From: bill.sloman@ieee.org   
      
   On 16/02/2026 4:20 am, Stefan Ram wrote:   
   > john larkin  wrote or quoted:   
   >> I recall someone making a laser sort of thing that dispenses a single   
   >> photon periodically.   
   >   
   >    So, the Heisenberg uncertainty principle basically says you can't set   
   >    up a state that's got a perfectly fixed number of photons at a su-   
   >    per well-defined frequency. Still, you can study what are called Fock   
   >    states, or number states, if the light field's spread over a pret-   
   >    ty narrow range of frequencies. In that case, a single-photon emitter   
   >    ends up acting like it's kicking out just one photon.   
   >   
   >    One of the old-school and simplest tricks to get something close to   
   >    single-photon light was just to tone down a normal laser until the   
   >    average number of photons per pulse was tiny. Since laser light fol-   
   >    lows a Poisson distribution, you can actually play with the odds of   
   >    getting one photon versus more than one. Like, if the average pho-   
   >    ton number mu=0.1, about 90% of the pulses have none, roughly 9% have   
   >    one, and around 1% spit out multiple photons.   
   >   
   >    Light from an ideal single-photon source acts totally quantum - it   
   >    shows antibunching, meaning there's always some nonzero delay between   
   >    photon hits. A basic laser doesn't do that; its second-order corre-   
   >    lation function equals one, so no antibunching there. But for stuff   
   >    like quantum cryptography, you need those antibunched photons.   
   >   
   >    A perfect single-photon source still doesn't exist, though. Right now,   
   >    people use things like single molecules, Rydberg atoms, diamond color   
   >    centers, or quantum dots to make single photons, and you can actually   
   >    see their antibunching if you set up the experiment right.   
      
   That's interesting. Have you got a link to more detailed discussion?   
      
   --   
   Bill Sloman, Sydney   
      
   --- SoupGate-Win32 v1.05   
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