double slit experiment
- View SourceI recently heard that, the double slit experiment
with single electrons or photons was never been made actually
because of technical difficulties.
What always been made was using ray of (multiple)
electrons or photons.
And, when scientists talk about double slit experiments
and say "even a single electron passes thru both slits"
is just a thought experiment based on calculated assumptions
in QM theory, referring to some other experiments
done about 70-80 years ago.
Is this true? Or up to what part it is true?
Or are there recent experiments, where single electrons/photons
send thru double slits, one after another
and have an acceptable interference pattern on the other side?
- View SourceFrom John Baez: Fourier transform land
In 1910 or thereabouts, Geoffrey Taylor placed a very weak light source
in a box on one side of a two-pinhole screen. He placed a photographic
film on the other side, then he went sailing for a few months. He
calculated that there was (with overwhelming probability) never more
than one photon at a time in the box. Nonetheless, when he returned from
his topsails and spinnakers to develop the film, he found the familiar
two-point-source diffraction pattern--- the very same diffraction
pattern that Thomas Young observed over a hundred years before.
>I recently heard that, the double slit experiment
>with single electrons or photons was never been made actually
>because of technical difficulties.
>What always been made was using ray of (multiple)
>electrons or photons.
>And, when scientists talk about double slit experiments
>and say "even a single electron passes thru both slits"
>is just a thought experiment based on calculated assumptions
>in QM theory, referring to some other experiments
>done about 70-80 years ago.
>Is this true? Or up to what part it is true?
>Or are there recent experiments, where single electrons/photons
>send thru double slits, one after another
>and have an acceptable interference pattern on the other side?
>To unsubscribe from this group, send an email to:
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
- View SourceYeah, thanks.
But 100 years...
Nobody else tried up to now ???
--- In bell_bohm@y..., Dan Bloomquist <dan@l...> wrote:
> From John Baez: Fourier transform land
> In 1910 or thereabouts, Geoffrey Taylor placed a very weak light
> in a box on one side of a two-pinhole screen. He placed a
> film on the other side, then he went sailing for a few months. He
> calculated that there was (with overwhelming probability) never
> than one photon at a time in the box. Nonetheless, when he returned
> his topsails and spinnakers to develop the film, he found the
> two-point-source diffraction pattern--- the very same diffraction
> pattern that Thomas Young observed over a hundred years before.
> Best, Dan.
> cemturgay wrote:
> >I recently heard that, the double slit experiment
> >with single electrons or photons was never been made actually
> >because of technical difficulties.
> >What always been made was using ray of (multiple)
> >electrons or photons.
> >And, when scientists talk about double slit experiments
> >and say "even a single electron passes thru both slits"
> >is just a thought experiment based on calculated assumptions
> >in QM theory, referring to some other experiments
> >done about 70-80 years ago.
> >Is this true? Or up to what part it is true?
> >Or are there recent experiments, where single electrons/photons
> >send thru double slits, one after another
> >and have an acceptable interference pattern on the other side?
> >To unsubscribe from this group, send an email to:
> >Your use of Yahoo! Groups is subject to
- View Source--- In bell_bohm@y..., "cemturgay" <cem.turgay@u...> wrote:
> I recently heard that, the double slit experimentThe location that a single particle is observed behind the double
> with single electrons or photons was never been made actually
> because of technical difficulties.
> What always been made was using ray of (multiple)
> electrons or photons.
> And, when scientists talk about double slit experiments
> and say "even a single electron passes thru both slits"
> is just a thought experiment based on calculated assumptions
> in QM theory, referring to some other experiments
> done about 70-80 years ago.
> Is this true? Or up to what part it is true?
> Or are there recent experiments, where single electrons/photons
> send thru double slits, one after another
> and have an acceptable interference pattern on the other side?
slit cannot indicate that this single particle could have gone
through both slits by 'interfering with itself', and thus the
experiment cannot be conducted with just one particle. So, the idea
behind the experiment is intrinsically one of the statistical
behavior of many particles passing through one or the other slit and
being observed with their locations behind the screen correlated. It
turns out that the pattern of landings behind the slits is as if the
particles, having apparently traversed independently through the
double slit apparatus, at distinct times, did indeed interfere with
- View SourceOn Tue, Nov 05, 2002 at 11:46:42PM -0000, Charles wrote:
> The location that a single particle is observed behind the doubleSure it can... just keep recording where single particles land
> slit cannot indicate that this single particle could have gone
> through both slits by 'interfering with itself', and thus the
> experiment cannot be conducted with just one particle. So, the idea
on the screen over time, and build a statistical graph from
that. They can't be interfering with each *other* if they don't
go through at the same time.
- View SourceOn Nov 08, 2002 at 12:44, Charles wrote:
>The location that a single particle is observed behind the doubleWeird, indeed...
>slit cannot indicate that this single particle could have gone
>through both slits by 'interfering with itself', and thus the
>experiment cannot be conducted with just one particle. So, the idea
>behind the experiment is intrinsically one of the statistical
>behavior of many particles passing through one or the other slit and
>being observed with their locations behind the screen correlated. It
>turns out that the pattern of landings behind the slits is as if the
>particles, having apparently traversed independently through the
>double slit apparatus, at distinct times, did indeed interfere with
On Nov 08, 2002 at 12:44, Jeff L.Jones wrote::
>Sure it can... just keep recording where single particles landOn contrary - all the evidences show they can!
>on the screen over time, and build a statistical graph from
>that. They can't be interfering with each *other* if they don't
>go through at the same time.
It seems that we people are still tip-toping around the same place, here:
If correlation is possible then only in space - we are stating readily,
when referring to foton interference.
And, meantime, the possible solution demands new revolutionary ideas.
One such fresh idea, I personally not remember I could met before,
seems to be contained within the Charle's suggestion:
>(...)particles, having apparently traversed independently through theLet us see if it occurs worthy of remembrance to wonder a little about this
>double slit apparatus, at distinct times, did indeed interfere with
What would be the physical sense of non-zero correlation-in-time, here?
(By the way, we should speak about convolution rather then the correlation,
here, I suppose. In any case, I will refer further to this more common
The only possible logical conclusion seems to be:
Nothing more or less then an existence of some interaction between photons.
But fotons as bosons do not interact one with another - seemingly the
wall... And maybe just another prejudice, only?
Because: What else if not the simple result of interaction under peculiar
phase in space conditions (i.e. refering to correlation in time)
the interference true meaning is?
And if so: In principle it should be possible to determine the character
of such an interaction by determining the dependence of time correlation
on the time intervals between each pair of fotons incoming one after
It does mean that an experimental verification is possible here.
We simply should try to measure not only the possibility of interference
of single photons sequentially travelling through double slit layout in some
but the degree of such an interference in dependence of the length of these
As I know, up to now, no such wide reaserches were conducted, yet.
(Dimly I remember description of some fresh experiment of this kind -
depicted somewhere in the net;
In any case I will try to find the adress in the pile of my archive CDs, to
address Cem's inquiry and
to refresh my memory in respect to that possible development of the proponed
I will know you all if I find out anything, of course.).
And possibly [more speculative remar, f only we are able to indicate the
speculative character of all presented here remarks]: To achieve this,
fotons interfering in such a way should exchange some travelling in time
particles (moving in the weirde sense dt/dx,
it is, in some sense, not(-only) in space but (most possibly - exclusively)
(In such a case we should wonder about new designum for best suitable signum
tachion, here - if only I have proper intuition of the one the tachions have
now; and better understanding of space-time designum in general.)
It would mean fotons feel the pattern of their tachion-in-new-sense fields
spreading in time and *react* as well mutually as onto themselves in
accordance to this pattern in dependence of the place they actually are.
If the alternative would be some kind of unknown interaction (field
spreading in space)
then the interference between separated in time photons would not be
What would be left would be the auto-interference. And the only known to me
of this very upset fact seems to be delivered by MWI.
So, in conclusion, we have two possible alternatives for explanation of
I) Interaction in time (only?) giving rise to time correlation (convolution)
of photons interfering in time.
II) Interaction above the time and beyond the space pointing directly at the
validity of MWI.
PS.: As this is my first active post to the bell_bohm group, I should
But in place of giving not interesting details concerning me personally,
I prefer to give the address of my page, where I had archivised a vital for
of the discussion at another yahoo forum I have been more active some time
ago (I mean FoR):
This deals, among other things, with some aspects of double slit experiment.
- View SourceDiscussion of thought experiment with separate electrons and a nice Java
applet may be find at :
*Maybe we could turn down the electron gun until the electrons were coming
out slowly enough for us to be sure it was one at a time. Lucky for us it
does just that. Use the minus and plus keys on your keyboard to control the
speed of the gun, and slow it down a lot. Then press your backspace key to
clear the screen.
Hey! The interference lines are building up anyway! How can it do that if
the electrons are really like little bullets? What are the electrons
interfering with? This is so strange...
(...) Well, it's not really possible to set up the experiment just the way
we've shown it here, with electrons being shot at a screen through a pair of
slits. The two slit experiment with light has been done many
times--originally by Thomas Young in 1801--but it's just not practical to do
exactly the same experiment with electrons. The equipment would have to be
made on an impossibly small scale to show the effects we've been discussing.
So the applet you saw is what's known as a thought experiment. It shows the
results that would be obtained, according to quantum theory, if a
hypothetical experiment like this could be performed.*
First single-photon measurements were reported in 1999:
16 July 1999:
*The ability of physicists to control single quantum particles, such as
individual atoms and photons, has increased greatly in recent years and has
allowed many "thought" experiments to be actually performed in the
laboratory. Experimental techniques have now advanced to the stage where it
is possible to repeatedly observe a single photon without destroying it. In
this latest breakthrough physicists at the Ecole Normale Supérieure in Paris
used rubidium atoms to observe the photon in a superconducting niobium
cavity (Nature 400 239).*
The Paris team used lasers to first select rubidium atoms with a very
well-defined velocity, and then prepare them in a highly-excited so-called
Rydberg state. The atoms were then passed through the niobium cavity, which
can store a single microwave photon for up to 1 millisecond. The experiment
is designed such that the energy of the microwave photon is the same as the
energy difference between two Rydberg in the atom.
If there is no photon in the cavity, nothing happens to the atom. If there
is one photon, however, the phase of the wave function describing the atom
is changed and this can be measured using interference techniques. These
techniques can also detect if the photon is in a quantum superposition of
zero-photon and single-photon states. If a second atom is sent through the
device, it yields the same result as the first one, showing that a QND
measurement has been made. It is not possible to extend the technique to
higher numbers of photons but it could be used to make a quantum logic
*1999 was a good year for precision experiments in quantum mechanics. Two of
the highlights were the repeated measurement of a single photon in a
superconducting cavity and the observation of quantum interference effects
in a beam of carbon-60 molecules. The single-photon experiment at the Ecole
Normale Supérieure in Paris was an example of a quantum non-demolition
measurement: the team was able to repeatedly observe the photon without
destroying it. The carbon-60 experiment at the University of Vienna in
Austria observed wave-like behaviour in a beam of carbon-60 molecules - the
largest particle for which quantum interference effects have been observed.*
In 1999 Prof. Anton Zeilinger's Quantum Optics Group (U. Vienna)
had developed an interferometer for large molecules:
Diffraction and Interference with Fullerenes: Wave-particle duality of C60
*We have observed de Broglie wave interference of the buckminsterfullerene
C60 with a wavelength of about 3 pm through diffraction at a SiNx absorption
grating with 100 nm period. This molecule is the by far most complex object
revealing wave behaviour so
far. The buckyball is the most stable fullerene with a mass of 720 atomic
units, composed of 60 tightly bound carbon atoms.
(...)Quantum interference experiments with large molecules, of the kind
first reported here, open up many novel possibilities among them decoherence
studies and nanolithography experiments.*
(...)Note that the ratio between the diameter of a buckyball (1 nm) and the
width of our diffraction grating slits (50 nm) compares favorably with the
ratio between the diameter of a football (22 cm) and the width of a goal
(732 cm) according to FIFA standards.
The distance between the source and the detector corresponds in this scaling
to the distance between the Earth and the moon.
- C60 powder is heated to ~ 600 ... 700°C in a resistively heated oven.
- The velocity distribution is very broad and faster than purely thermal.
- The molecular de Broglie wavelength is centered at ~ 2.5 pm.
- The de Broglie wave length is thus ~ 400 times smaller than the size of
(1nm diameter of the electron shell)
- The hot and divergent beam is collimated to a pencil of ~ 10µrad
Buckyballs that pass the second slit are transversely cold
- The SiN diffraction grating has a nominal gap width of 50nm and a grating
constant of 100nm
- After free evolution over 1m the molecules are detected via thermionic
ionization by a tightly
focused Argon ion laser beam at 24 W.
- The positive ions are counted by a secondary electron counting system.
Interpretation of the diffraction curve
- Interference fringes can clearly be seen*
They observed 200 counts/s for single peak (without grating)
1250 counts/50s central peak + 2 additional peaks 650 counts/50s (with
(25 counts/s + 2 x 13 counts/s)
Is this enough to speak about C60 balls parade through the slits of the
I believe it is. There is very little probability that two different C60
balls met themselves at the same point of the screen. So - in most cases
this is just a single ball at every count with its matter wave being
actually passed through many of slits of the grating simultaneously.
And how it is possible that it went through at least two gates 50 nm apart
being 1 nm particle and having associated de Broglie wavelength 0.0025 nm?
It just does mean that the associated wave packet has the transverse space
range of 2000 wavelengths, at least.
They reported new version of this experiment lately... Now they use a
standing light wave as the diffraction grating for the Fullerenes C60 and
*The standing light wave constitutes a periodic structure with a periodicity
of half of the laser wavelength, i.e. 257 nm. The most probable velocity of
the fullerenes amounts to 120 m/s, which corresponds to a de Broglie
wavelength of 4,6 pm (4,6*10-12 m) for C60 and 4,0 pm for C70. So we expect
diffraction angles for these fullerenes of 18 µrad and 15 µrad,
respectively. In a photon picture the observed deflection amounts to twice
the photon recoil of the green laser photons.
By varying the power of the standing light wave the induced phase shift and
so also the relative height of the individual diffraction orders can be
varied, as shown in figure 2. For comparison also the undiffracted
beamprofile is shown on top. In contrast to atoms the absorption of the
'grating' photons doesn't lead to spontaneous emission but to an internal
heating of the molecule, so the absorption of n photons deflects the
fullerene by n photon recoils. Twice the mean number of absorbed photons is
given by the imaginary part of the mean phase shift , quoted in fig. 2. The
resolution of our detector is good enough to resolve the individual
diffraction peaks but the absorption of an odd number of photons fills up
the minima in between and decreases the contrast.
(...) In contrast to the extremely fragile material structures used in our
previous interference experiments standing light waves proved to be a
promising alternative - especially for the coherent manipulation of even
larger molecules: they have perfect periodicity, high transmission and
cannot be blocked or destroyed by the molecules.*
In 2000 the group of Prof. David E. Pritchard of Massachusetts Institute of
operated atom interferometer of interest here:
*We are pioneering new measurement techniques using coherent atom optics
(such as beam-splitters, mirrors and lenses) to manipulate matter waves. We
operate an atom interferometer, similar to a Mach-Zhender optical
interferometer, which splits deBrogile waves of matter into two physically
separated paths. After an interaction region where each atom can pass
simultaneously on both sides of a metal foil, the matter waves recombine,
forming interference fringes. We monitor the phase and contrast of these
fringes, which are extremely sensitive to any interactions experienced by
In the year 2000 we completed three experiments on decoherence. Presently,
in Spring 2001, we are midway through a measurement of the matter wave index
of refraction, and we are developing a novel atom optic for velocity
multiplexing. Each project described in this report refines atom
interferometry as a tool for making measurements of atomic properties and
probing fundamental issues in quantum physics.
And photons once more... The most promising seems to be rapidly developing
nowadays quantum dots (QD) technology:
12 May 2000
PhysicsWeb - Quantum dots detect single photons
*Researchers at Toshiba Research Europe in Cambridge, UK, have developed a
single-photon detector based on quantum dots. It is the first time quantum
dots have been used to detect individual photons at visible or near-infrared
wavelengths, Andrew Shields of Toshiba told the CLEO conference in San
Francisco this week. The quantum dot device consists of a transistor made of
different layers of gallium arsenide and aluminium gallium arsenide. *
During 7th Conference of Laser Technology at Swinoujscie (Poland) held on
Sept 23-27, 2002,
I have met info on this year first industrial implementations of QD lasers
(A. Jelenski: Lasery z kropkami kwantowymi [Lasers with Quantum Dots], the
material will be published in SPIE soon). It does mean it is rapidly
developing technology, really.
Prof. Andrzej Jelenski of Instytut Technologii Materialow Elektronicznych,
*Advantages given by a discrete energy spectrum and efficient overlap of
electron and hole wave function were already recognised for several years
and first papers on the utilisation of quantum dot arrays for light
appeared already in the 80-ies. However because of technological
difficulties more than a decade was needed for manufacturing the first
quantum dot (QD) lasers, and first industrial implementations will take
place only this year. (...) many major laboratories around the world work
actually on research and development of QD laser.*
Actually the horizontal (edge) QD lasers are manufactured - not suitable for
the goals of single-photon interferometry. But the vertical versions of QD
lasers should make possible to achieve development of QD lasers with a
single quantum dot. When we will have single QD lasers then, having
single-photon QD detectors, the true fully controlled direct strong
verification of 2 slit experiment will be possible, finally.
- View SourceAnd here is another pack of relevant comments:
Talking physics with the Dalai Lama
4 August 1998
*(...)Zeilinger had invited the Dalai Lama to his laboratory following a
meeting at Dharamsala in Northern India last October at which he and four
other physicists had, over the course of five days, discussed physics and
cosmology with the Buddhist leader. In Dharamsala, Zeilinger had
demonstrated some basic quantum phenomena - such as wave-particle duality -
using a laser-based double-slit experiment with a photomultiplier tube
connected to a loud-speaker. The Dalai Lama's visit to Innsbruck allowed
other quantum effects to be demonstrated for him.
Zeilinger says that the Dalai Lama did not have a problem with photons
having both particle and wave-like properties, but was reluctant to accept
that individual quantum events are random. For example, he refused to accept
that we cannot know which path a photon takes in a two-path quantum
interference experiment. Zeilinger notes that continuity of existence is
very important to Buddhists because it leads to reincarnation.
However, observation plays a key part in what we can know in both quantum
theory and Buddhism, and Zeilinger was surprised to learn that the Dalai
Lama agreed that there are not only limits on what we can measure, but also
limits on what we can know, even in principle.(...) *
To see more:
The many wavelengths of light
Physics in Action: August 1999
*(...)Sebastião de Pádua and colleagues at the Universidade Federal de Minas
Gerais in Belo Horizonte, Brazil, have now measured the de Broglie
wavelength of a two-photon wave packet in a Young's double-slit experiment
(E J S Fonseca et al. 1999 Phys. Rev. Lett. 82 2868). They used a nonlinear
crystal to "down-convert" 351 nm wavelength photons from an argon laser into
pairs of 702 nm photons, which were then directed onto a double slit.
Avalanche photodiodes were used to detect the fringes formed by the
interference between the two paths from the source to the detector.(...)*
As we see, from our point of interest, they do vsio-na-abarot... Seemingly
there is no point in conducting such an experiment but the demonstration of
technical advancement... In other words: nobody doubts the results they
should obtain before ... they were obtain. If only they could block out
every one of pair and make parade of single photons... But they surely can
not. There is still a beam of photons left.
But there is no need in conducting the exact 2-slit experiment to anticipate
The number of interference experiments were reported lately in reference to
Quantum Comps (QC).
And they demonstrate the same in a slightly different, technically more
Fundamentals of quantum information
Feature: March 1998
*(...)Quantum interference can be explained by saying that the particle is
in a superposition of the two experimental paths: passage through the upper
slit> and passage through the lower slit>. Similarly a quantum bit can be in
a superposition of 0> and 1>. Experiments in quantum information processing
tend to use interferometers rather than double slits but the principle is
the same (see http://physicsweb.org/box/world/11/3/9/world-11-3-9-1 ). So
far single-particle quantum interference has been observed with photons,
electrons, neutrons and atoms. (...)*
Kandydatka 18: Ma³gorzata >>> http://link.interia.pl/f1679