# I Is it theoretically possible to measure polariton mass?

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1. Aug 11, 2017

### Habeebe

Take it slow, polaritons are a new concept for me. Anyways, I'm trying to get some intuition for excitation polaritons having mass. Is this a quantity that we could directly measure, at least in theory if not practically? How would we separate the mass of the polariton itself from the mass of the particles that are creating the polariton? Are the things causing polaritons always seperate from the polaritons themselves, or are they sometimes a "part" of the polariton? I'm thinking here specifically of a situation like a photon interacting with some EM field, is the photon still a seperate entity?

Sorry for the barrage. Most of the stuff I've dug up so far is written a little above my pay grade so I'm trying to get a better handle on it.

2. Aug 12, 2017

### ZapperZ

Staff Emeritus
From the way you are asking this ("... How would we separate the mass of the polariton itself from the mass of the particles that are creating the polariton... "), I need to make sure something is clarified first as the starting point. Are you familiar with the concept of "quasiparticles", as in the Fermi Liquid theory?

Zz.

3. Aug 12, 2017

### Habeebe

Not at all. I mean I've heard cliff note's style version of what quasiparticles are, but that's it. I'll look into Fermi Liquid theory.

4. Aug 16, 2017

### DeathbyGreen

A polariton is a quasiparticle like ZapperZ said. A quasiparticle is a collective movement of a bunch of individual particles. Since a quasiparticle is a collective excitation, when we speak about quasiparticle mass we refer to effective mass. When a quasiparticle moves through a medium it causes fluctuations in the spacing of nearby lattice ions and surrounding particles; the size of the fluctuations in a medium a quasiparticle causes is related to its effective mass. If you imagine the quasiparticle as a single particle, and insert it into a lattice, the size of the fluctuations it causes would be due to its (effective) mass.