Wednesday, June 29, 2011

Experimental Evidence for Photons

Atoms give off and absorb quantized amounts of energy.  Most people assume that light comes in quantized amounts of energy called photons.  But what if there is only waves and matter just absorbs quantized amounts of energy?  Maybe the energy absorbed came from many different directions and just happen to add together at that point to the right amount for that atom to change states?

Photon detectors go off rapidly even in complete darkness.  They are in fact rated with a dark count rate.  Random thermal noise sets off a photon detector that is supposed to only detect photons of a certain frequency.  Since the energy states of atoms are quantized, a photon detector would receive a quantum of energy, even if the source was not quantized.  If random thermal noise can add together to trip the photon detector, then why can't some real input and some random thermal noise also trip the photon detector?   Anyway, that a photon detector is discrete does not prove photons exist.

So I would like to see solid experimental evidence that photons are real and not just a useful way of thinking about light.   Here is one experiment that would be interesting. 
Imagine the single photon source is generating a photon every 1 ms.  The two photon detectors have synchronized their clocks and digitally record the times of each photon detection event (I am told this is called "time-tagged mode measurement").   After running for awhile we can analyze the data.  It should be clear where the 1 ms clock comes down in the data and we can discard dark count detections off of this time.  We also need to discard data shortly after dark count events as it takes the detectors awhile to recover from a detection and we want data from when both were ready.  Then with the remaining data we see how often when one detector goes off the other also goes off.   If photons are real and we have a single photon source, then when one detector goes off the other should not go off.   If light is really just waves then when one detector goes off it should not reduce the chances of the other going off in that time slot.

Some experiments have used heavily attenuated light sources and then asserted that they were single photon at a time sources.  This is not totally correct.  It would be much better to use the new true single photon source devices.

There have been experiments similar to mine but using beam splitters instead of fibers.  However, it might be that at single photon energy levels a beam splitter either sends the energy one way or the other but not both.  So maybe the beam splitters have made it look like there are photons.  This is why I think my experiment with fibers is worth doing, if it has not already been done.

A single-photon avalanche diode is a photon detector in silicon, so the prices are getting affordable.   A quantum-dot makes a real single photon source.  This is also in silicon and so prices are getting reasonable.  So the equipment to do this experiment is getting better and cheaper.

Some experiments show that the energy a single electron can give off or absorb is proportional to the frequency.  This is the E=hf formula.  Most interpret this to indicate that photons are real and quantized but I think this could also just be a property of matter.  It might not say anything about how energy is transported.    So I find these experiments not conclusive.

After 100 years of believing in photons there should be some good experimental evidence.   Does anyone know any?   I would pay $200 US for the first link in these comments to an experiment published openly on the net (no pay access stuff) that is as convincing to me as the above experiment would be (no beam splitter, not just E=hf).  If someone has a single photon source and two photon detectors and would be willing to do my experiment for some modest funding please contact me.

One very good experiment uses a beam splitter but is able to show either anti-correlation or interference after the beam splitter when at single photon energy levels.

A second very good experiment is Quantum transduction of telecommunications-band single photons from a quantum dot by frequency upconversion.

I still think my experiment would be simpler and more conclusive.

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