7 ms·

Double-Slit Experiment Carried Out with 114-Atom Molecules

77 points by mikecane 15y ago

pmjordan 15y ago
Slightly more info (and fewer distasteful ads) here: http://www.livescience.com/19268-quantum-double-slit-experiment-largest-molecules.html http://www.livescience.com/19268-quantum-double-slit-experim...
yread 15y ago
Here is the original paper: http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2012.34.html http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano... They used "derivatives of phthalocyanine molecules" with 1298 AMU. The methods how they got the results (for example making a slit 10 nm wide) seem to be even more interesting than the result
- jessriedel 15y ago
  The same group had already published last summer about interfering 6000 amu molecules. http://www.nature.com/ncomms/journal/v2/n4/full/ncomms1263.html http://www.nature.com/ncomms/journal/v2/n4/full/ncomms1263.h... The interesting aspect of the OP experiment appears to be that they have a real-time movie.
simonh 15y ago
Call me when they repeat the experiment with cats.
Jabbles 15y ago
"Researchers were puzzled"... - I doubt they were, "Softpedia". This is entirely expected and in line with all previous results. For example http://physicsworld.com/cws/article/news/2952 http://physicsworld.com/cws/article/news/2952 That's not to say it was a waste by any means - the techniques used will hopefully be useful to other scientists, and confirmation is always good :)
- dhimes 15y ago
  It will be fascinating to see the transition between the small, definitely-quantum realm, and the intermediate, quantum-effects-get-washed-out-by-X realm. X = ? Size? Internal entropy?
  - onemoreact 15y ago
    The more fascinating question for me is can you demonstrate the double slit experiment on something small enough that you can detect the effect in two separate scales with the same object.
    - dhimes 15y ago
      Do you mean like seeing the diffraction envelope of the two-slit experiment?
      - onemoreact 15y ago
        I mean build 1,000 tiny devices can preform the two-slit experiment. Repeat the two-slit experiment using those devices as the projectiles. Then see if the internal decoherence counts as external decoherence. PS: I have no idea if this is possible, or what other QM equivalents of this might be.
        dhimes 15y ago
        That would be a cool experiment. I would wonder if, in measuring two superimposed patterns, the order of measuring is important. Does measuring the small pattern destroy the large and vice-versa?
  - powertower 15y ago
    It probably has just as much to do with the speed of the "thing", as the size of the "thing". If you could send a cluster of molecules at relative speeds (to c) through a double-slit setup, you might get the pattern.
dazzawazza 15y ago
Can someone please explain why this happens? I understand that for electrons, photons (or any fundamental particle?) there is a duality, but when you get a molecule, in my mind, it's now a thing, like a cat or a person. I know that if I did the double slit experiment with a people or cats I'd get a different result. Why do these molecules not behave like cats being thrown at a slit.
- mikecane 15y ago
  It makes me wonder, is speed a factor? How fast are they traveling?
  - pmjordan 15y ago
    Velocity is part of the wave function, but varying it shouldn't affect the qualitative result of the experiment. It will change the specific intensity pattern on the detector side.
  - jessriedel 15y ago
    It's not a speed factor. The possibility for observing quantum interference is controlled by the amount of environmental decoherence. (This is roughly the amount of interaction with the rest of the universe.) Decoherence is eliminated by working in a high vacuum, carefully designing the slits, etc. In principle, interference of macroscopic object is possible, but the sources of decoherence generally increase exponentially with object size. If you look at figure 3, you can see that the molecules are traveling at 10-100 meters per second, depending on size.
- knodi 15y ago
  No one can explain this currently.
  - dhimes 15y ago
    It depends, or course, on just what you mean by "explain."
  - 15y ago
nateberkopec 15y ago
"'If you talk to the community, maybe 50 percent would say this is normal because it's quantum physics, and the other 50 percent would really scratch their heads because it's quantum physics,' adds the scientist, who was one of the leaders on the new project." Quote of the year.
- Arjuna 15y ago
  Great quote. Speaking of quotes, I like the following quote (or really, quoted section) from Dr. Feynman's lecture entitled, "Probability and Uncertainty - The Quantum Mechanical View of Nature." [1] In this lecture, he describes the double-slit experiment. This section blows me away every time I watch it: "Here are the circumstances: source, strong light source; tell me, behind which hole will I see the electron? You say, "Well, the reason you can't tell through which hole you're going to see the electron is, it's determined by some very complicated things back here: if I knew enough about that electron - it has internal wheels, internal gears, and so forth - and that this is what determines through which hole it goes. It's 50/50 probability because, like a die, it's set sort of at random - and if I were to have studied it carefully enough, your physics is incomplete: if you get a complete enough physics, then you'll be able to predict through which hole it goes." That's the "hidden variable" theory, so called. Well, that's not possible. It is not due to a lack of detailed knowledge that we cannot make a prediction, because I said that if I didn't turn on the light, I should get this interference pattern. If I have a circumstance in which I get that interference pattern, then it is impossible to analyze it in terms of saying, it goes through here or here, because that curve is so simple, mathematically - a different thing than the contribution of this and this as probabilities. So if it were possible for you to have determined through which hole it was going to go if I had the light on, the fact that I had the light on hasn't got anything to do with it! Whatever gears there are back here that you observe, which permitted you to tell me whether is was going to go through 1 or 2, you could have observed if I had the light off. And therefore you could have told me with the light off which hole - each time an electron goes - which hole it's going to go through. But if you can do this, then that curve would have to be represented as the sum of those that go through there and those that go through there - and it ain't. Therefore, it's impossible to have information ahead of time as to which hole it's going to go through when the light is out - or when the light is on, or out - in a circumstance where the experiment is set up that can produce this interference pattern. It is not a lack of unknown gears - a lack of internal complications - that makes nature have probability in it; it seems to be in some sense intrinsic. Someone has said it this way: "nature herself doesn't know which way the electron is going to go." A philosopher once said (a pompous one): "it is necessary for the very existence of science that the same conditions always produce the same result." Well, they don't: if you set up electrons in any way - I mean, you set up the circumstance here, in the same conditions every time, and you cannot predict behind which hole you'll see the electron. They don't - and yet the science goes on in spite of him." [1] https://www.youtube.com/watch?v=ePN82VM4miU https://www.youtube.com/watch?v=ePN82VM4miU
radarsat1 15y ago
If they tried with a large enough object I wonder if they could film it going through the slits, like with a high-speed camera. I guess individual molecules can't be photographed without an electron microscope though.
- maggit 15y ago
  No, that would change the experiment into "Which slit does the object pass through?", instead of the current experiment "How does a beam of objects manipulate the wall behind these slits?" Observing the object in either one of the slits would remove the necessary precondition for getting the interference pattern on the wall, so the pattern would no longer be there in your experiment.
- pmjordan 15y ago
  As soon as you know where the particle is, you're collapsing the wavefunction (the photons are interacting with the particle), so that won't work.
- simonh 15y ago
  If anything interacts with the object in-transit, such as photons bouncing off it to take pictures, then it's quantum wave function would collapse and nolonger be uncertain. It would essentially 'force' particle-like behaviour.
- ovi256 15y ago
  Well, as soon as you "observe" it, the wavefunction collapses. In this experiment, they observe it way after it passes through the slits, so the quantum can pass through both slits. If you observe it before passing, if that's possible, the wavefunction will collapse at that moment, and the quantum will pass, like a particle, through a single slit. No idea how it would be possible to observe it mid-flight though.
  - dhimes 15y ago
    Well, as soon as you "observe" it, the wavefunction collapses ...according to the most commonly accepted interpretation at any rate.
jessriedel 15y ago
The same group has proposed an improved version of the experiment with 1,000,000 amu gold clusters or larger. http://iopscience.iop.org/1367-2630/13/7/075002 http://iopscience.iop.org/1367-2630/13/7/075002
jcdreads 15y ago
Primary source: http://www.quantumnano.at/ http://www.quantumnano.at/
deleted 15y ago
[deleted]
philh 15y ago
For those who find quantum physics weird, I've been reading through Eliezer Yudkowski's "quantum physics sequence". I'm only part-way through, but it has somewhat demystified things for me. It takes the approach of not trying to explain things in terms of bizzare classical physics approximations. http://lesswrong.com/lw/r5/the_quantum_physics_sequence/ http://lesswrong.com/lw/r5/the_quantum_physics_sequence/ I'd say you can probably skip most of the preliminaries. But I didn't, so I'm not sure.

77 points by mikecane 15y ago

Slightly more info (and fewer distasteful ads) here: http://www.livescience.com/19268-quantum-double-slit-experiment-largest-molecules.html http://www.livescience.com/19268-quantum-double-slit-experim...

yread 15y ago

Here is the original paper: http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2012.34.html http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano... They used "derivatives of phthalocyanine molecules" with 1298 AMU. The methods how they got the results (for example making a slit 10 nm wide) seem to be even more interesting than the result

jessriedel 15y ago
The same group had already published last summer about interfering 6000 amu molecules. http://www.nature.com/ncomms/journal/v2/n4/full/ncomms1263.html http://www.nature.com/ncomms/journal/v2/n4/full/ncomms1263.h... The interesting aspect of the OP experiment appears to be that they have a real-time movie.

simonh 15y ago

Call me when they repeat the experiment with cats.

Jabbles 15y ago

"Researchers were puzzled"... - I doubt they were, "Softpedia". This is entirely expected and in line with all previous results. For example http://physicsworld.com/cws/article/news/2952 http://physicsworld.com/cws/article/news/2952 That's not to say it was a waste by any means - the techniques used will hopefully be useful to other scientists, and confirmation is always good :)

dhimes 15y ago
It will be fascinating to see the transition between the small, definitely-quantum realm, and the intermediate, quantum-effects-get-washed-out-by-X realm. X = ? Size? Internal entropy?
- onemoreact 15y ago
  The more fascinating question for me is can you demonstrate the double slit experiment on something small enough that you can detect the effect in two separate scales with the same object.
  - dhimes 15y ago
    Do you mean like seeing the diffraction envelope of the two-slit experiment?
    - onemoreact 15y ago
      I mean build 1,000 tiny devices can preform the two-slit experiment. Repeat the two-slit experiment using those devices as the projectiles. Then see if the internal decoherence counts as external decoherence. PS: I have no idea if this is possible, or what other QM equivalents of this might be.
      - dhimes 15y ago
        That would be a cool experiment. I would wonder if, in measuring two superimposed patterns, the order of measuring is important. Does measuring the small pattern destroy the large and vice-versa?
- powertower 15y ago
  It probably has just as much to do with the speed of the "thing", as the size of the "thing". If you could send a cluster of molecules at relative speeds (to c) through a double-slit setup, you might get the pattern.

dazzawazza 15y ago

Can someone please explain why this happens? I understand that for electrons, photons (or any fundamental particle?) there is a duality, but when you get a molecule, in my mind, it's now a thing, like a cat or a person. I know that if I did the double slit experiment with a people or cats I'd get a different result. Why do these molecules not behave like cats being thrown at a slit.

mikecane 15y ago
It makes me wonder, is speed a factor? How fast are they traveling?
- pmjordan 15y ago
  Velocity is part of the wave function, but varying it shouldn't affect the qualitative result of the experiment. It will change the specific intensity pattern on the detector side.
- jessriedel 15y ago
  It's not a speed factor. The possibility for observing quantum interference is controlled by the amount of environmental decoherence. (This is roughly the amount of interaction with the rest of the universe.) Decoherence is eliminated by working in a high vacuum, carefully designing the slits, etc. In principle, interference of macroscopic object is possible, but the sources of decoherence generally increase exponentially with object size. If you look at figure 3, you can see that the molecules are traveling at 10-100 meters per second, depending on size.
knodi 15y ago
No one can explain this currently.
- dhimes 15y ago
  It depends, or course, on just what you mean by "explain."
- 15y ago

nateberkopec 15y ago

"'If you talk to the community, maybe 50 percent would say this is normal because it's quantum physics, and the other 50 percent would really scratch their heads because it's quantum physics,' adds the scientist, who was one of the leaders on the new project." Quote of the year.

Arjuna 15y ago
Great quote. Speaking of quotes, I like the following quote (or really, quoted section) from Dr. Feynman's lecture entitled, "Probability and Uncertainty - The Quantum Mechanical View of Nature." [1] In this lecture, he describes the double-slit experiment. This section blows me away every time I watch it: "Here are the circumstances: source, strong light source; tell me, behind which hole will I see the electron? You say, "Well, the reason you can't tell through which hole you're going to see the electron is, it's determined by some very complicated things back here: if I knew enough about that electron - it has internal wheels, internal gears, and so forth - and that this is what determines through which hole it goes. It's 50/50 probability because, like a die, it's set sort of at random - and if I were to have studied it carefully enough, your physics is incomplete: if you get a complete enough physics, then you'll be able to predict through which hole it goes." That's the "hidden variable" theory, so called. Well, that's not possible. It is not due to a lack of detailed knowledge that we cannot make a prediction, because I said that if I didn't turn on the light, I should get this interference pattern. If I have a circumstance in which I get that interference pattern, then it is impossible to analyze it in terms of saying, it goes through here or here, because that curve is so simple, mathematically - a different thing than the contribution of this and this as probabilities. So if it were possible for you to have determined through which hole it was going to go if I had the light on, the fact that I had the light on hasn't got anything to do with it! Whatever gears there are back here that you observe, which permitted you to tell me whether is was going to go through 1 or 2, you could have observed if I had the light off. And therefore you could have told me with the light off which hole - each time an electron goes - which hole it's going to go through. But if you can do this, then that curve would have to be represented as the sum of those that go through there and those that go through there - and it ain't. Therefore, it's impossible to have information ahead of time as to which hole it's going to go through when the light is out - or when the light is on, or out - in a circumstance where the experiment is set up that can produce this interference pattern. It is not a lack of unknown gears - a lack of internal complications - that makes nature have probability in it; it seems to be in some sense intrinsic. Someone has said it this way: "nature herself doesn't know which way the electron is going to go." A philosopher once said (a pompous one): "it is necessary for the very existence of science that the same conditions always produce the same result." Well, they don't: if you set up electrons in any way - I mean, you set up the circumstance here, in the same conditions every time, and you cannot predict behind which hole you'll see the electron. They don't - and yet the science goes on in spite of him." [1] https://www.youtube.com/watch?v=ePN82VM4miU https://www.youtube.com/watch?v=ePN82VM4miU

radarsat1 15y ago

If they tried with a large enough object I wonder if they could film it going through the slits, like with a high-speed camera. I guess individual molecules can't be photographed without an electron microscope though.

maggit 15y ago
No, that would change the experiment into "Which slit does the object pass through?", instead of the current experiment "How does a beam of objects manipulate the wall behind these slits?" Observing the object in either one of the slits would remove the necessary precondition for getting the interference pattern on the wall, so the pattern would no longer be there in your experiment.
pmjordan 15y ago
As soon as you know where the particle is, you're collapsing the wavefunction (the photons are interacting with the particle), so that won't work.
simonh 15y ago
If anything interacts with the object in-transit, such as photons bouncing off it to take pictures, then it's quantum wave function would collapse and nolonger be uncertain. It would essentially 'force' particle-like behaviour.
ovi256 15y ago
Well, as soon as you "observe" it, the wavefunction collapses. In this experiment, they observe it way after it passes through the slits, so the quantum can pass through both slits. If you observe it before passing, if that's possible, the wavefunction will collapse at that moment, and the quantum will pass, like a particle, through a single slit. No idea how it would be possible to observe it mid-flight though.
- dhimes 15y ago
  Well, as soon as you "observe" it, the wavefunction collapses ...according to the most commonly accepted interpretation at any rate.

jessriedel 15y ago

The same group has proposed an improved version of the experiment with 1,000,000 amu gold clusters or larger. http://iopscience.iop.org/1367-2630/13/7/075002 http://iopscience.iop.org/1367-2630/13/7/075002

jcdreads 15y ago

Primary source: http://www.quantumnano.at/ http://www.quantumnano.at/

deleted 15y ago

[deleted]

philh 15y ago

For those who find quantum physics weird, I've been reading through Eliezer Yudkowski's "quantum physics sequence". I'm only part-way through, but it has somewhat demystified things for me. It takes the approach of not trying to explain things in terms of bizzare classical physics approximations. http://lesswrong.com/lw/r5/the_quantum_physics_sequence/ http://lesswrong.com/lw/r5/the_quantum_physics_sequence/ I'd say you can probably skip most of the preliminaries. But I didn't, so I'm not sure.