Laser linewidth in a STIRAP process

In summary, STIRAP is a form of adiabatic passage where the quantum state needs to be preserved. The laser linewidth plays a crucial role in the success of STIRAP, as a broader laser linewidth can lead to lower population transfer efficiency due to loss caused by laser noise. The excited state linewidth also needs to be smaller than the pulse duration to avoid spontaneous decay and maintain the coherence of the system.
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Malamala
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Hello! In a STIRAP process, for the right parameters (assuming a ##\Lambda##-type transition), the lifetime of the excited state doesn't come into play, so one can achieve very narrow linewidths of the measured transition of interest, regardless of the linewidth of the intermediate, excited state. However, I am not sure I understand how does the laser linewidth come into play. I imagine that if the linewidth of the laser is bigger than the splitting between the 2 levels I am connecting (basically if the laser linewidths are bigger than the difference between the 2 laser frequencies) I won't be able to induce STIRAP (right?), so I can't have arbitrary large laser linewidths (unlike the case of the excited state, whose linewidth can in principle can be as large as possible, given that it is usually very far away from the 2 levels I am interested in). So how does the laser linewidth come into play? Is the transition linewidth actually limited by the laser linewdith? Or the laser linewidth doesn't matter as long as it is smaller than the splitting between the 2 levels? Thank you!
 
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Malamala said:
So how does the laser linewidth come into play?
STIRAP is a form RAP (adiabatic passage). Adiabatic passage means that the quantum state needs to be preserved. If your laser linewidth is broader than the splitting between the bottom 2 states, then you will progress into a mixed state as the randomized fluctuation of the laser phase will scramble the phase of the atomic state.

Malamala said:
Or the laser linewidth doesn't matter as long as it is smaller than the splitting between the 2 levels?
The broader the laser linewidth, the lower your population transfer efficiency will be with STIRAP. This is again because of loss as the excited state atoms are randomly shuffled back into the ground state by laser noise.

Malamala said:
unlike the case of the excited state, whose linewidth can in principle can be as large as possible, given that it is usually very far away from the 2 levels I am interested in
This isn't inexactly true. The excited state linewidth has to be smaller than 1 over the pulse duration. Otherwise, you'd see spontaneous decay during your STIRAP pulses, and that has a similar effect of scrambling the coherent state during the adiabatic process. The result would also be atoms returning to the ground state.
 
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1. What is laser linewidth in a STIRAP process?

Laser linewidth refers to the spectral width or range of frequencies that make up a laser beam. In a STIRAP (Stimulated Raman Adiabatic Passage) process, the laser linewidth is an important factor that affects the efficiency and accuracy of the process.

2. How does laser linewidth affect the STIRAP process?

The laser linewidth affects the STIRAP process in two main ways. Firstly, a larger laser linewidth can result in a decrease in the efficiency of the process, meaning that less of the initial population will be transferred to the desired state. Secondly, a smaller laser linewidth can lead to a higher level of precision in the process, resulting in a more accurate transfer of population.

3. What is the ideal laser linewidth for a STIRAP process?

The ideal laser linewidth for a STIRAP process depends on the specific system and parameters being used. In general, a smaller laser linewidth is preferred for higher precision, but it is also important to consider the trade-off with efficiency. A laser linewidth that is too small can also lead to technical challenges and higher costs.

4. How can the laser linewidth be controlled in a STIRAP process?

The laser linewidth can be controlled in a STIRAP process by using a laser with a narrower linewidth, using a laser stabilization system, or using techniques such as spectral filtering or frequency modulation. It is important to carefully consider the system and parameters to determine the most effective method for controlling the laser linewidth.

5. Are there any other factors that can affect the laser linewidth in a STIRAP process?

Yes, there are other factors that can affect the laser linewidth in a STIRAP process. These include temperature fluctuations, mechanical vibrations, and external electromagnetic interference. It is important to carefully design and control the experimental setup to minimize the impact of these factors on the laser linewidth.

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