Light - stopped or trapped inside a crystal?

[San K]

Light -- stopped or trapped inside a crystal?

In the below experiment:

http://www.extremetech.com/extreme/...-inside-a-crystal-the-basis-of-quantum-memory

Opaque crystal of yttrium silicate doped with praseodymium1. Is light stopped or trapped (i.e. internally reflecting, bouncing off the "walls")?

2. Will quantum coherence be preserved as long as the photon stays inside the crystal?

3. Is light "slowed" in water because of absorption and re-emittance of the photon?

 

[coktail]

Thanks for posting. I have the same question. They also talked about this in the following episode of Radiolab: http://www.radiolab.org/2013/feb/05/

 

[dlgoff]

In the below experiment:

http://www.extremetech.com/extreme/...-inside-a-crystal-the-basis-of-quantum-memory

Opaque crystal of yttrium silicate doped with praseodymium


1. Is light stopped or trapped (i.e. internally reflecting, bouncing off the "walls")?

Do Photons Move Slower in a Solid Medium?

 

[coktail]

I'm bumping this thread in hopes that somebody has an answer regarding this experiment. Thanks!

 

[f.wright]

San K,
Read the Wikipedia article on Electromagnetically induced transparency. You will see that the answer to your question 1 is no. The answer to question 2 is yes. As far as question three goes; when light passes from a medium of lower refractive index to a medium of higher refractive index, the group velocity slows down. This is a completely different optical process from EIT.

 

[Zarqon]

With regards to your specific question f.wright above me answered it correctly, but I can still expand on these results a bit.

Slowed and stopped light of pulses happens when the dispersion profile contains very steep slopes, as the group velocity of a pulse inside a medium depends on the derivative of the group refractive index with respect to frequency. In addition, one can see that while the pulse is being slowed down by this effect, an increasing part of its energy is actually stored in the material. A kind of pseudoparticle is formed, called a polariton, which is a coupled system of a photon and a material excitation. Stopped light is a special case when all of the energy has been converted into the material. Hope that makes things a bit more clear.

 

[San K]

Thanks Zargon, f.wright and coktail.

Good introduction to the term "polariton"

 

[San K]

Stopped light is a special case when all of the energy has been converted into the material.

can the converted energy be held (in the material) for upto to, say, an hour and then later re-converted back as a photon? ...that emits out of the material

 

[Zarqon]

can the converted energy be held (in the material) for upto to, say, an hour and then later re-converted back as a photon? ...that emits out of the material

Yes, in principle it can, it depends on the coherence time of the material. In the quoted paper, the hyperfine levels of Praseodymium is used, which have a max of about 1 minute, which they reach. But there are other rare-earth elements which can be used as well, for example Europium where the theoretical coherence time is several days.