Questions tagged [cold-atoms]

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How is the pressure derived from the Gibbs-Duhem equation, within the Local Density approximation? (Problem in calculating an integral)

Following this reference https://www.nature.com/articles/nphys1477.pdf (starting from Eq 3), I am trying to understand the details in the derivation of the pressure along the x axis p(x,y=0,z=0) from ...
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Calculating the Feshbach resonances between carbon atoms

From my understanding, Feshbach resonance is a scattering resonance that occurs when the energy of an atom pair coincides with the energy of a molecular bound state. Feshbach resonances are ...
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Question about the energy levels of Rubidium atom - how to understand this energy level diagram?

But today when I try to read some papers working with Alkaline atom, I couldn't figure out how they plot the Rubidium energy level. From my undergraduate study, I thought the diagram of Rubidium atom ...
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Phase space density for Bose-Einstein condensation

A figure of merit for Bose-Einstein condensation is the phase space density which can be defined as $$\rho=n\lambda_T^3,$$ where $n$ is the number density of atoms and $\lambda_T$ the thermal de ...
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Confusion over Feynman’s description of the Wu experiment for parity violation

In his lecture on symmetry in physical law, Feynman said: Using a very strong magnet at a very low temperature, it turns out that a certain isotope of cobalt, which disintegrates by emitting an ...
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How is two-level optical transition in a spin 1 system affected by the third level?

Suppose you have a spin-1 system. Let us resonantly drive the transition between any 2 levels (say 0 1 transition). How would the the presence of the third level (-1) state affect this transition? We ...
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How to calculate scattering length for system with particles with different lengths

I am confused by the concepet of scattering length and how to calculate it. Suppose we have a system whose Hamiltonian is: $$\hat{H}=\int\text{d}\vec{r}\left(\hat{a}^{\dagger}\frac{\nabla^{2}}{2m}\hat{...
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How are the wavelengths calculated to hold and combine atoms in optical trapping?

I am reading this article of scientists who combined individual atoms using optical tweezers. One optical tweezer used a 700 nm-wavelength light to hold the sodium atom while the other optical ...
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What system has a spectral series in the radio spectrum?

As an electron energy level has an emission level depending upon the excitation, is it possible for a system such as a Rydberg atom to have emissions in the low side of the frequency range?
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Hypersonic Bose–Einstein condensate

In this nature paper, a BEC is accelerated around a smooth ring-shaped waveguide within a vacuum chamber at UHV. The BEC reaches speeds up to 16 times the condensate's speed of sound. What is the ...
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Doppler cooling limit and the Heisenberg uncertainty limit

In laser cooling, the forces arise because of the discreet momentum exchange between the atoms and the laser field. This exchange of momentum also constitutes a heating mechanism. Relating the heating ...
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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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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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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 ...
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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 ...
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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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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}=\...
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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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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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1 answer
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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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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 ...
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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 "...
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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 ...
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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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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 ...
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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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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 ...
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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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-1 votes
1 answer
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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 ...
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1 answer
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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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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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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-...
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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,\...
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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 ...
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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 ...
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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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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 ...
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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-...
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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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4 votes
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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 ...
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1 answer
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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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1 vote
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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 ...
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$\Delta \ell = 0, \ell = 0 \rightarrow \ell = 0$ 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 ...
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2 votes
1 answer
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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 ...
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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} ...
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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 ...
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5 votes
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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 ...
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12 votes
1 answer
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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 ...
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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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4 votes
2 answers
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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? ...
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