

Double-Slit Experiment Carried Out with 114-Atom Molecules - mikecane
http://news.softpedia.com/news/Double-Slit-Experiment-Carried-Out-with-114-Atom-Molecules-260810.shtml

======
nateberkopec
"'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
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>

~~~
moheeb
Image if you were God...What fun would it be if every question were answered
yes?

~~~
kenj0418
yes

------
yread
Here is the original paper:
[http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano...](http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2012.34.html)

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
The same group had already published last summer about interfering 6000 amu
molecules.

[http://www.nature.com/ncomms/journal/v2/n4/full/ncomms1263.h...](http://www.nature.com/ncomms/journal/v2/n4/full/ncomms1263.html)

The interesting aspect of the OP experiment appears to be that they have a
real-time movie.

------
dazzawazza
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.

~~~
DanBC
Has anyone tried the experiment with something obviously larger and not
quantum-scale, such as table tennis balls?

(Search finds lots of pages using table tennis balls as a help for visualising
atoms or electrons or molecules.)

Here's a page (with many puns) about what you'd need to try the experiment
with cats.

([http://www.askamathematician.com/2010/12/q-can-you-do-the-
do...](http://www.askamathematician.com/2010/12/q-can-you-do-the-double-slit-
experiment-with-a-cat-cannon/))

~~~
dhimes
The wave-effects depend on the fact that the wavelength is of a size that is
comparable to the size of the object it's interacting with. Think about
optics: observing an interference or diffraction pattern is easier when the
light interacts with very small structures (the patterns on a cd, for
example), the same is true for "matter" waves.

The catch is, the wavelength is of the order of h/momentum or h/(mass *
velocity) where h (Planck's constant) is a really, really small number.

When mass is something like an ordinary object, then the size of the "slits"
becomes so small that we can't imagine how conduct the experiment.

~~~
jessriedel
<s>This is mostly wrong</s>. When the de Broglie wavelength becomes smaller
than the size of the object, observing quantum inference becomes harder, but
it's certainly not impossible.

In this experiment, the molecules (~10^2 atoms) are a few nano meters across
and the de Broglie wavelength is a few hundredths of a nanometer. The same
group is planning on future experiments with 10^6 atoms, where the wavelength
will be _much_ smaller than the object.

~~~
dhimes
Um, how, exactly, is what I said wrong?

~~~
jessriedel
I more-or-less take back what I said. On first reading, your comment sounded
to me like you were claiming that these effects go away for large objects
rather than merely becoming very hard to see. In particular, this

>When mass is something like an ordinary object, then the size of the "slits"
becomes so small that we can't imagine how conduct the experiment.

I think is misleading. Experiments demonstrating quantum interference of
macroscopic objects are very easy to imagine and are limited by _logistical_
concerns rather than fundamental physics. In particular, an experiment
interfering objects large enough to see with the naked eye is very likely to
occur this century, so I object to calling it "unimaginable".

But you were mostly right. I'm sorry.

~~~
carbocation
The de Broglie wavelength of a baseball is something like 20 orders of
magnitude smaller than a proton. If you imagine this to be something that
might be probed in the next few centuries, I'd be interested to hear more.

~~~
jessriedel
I'd be willing to bet (e.g. longbets.org) that objects of size 10^15 amu
(which is large enough to be visible to the naked eye) will be interfered in
this century. Baseballs are 10 orders of magnitude larger.

In any case, the point is that it's _not_ a matter of the slits becoming too
small. It's a matter of controlling environmental decoherence.

~~~
carbocation
And this is one of the reasons I love HN. I would be interested in hearing
more sometime. For example, if you were to write up a speculative blog post
and submit it here...

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

------
Jabbles
"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>

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
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
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
Do you mean like seeing the diffraction envelope of the two-slit experiment?

~~~
onemoreact
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
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?

------
jcdreads
Primary source:

<http://www.quantumnano.at/>

------
jessriedel
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>

------
radarsat1
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.

~~~
ovi256
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
_Well, as soon as you "observe" it, the wavefunction collapses_

...according to the most commonly accepted interpretation at any rate.

~~~
judofyr
I think he mixed up the observation and the conclusion/interpretation:

 _Well, as soon as you "observe" it, we will no longer see an interference
pattern_

~~~
ovi256
>Well, as soon as you "observe" it, we will no longer see an interference
pattern

That's not strictly true, because the experiment is observing the quantum, and
it is seeing an interference pattern. The critical thing is that they're
observing it after the quantum has gone through the slits, so as it passes
through the slotted wall, it's wavefunction is not constrained. So the moment
of observation is very important.

------
philh
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/>

I'd say you can probably skip most of the preliminaries. But I didn't, so I'm
not sure.

------
simonh
Call me when they repeat the experiment with cats.

