Questions tagged [cold-atoms]
118 questions
21
votes
3 answers
Are the recently observed Dirac monopoles separable?
I just went through Observation of Dirac monopoles in a synthetic magnetic field.
What exactly has been observed?
More importantly, are these monopoles localized inside the apparatus (no stray monopole field lines coming out), or can they be used to…
Manishearth
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17
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2 answers
Why are Alkali atoms used in many Cold Atom experiments?
It seems that alkali atoms are often used in cold atom experiments. The first BEC was formed with alkali atoms, and many modern experiments used Alkalis. What is special about having a single electron in the outer most orbital that is useful for…
Zonova
- 339
14
votes
1 answer
When are two fermions considered identical?
I am a bit confused about the terminology concerning identical fermions. In quantum mechanics, identical fermions need to obey certain anticommutation relations i.e. have an antisymmetric total wavefunction (product of spatial and spin parts) under…
JayKay
- 143
13
votes
1 answer
Why is the density of a BEC so low?
I've just begun reading C. Pethick and H. Smith's textbook "Bose-Einstein condensation in dilute gases" (Cam. Uni. Press). In the Introduction, they contrast the density of atoms at the centre of a BEC cloud to other phases of matter. To quote from…
dBozwerf
- 133
10
votes
1 answer
How to perform stroboscopic measurements for Floquet topological insulators?
Floquet topological insulators (arXiv:1008.1792, arXiv:1211.5623) have attracted much research interests in condensed matter physics. The goal is to realize topological insulators from trivial insulators by applying periodic driving forces. The idea…
Everett You
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9
votes
1 answer
Natural linewidth of hyperfine levels?
The D2 line of $^{87}\mathrm{Rb}$ is the transition between the $5^2\mathrm P_{3/2}$ and the $5^2\mathrm S_{1/2}$ states. Its linewidth $\Gamma$ is always quoted to be $\sim 6\ \mathrm{MHz}$.
But both states have hyperfine splittings.
The transition…
SuperCiocia
- 25,602
8
votes
1 answer
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. From quantum mechanical scattering theory, one…
TikTak
- 81
7
votes
2 answers
Polarization of light and transitions in a Magneto Optical Trap
After reading this question, I realized that I didn't really understand how a MOT works in detail. I was always relying on the simplistic picture given in textbooks which never addresses the actual polarization of the light: they seem to make no…
Banjo
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7
votes
2 answers
The calculation of the entropy of a single atom
I used to think that the entropy of a single atom could not be calculated, for in my mind only the entropy of a system containing many atoms could be calculated.
But my professor told me the entropy of a single atom also makes sense, without telling…
A. Shaw
- 91
7
votes
1 answer
Why isn't ice a good electrical conductor?
Water can conduct electricity, and some solids can conduct. Why can't ice? Are ice molecules too packed together to let valence shell electrons bounce across each other to create electrical charge? Does ice stop conducting completely at absolute…
nelomad
- 233
6
votes
3 answers
What is a degenerate Fermi gas?
In ultracold atoms, it is generally talked of a degenerate Fermi gas. What does degenerate mean here?
cleanplay
- 1,555
6
votes
4 answers
Gas or liquid? a Bose-Einstein condensate
It is often said that a Bose-Einstein condensate of cold atoms is a gas. But because of Andrews' discovery of the critical temperature, we know that a gas and a liquid is not fundamentally different. So, why is it called a gas but not a liquid?
poisson
- 2,185
6
votes
1 answer
BCS pairing and BEC pair between Fermions
In many lecture notes, it points out
We can tune the scattering length, using Feshbach resonance, to realize crossover from BCS to BEC in degenerate Fermi gases. When the scattering length is negative(positive), we get BCS(BEC) pairing.
In my…
xiang sun
- 870
6
votes
1 answer
Superfluid-Mott insulator transition in Bose-Hubbard model in terms of vortex condensation
I have heard that there is some effective field theoretic type understanding of the superfluid-Mott insulator transition in Bose-Hubbard model. It says if the system is in a superfluid phase where the $U(1)$ symmetry is broken, then by proliferating…
Mr. Gentleman
- 1,606
5
votes
2 answers
How to realize long-range interaction of colds atom in an optical lattice?
In the Bose-Hubbard model of cold atoms in an optical lattice, we consider only the short-range interaction or on-site interaction. Is it possible to realize long-range interaction similar to Coulomb interaction in the cold atom experiment?
Timothy
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