Download Experiments in “Quantum Erasure” and “Delayed

Experiments in
“Quantum Erasure” and “Delayed Choice”
Preventing the simultaneous acquisition of probabilistic
and deterministic results for the same result set
(31 Slides)
Norman Christopher Valleĵo
Copyright © 2011
http://www.normanchristophervallejo.com.au
Linked contents
1. Light
2. Interference
3. Particle diffraction
4. Single-slit diffraction
5. Double-slit diffraction
6. Double-slit diffraction (particle by particle)
7. Determining “which path” information
8. Photon entanglement
9. “Delayed Choice”
10. “Quantum Erasure”
11. More realistic experimental arrangements
Light
 Light is made of particles that exhibit wave
properties
 These are called photons
 They are fundamental and cannot be split
 Their wave functions obey probabilistic law
 They can also Constructively and
Destructively interfere
Photon
-Fundamental particle
-Smallest unit of light
-Comprise light waves
Interference
 If two particles collide, the high point of one
wave can add with the high point of the other
effectively amplifying the particle’s energy
 Alternatively, the high point of one wave can
add with the low point of the other effectively
neutralising the particle
Constructive interference
Destructive interference
Particle diffraction
 The late famous physicist Richard Feynman
hinted: To understand Quantum Physics,
understand Young’s Double-slit experiment
 Young’s Double-slit experiment involves
shining light at two openings and observing
the pattern created on a screen
 There are some startling results for the
uninitiated
Single-slit diffraction
 Light shown through a single-slit reveals a
diffraction pattern which is approximately
centered as a main band. Minor bands also
exist further out from the centre.
Light
source
Screen has a
single-slit
opening
Relative graphical
distribution of
particle hits
"Single-slit“
pattern forms
Double-slit diffraction
 Light shown through a double-slit reveals a
diffraction pattern which has more bands,
the result of constructive and destructive
interference by “out of phase” particles.
Screen has a
double-slit
opening
Light
source
Relative graphical
distribution of
particle hits
“Double-slit“
pattern forms
Distances to
the same point
are different
Double-slit diffraction
(particle by particle)
 Light shown through a double-slit fired one
particle at a time, still builds a double-slit
diffraction pattern over time!
 Particle size does not span both slits.
Light
source
Screen has a
double-slit
opening
Relative graphical
distribution of
particle hits
Particles fired one at a time.
"Double-slit" pattern still forms !
Double-slit diffraction
(particle by particle)
 We would assume that because one particle
at a time could not interfere with both slits
that we should get two single-slit patterns
past each opening.
 Experiment has never shown this to occur.
 Conclusion is that particles are probabilistic
in their flight until impact.
 Experiment supports this view.
 Photons remain higher dimensional until
localised by knowledge of their state.
Double-slit diffraction
(particle by particle)
 Up until the impact screen, the particle has a
chance of being in any of the set of two
trajectories that exit the slits and impact at one
point on the screen.
 At the screen, it has no chance of passing it.
 It therefore “descends” out of higher dimensional
reality and “chooses” probabilistically any point
where the double-slit pattern can form.
 Quantum physics shows us that particles are
higher dimensional until they are measured.
Double-slit diffraction
(particle by particle)
 Three particle hits. One after another.
 Photon traverses entire distance from point
of departure to the screen as a probability.
 It remains higher dimensional until hitting.
Light
source
Screen has a
double-slit
opening
Range of probable
flight paths.
Particles suffer a
random "collapse“ to
one set of two flight
paths for each of the
three particles.
Three particle
hits.
The final twin
trajectories that each
particle assumes out of
the entire range, are
random. Higher
dimensional photon has
"collapsed" to an actual
probabilistic position on
a screen.
We have determined
 Light particles are probabilistic by nature
and this has been experimentally verified.
 They interfere with their own probable
trajectories in “flight”.
 When we acquire knowledge of their state
(determining their position for instance), the
determination will be a probabilistic selection
from the set of probable flight paths that
exist up until that determination.
Trying to cheat
Determining “which path” information
 Q: What happens if we try and find out
which slit the photon transits?
 A: Then the double-slit pattern never forms.
 Two single slit patterns form, one in front of
each opening.
Light
source
Detectors register which
path the photon took
A
B
Determining "which path" information
prevents probabilistic interference
Relative graphical
distribution of
particle hits, built
up over time.
Conclusion
 Knowledge and state in the universe, are
linked at a fundamental level.
 If you don’t “know” where a particle is, then
it is in all of its possible trajectories, as a
probability.
Now we get really clever!
Photon entanglement
 Certain crystals are able to convert a photon
of set energy to two photons of half energy.
 The two particles can then be seen to be
strangely connected from that point forward.
 This is called “entanglement”.
Crystal converts one
photon into two
Photons must
conserve spin and are
therefore "marked".
One will be positive,
the other negative.
Observing the state of
one particle later will
tell us about its partner.
This happens like
"telepathy" so to
speak.
“Delayed choice”
 We now investigate what happens when a
set of entangled photons is observed to
have interacted in separate areas ‘Main’ and
‘Test’ of the same experiment.
 We use a double-slit apparatus with a
crystal placed in front of both openings.
 We direct one of the two entangled photons
to a normal screen Main and the other to the
Test area.
Experimental arrangement
Main
PAB
Given no information has been
gathered before impact occurs,
particle P should be able to hit
anywhere for a double-slit pattern.
A
B
There is a time difference between
T1 and T2. Particle PAB hits way
before its entangled partner is
detected at either DA or DB.
?
Crystals do not detect
anything. They simply
create two entangled
photons from one initial
photon.
Test
PA
?
DA
PB
At time T1, neither
photon has been
detected.
T1
T2
DB
Detectors can now find which
slit the photon transited for its
entangled partner that hit the
Main screen
“Delayed choice”
 We should be able to “cheat” and allow the
double-slit pattern to form (given the photon
went through two openings higher
dimensionally and interfered with itself) but
still find out which opening it went through in
reality by detecting its entangled partner
afterward.
“Delayed choice”
 Remember, both entangled photons can basically
be viewed as the same particle, so if one impacts
on the Main screen under double-slit conditions
first, and the other is detected at the detectors
later, then we have verified a contradictory reality
of a photon that went through two slits and
interfered with itself but detected it later as only
going through one...
 Given no “which path” information has been
determined before the Main screen impact, there
should be a double-slit pattern on the Main screen
and the partner entangled photon travels onward
to hit the detectors…we have “beaten” the
experiment.
“Delayed choice”
 The Main screen pattern then should be
formed well in advance of detecting anything
at detectors. So…
 Q: What does the Main screen show?
 A: No double-slit pattern has formed!
 There are two single slit patterns, one
behind each opening.
Formation of Single-slit pattern
without determining “which path”
information…yet…
PA
A
However Single-slit patterns have
formed without detecting
which slit the photon transited.
B
PB
?
Without detection this photon
is free to interfere with its own
probable flight paths and
impact anywhere on the
screen at a Double-slit
position
At this point in time,
neither photon has
been detected.
?
T1
Experiment therefore reveals the
double-slit pattern IS NOT formed
although we have not yet determined
which slit the photon transited
“Quantum Erasure”
 Effectively this means, particle P ‘knew’ in
advance that “which path” information was
to be determined about it in the future at the
detectors and therefore it collapsed as an
“actual” in advance at the Main screen to
whatever opening its partner passed
through probabilistically in the future.
 By acquiring deterministic results in the
future, we have erased double-slit
interference in the past; “Quantum Erasure”
“Delayed choice”
 Or, the double-slit hit occurs at the Main
screen, then once detected at the detectors,
the result is changed back in time at the
Main screen to be only a matching single-slit
hit.
 We could choose to put a screen in front of
the detectors (or remove them altogether),
thereby blocking “which way” information to
see if the diffraction pattern still forms on
both screens. Indeed this will happen.
Blocking detection
PAB
A
Double-slit patterns will form on both
screens given no "which way“
information has been acquired in
entire experiment.
B
PAB
DA
DB
T1
T2
Detectors
now
blocked
“Delayed choice”
 We are therefore free to choose what
information we want to observe after the
photon impacts on the Main screen by
determination or ignorance of “which way”
information at a later point in time at the Test
detectors
i.e. “Delayed Choice”.
The experiments would look
more like the following…
Use up and down arrows
to get a better feel for the
difference between the
two experiments
“Delayed choice” Probabilistic
Next
“Delayed choice” Deterministic
Previous
Conclusion
 The simultaneous acquisition of probabilistic
and deterministic results, for the same result
set, is forbidden to occur in physical reality.
 Q: Why…and how is this carried out?
 A: Read the disproof!
Real experiment
 Real experimental arrangements use much
the same setup only they are more
complicated in the ‘Test’ section.
 They use beam splitters and more crystals
to combine paths after the Main screen so
that both sets of results are obtained for the
same photon.
 Detectors replace screens.
 It then becomes only a matter of looking at
selected result sets to “choose” the
outcome. See over…
Diagram: Patrick Edwin Moran (2007)
Reproduced with kind permission
Norman Christopher Valleĵo
Author
“Trans-dimensional Evolution
The scientific disproof of Darwin’s Theory of Evolution”
http://www.normanchristophervallejo.com.au