Questions tagged [cold-atoms]
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91
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How to solve a toy model like one dimension t-J + Bose-Hubbard model? Gutzwiller mean field?
I want to think about a toy model like this, t-J + Bose-Hubbard model, how to do it?
Can we use the mean field method? such as Gutzwiller mean field?
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6 views
Effects of Non-Linear Atomic Laser
As "lasers" formed from the stimulated emission of Bose-Einsten condensates do not follow Maxwell's linear equation's which are normally used when calculating current lasers, how would this ...
0
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2answers
51 views
Is it possible to laser cool without using spatially-varying magnetic fields and above zero degrees?
As the title says, is it possible to laser cool without generating a weak quadrupolar magnetic field? Also, if I wasn't trying to achieve extremely low temperatures is it possible to use laser cooling ...
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0answers
28 views
BEC Relaxation to Dispersion Minimum
I am reading this paper, which looks at the emergence of a double well dispersion in an optical lattice through shaking as in the figure below.
I am curious as to what mechanism results in the atoms ...
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39 views
How to get the chemical potential self-consistently for a given filling factor n
Considering tight binding model(such as Hubbard model), according to BdG mean field theory,we can get the BdG equation and self consistent equations.for a fixed particle system, we need to adjust the ...
6
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1answer
98 views
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 ...
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32 views
Is there a laser in which based on Ytterbium
I understand that Ytterbium can emit a photon with a relatively high and very accurate frequency (narrow band of frequency). I also know that Ytterbium is being used to verify frequency in atomic ...
1
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1answer
48 views
How is three-dimensional laser cooling possible?
I am a bit confused about laser cooling an atom in all three dimensions. I think I have understood the one-dimensional case: The atom absorbs doppler-shifted laser light and the momentum in this ...
0
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1answer
53 views
Why do atoms oscillate at absolute zero? [duplicate]
I have heard that average kinetic energy of atoms is directly proportional to the absolute temperature. Then why don't atoms come to a stop at absolute zero ($T=0K$).
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2answers
78 views
Can we make cold without producing heat?
It seems to me you can put a heater on without expelling cold to the other room like an air conditioner and freezer would. Is there a way to reduce heat locally by slowing down molecules for example?
...
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1answer
65 views
Two different to do Bogobliubov transformation but sees to be contradictary
When try to do bogoliubov transformation on a weak-interaction cold atoms with uniform velocity $\vec{v}$, I used two different approaches, giving two different results.
The Hamiltonian is
$$\hat{H}=\...
2
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2answers
135 views
What wavelengths are used practically in optical trapping?
I am currently working on my Master thesis in a cold atom research group, and have irritatingly found -- or rather not found -- that no book or paper seems to explicitly mention what wavelengths are ...
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2answers
80 views
What is the longest wavelength ever measured for a Black Body?
As said in the title, I am curious about the reported measurements for cooled black bodies. Any source is welcome.
I am neither interested in any thought experiment nor in the well-established law of ...
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56 views
Any introductory books/articles on ultra-cold atoms?
I am currently only a high school student wanting to pursue physics at the tertiary level of education.
Are there any books people can recommend on ultra-cold atoms? I would like to discover more ...
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1answer
48 views
Using an electric/magnetic field to cool particles
I was just thinking that temperature and the motion of atoms are connected. Hence, I was wondering why we can’t just use a magnetic or electric field to hold atoms more or less in place, lowering ...
3
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1answer
112 views
What is a good definition for what this article talking about when it refers to “Universal Physics”?
I was puzzled when I read
"Precise measurements find a crack in universal physics
by Ingrid Fadelli" (Phys.org, Jan. 15, 2020). The article has some vague statements in the opening paragraphs about "...
0
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1answer
30 views
Transitions within magnetic sub levels: evaporative cooling to Bose Einstein Condensation
Consider a Ioffe-Pritchard trap geometry.
Evaporative cooling works by decreasing the trap depth to remove atoms which are more energetic than average; this leads to cooling. This is done by using ...
0
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1answer
40 views
What is the classical counterpart of ultra-cold atoms?
I'm studying quantum chaos in ultra-cold atoms. However, quantum chaos denotes the quantum mechanics of classically chaotic systems and it is not clear to me what is the classical counterpart of ...
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22 views
Does the size, and distance between, expanding ultracold gas clouds depend on the populations in each cloud?
Say you had some $^{87}$Rb atoms at a few kelvin and you knew that the atoms were
distributed among the magnetic sub-levels of a hyperfine manifold. You want to know the relative population of each by ...
11
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1answer
504 views
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 ...
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2answers
46 views
How are atoms formes by electromagnetic waves that a specific frequency? [closed]
I came up something like this- Every piece of matter has a resonancefrequency or series of frequenciesbecause all matter is made up of atoms. Atoms are formed by electromagnetic waves that have a ...
0
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1answer
116 views
Is it BEC-BCS crossover the natural framework to explain superconductivity from ultracold atoms?
I know that superfluidity and superconductivity have very distinct characteristics and have specific theories. However, it seems that in ultra-cold atomic gases these phenomena can be understood by a ...
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1answer
105 views
speed of freezing vs. moving [closed]
An idea came to my mind and like to discuss it.
We know that out there in the space the absolute zero (aka. -273 C) is almost reached where all the particles and atoms would freeze up and stop giving ...
3
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1answer
88 views
In AMO experiments, how do cold alkali metal atoms remain gaseous?
My focus is on condensed matter physics, so I've never really explored this question although it always seemed curious to me. My "immediate reaction" intuition would dictate that cold metal atoms ...
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1answer
36 views
What laser frequency is needed for the Doppler cooling of iron?
What laser frequency is needed for Doppler cooling iron? How do you determine this frequency?
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1answer
151 views
Is the ground state a Schrödinger cat state?
Consider the following Bose-Hubbard Hamiltonian which describes a Bose-Einstein condensate confined in a two-well potential:
$$
H= -T(a_L^\dagger a_R + a_L a_R^\dagger ) + \frac{U}{2}(n_L^2+n_R^2-...
0
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1answer
29 views
Fermi-Hubbard model: adiabatically change tunnelling
Consider the 3D Fermi-Hubbard model in a cold-atom setting (harmonic confinement, $\epsilon_i$):
$ H = - t \sum_{\langle i, j\rangle, \sigma} c^{\dagger}_{i, \sigma}c_{j,\sigma} + U\sum_{i}n_{i,\...
0
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1answer
215 views
What is the (quantum) definition of thermal equilibrium?
What is the necessary condition for a quantum system to be in thermal equilibrium? The quantum systems I have in mind are a bunch of cold atoms, of photons in a cavity.
Does a system need to obey a ...
0
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1answer
149 views
If an atom is in its ground state, has the atom the lower energy possible and there is its lower temperature?
"In the lowest energy state, the constituents of the atom (the nucleus and the orbiting electrons) are arranged so that the total energy in the system is minimal. This is called the ground state of ...
3
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1answer
113 views
Is there an intuitive reason as to why there is no phase transition to get to a degenerate Fermi gas?
Cooling a bosonic gas leads to a phase transition into the Bose-Einstein condesate. This is characterised by a symmetry broken ( U(1), by choosing a specific phase for the macroscopic wavefunction) ...
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0answers
59 views
Why does $[H,N]=0$ violate with superfluid phase judgement $\left<b\right>=0?$
I'm working with the standard Boson Hubbard model. It's Hamiltonian is defined in Fock space and commutes with total particle number N.
$$[{{\hat H}_{BH}},\hat N] = 0$$
So I can simultaneously ...
0
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1answer
72 views
Resource request: Superfluid helium
I am wondering if anybody could recommend any good textbooks on the subject. So far, I have discovered (but not yet had a chance to read), a chapter in Landau-Lifshitz fluid mechanics (love Landau-...
0
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1answer
411 views
Hard-core bosons and fermions - spinless?
The introduction to this paper about bosonic atoms expanding in an optical lattice says the following:
Are hard-core bosons mapped to spinless fermions?
Because this link shows the mapping ...
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0answers
120 views
Cold atoms: how does evaporative cooling work?
I understand the principle of evaporative cooling (for the creation of a Bose-Einstein Condensate), but I do not find any reference which explains mathematically this process and which explains what ...
0
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1answer
110 views
Potential lineshapes of a BEC in a magnetic trap
We considere a Bose-Einstein Condensate (BEC) of atoms occupying a magneticaly trapped atomic state $|m_{F}=-1\rangle$. One can then use a radio-frequency field to extract atoms from the BEC by ...
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0answers
84 views
Feshbach resonance - Magnetic Field/Spin Orientation
I have been reading about Feshbach resonance in ultra cold atoms and there were some areas I'd like to understand better/have questions about:
i) As the atoms approach each other, can their spins be ...
0
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1answer
162 views
$\Delta \ell = 0, \ell = 0 \rightarrow \ell = 0$ transition in atomic ground state
Assume I am in the $S_{1/2}$ state of, say, Rubidium:
Let's say I am in the higher $>F\rangle$ state ($3$ for $^{85}\textrm{Rb}$, $2$ for $^{87}\textrm{Rb}$), how do I decay to the lowest ground ...
2
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1answer
73 views
Atom interferometry,gravity and inertia: What can it measure that light interferometry can't? [closed]
What previously unexplored effects in gravity and inertia can be examined with atom interferometry in ways that hasn't already been done through light interferometry?
Can atom interferometry be used ...
3
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1answer
47 views
Quasi-classical energies for neutron in gravitational potential [closed]
Lets consider a ultra cold neutron gas in a gravitational potential. The known quasi-classical energy up to the classical turning point is
$$
E_n =\sqrt[3]{\frac{9m}{8}(\pi\hbar g (n-\frac{1}{4}))^2} ...
1
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1answer
42 views
Energy conservation in Kapitza-Dirac diffraction?
In Kapitza-Dirac diffraction, a standing wave of light (wavevector of single wave $k$) is pulsed on for a very short period of time ($\sim \mu s$) onto a bunch of cold atoms. This results in the atoms ...
5
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1answer
979 views
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 ...
11
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1answer
2k views
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 ...
0
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1answer
46 views
Looking for chemicals to melt ice
This might sound like science fiction but I am trying to learn if there is a chemical or material that can convert cold into heat. It also could be kinetic as well. An example would be placing a ...
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2answers
602 views
What is the advantage of making a BEC in space?
The NASA Cold Atom Laboratory, which I believe is slated to launch this year, has the goal of putting a Bose Einstein Condensate (BEC) apparatus on the ISS. What is the advantage of doing this? ...
4
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1answer
219 views
Is Bose-Einstein condensate in the optical lattice a single mode condensate?
I recently read about BEC loaded into the optical lattice p.200
Looking at a condensate released from a lattice after a
time of flight typically on the order of a few milliseconds
amounts to ...
2
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1answer
104 views
Optical pumping & spin-changing collisions
Optical pumping is the method of 'pumping' all the electrons in the upmost $m_F$ state of the ground state, by shining $\sigma^+$ light such that eventually all the electrons end up in this state ...
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1answer
232 views
Arbitrariness of phase in the definition of the Fock state leads to lack of squeezing
Every state in quantum mechanics is defined up to a global phase. In other words, quantum states $|\psi'\rangle = e^{i\varphi}|\psi\rangle$ which differ just by a phase factor are indistinguishable. ...
2
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1answer
308 views
Labelling hyperfine structure states in strong magnetic field
I am trying to work out the frequency shifts to the hyperfine energy levels in $^{39}$K $\,$ S$_{1/2}$ (the ground state).
I diagonalise the Hamiltonian for different values of the $B_z$ field, with ...
2
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2answers
443 views
Dipole interaction for a two-level system in a trap potential
Consider a two-level system under the following Hamiltonian:
$H=H_{I}+H_{E}+H_{dip}$
where $H_I$ is the Hamiltonian for the two internal states of the two-level system $span \{\left |e \right> {,}...
1
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1answer
102 views
Is 3D optical lattice just a stack of 2D lattices?
I am confused about the idea of 3D optical lattice. Many papers use 3D optical lattice to study bosons behavior, but is it really a 3D system where atoms interact in all three directions or is it just ...
