The tag has no usage guidance.

learn more… | top users | synonyms

1
vote
2answers
239 views

Oscillation of a Bose Einstein condensate in a harmonical trap

We were asked to try to make a theoretical description of the following phenomenon: Imagine a 2D Bose Einstein condensate in equilibrium in an harmonical trap with frequency $\omega$. Suddenly the ...
4
votes
1answer
390 views

Hamiltonians, density of state, BECs

When working with Bose-Einstein condensates trapped in potentials, how can one tell what the density of state of a system of identical bosons given the Hamiltonian, $H$? (I have been told that it is ...
3
votes
1answer
183 views

Correct way to do a Thomas-Fermi approximation for cold gases

I have calculated the total Gross-Pitaevskii energy for a 2D Bose-Einstein condensate in an harmonical trap, using a variational gaussian wave function with a variational parameter b. Now I want to ...
2
votes
1answer
72 views

Feshbach resonance in simple terms

I was reading up Feshbach resonances in cold atoms and I was unable to grasp the concept. I will tell you what I have understood. We consider two body scattering processes elastic as well as ...
2
votes
1answer
100 views

Bose Einstein condensation and macroscopic occupation

If have been thought, that Bose Einstein condensation occurs of the ground-state is occupied macroscopically, so $n_0\in \mathcal{O}(N)$ when performing the thermodynamic limit. So naively, this ...
0
votes
1answer
44 views

Why do different phases of matter coexist?

Say at a critical temperature $T_c$ there is a phase transition. If we had water, $T_c$ for the liquid-solid transition is $0 ^\circ$C. If we left a block of ice at $1 ^\circ$C for a bit, it will ...
0
votes
1answer
52 views

physics of the beaker experiment for superfluid helium

here is an illustration and explanation of the beaker experiment over superfluid helium: So, according to this experiment, can anyone say what is the cause? I mean the superfluids are disconnected ...
0
votes
1answer
42 views

How do I evaluate the angular momentum of the wave function?

I'm working with Bose-Einstein condensates and running a 2D single component Gross-Pitaevskii equation solver for the simulations in MATLAB. The way it works is that it numerically solves the GP ...
9
votes
0answers
230 views

Linear response theory for Gross Pitaevskii equation

I am trying to linearize the following GP eq: \begin{equation} i\partial_{t}\psi(r,t)=\left[-\frac{\nabla^{2}}{2m}+g\left|\psi(r,t)\right|^{2}+V_{d}(r)\right]\psi(r,t) \end{equation} The ansatz for ...
6
votes
0answers
80 views

What is the largest number of bosons placed in a BEC?

What is the record for the largest number of bosons placed in a Bose-Einstein condensate? What are the prospects for how high this might get in the future? EDIT: These guys reported 20 million ...
5
votes
0answers
95 views

BEC in a rotating disc

Goodmorning everybody, I have to run a numerical simulation of a Bose-Einstein condensate on a rotating disc. Now, my problem is that I became suspicious about the equation I'm using, since the final ...
4
votes
0answers
398 views

Toward the establishment of non-equilibrium (quasi-equilibrium) magnon BEC theory

In 2006, Demokritov et al have reported that they have achieved the observation of quasi-equilibrium magnon Bose-Einstein condensation (BEC) in YIG at finite (room) temperature by using the method ...
3
votes
0answers
107 views

Gravastars: Are they observationally distinguishable from Black-Holes?

Are observations of Hawking radiation at the acoustic event horizon in Bose-Einstein condensates consistent with Gravastars? To reconcile the second law of thermodynamics with the existence of a ...
3
votes
0answers
102 views

positronium BEC stability

After reading this article regarding Positronium BEC formation (for lasing purposes), there is a mention in there regarding Ps "up" atoms not annihilating with "down" atoms, the article is pretty ...
3
votes
0answers
191 views

Matter-wave interference from free falling cold atoms

and another exam question, this is about current research: Interference of matter waves has been studied using ultra-cold atoms. The phase of a matter wave for free-falling cold-atoms at time $t$ ...
3
votes
0answers
745 views

How do I derive the critical temperature for bose condensation in two dimensions?

In class we derived the 3D case, but there's a step I don't understand: $$ N = g \cdot {V \over (2 \pi \hbar)^3} \cdot \int\limits_{0}^{\infty}{1 \over{e^{\left( E_p \over{K_B T}\right)}-1}} d^3 p = ...
2
votes
0answers
160 views

Bose-Einstein condensation in 3D

I have read in many books that BEC takes place in momentum space and in only 3-dimensions. What is meant by this statement?
2
votes
0answers
157 views

Deriving the “total” Bose Einstein density of states, including the condensate

Is is possible to derive the Bose-Einstein density of states containing the delta function representing the BE condensate?
1
vote
0answers
18 views

SU(3) squeezing parameter

Spin squeezing is a strategy to improve the precision of quantum interferometry below the shot-noise limit. In order to quantify the amount of squeezing one can calculate the spin-squeezing parameter ...
1
vote
0answers
36 views

Is there a local canonical ensemble partition function for a Bose-Einstein gas?

The grand canonical partition function for a Bose-Einstein gas is $$ Z_{\text{grand bos}} = \exp \left( \sum_{j=0}^{\infty} -\ln \left( 1-e^{\beta(\mu-\epsilon_j)} \right)g_j \right) $$ where $\beta$ ...
1
vote
0answers
25 views

How is it possible to combine various techniques in cold atom experiments?

I’ve been reading about laser-trapped cold atoms (6Li in particular, which is a fermion) and was amazed at the number of things to keep track of in the experiments, just to gain that degree of control ...
1
vote
0answers
23 views

Interactions and scattering length in Feshbach resonances

In the context of cold atoms, one can make use of the Feshbach resonance mechanism to alter the sign and value of the two-particle scattering length by applying and varying an external magnetic field. ...
1
vote
0answers
23 views

Role of BEC in atom interferometry

What is the major advantage of using Bose-Einstein condensate in atom interferometry compared with other sources of atoms? Detectors measure population difference in two arms of the interferometer. I ...
1
vote
0answers
66 views

Bose-Einstein condensation as a phase transition

1.How does a non-interacting system exhibit phase transition? 2.Is partition function of BEC is non-analytic (just like in the ordinary phase transitions)? 3.What is the order of BEC phase ...
1
vote
0answers
39 views

Nonlocal interaction effects on bose-einstein condensates

I'm studying an interacting bose-einstein condensate using the energy functional proposed in this paper K. Huang, C.N. Yang, Phys. Rev. 105 $$ E\left[\phi\right] = \int d^3\vec{r} ...
1
vote
0answers
47 views

Bose-Einstein Condensate

In lieu of recent research showing the possibility of obtaining the Bose-Einstein condensate Nq, in certain polymers is there any statistical mechanical way of figuring out the frequency with which ...
1
vote
0answers
106 views

Temperature of Bose-Einstein-Condensate in space

Recently I heared a talk by Bill Phillips, who talked about the coldest temperatures in the universe. Among others, he sayed that the coldest temperatures created at the moment are BECs, which can ...
1
vote
0answers
56 views

Condensate fraction and single-particle density matrix

In Bose–Einstein condensation (BEC), how to prove the largest eigenvalue of the single-particle density matrix $$\rho_{ij}=\frac{\langle\Psi|a_i^{\dagger}a_j|\Psi\rangle}{N}$$ is ...
1
vote
0answers
103 views

How many ways are there to distribute M excitations of N identical particles among K=3 quantum harmonic oscillators?

I'm trying to numerically calculate a partition function of N non-interacting but identical particles in a 3D SHO. To do this, I'd like to know the degeneracy of $M$ excitations, $N$ indistinguishable ...
1
vote
0answers
162 views

Fock picture of bosonification in condensates

I want to understand how bosonification in a condensate must be interpreted in the Fock states picture Say i have uncoupled fermions in a set of states $E_1$, $E_2$ ... over the vacuum $E_0$. They ...
0
votes
0answers
14 views

What does the particle to volume density physically mean for Bose-Eisenstein condensate?

The average number of particles $\langle N\rangle$ for a Bose-Eisenstein condensate in 3D is given as $$ \dfrac{\langle N\rangle}{V} = \dfrac{V^{-1}}{e^{\beta (0-\mu)}-1} + \int_{0}^{\infty} ...
0
votes
0answers
29 views

bose einstein phase transition

From Carter's book Thermodynamics and Statistical Mechanics, the partition function of a bose-einstein gas in $d$ dimensions is $$ \ln(Z) = ...
0
votes
0answers
13 views

how to show that the chemical potential goes with O(1/V)?

In statistical mechanics books $\mu=O\left(\frac{1}{V}\right)$ is being used to show the nature of the chemical potential when $T\to0$ Unfortunately, I was not able to figure out how to see how this ...
0
votes
0answers
25 views

Pauli Master Equation usable for Bose-Einstein condensation?

As I am not an expert in the field, please correct me accordingly. Now to my problem: I wondered whether it is justified to use the Pauli Master Equation (i.e. linear coupling to markovian ...
0
votes
0answers
37 views

About imaginary time evolution method

When I try to work out the ground state of a system, there is a method making use of imaginary time and splitting operators, I wan to know, when the ground state is fine and satisfying for my purpose? ...
-1
votes
0answers
28 views

Can steel rods be welded using “cold”?

Can steel rods be welded together by lowering the temperature to a point where each end becomes a BEC?