Double Slit Experiment: Exploring Quantum Physics for Advanced Amateurs

In summary: Zz.In summary, the speaker has an advanced amateur's understanding of quantum physics, but is confused by the usage of the 'double slit experiment' to explain classical and quantum behaviors. They question how we can be sure that only a single particle is being emitted at a time in the experiment and if there are devices that can reliably detect a single photon. They also mention the use of entanglement experiments and the importance of accurate detector calibration.
  • #1
jeffceth
40
0
I have an advanced amateur's(if there is such a thing) grasp of the concepts of quantum physics. However, the typical usage of the 'double slit experiment' to explain an observation of the differences between classical and quantum behaviours confuses me.

The specific case, of course, is when only a single particle is shot at the two slits and yet, over time, a compendium of such cases will retain the pattern of cancellation and reinforcement found with a large number of 'simultaneous' particles. My question is this: how can we, in fact, be sure that only a single particle is being emitted at a time in our experiment? Presumably there would be a high degree of uncertainty associated with such a precise declaration, wouldn't there?

For the record, I happen to think quantum theory is a pretty good approximation of our observed phenomena, I just don't completely understand this example.


sincerely,
thatwouldbeme
 
Physics news on Phys.org
  • #2
jeffceth said:
My question is this: how can we, in fact, be sure that only a single particle is being emitted at a time in our experiment? Presumably there would be a high degree of uncertainty associated with such a precise declaration, wouldn't there?

No, you would detect one particle at a time. The pattern that results from many particles then shows the interference.
 
  • #3
This is an example of what DrChinese is describing.

http://www.optica.tn.tudelft.nl/education/photons.asp

We can deduce that one photon passes through at a given time from the calculation of how many photons are there per second and, on avarage, the separation between them. Since the equipment is not several kilometers long by orders of magnitude, it is a safe bet that on average, one has only one photon at a time passing through the slits.

Zz.
 
Last edited by a moderator:
  • #4
ZapperZ said:
This is an example of what DrChinese is describing.

http://www.optica.tn.tudelft.nl/education/photons.asp

We can deduce that one photon passes through at a given time from the calculation of how many photons are there per second and, on avarage, the separation between them. Since the equipment is not several kilometers long by orders of magnitude, it is a safe bet that on average, one has only one photon at a time passing through the slits.

Zz.


I understand that we can calculate the average distance between photons and suppose it is the actual distance, but wouldn't the nature of quantum physics itself suggest that because in whatever medium the photons are being produced it requires a minimum charge to release a photon at all we essentially have the equivalent of a huge bank of capacitors charging up and releasing, which might tend to drastically increase simultaneous emissions if the energy source had any sort of wave period to it? Generally speaking, what sort of mechanisms might one employ to reduce the possibility of such an effect?

sincerely,
thatwouldbeme


p.s. DrChinese: do we really have devices that will reliably detect a single photon? In practice it seems we usually have to use a photon multiplier in order to measure what we suppose to be single-photon events.
 
Last edited by a moderator:
  • #5
jeffceth said:
I understand that we can calculate the average distance between photons and suppose it is the actual distance, but wouldn't the nature of quantum physics itself suggest that because in whatever medium the photons are being produced it requires a minimum charge to release a photon at all we essentially have the equivalent of a huge bank of capacitors charging up and releasing, which might tend to drastically increase simultaneous emissions if the energy source had any sort of wave period to it? Generally speaking, what sort of mechanisms might one employ to reduce the possibility of such an effect?

I have no idea what you just said. If I use a laser (which is what is used in the experiment that I cited in the link), where is the "bank of capacitors" here?

Zz.
 
  • #6
jeffceth said:
how can we, in fact, be sure that only a single particle is being emitted at a time in our experiment?
do we really have devices that will reliably detect a single photon?
Basically you’re questioning the ability of experimentalist’s hardware capabilities. To be sure they test them to build reliable methods. Low but uniform power output - into Filter densities and or crossed polar filters to bring the photon rate down. Lots of test exposures or Detector counts to confirm they can reliably produce one photon per some unit of time, whatever. Statistically you may have a chance of two coming close together. To avoid that issue, the problem becomes how fast can you send them to avoid having two come out together. After all it can be a long slow tedious work made worse if you insist on say one photon per minute. You want the highest rate that still works correctly by never sending two at once. Theoreticians need to trust the experimenters, and they do that by verifying the work. And even then getting it repeated by someone else.

Detecting a single photon?
As you say you have a grasp of the concepts of quantum physics, then you must know some about entanglement experiments. Those very much depend on testing correlations of detections of individual photons or particles don’t they?
 
  • #7
jeffceth said:
p.s. DrChinese: do we really have devices that will reliably detect a single photon? In practice it seems we usually have to use a photon multiplier in order to measure what we suppose to be single-photon events.

Oh, absolutely. They can be calibrated to extremely high accuracy. In fact, entanglement is now routinely used to actually assist in detector calibration and analysis of detector efficiency and accuracy because of experiments like this one:

P. Grangier, G. Roger, and A. Aspect, "Experimental evidence for a photon anticorrelation effect on a beam splitter: A new light on single-photon interferences," Europhys. Lett. 1, 173-179 (1986).

To quote the authors: "A single photon can only be detected once." Using PDC, this is done routinely these days; check out this PDF of an undergraduate experiment that replicates the above: http://marcus.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf . To many standard deviations of accuracy, individual photons are detected within time windows that support theoretical predictions. Check out the article to see how this is done. There are articles out there - I don't have a reference at my fingertip - that explain in greater detail how manufacturers rate their detectors and insure that they perform as described.
 
Last edited by a moderator:
  • #8
Of course, entanglement. Yeah, I should have known that. I pretty much should have been able to answer that myself. Thanks for taking the time though, guys! I guess ultimately even with a high probability of multiple photon incidents the highest cancellation zones would still fail to get pretty much any hits, where as we would expect a large number of the single-photon cases to hit there otherwise, so it doesn't take a whole lot to produce a statistically significant result in that way, too.
 
  • #9
jeffceth said:
even with a high probability of multiple photon incidents the ...
I doubt a good experamenter would accept that, and would only use a very low probablity of multiple photons.
 

Related to Double Slit Experiment: Exploring Quantum Physics for Advanced Amateurs

1. What is the double slit experiment?

The double slit experiment is a fundamental experiment in quantum physics that demonstrates the wave-particle duality of light and matter. It involves shining a beam of particles or light through two parallel slits and observing the resulting interference pattern on a screen behind the slits.

2. Why is the double slit experiment important?

The double slit experiment is important because it provides evidence for the wave-particle duality of quantum objects. This means that particles, such as electrons, can exhibit properties of both waves and particles. This has significant implications for our understanding of the behavior of matter at the smallest scales.

3. What are the possible outcomes of the double slit experiment?

The possible outcomes of the double slit experiment depend on whether the experiment is performed with particles or light. If performed with particles, the outcome will be a pattern of interference fringes, indicating the wave-like behavior of the particles. If performed with light, the outcome will be a diffraction pattern, also indicating the wave-like behavior of light.

4. Can the double slit experiment be performed with macroscopic objects?

No, the double slit experiment can only be performed with quantum objects, such as electrons or photons. This is because macroscopic objects are too large and complex to exhibit the wave-like behavior observed in the experiment.

5. How does the double slit experiment relate to the uncertainty principle?

The double slit experiment is closely related to the uncertainty principle, which states that the more precisely we know the position of a particle, the less precisely we can know its momentum, and vice versa. In the double slit experiment, the act of measuring the position of a particle at the slits changes its momentum, resulting in the observed interference pattern.

Similar threads

  • Quantum Physics
2
Replies
36
Views
3K
Replies
42
Views
2K
  • Quantum Physics
Replies
14
Views
2K
  • Quantum Physics
2
Replies
49
Views
3K
Replies
60
Views
3K
Replies
3
Views
950
  • Quantum Physics
Replies
17
Views
1K
  • Quantum Physics
Replies
2
Views
744
  • Quantum Physics
Replies
19
Views
1K
  • Quantum Physics
Replies
4
Views
882
Back
Top