173986
The variance of the photon number distribution is Using commutation relations , this can be written as This can be written as The second-order intensity correlation function ( for zero delay time ) is defined as This quantity is basically the probability of detecting two simultaneous photons , normalized by the probability of detecting two photons at once for a random photon source .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 None