curve with respect to time. To do this, we had to scale data from different wavelengths so we had just the one variable for the flux. Essentially we took each value for flux density and multiplied it by three over the frequency raised...

I am following this: avntraining.hartrao.ac.za/images/Error_Analysis.pdf I have a ruler with an uncertainty of ± 0.5mm. I made a calculation subtracting one measurement of the ruler, from another measurement, making the uncertainty for the data ± 1.0mm. As I have four trials, I calculated the...

Here's what I think I understand: First off, the GHZ state ##|GHZ \rangle = \frac {|000\rangle+|111\rangle} {\sqrt 2}##, and ##\sigma_x## and ##\sigma_y## are the usual Pauli matrices, so the four operators are easy to calculate in Matlab. I'm thinking the expectation values of each operator...

Am I correct in thinking that the system measures the probability |<f|1>|^2 for some state <f|? Then the probabilities for each of the six states would be: |<0|1>|^2= 0 |<1|1>|^2= 1 |<+x|1>|^2= |(1/√2)|^2 = 1/2 |<-x|1>|^2= |(-1/√2)|^2 = 1/2 |<+y|1>|^2= |(-i/√2)|^2 = 1/2 |<-y|1>|^2= |(i/√2)|^2...

Summary: This is a hobbyist project I am working on. I am building an instrument to measure radiance from the sun at 500 nm, using optically filtered photodetector with bandwidth ± 10 nm. This type of science can be called Sun Photometry, so let's get to it! Geometry for Optics: The sun has an...

Suppose I measure the distance between two objects for three trials. The two objects then get farther away, and I measure the distance between them again for three trials. I repeat this for 3 more different distances, getting a total of 15 measurements (3 trials for 5 distances). I then compute...

Summary:: That is the problem down there. The scale on a map is 1 inch (in.) ? 80 miles (mi). If two cities are 2 & 3/4in. apart on the map, what is the actual distance between the cities? So what I did was convert the scales 80/1 mi per in. and multiplied it to 2 & 3/4in which I got an answer...

This seems like a trivial question at first, but I am struggling how to get it right. If I have 2 GPS (lat, lon, height) observations P1 and P2 taken at some height from the Earth's surface, how do I calculate the straight line distance between them? I am using the picture below to illustrate...

Given a wave function \Psi which is an eigenstate of a Hermitian operator \hat{Q}, we can measure a definite value of the observable corresponding to \hat{Q}, and the value of this observable is the eigenvalue Q of the eigenstate $$ \hat{Q}\Psi = Q\Psi $$ My question is whether it's a postulate...

What does a measure of 2000 µW/m² electromagnetic radiation by "Hf35c Rf Analyze (800mhz – 2.5 Ghz)" radiation meter mean? Is it too high? see this link: https://www.electrahealth.com/hf35c-radio-frequency-meter.html it shows that “1000 or more µW/m²” in the meter is “Extreme Concern”, does it...

Hello, I'm using photo-sensors from commercial and industrial cameras to document an experiment. Afterwarde I evaluate the change in brightness during the test of a fixed segment of every image I took. The ambient light condition is stable and the images are in raw files, but I'm unsure how raw...

Most gauge transformations in the standard model are easy to see are measurement invariant. Coordinate transformations, SU(3) quark colours, U(1) phase rotations for charged particles all result in no measurable changes. But how does this work for SU(2) rotations in electroweak theory, where...

Is instantaneous limited to our in ability to continue to count time faster.

Assuming you are in the field and don't have any device to weigh, measure volume, or measure time. How would one establish accurate measurements? Where does one start?

I will refer to the spin example outlined in the opening chapters of the Theoretical minimum. Suppose we prepare a spin with a z component of +1. If we rotate the apparatus about 180 degrees, the ‘classical component’ of the prepared spin vector along the new axis of the detector is -1, so...

Hello, I am interested in weak measures since I discovered this paper: https://arxiv.org/ftp/arxiv/papers/1206/1206.6224.pdf I understood that retro-causality is only an interpretation and that's not more exploitable than the famous experiments of quantum gum delayed choice. In fact, we...