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I want to create a 1 meter BEC


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15 minutes ago, swansont said:

You’re just trolling me now. 

My bad @@, I will answer this myself, with a supporting article(no procedure though it is pop sci). https://physicsworld.com/a/taming-light-with-cold-atoms/

"What we did was to cool sodium atoms to just 50 billionths of a degree above absolute zero and then illuminate them with a carefully tuned laser beam. This “coupling laser” changed the optical properties of the atoms so dramatically that when a separate laser pulse was sent through the cloud of atoms, its speed was reduced by a factor of some 20 million. The size of the light pulse was also affected, shrinking from 1 km in free space to only 0.05 mm inside the medium. The pulse was then completely contained within the 0.1 mm long, cigar-shaped ultracold-atom cloud."

It seems two lasers are used, one to change the optical property and another one as light storage. This is a bit different from the rubidium method.

P.S. I am calling it a day. I will drop by to learn more science from you guys in a bit.

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If you are so knowledgable about BEC why don't you share your science? You think a video from Harvard Institute is sci-fi?

No you are trying to cool down the precession with atom's rotational frequency absorption of electromagnetic radiation, IOW make the atom spin slower. Laser cooling does not cause confinement, bu

Then you should do that.

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3 hours ago, fredreload said:

My bad @@, I will answer this myself, with a supporting article(no procedure though it is pop sci). https://physicsworld.com/a/taming-light-with-cold-atoms/

"What we did was to cool sodium atoms to just 50 billionths of a degree above absolute zero and then illuminate them with a carefully tuned laser beam. This “coupling laser” changed the optical properties of the atoms so dramatically that when a separate laser pulse was sent through the cloud of atoms, its speed was reduced by a factor of some 20 million. The size of the light pulse was also affected, shrinking from 1 km in free space to only 0.05 mm inside the medium. The pulse was then completely contained within the 0.1 mm long, cigar-shaped ultracold-atom cloud."

It seems two lasers are used, one to change the optical property and another one as light storage. This is a bit different from the rubidium method.

No, it isn’t. The technique is called electromagnetically induced transparency (EIT). The problem here is that the article you read was filtered through the reporter and watered down. Information was omitted. But you won’t notice this if you lack understanding of the physics involved. You just see the buzzwords, and compare them to other buzzwords.

It’s like using Cliff Notes for literature. Reading a summary of the book rather than the book itself. 

There are difference between the experiments, but AFAIK using EIT is not one of the differences. (it would be nice to check, but you need to link to journal papers or the ArXiv preprint to see those details)

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On 2/5/2021 at 11:30 PM, swansont said:

No, it isn’t. The technique is called electromagnetically induced transparency (EIT). The problem here is that the article you read was filtered through the reporter and watered down. Information was omitted. But you won’t notice this if you lack understanding of the physics involved. You just see the buzzwords, and compare them to other buzzwords.

It’s like using Cliff Notes for literature. Reading a summary of the book rather than the book itself. 

There are difference between the experiments, but AFAIK using EIT is not one of the differences. (it would be nice to check, but you need to link to journal papers or the ArXiv preprint to see those details)

Hmm, my guess for the term atomic resonance is that the atom has to be locked in it position first, then apply resonance frequency say 500MHz to slow it down. For example, MRI(magnetic resonance imaging), there is also the term resonance in it, but since the water molecules are already locked inside the body, it becomes easier to lined them up with the magnetic field and apply the radio wave frequency afterward. Same goes for the magneto-optical trap, the 780nm laser is there as a doppler shift to counteract the bulk majority of the momentum of the gas particle, also the other side of the laser, leaving 500MHz acting as its resonance frequency. Let me know if my assumption is correct.

So I could have 780nm on one side of the laser and the other side laser has 780nm-500MHz to work with(I know one is wavelength and one is frequency, but just bear with me).

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42 minutes ago, fredreload said:

Hmm, my guess for the term atomic resonance is that the atom has to be locked in it position first, then apply resonance frequency say 500MHz to slow it down. For example, MRI(magnetic resonance imaging), there is also the term resonance in it, but since the water molecules are already locked inside the body, it becomes easier to lined them up with the magnetic field and apply the radio wave frequency afterward. Same goes for the magneto-optical trap, the 780nm laser is there as a doppler shift to counteract the bulk majority of the momentum of the gas particle, also the other side of the laser, leaving 500MHz acting as its resonance frequency. Let me know if my assumption is correct.

So I could have 780nm on one side of the laser and the other side laser has 780nm-500MHz to work with(I know one is wavelength and one is frequency, but just bear with me).

This is pretty much all wrong

An atom doesn’t have to be locked in position - you’re trying to slow it down! It’s moving!

The resonance frequency is not 500 MHz, as I have stated multiple times

MRI and trapping are very different, yet you continue to represent them as almost interchangeable 

A laser is not “there as a doppler shift” - that makes no sense. Neither does “other side of the laser, leaving 500MHz acting as its resonance frequency”

You aren’t going to piece this together without understanding the fundamentals on which it’s based, and it’s pretty obvious you don’t.

 

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1 hour ago, swansont said:

This is pretty much all wrong

An atom doesn’t have to be locked in position - you’re trying to slow it down! It’s moving!

The resonance frequency is not 500 MHz, as I have stated multiple times

MRI and trapping are very different, yet you continue to represent them as almost interchangeable 

A laser is not “there as a doppler shift” - that makes no sense. Neither does “other side of the laser, leaving 500MHz acting as its resonance frequency”

You aren’t going to piece this together without understanding the fundamentals on which it’s based, and it’s pretty obvious you don’t.

 

Ya, else there would be CoM motion. Have you tried something of a higher frequency like x-ray? It is like trying to stop a spinning globe on 6 sides.

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13 minutes ago, fredreload said:

Ya, else there would be CoM motion. Have you tried something of a higher frequency like x-ray?

Why would you? Do you have any physics reason for this? 

 

13 minutes ago, fredreload said:

It is like trying to stop a spinning globe on 6 sides.

No, not so much.

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14 minutes ago, swansont said:

Why would you? Do you have any physics reason for this?

Well, if I shown a flash light in 6 directions with sodium atoms inside a vacuum in a dark room would it work @@?

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29 minutes ago, fredreload said:

Well, if I shown a flash light in 6 directions with sodium atoms inside a vacuum in a dark room would it work @@?

No.

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3 hours ago, swansont said:

Why would you? Do you have any physics reason for this?

The atoms or if I use as an example the water molecules pretty much absorb light of all wavelength ranging from radio wave to gamma ray(perhaps), the important part is you want to lock the atom in place, like trying to stop a spinning globe in place, so if the wavelength is too long, like if I touch the globe once every second, it would not stop as oppose to using an x-ray(the shorter the wavelength the better), the thing is it needs to be applied in equal from six directions(if not 8), or else it would get push around in the opposite direction of the laser. So alignment is very important.

If you decide to switch to incandescent/black body radiation to light up the atoms it could work, but you still need good lasers' alignment from all directions(so you need some type of filter to get a coherent light beam). Wish you luck

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11 hours ago, fredreload said:

Why not?

Why do you think it would?

 

9 hours ago, fredreload said:

The atoms or if I use as an example the water molecules pretty much absorb light of all wavelength ranging from radio wave to gamma ray(perhaps),

But we were talking about a vapor of alkali atoms.

9 hours ago, fredreload said:

the important part is you want to lock the atom in place, like trying to stop a spinning globe in place,

Spinning and translating are not the same thing. They are orthogonal degrees of freedom. 

9 hours ago, fredreload said:

so if the wavelength is too long, like if I touch the globe once every second, it would not stop as oppose to using an x-ray(the shorter the wavelength the better),

That’s a matter of how often you interact, not the frequency of the light. Absorbing a photon is a single event.

9 hours ago, fredreload said:

the thing is it needs to be applied in equal from six directions(if not 8), or else it would get push around in the opposite direction of the laser. So alignment is very important.

Pushed in the opposite direction of the laser? That would violate conservation of momentum.

9 hours ago, fredreload said:

If you decide to switch to incandescent/black body radiation to light up the atoms it could work,

No.

9 hours ago, fredreload said:

but you still need good lasers' alignment from all directions(so you need some type of filter to get a coherent light beam). Wish you luck

Alignment and coherence are very different things.

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14 hours ago, swansont said:

Why do you think it would?

Well, visible light/flash light is 780nm, precisely the range for lighting up rubidium atoms. Although flash lights are not as precise and coherent than lasers. But you could create a magneto-optic trap with flash lights.

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But we were talking about a vapor of alkali atoms.

Alkali atoms also absorb a wide range of electromagnetic radiation including x rays.

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Spinning and translating are not the same thing. They are orthogonal degrees of freedom. 

You are trying to stop both the rotation and  translation from 6 sides. Imagine tapping a balloon from 6 sides.

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That’s a matter of how often you interact, not the frequency of the light. Absorbing a photon is a single event.

Ya, but the amount of photons it absorbs varies with the frequency of light. I got an article here to prove just the case, and I will make a summary below.

"The absorbed radiation is quickly emitted by the atom, either through stimulated emission or spontaneous emission. Stimulated emission occurs in the same direction as the absorption, and the recoil effect accelerates the atom back to its original velocity so that the absorption and emission effects cancel. Spontaneous emission, on the other hand, results in a random emission of a photon (and hence recoil of the atom) in any direction, with the net effect that, on average, the atom slows down in the direction of the absorption.z
For a typical sodium atom, the initial velocity in the atomic beam is about 1000 m·s−1 and the velocity change per photon absorbed is 3 cm·s−1. This means that the sodium atom must absorb and spontaneously emit over 3 × 104 photons to be stopped. It can be shown that the maximum rate of velocity change for an atom of mass m with a photon of frequency v is equal to hv/2mc where h and c are Planck's constant and the speed of light, and τ is the lifetime for spontaneous emission from the excited state. For sodium, this corresponds to a deceleration of about 106 m·s−2. This should be sufficient to stop the motion of 1000 m·s−1 sodium atoms in a time of approximately 1 ms over a distance of 0.5 m, a condition that can be realized in the laboratory."
 
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The spontaneous emission implies there's a lower limit to the average velocity of an atom that you can achieve, so a limit to the cooling. Even if absorption brought an atom to complete rest, re-emission would propel it in a random direction.

1 hour ago, fredreload said:

Well, visible light/flash light is 780nm, precisely the range for lighting up rubidium atoms. Although flash lights are not as precise and coherent than lasers. But you could create a magneto-optic trap with flash lights.

Why might a laser be preferred over a flashlight? What are some problems you might run into using a flashlight? By the way, how many atoms are you cooling? How dense is this cloud?

1 hour ago, fredreload said:

Alkali atoms also absorb a wide range of electromagnetic radiation including x rays.

You could also try a microwave oven, to bombard it with microwaves. You could add a toaster, and let it absorb infrared. But will that cause spontaneous emission like in what you quoted? And how do you get the atoms moving toward these heat sources to preferentially absorb the light? Why does resonance matter, in what gets absorbed and what is emitted, if the atoms can simply absorb light of many different wavelengths?

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2 hours ago, md65536 said:

Why might a laser be preferred over a flashlight? What are some problems you might run into using a flashlight? By the way, how many atoms are you cooling? How dense is this cloud?

I am cooling a 1 meter BEC so I prefer flash lights @@, although I might go with x rays because it has a higher frequency(both can be produced in large quantities).

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You could also try a microwave oven, to bombard it with microwaves. You could add a toaster, and let it absorb infrared. But will that cause spontaneous emission like in what you quoted? And how do you get the atoms moving toward these heat sources to preferentially absorb the light? Why does resonance matter, in what gets absorbed and what is emitted, if the atoms can simply absorb light of many different wavelengths?

Microwave would not work, you need something shorter than 780nm to keep the atoms in place. Microwave only has a milimeter wavelength(see below).

1920px-EM_spectrum.svg.png

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5 hours ago, fredreload said:

You are trying to stop both the rotation and  translation from 6 sides. Imagine tapping a balloon from 6 sides.

 

You keep mentioning "all 6 directions" as though 6 was some magic number.

 

Do you not realise the basic mechanics that momentum directed along 2 of those 6 directions cannot affect spin?

You are just throwing things out without thinking them through.

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1 hour ago, studiot said:

 

You keep mentioning "all 6 directions" as though 6 was some magic number.

 

Do you not realise the basic mechanics that momentum directed along 2 of those 6 directions cannot affect spin?

You are just throwing things out without thinking them through.

Tapping on 6 sides has a brake effect on the CoM motion of the atoms, I said rotation(CoM motion) not spin.

P.S. Would it have a brake effect @@? This is a bit of a speculation

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1 hour ago, fredreload said:

Tapping on 6 sides has a brake effect on the CoM motion of the atoms, I said rotation(CoM motion) not spin.

P.S. Would it have a brake effect @@? This is a bit of a speculation

Does it ?

Take a ball such as the Earth, which has a spin about its axis and a rotation in the plane of the ecliptic.

All rotations are planar motions so adding or subtracting momentum perpendicular to this plane make no difference to the rotation ie no braking effect for 2 of the four possible directions.

Also 'tapping' the Earth at the north and south poles, along the line of the spin axis does not affect the spin.

That leaves 4 direction out of 6 as I said.

 

Have you not mentioned spin reduction here ?

On 2/3/2021 at 4:40 PM, fredreload said:

No you are trying to cool down the precession with atom's rotational frequency absorption of electromagnetic radiation, IOW make the atom spin slower.

 

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55 minutes ago, studiot said:

Does it ?

Take a ball such as the Earth, which has a spin about its axis and a rotation in the plane of the ecliptic.

All rotations are planar motions so adding or subtracting momentum perpendicular to this plane make no difference to the rotation ie no braking effect for 2 of the four possible directions.

Also 'tapping' the Earth at the north and south poles, along the line of the spin axis does not affect the spin.

That leaves 4 direction out of 6 as I said.

 

Have you not mentioned spin reduction here ?

 

Then how do you propose we slow down the rotation of the atoms = =? Or does it not matter for laser cooling?

P.S. I was thinking the stimulated emission recoil would brake(atomic friction) it, I could be wrong

P.S. For instance I got a rotating metal ball, I use a magnet to push it on both sides, it would slow down right? But such might not apply on an atomic scale

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1 hour ago, fredreload said:

Then how do you propose we slow down the rotation of the atoms = =? Or does it not matter for laser cooling?

 

Still considering basic mechanics.

You have correctly distinguished between rotation and spin.

Do you understand the difference ?

Gaseous atoms do not rotate. But they do spin. They have no internal axis to rotate or tumble about, unlike molecules. They do not rotate about external axes because their motion is random.

Gaseous molecules can spin, they can also rotate about non centroidal axes within the molecule, but they do not rotate about external centres as their motion, like that of atoms is random.

You should also reconsider your proposal for momentum transfer in slowing things down.
The  direction of impact in relation to the centre of rotation will determine its ability to affect rotation about internal or external axes and to affect spin.
 

However this is just a coarse classical start.

The next step is to realise that with atoms and some extent molecules the mechanics is more subtle because both have structure.

Since in a semi classical analysis you have spinning electrons orbiting a massive nucleus, like the Earth and the Sun, you have angular momentum for both spin and rotation combined.
This situation becomes at the same time both simpler and more complicated/difficult when you consider photon atom/molecule interaction because the scale of things is such that you need to move to quantum mechanics to obtain correct models of the interactions.
It is these interactions you need to consider here.

However it is you proposal and your thread so it is up to you to work through the detail, rather than just guess.

 

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9 hours ago, fredreload said:

Well, visible light/flash light is 780nm, precisely the range for lighting up rubidium atoms. Although flash lights are not as precise and coherent than lasers. But you could create a magneto-optic trap with flash lights.

780 is in the infrared, and flashlights are not single-frequency 

 

9 hours ago, fredreload said:

Alkali atoms also absorb a wide range of electromagnetic radiation including x rays.

Specific frequencies over a wide range. The absorption spectrum is discrete. A couple of wavelengths in the visible, at best.

The ionization energy of Rb is a little over 4 eV. x-rays would remove an electron.

 

9 hours ago, fredreload said:

You are trying to stop both the rotation and  translation from 6 sides. Imagine tapping a balloon from 6 sides.

What rotation?

 

9 hours ago, fredreload said:

Ya, but the amount of photons it absorbs varies with the frequency of light. I got an article here to prove just the case, and I will make a summary below.

Yes, and nothing you’ve presented thus far addresses this.

9 hours ago, fredreload said:
"The absorbed radiation is quickly emitted by the atom, either through stimulated emission or spontaneous emission. Stimulated emission occurs in the same direction as the absorption, and the recoil effect accelerates the atom back to its original velocity so that the absorption and emission effects cancel. Spontaneous emission, on the other hand, results in a random emission of a photon (and hence recoil of the atom) in any direction, with the net effect that, on average, the atom slows down in the direction of the absorption.z
For a typical sodium atom, the initial velocity in the atomic beam is about 1000 m·s−1 and the velocity change per photon absorbed is 3 cm·s−1. This means that the sodium atom must absorb and spontaneously emit over 3 × 104 photons to be stopped. It can be shown that the maximum rate of velocity change for an atom of mass m with a photon of frequency v is equal to hv/2mc where h and c are Planck's constant and the speed of light, and τ is the lifetime for spontaneous emission from the excited state. For sodium, this corresponds to a deceleration of about 106 m·s−2. This should be sufficient to stop the motion of 1000 m·s−1 sodium atoms in a time of approximately 1 ms over a distance of 0.5 m, a condition that can be realized in the laboratory."

As I said, I’ve been doing this for a while, so I hope you didn’t post this to educate me.

Now, the big question: did you understand any of this, and can you apply it?

Can you see how it doesn’t mention rotation? Can you see how the slowing takes a half a meter, so a lower scatter rate or momentum of the photon by more than a factor of 2 means you can’t do this in a 1 meter system? (so a momentum a factor of tens of thousands smaller means this is impossible for RF)

1 hour ago, fredreload said:

Then how do you propose we slow down the rotation of the atoms = =? Or does it not matter for laser cooling?

It does not matter. The atoms are not rotating. 

 

49 minutes ago, studiot said:

Gaseous atoms do not rotate. But they do spin. They have no internal axis to rotate or tumble about, unlike molecules. They do not rotate about external axes because their motion is random.

I would say they have spin, but it’s quantized, and not physical spin. It’s not something that is being reduced, so fredreload bringing it up repeatedly is based on misconceptions 

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Can you see how the slowing takes a half a meter, so a lower scatter rate or momentum of the photon by more than a factor of 2 means you can’t do this in a 1 meter system? (so a momentum a factor of tens of thousands smaller means this is impossible for RF)

Yes, I've known for a long time you cannot apply RF in this system since the post I mentioned x ray = =, but thanks still

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780 is in the infrared, and flashlights are not single-frequency 

Does it have to be the same frequency @@? It would be easy to apply a filter though

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14 minutes ago, fredreload said:

Yes, I've known for a long time you cannot apply RF in this system since the post I mentioned x ray = =, but thanks still

The fact that you are mentioning anything other than the D2 resonance suggests you don’t understand how it works.

14 minutes ago, fredreload said:

Does it have to be the same frequency @@? It would be easy to apply a filter though

Yes. If you have to ask, or think a filter would work, you don’t understand what’s going on.

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59 minutes ago, swansont said:

Yes. If you have to ask, or think a filter would work, you don’t understand what’s going on.

Something like an optical filter, but the light could be scattered meaning it goes in all random directions like a shot gun. You're saying this won't work because it is scattered?

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13 minutes ago, fredreload said:

Something like an optical filter, but the light could be scattered meaning it goes in all random directions like a shot gun. You're saying this won't work because it is scattered?

You want the light going to the atoms in a collimated beam, so what does scattering it in all directions get you?

 

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