Quantum Definition and 999 Threads

Hi, Is anybody able to explain how energy is "distributed" in the many-worlds interpretation. I'm using scare quotes as I think this may be the wrong line of thought. It's tempting to imagine energy being distributed amongst subsequent branches as the wave function evolves but I'm not certain...

I have a question about quantum entanglement, I see saying that it would not be possible to communicate faster than light using this technique, but for example, and I understand that it is not the information that travels, however if for example we use the interval of the measurement and read as...

Greg Bernhardt submitted a new blog post 9 Reasons Quantum Mechanics is Incomplete Continue reading the Original Blog Post.

Hi. I'd like to ask what are the differences between Particle Physics, Quantum Field Theory and the Standard Model. I see these names of physics courses but I want to confirm if I understand the difference. My understanding is that when students learn particle physics in their undergraduate...

Let us introduce a new rule. You can criticize any QM interpretation you want, but to avoid too much philosophy the argument must be extremely concise. For definiteness, it may contain maximally 2 sentences, 1 equation and 1 reference. The general rule is - less is more. Here is my take. In...

Hi there, Question from a biologist with very poor background in physics, but willing to understand quantum physics. I think quantum entanglement shocks everyone, even if it has been proven right. I would love to know if there is any hypothesis or crazy theory out there to explain why or how...

Recently, I've been told I was wrong concerning the nature of stationary states and diffusion being related. Even though I pointed out to the people involved that I was merely paraphrasing Max Born, who was apparently quoting the same idea as Linus Pauling. No one has been able to tell me...

In classical mechanics I would say: a particle can have any initial position and velocities, Newton laws give you the evolution of the particle: F=ma , is the basic equation, if you know the forces acting on the particle by solving this equation you get the future values for velocity and...

I would like to know which books are the main sources for the Quantum mechanics 1/2 courses, and the professors use them most during their courses? Thanks for you reply in advance.

Hi. I really like this book (2nd edition) and was thinking of buying it. I have seen mention of a new edition , the 3rd edition but it seems to be unavailable to buy. Anyone know if the 3rd edition is out yet or soon ? Thanks

Hello, I was wondering if any of you know about good books on various qubit approaches for making quantum computers. There are a lot of road maps on the internet covering the pros and cons of each approach (for example: https://qt.eu/app/uploads/2018/04/QT-Roadmap-2016.pdf ) but I was hoping...

In my textbook, quantum states are infinite dimensional vectors. But I was watching a lecture on QM and the professor referred to ##|v> <u|## as itself being a quantum state. Also I saw online people saying the same thing. Are tensor products just things that tell you whether or not the two...

i don't understand, how does quantum eraser not imply time travel? i firmly don't believe in retrocausality, but it really does seem to imply it . can someone please explain in layman terms? in here paul davies says observers now can "constrain" the past, does this mean our perception of...

Hi, I'm currently working on showing the relation of quantum fidelity: The quantum “fidelity” between two pure states ρ1 = |ψ1⟩⟨ψ1| and ρ2 = |ψ2⟩⟨ψ2| is given by |⟨ψ1|ψ2⟩|^2. Show that this quantity may be written as Tr(ρ1ρ2). I've been following the wikipedia page on fidelity but can't...

Hi! Sorry for the bad English! I'm trying to get a better understanding in quantum mechanics by doing the math of quantum circuits and I'm stuck! So, please, if someone can, help me! =) I'm trying to the math of this circuit: q0 ... l 0 ) .... x ... (I) q1 ...

Homework Statement Suppose two polarization-entangled photons A and B in the following Bell state: \begin{equation} \Phi=\frac{1}{\sqrt{2}}\bigl(\left|H_{A},H_{B}\right\rangle + \left| V_{A},V_{B}\right\rangle\bigr) \end{equation} 1. What is the state if the photon A passes through a...

Hi all, I recently started learning about quantum scattering in school and came across a few things I find confusing. Thanks in advance for any assistance! 1. Plane wave approximation to incident waves. In past QM courses, I kept reading that plane waves were not "physical" since they do not...

"Schrödinger's Bacterium" Could Be a Quantum Biology Milestone I can't believe I'm only seeing this article now. Achieving quantum mechanical effects with large systems, especially complicated ones such as bacteria - let alone one in vivo - has been a longstanding goal in experimental QM. To...

Hi everyone! Sorry for the bad English! I'm trying to read the "entanglement between photons that never coexisted " from 2012. Avaliable at: https://arxiv.org/abs/1209.4191 And there's this equation: ## |φ± \rangle = \frac 1{√2}(|HaHb ± |VaVb\rangle) ## ## |ψ± \rangle = \frac 1{√2}(|HaVb ±...

Hi all, I have a question relating to the title above. The uncertainty relation tells us that an electron that is localised (in terms of its PDF) is space has a large uncertainty in momentum space. However in classical electrostatics/dynamics we seem to make attempts to do things like...

Hi. This is my first posting on the Physics Forum so please forgive any issues as a result. I am a (reasonably educated) lay person with a strong physics interest with extensive readings -- so please be patient with my questions. :-> My questions and interest in these issues are sincere. I...

NOVA presents a show on Einstein and Quantum Entanglement:

How to prove the dipole moment of an isolated quantum system in isotropic space is identically equal to zero, unless there exists an accidental degeneracy. Thanks in advance

In one dimensional system the boundary condition that the derivative of the wave function Ψ(x) should be continuous at every point is applicable whenever?

I have got a simple qstion. We have a particle in 1d oscillator with E0( fundamental level).We know that phi~ e^-x^2 for any x, so We can measure a position and get a value x=a, such that V(a)>E0 . In this case T<0 so the velocity of the particle is imaginary, how is this even possible?, (a real...

Homework Statement Consider a solution in which 99% of the atoms are 4He and 1% are 3He. Assuming that the 3He atoms behave as an ideal gas of spin-1/2 particles determine the Fermi energy of the 3He atoms. You may assume that one mole of 4He occupies a volume of 28 cm3.Homework Equations EF =...

In a discussion between Sam Harris and Brian Greene, at this point, Brian stated that even if we return the brain and all the environment to its previous state, we "WON'T MAKE THE SAME NOISES"; I know that for example, indeterminacy in determining the precise time of decay of an atom (and the...

OK, going to ask a question that I sort of know is going to be shot down but at the moment I can't make sense of this. If I send a machine/robot with a particle that is quantum entangled with another particle that is left on earth. When one particle is blue the other is red. The machine also...

Thought you all might be interested in this article. It could just be hype, but there also might be something deeper to it. You hear of so many schemes of tying together quantum mechanics with a relativistic understanding of gravity, that it's easy to respond to yet another announcement like...

Homework Statement We are given the Lagrangian density: $$ \mathcal{L}=\partial^\mu \phi ^* \partial_\mu \phi - m\phi^* \phi +\sum_{\alpha =1} ^2 ( \overline{\psi}^\alpha (i\gamma^\mu \partial_\mu -m)\psi^\alpha -g\overline{\psi}^\alpha\psi^\alpha \phi^* \phi) $$ , where ##\phi## is a complex...

Homework Statement The question is; for a qunatum mechanical particle, Ψ(x) = [1/(a1/2.π1/4)].[e-(x-xo)2/2a].[eip0x/h] in here, x0, p0 and h are constants, so, Homework Equations what are the <x>; expetation value, and <P>;expectation value of momentum ? The Attempt at a Solution , [/B]...

The question is; for a qunatum mechanical particle, Ψ(x) = [1/(a1/2.π1/4)].[e-(x-xo)2/2a].[eip0x/h] in here, x0, p0 and h are constants, so, what are the <x> and <P> ?

Hello. Recently Scientific American magazine carried an article about the work of the authors of this paper. https://arxiv.org/abs/1502.04573 The Undecidability of the Spectral Gap. The SciAm article is linked to here -...

Does anybody know if there is work being done on quantum locality vs nonlocality. Specifically, approaching the Planck scales there is no nonlocality. That is all points in space and time are local. This would also provide an explanation for Einstein Minkowsky's space time. Any material /...

When defining quantum fields as a sum of creation and annihilation operators for each momenta, we do it in analogy with the simple example of the harmonic oscillator in quantum mechanics. But why do we assume that the coefficients in the expansion can be interpreted in the same way as in the...

Homework Statement input state is |1>(tensorproduct)(2|0>+|1>). Homework Equations Find the probability of the outcomes being 0 and 1 measuring the second qubit. And then what the outcome states of each are. The Attempt at a Solution I have attempted this problem and for the probability of...

According to QFT, are there hydrogen bonds or Van der Waals force? Or this an outdated concept of classical physics?

Hi all, I have been trying to read up on quantum foundations after being first introduced to it on this Perimeter Institute page: https://www.perimeterinstitute.ca/research/research-areas/quantum-foundations/more-quantum-foundations However, I have had difficulty finding notes and papers on...

Can anyone tell me, What quantum state really is? Is it applicable for all sub atomic particles? Then, Can anyone explain how two electron are never in same quantum state. And Does proton or neutron follows the same law as electron for obtaining unique quantum state.

Homework Statement [/B] (Working through a problem from a practice set for which I have a solution available, but still don't understand. I get the same answer as they do for part a, but get lost in part b, I think. Relevant portions below) Consider a two-state quantum system. In the...

The FMO complex has a size that is within the typical size range for quantum dots, and absorbs photon energy at what appears to be an effective bandgap between 2-3 eV. While various techniques have been used to investigate the behavior of the FMO complex, such as femto photography or...

Many people talking about there are similarities and common positions in quantum entaglement and superposition with entropy. I need to know about this phenomenon

I was wondering how to measure the first or even the second qubit in a quantum computing system after for example a Hadamard Gate is applied to the system of these qubits: A|00>+B|01>+C|10>+D|11>? A mathematical and intuitive explanation would be nice, I am a undergraduate sophomore student...

Do electron minibands in quantum dot solids have a potential?

Hi, In this presentation about quantum optics it is mentioned that the same quantum state |Ψ> has different expressions in different mode bases : factorized state or entangled state. This presentation is related to this video : In some way entanglement isn't intrinsic. It depend on the...

Hi guys, Merry Christmas to you all! I wanted to know whether a neutral pion can be made up of a strange quark and an anti-strange quark. I know that the kaon is the only strange meson and all variations contain an s quark but wouldn't the strangeness be zero in an s quark/anti-s quark pair as...

Hi all! Happy New year! I will select my supervisor soon but i want to involve in the field that uses QM or GR frequently I love physics and i want to apply physics to explain astrophysical phenomenon. I know that Compact objects and Astrochemistry use such physics but i wonder to know more...

Hello, The state | W \rangle = \frac { 1 } { \sqrt { 3 } } ( | 001 \rangle + | 010 \rangle + | 100 \rangle ) is entangled. The Schmidt decomposition is : What would the Schmidt decomposition be for | W \rangle ? I am also intersted in writing the reduced density matrix but I need the basis...

Homework Statement Show that ##[L_{x}^2,L_{y}^2]=[L_{y}^2,L_{z}^2]=[L_{z}^2,L_{x}^2]## Homework Equations ##L^2 = L_{x}^2+L_{y}^2+L_{z}^2## ##L_x = yp_z-zp_y## ##L_y = zp_x-xp_z## ##L_z = xp_y-yp_x## ##[x_i,p_j]=iħδ_{ij}## ##[L_x,L_y]=iħL_z## ##[L_y,L_z]=iħL_x## ##[L_z,L_x]=iħL_y##...