Cooling Near Absolute Zero: What's Used?

In summary, in order to cool something to near absolute zero temperatures, liquid helium can be used to reach 4 Kelvin, and then elaborate setups using lasers can cool it even further. These setups involve setting the laser frequency just below the frequency at which atoms will absorb it, causing them to be kicked in the opposite direction of their motion and thus slowing them down. This results in an overall cooling of the atoms and a decrease in temperature. The most basic setup involves two opposing laser beams, while more complex setups use three sets of opposing beams in different directions.
  • #1
Stevedye56
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I am aware that absolute zero can not be achieved by cooling a substance since absolute zero is zero-point energy. I was just wondering what is used (coolant wise and apparatus wise) to cool something near this temperature since there some experiments such as the Boise-Einstein Condensates which require near absolute zero temperatures.

-Steve
 
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  • #2
With liquid helium you get down to 4 Kelvin. After that elaborate set ups cool it even further using lasers. Instead of a laser heating up the gas, it is actually taking heat away.
 
  • #3
I believe heat can be extracted letting for instance liquid hydrogen evaporate on the surface of the container. The evaporation is endothermic and will absorb some of the energy from whatever you want to cool. I'm not quite clear on how to cool something with a laser as a laser will add energy rather than take it away...
 
  • #4
The lasers are set up in such a way so that on average they kick the atoms in direction opposite of the atomic velocity i.e. cooling them.

That is achieved by setting the laser frequency a little below the frequency at which the atoms will absorb it. That way, only atoms moving AGAINST the laser light will see it dopler shifted to the right higher frequency, absorb it and get a kick in direction opposite of their motion.

In this way, on average, atoms get more absorbtion kicks opposite to their motion. Of course, later they reemit the light by spontaneous emission but the kicks of the spontaneous emission have no preferred direction. The result is on average, atoms are kicked opposite of their motion and slowed down. Since temperature is a measure of the atomic translational kinetic energy, the atomic gas is cooled down.

The most basic set up is two laser beams opposing each other and cooling in two opposite directions and the atomic sample in the middle. More elaborate set up is 3 couples of opposite beams along the X, Y, Z directions.
 
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  • #5
smallphi said:
The lasers are set up in such a way so that on average they kick the atoms in direction opposite of the atomic velocity i.e. cooling them.

That is achieved by setting the laser frequency a little below the frequency at which the atoms will absorb it. That way, only atoms moving AGAINST the laser light will see it dopler shifted to the right higher frequency, absorb it and get a kick in direction opposite of their motion.
Thank you. That is an extremely succinct explanation of something that was heretofore a mystery to me.
 
  • #6
smallphi said:
The lasers are set up in such a way so that on average they kick the atoms in direction opposite of the atomic velocity i.e. cooling them.

That is achieved by setting the laser frequency a little below the frequency at which the atoms will absorb it. That way, only atoms moving AGAINST the laser light will see it dopler shifted to the right higher frequency, absorb it and get a kick in direction opposite of their motion.

In this way, on average, atoms get more absorbtion kicks opposite to their motion. Of course, later they reemit the light by spontaneous emission but the kicks of the spontaneous emission have no preferred direction. The result is on average, atoms are kicked opposite of their motion and slowed down. Since temperature is a measure of the atomic translational kinetic energy, the atomic gas is cooled down.

The most basic set up is two laser beams opposing each other and cooling in two opposite directions and the atomic sample in the middle. More elaborate set up is 3 couples of opposite beams along the X, Y, Z directions.


Thanks, that was a great explanation. :biggrin:
 

FAQ: Cooling Near Absolute Zero: What's Used?

What is absolute zero?

Absolute zero is the theoretical temperature at which all thermal motion ceases, also known as 0 Kelvin or -273.15 degrees Celsius. It is considered to be the lowest possible temperature in the universe.

What is used to cool objects near absolute zero?

Objects near absolute zero are typically cooled using a combination of techniques such as laser cooling, evaporative cooling, and magnetic cooling. Some common cooling agents used include helium-3, helium-4, and liquid nitrogen.

What is laser cooling?

Laser cooling is a technique that uses lasers to slow down and cool the motion of atoms or molecules. This is accomplished by tuning the laser to a specific frequency that corresponds to the energy level of the atom or molecule, causing it to absorb and emit photons and lose energy in the process.

What is evaporative cooling?

Evaporative cooling is a process in which a liquid is converted into a gas, absorbing heat energy in the process and cooling the surrounding environment. This is often used in combination with other cooling techniques to reach temperatures close to absolute zero.

What is magnetic cooling?

Magnetic cooling is a process that uses a magnetic field to manipulate the spin of atoms or molecules, causing them to lose energy and cool down. This technique is commonly used in combination with other cooling methods to achieve extremely low temperatures.

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