States Definition and 1000 Threads

Is it not possible to deduce quantum states from a density matrix?

Is it actually possible to calculate the probability of field states in QFT? For example the probability of some scalar field being found as some function f(x,t), i find this problem ignored in most texts.

I have few questions to ask: 1. Can a photon state be written as |ψ> = [cos(θ) sin(θ) exp(i*ø)] in column vector form 2. When a general photon state|ψ> = [cos(θ) sin(θ) exp(i*ø)] passes through a linear polarizer [1 0; 0 0] we get [cos(θ) 0] at the output but not [1 0] as is usually...

Hey, I've been searching around for papers reporting on the creation of relatively large cat states, the largest I have been able to find are by Wineland, and are on the scale of nano meters. Does anyone know of any articles where such states have been created (experimentally) and reported...

In any textbooks I have seen, vacuum states are defined as: a |0>= 0 What is the difference between |0> and 0? Again, what happens when a+ act on |0> and 0? and Number Operator a+a act on |0> and 0?

When we add the angular momenta of two particles, J1 and J2, we get that the resulting total angular momenta is in the range |J1-J2| < J < J1+J2 but according to the Clebsh-Gordan table some coefficients are zero. Does it mean that not all combinations between |J1-J2| and J1+J2 are possible?

In thermodynamics what is meant by "the number of individual states that belongs to one energy level"?My current understanding is that different individual states of one energy means a system with different pressure,volume and temperature that belongs to a particular energy level? please can...

Homework Statement Given the delta function -α[δ(x+a) + δ(x-a)] where α and a are real positive constants. How many bound states does it possess? Find allowed energies for \frac{hbar2}{ma} and \frac{hbar2}{4ma} and sketch the wave functions. Homework Equations I know there are three parts of...

This is how one poster tried to explain it to me but for people who have only taken a basic physics course in college it leaves a lot wanting. "If a system is in a pure state, and you know what the pure state is, then your knowledge of the system is complete, and all uncertainty is quantum...

Consider a monatomic gas of hydrogen (just to make the example as simple as possible) at a temperature T. If I use Boltzmann statistics, I would say that the probability of finding any arbitrary atom at energy E should be proportional to ##g_i e^{-E_i/(k_BT)} / Z(T)## where ##g_i## is the...

Homework Statement Using the dispersion relation at the Dirac Point calculate the electron density of states for graphene in both the valence and conduction band. Homework Equations ρ = density of states = k2/pi2 The Attempt at a Solution I looked up what Dirac Points...

A quick and simple question: one always talks about BPS states annihilating half the supercharges. What does that mean exactly? For example, in a pedagogical article by Alvarez-Gaumé and Hassan they give the anticommutator of one set of supercharges to be \{b_\alpha, b_\beta^\dagger \} =...

How can we define density of state in continuous energy? As the term energy state comes from quantum mechanics which deals with discrete energies. Thanks in advance

To take into account the density of states for an ideal gas, we first calculate it ignoring the spin. Then to take into account the spin for a system of electrons we put the number 2 for two spin directions. Why don't we do such this for a boson gas? For example if we have a gas of spin 1...

e=mc^2 states mass and energy are interchangeable but ?? But daltons law of constabt mass is voilated as states that while a reaction the mass of product = mass of reactant any explanations?

Hi, Seasons greetings to everyone :-) I've been revising statistical mechanics and have stumbled across an area that I've always been a little 'hazy' on. By the term 'single-particle' state, is it meant that this is a particular quantum state that one (or more) particle(s) can occupy, a...

In Graph States for Quantum Secret Sharing on page 3 : I understand that $$\mathop \otimes \limits_i Z_i^{{l_{i2}}} = Z_1^{{l_{12}}} \otimes Z_2^{{l_{22}}} \otimes Z_3^{{l_{32}}}$$ But I don’t understand why $$\left| G \right\rangle = \left( {\frac{{\left| {0 + + } \right\rangle +...

I have a question about allowed transitions and molecular states. For an electric dipole transition between two states (say molecular or atomic) to have a non-zero probability of occurring, the transition dipole moment \langle \psi_{f}|\textbf{μ}\left|\psi_{i} \right \rangle must be non-zero...

I do not understand the attached picture excerpt from Kittel Thermal Physics (first sentence up to 'eqn' (7) ). I would expect the moments to go down in increments of one, not two. I think the subsequent paragraph tries to explain why, although I am not sure this is indeed the purpose...

Homework Statement See attachment Homework Equations The Attempt at a Solution (i) |\Psi(t)_{1}>=e^{{-itE_{1}/\hbar}}\frac{1}{\sqrt{2}}(|z^{+}>+|z^{-}>) |\Psi(t)_{2}>=e^{{-itE_{2}/\hbar}}\frac{1}{\sqrt{2}}(|z^{+}>-|z^{-}>) where...

\HugeHomework Statement Consider a state of the EM field which satisfies \left\langle \textbf{E}_x(\vec{r})\right\rangle =f(\vec{r}) Find a coherent state which satises these expectation values.Homework Equations \textbf{E}(\textbf{r})=\frac{i}{\sqrt{2 V}}\sum _{\textbf{k},\lambda }...

Homework Statement There is a thin tube in which a finite potential trap has been set up where V2 = 0 V. An electron is shown traveling rightward toward the trap, in a region with a voltage of V1 = -9.00 V, where it has a kinetic energy of 2.00 eV. When the electron enters the trap region...

Homework Statement Consider a potential function V(x) such that: $$ \begin{cases} V(x)\leq 0\text{ for }x\in[-x_0,x_0] \\ V(x)=0 \text{ for }x\not\in[-x_0,x_0] \end{cases} $$ Show, using the variational method that: (a) In the 1-dimensional case \lambda^2V(x) always possesses at...

Homework Statement A particle is confined to a two-dimensional box defined by the following boundary conditions: U(x, y) = 0 for \frac{-L}{2} ≤ x ≤ \frac{L}{2} and \frac{-3L}{2} ≤ y ≤ \frac{3L}{2}, and U(x, y) = ∞ outside these ranges. Determine the energies of the three lowest energy states...

Homework Statement Hey dudes So here's the question: Consider the first excited Hydrogen atom eigenstate eigenstate \psi_{2,1,1}=R_{2,1}(r)Y_{11}(\theta, \phi) with Y_{11}≈e^{i\phi}sin(\theta). You may assume that Y_{11} is correctly normalized. (a)Show that \psi_{2,1,1} is orthogonal...

Homework Statement Find the density of states g(ε) for an ideal quantum gas of spinless particles in dimension d with dispersion relation  ε= α|p|s , where ε is the energy and p is the momentum of a particle. The gas is confined to a large box of side L (so V = Ld) with periodic boundary...

Homework Statement The wave function for a system of two hydrogen atoms can be described approximately in terms of hydrogen wave functions. (a) Give the complete wave functions for the lowest states of the system for singlet and triplet spin configurations. Sketch the spatial part of each...

what do you mean by density of states ? can you please explain to it ?

I'm wondering what the name of a switch that alternates between two states only when depressed. An example would be a flashlight, where if you click it once, it turns on, and if you click it off, it turns off (no need to hold down the button to get a continuous light).

I've always taken this for granted. Now I am looking for an answer. When electron jumps from a higher orbit to lower orbit it releases energy. Why is the energy in the form of photon? I will take another example which will make my question easy to understand. When two electrons are kept...

Homework Statement A system is made of N 1D simple harmonic oscillators. Show that the number of states with total energy E is given by \Omega(E) = \frac{(M+N-1)!}{(M!)(N-1)!} Homework Equations Each particle has energy ε = \overline{h}\omega(n + \frac{1}{2}), n = 0, 1 Total energy is...

Is there a way to write p1 |v1> + p2 |v2> if it is not a pure state but a mixture? thanks.

What are the differences between the triplet and singlet states. triplet state-- parallel spins-- S=1 , 2S+1=3 Singlet state-- Paired spins---S=0 , 2S=1= 1 singlet state has paired spins of electrons in the same orbit, thus there are repulsion force between the two electron in the same...

Hello everybody, I have a question which might be silly. Nevertheless: Can exited states exist if you know that the ground state do not exist? Will in such a case first exited state become the ground state? Thanks.

Homework Statement What is the expectation value of \hat{S}_{x} with respect to the state \chi = \begin{pmatrix} 1\\ 0 \end{pmatrix}? \hat{S}_{x} = \frac{\bar{h}}{2}\begin{pmatrix} 0&1\\ 1&0 \end{pmatrix}Homework Equations <\hat{S}_{x}> = ∫^{\infty}_{-\infty}(\chi^{T})^{*}\hat{S}_{x}\chi...

Homework Statement An atom in an excited state has a lifetime of 1.2 x 10 -8 sec; in a second excited state the lifetime is 2.3 x 10 -8 sec. What is the uncertainty in energy for the photon emitted when an electron makes a transition between these two levels? Homework Equations...

Forgive me as I have no formal secondary education so my actual knowledge of terms and what not is limited but I am working on a theory that has me wanting to explore the varying chemical states of matter and what defines them. For example, how Nitrogen can be both a gas and a liquid in room...

Hi guys, Just a quick question, is the following statement true (it seems to be implied in the article I'm looking at); Ʃ(|α|2)n = 1 (The sum over n=0 to infinity) Thanks to anyone who takes a look.

Do protons and neutrons have excited states? This page shows some simulated shapes of protons. http://discovermagazine.com/2003/aug/breakprotons Do the different shapes have to do with different energy states of the proton?

Hi folks -- quick question. I appreciate that entangled states in quantum mechanics may not be bound states. But when we have bound states, are the particles always entangled with one another? Thanks a lot!

For a free electron gas the procedure for determining the density of states is as follows. Apply periodic boundary conditions to the free electron waves over a cube of side L. This gives us that there is one state per volume 2\pi/L3=2\pi/V And from there we can find the number of states at a...

In the double delta function potential well, where one delta function ( -αδ(x) ) is at -a and one at +a, if the energy is less than zero, there can be either one or two bound states, depending on the magnitude of α...if α is large enough, there can be two bound states, but if α is small, there...

I know coherent states are minimal uncertainty states and can provide a link from quantum to classical physics.But when I hear fermions can't have coherent states,or at least are limited in this sense,I can't see any relationship! What's the point? And...another thing...is there sth called...

Consider the Gaussian Integral (eqn 2.64).. is anyone able to explain how the constant of normalization is rationalised?

Homework Statement Explain why, as the atomic number increases, the 4s electronic states fill before the 3d states. The fact that they fill first means they are lower energy. You must explain why they are lower energy. Homework Equations The Attempt at a Solution First, I'm aware...

With great interest I read an article about a paper where scientists were able to create two photon bound states ("molecules of light"). http://physicsworld.com/cws/article/news/2013/sep/26/physicists-create-molecules-of-light I was quite astonished since light normally does not...

Homework Statement A particle of mass m is trapped in a one-dimensional infinite square well running from x= -L/2 to L/2. The particle is in a linear combination of its ground state and first excited state such that its expectation value of momentum takes on its largest possible value at...

My book gives a treatment of this problem for crystal vibrations, but I don't really understand it. It says: There is one allowed value of K per volume (2\pi/L)3. But at the same time it has just shown that Kx,Ky,Kz can take values ±2\pi/L which would certainly lead to more combinations of...

A particle of mass m is trapped in a one-dimensional infinite square well running from x= -L/2 to L/2. The particle is in a linear combination of its ground state and first excited state such that its expectation value of momentum takes on its largest possible value at t=0.I know the process of...

So, I've read conference proceedings and they appear to talk about counter-intuitive it was to create an infinite-energy state for the harmonic oscillator with a normalizable wave function (i.e. a linear combination of eigenstates). How exactly could those even exist in the first place?