complementarity with single slit diffraction

[DParlevliet]

In Wikipedia "Double slit" the principle of complementarily is defined as "that photons can behave as either particles or waves, but not both at the same time", stating that an interference pattern disappears when the path of the particle is known. But with a single slit you know the path and still the photon diffracts, which is a wave effect. So how is complementarity exactly defined in this case ?

[swansont]

There is diffraction but not the same interference that you get in a double slit. You know that a photon goes through the slit, but the path from the slit to the screen is not known until the photon is detected, so you can still see wave effects.

[DParlevliet]

And when I place a second slit just above the detector. Then, just as with the first slit, I know in advance which path it will take. Still it will have (wave) diffraction at the first slit.

[swansont]

And when I place a second slit just above the detector. Then, just as with the first slit, I know in advance which path it will take. Still it will have (wave) diffraction at the first slit.

 

I don't understand your setup. Just above? Do you mean in front of? If you place a slit immediately in front of the detector, your signal decreases. You don't detect and thus don't know the path of photons that don't pass through the second slit.

[DParlevliet]

Yes, in front of the detector. The first slit also degreases the signal. If you say that you know the path of a photon going through the first slit ( but you don't detect and thus don't know the path of photons that don't pass through the first slit) then it's the same with the second slit. So how does one define exactly "knowing which path"

[swansont]

"Which path" is terminology usually reserved for interference effects of adjacent slits.

 

The detector reacts to individual photons. Putting a slit in front of the detector doesn't have an effect on that, since there is no chance for further diffraction.

[DParlevliet]

Yes, but terminology must be exactly defined. Diffraction is also an interference effect. So if one state that measurements show that knowing through which slit the particle goes does disappear a certain interference effect, then that is right. But if one claims that this is caused by a fundamental principle of complementary, so acts general also outside the double slit, one must define "which path" and "interference" more accurate

[DParlevliet]

The detector reacts to individual photons

Indeed, but a spatial detector shows at the same time particle effects (the absorbed photon as a single pulse) and wave effects (the place where it is absorbed). Also with a double slit a detector shows both the single photons as the interference pattern. With a single slit that is the same, only the inteference looks different (diffraction is also an interference effect).

 

 

Putting a slit in front of the detector doesn't have an effect on that, since there is no chance for further diffraction.

But there is diffraction between the first and second slit.

[swansont]

Indeed, but a spatial detector shows at the same time particle effects (the absorbed photon as a single pulse) and wave effects (the place where it is absorbed). Also with a double slit a detector shows both the single photons as the interference pattern. With a single slit that is the same, only the inteference looks different (diffraction is also an interference effect).

 

 

But there is diffraction between the first and second slit.

 

Yes, exactly. There is diffraction after the first slit. The second slit is placed after that diffraction occurs, and so has no effect on it. The detector does not demonstrate wave effects at all, just the behavior at the point of detection.

[DParlevliet]

But isn't diffraction a wave effect?

[swansont]

Yes, and diffraction is occurring ion the space between the masks, where you haven't localized the photon. If there was space between the mask and the detector, you would also see diffraction. Addingthe second mask doesn;t change anything, since the detector already localizes the photon.

[DParlevliet]

Perhaps I understand. My first confusion was that it is sometimes stated that a photon is a particle or wave but not both at the same time. But a photon always has both particle and wave properties, but they cannot be measured at the same time.

 

According your explanation between slit and detector you don't know exactly the position, so there can be wave effect. Then the detector measures the effect of both particle and wave between slit and detector?

 

What is the cause of this. Is it the fact that a wave and particle classical cannot be combined or can diffraction be calculated with Heisenberg uncertainty?

[swansont]

Perhaps I understand. My first confusion was that it is sometimes stated that a photon is a particle or wave but not both at the same time. But a photon always has both particle and wave properties, but they cannot be measured at the same time.

 

According your explanation between slit and detector you don't know exactly the position, so there can be wave effect. Then the detector measures the effect of both particle and wave between slit and detector?

 

What is the cause of this. Is it the fact that a wave and particle classical cannot be combined or can diffraction be calculated with Heisenberg uncertainty?

 

The cause is, AFAIK, unknown. That's a foundational issue, and the answer lies in metaphysics rather than physics. The problem crops up when you take the phrase this is a particle or this is a wave literally. We don't know what it is. We can describe how it behaves: it behaves as a wave, but with certain particle-like properties (e.g. localization) thrown in under some circumstances.

[DParlevliet]

Thanks, that was what I was looking for. But that makes it vulnerable to interpreting language or (even worse) philosophy or science-religion. In science one must use an exact formula or description.

 

It must be described more precise what excludes what and when. With a single slit a detector measures in the pulse the particle energy and at the same time in the detection position the wave amplitude, so both a particle and a wave property. The "which path" is not an accurate description. As above with one slit I think the path is known, but you don't. But with a double slit with "marked" photons it is told that the path is known, but according your view the path is unknown between slits and detector. So "which path" depends on interpreting language, which is not science.

[swansont]

Thanks, that was what I was looking for. But that makes it vulnerable to interpreting language or (even worse) philosophy or science-religion. In science one must use an exact formula or description.

And science deals with what happens, but not, fundamentally, why it happens.

 

It must be described more precise what excludes what and when. With a single slit a detector measures in the pulse the particle energy and at the same time in the detection position the wave amplitude, so both a particle and a wave property. The "which path" is not an accurate description. As above with one slit I think the path is known, but you don't. But with a double slit with "marked" photons it is told that the path is known, but according your view the path is unknown between slits and detector. So "which path" depends on interpreting language, which is not science.

If there is more than one possible resulting location involving diffraction, the path is not known. A slit forces a particular trajectory by ruling out the other possibility or possibilities. A slit right in front of the detector rules nothing out for a single photon — it's indistinguishable from just having a small detector. There is no distance for a wave to propagate — and that's something that shows up in an equation: the location of a diffraction peak depends on the length from the slit to the screen.

[DParlevliet]

 

If there is more than one possible resulting location involving diffraction, the path is not known. A slit forces a particular trajectory by ruling out the other possibility or possibilities. A slit right in front of the detector rules nothing out for a single photon — it's indistinguishable from just having a small detector. There is no distance for a wave to propagate — and that's something that shows up in an equation: the location of a diffraction peak depends on the length from the slit to the screen.

 

Let us remove the slit in front of the detector. I used it against an argument, but it now confuses. So a single slit and a detector. If a photon is detected, then the detector measures at the same time a particle property and a wave property. So it seems to be possible to measure some wave/particle properties at the same time .

[swansont]

 

Let us remove the slit in front of the detector. I used it against an argument, but it now confuses. So a single slit and a detector. If a photon is detected, then the detector measures at the same time a particle property and a wave property. So it seems to be possible to measure some wave/particle properties at the same time .

 

What wave property is being detected?

[DParlevliet]

The magnitude, which determines the possibility of absorption at that position.

[swansont]

The magnitude, which determines the possibility of absorption at that position.

 

That's number of photons. Amplitude is not inherently a wave property.

[DParlevliet]

I don't mean the detector signal output magnitude, but the amplitude of the wave. This amplitiude is determined by wave formula.

[swansont]

I don't mean the detector signal output magnitude, but the amplitude of the wave. This amplitiude is determined by wave formula.

 

The amplitude is also the number of photons. Having an amplitude is not exclusive to wave behavior. It's signal strength.

[DParlevliet]

Indeed, when you measure more photons, then the detector amplitude is determined both by number of particles and wave. So you measure both particle and wave properties. The amplituide outside the detecter center is caused by wave properties.

[swansont]

Indeed, when you measure more photons, then the detector amplitude is determined both by number of particles and wave. So you measure both particle and wave properties. The amplituide outside the detecter center is caused by wave properties.

 

Yes, amplitude is a property of both. However, if you notice the discrete changes in amplitude, that's a particle property.

[DParlevliet]

 

Yes, amplitude is a property of both. However, if you notice the discrete changes in amplitude, that's a particle property.

What do you mean with change? For instance a single photon is detected outside the center of the detector. This output cannot be expalined by only particle or only wave. One has to use both particle and wave properties/formula, at the same time.

[swansont]

At any point the detection value will increment in discrete values, rather than a continuum.