1
vote
1answer
55 views

How do you actually cool the atoms to create the Bose-Einstein Condensate?

What is the actual way you cool atoms to a low enough temperature that you can observe their quantum behavior at a macroscopic level, like in the Bose-Einstein Condensate? ...
2
votes
1answer
84 views

Proof of the conservation of the energy functional for the Gross-Pitaevskii equation?

From the Gross-Pitaevskii equation \begin{equation}i\hbar\frac{\partial\psi}{\partial t}=\left(-\frac{\hbar^2}{2m}\nabla^2+V+g|\psi|^2\right)\psi\end{equation} using the variational relation ...
0
votes
2answers
112 views

Bose Einstein condensates and gravity

Are Bose Einstein condensates affected by gravitational attraction ? In sufficient quantity, do Bose Einstein condensates exert a gravitational force ?
1
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0answers
26 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 ...
10
votes
1answer
156 views

How to exchange light and matter?

A while ago an experiment demonstrated that it is possible to stop a light pulse in a supercooled sodium cloud, store the data contained within it, and totally extinguish it, only to reincarnate the ...
1
vote
1answer
97 views

Some conceptual questions in BEC

In Bose-Einstein condensate (BEC), people often say there is a well defined macroscopic phase. What exactly the macroscopic phase is? (a phase factor $\mathrm{e} ^{i\phi}$ in a many-body wavefuction?) ...
2
votes
1answer
91 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 ...
1
vote
1answer
124 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 ...
1
vote
1answer
96 views

Spinor and Scalar Bose-Einstein condensate

I read about an order paramater that describes a Bose-Einstein condensate. But I don't understand, the classification into "scalar" condensate and "spinor" one. Is it linked with spin of atoms that ...
5
votes
0answers
84 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 ...
6
votes
2answers
298 views

Change of basis in non-linear Schrodinger equation

At the mean-field level, the dynamics of a polariton condensate can be described by a type of nonlinear Schrodinger equation (Gross-Pitaevskii-type), for a classical (complex-number) wavefunction ...
4
votes
1answer
155 views

First order coherence function in terms of momentum distribution function

Can someone show me how the first order coherence function $G^1(r,r')\equiv \left \langle \hat{\Psi}(r)\hat{\Psi}(r') \right \rangle $ for a system of bosons is related to the momentum distribution ...
5
votes
2answers
537 views

What prevents bosons from occupying the same location?

The Pauli exclusion principle states that no two fermions can share identical quantum states. Bosons, one the other hand, face no such prohibition. This allows multiple bosons to essentially occupy ...
2
votes
1answer
130 views

Why People talk so much about Feshbach resonance while dealing with Bose-Einstein Condensate (BEC)?

Why People talk so much about Feshbach resonance while dealing with Bose-Einstein Condensate (BEC)? Why not tune the system near the resonance and measure the effect on BEC formation?
1
vote
2answers
398 views

What does the wavefunction of atom look like at low temperature?

I am reading an introduction material on Bose-Einstein condensation (BEC) at low temperature and it stated that when the temperature approaches zero kelvin, almost all atoms are degenerated into the ...
1
vote
0answers
93 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 ...
18
votes
2answers
711 views

Can bosons that are composed of several fermions occupy the same state?

It is generally assumed that there is no limit on how many bosons are allowed to occupy the same quantum mechanical state. However, almost every boson encountered in every-day physics is not a ...
3
votes
2answers
908 views

Why water is not superfluid?

My question is in the title. I do not really understand why water is not a superfluid. Maybe I make a mistake but the fact that water is not suprfluid comes from the fact that the elementary ...
3
votes
0answers
173 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 $t$ ...
6
votes
1answer
418 views

Expansion of multi-particle state vector as a sum of n-entangled states

Physically, quantum entanglement is ranged from full long-range entanglement (Bose-Einstein condensate), described by a basis of states that look like this: $$ |\Psi\rangle = |\phi_{i_{0} i_{1} ... ...
12
votes
3answers
1k views

trying to understand Bose-Einstein Condensate (BEC)

I am a computer scientist interested in network theory. I have come across the Bose-Einstein Condensate (BEC) because of its connections to complex networks. What I know about condensation is the ...
7
votes
4answers
9k views

Practical applications for a Bose-Einstein condensate

What are the main practical applications that a Bose-Einstein condensate can have?