Laser Cooling: Understanding the Limits of Reaching v=0 in Doppler Cooling

In summary, the conversation discusses the concept of cooling an atom to v=0 and why it is not possible due to random recoil from spontaneous emission and quantum effects. While the average velocity can approach 0, the instantaneous velocity will not due to these factors.
  • #1
Niles
1,866
0
Hi

I keep reading that an atom cannot be cooled to v=0 because of random recoil from spontaneous emission, i.e. a random walk in momentum space.

If it is a random walk, then - on average - we don't have any net motion, i.e. we stay at the initial position. This also holds in momentum space. But if we stay at the same position (on average), then why aren't we able to go to v=0?


Niles.
 
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  • #2
The average velocity can become arbitrarily close to 0, but the instantaneous velocity will not... for the above reasons. That's taking poisson noise into account, but there are also the quantum effects which prevent it.
 

1. What is laser cooling?

Laser cooling is a process in which a group of atoms or molecules are slowed down and cooled to very low temperatures using laser light. This technique is used in many scientific and technological applications, such as creating ultra-cold quantum gases and precision measurements.

2. How does laser cooling work?

Laser cooling works by using the photons (particles of light) emitted by a laser to transfer energy to the atoms or molecules in a sample. As the atoms absorb and then re-emit these photons, their motion is slowed down, resulting in cooling of the sample.

3. What is Doppler cooling?

Doppler cooling is a type of laser cooling that relies on the Doppler effect to slow down atoms or molecules. The Doppler effect is the change in frequency of light or sound waves due to the relative motion between the source and the observer. In Doppler cooling, the laser light is tuned to a frequency slightly lower than the resonance frequency of the atoms, causing the atoms to absorb and emit more photons in the direction of their motion, thus slowing them down.

4. What are the limits of reaching v=0 in Doppler cooling?

The main limitation of reaching v=0 (absolute zero) in Doppler cooling is the existence of a minimum achievable temperature called the Doppler limit. This limit is determined by the initial temperature of the atoms, the intensity and detuning of the laser light, and the properties of the atomic transitions. It is impossible to cool a sample beyond this limit using Doppler cooling alone.

5. What are some applications of laser cooling?

Laser cooling has many important applications in physics, chemistry, and engineering. Some examples include producing Bose-Einstein condensates, which are a state of matter with unique quantum properties, and trapping and manipulating individual atoms for use in quantum computing. Laser cooling is also used in precision measurements, such as in atomic clocks and gravitational wave detectors.

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