Transcript Quantum Entanglement, Nonlocality, and Back-In

Quantum Entanglement,
Nonlocality, and
Back-In-Time Messages
John G. Cramer
Professor Emeritus of Physics
University of Washington
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Causality & Retrocausality
The Law of Causality: A cause must precede its
effects in all reference frames.
In quantum mechanics, there are apparent violations of
this principle. One example is Wheeler’s Delayed Choice
Experiment, in which a photon of light is made to pass
either through one slit or two slits, depending on which
measurement action that is taken after the light has
already passed the slit system. This is called
retrocausality, an effect that appears to precede its cause.
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Evidence for Retrocausality:
Publicity Precedes the Experiment
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New Scientist
September 30, 2006
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Seattle Post Intelligencer
November 15, 2006
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… and Even More Evidence
Men’s Journal
October, 2007
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Seattle Metropolitan Magazine
October, 2007
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Quantum Entanglement
and Nonlocality
“Spooky Actions-at-a-Distance”
Albert Einstein
Entanglement
and Nonlocality
Entanglement: The separated but
“entangled” parts of the same quantum system
can only be described by referencing the
state of other part.
The possible outcomes of
measurement M2 depend of the
results of measurement M1, and
vice versa. This is usually a
consequence of conservation laws
(conservation of momentum, angular
momentum, energy, …).
Entangled
Photon
Source
Nonlocality: This “connectedness” between
the separated system parts is called quantum
nonlocality. It should act even of the system
parts are separated by light years. Einstein
called this “spooky actions at a distance.”
Measurement 1
M1
Entangled
photon 1
Nonlocal
Connection
Entangled
photon 2
M2
Measurement 1
Interference of Waves
Light travels as a wave, but leaves and arrives as a particle.
(E = hn) We can select wave-like behavior or particle-like behavior by
choosing what to measure. Wave-like behavior shows up as interference.
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One-Slit Diffraction
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Two-Slit Interference
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Turning Interference
On and Off
Two-slit
Interference
Pattern
Waves that cannot be distinguished will interfere.
No Two-slit
Interference
Pattern
H
V
Waves that can be distinguished (e.g., by polarization) will not
interfere.
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Shih Ghost Interference
Experiment (1995)
(a) Two slits
(b) One slit
Note the use
of coincidence
Klyshko Reflection
Dopfer Position-Momentum
EPR Experiment (1998)
LiIO3
Down-Conversion
Crystal
“Heisenberg” Lens
f = 86 cm
“Heisenberg”
Detector D1
28.2o
Laser Beam
Stop
Auxiliary
Lens
Double Slit System
a = 75 mm, d = 255 mm
f
Momentum
Double-Slit
Detector D2
Birgit Dopfer
PhD Thesis
U. Innsbruck, 1998.
Coincidence
Circuit
or
f
2f
Note the use
of coincidence.
2f
Position
Detecting Interference
Mach-Zehnder
Interferometer
MZ Advantages: Interference with full incident beam.
MZ Disadvantages: (1) Extremely difficult to align
(4 reflecting surfaces aligned to wavelength-scale
precision); (2) Path is momentum-independent.
Cramer
Half-Slit
Interferometer
Periodically Poled
Nonlinear Crystal
ppKTP = periodically poled KTiOPO4
(potassium titanyl phosphate)
Phase Matching: kP = kS + kI + 2p/L
Mark III Nonlocal
Quantum Communication Test
Signal is sent by
moving splitter in/out.
In = interference
(wave)
Out = no interference
(particle)
3
APD
Detectors
4
1
Receive
Splitter
Half-Slit
Interferometer V
D-mirror
The D-mirrors intercept and
deflect one-half of each of the
beams of entangled photons.
90°
Pentaprism
Send
Splitter
In/Out
APD
Detectors
2
D-mirror
90°
Pentaprism
Crystal Oven
Mirror
Half-Slit
Interferometer H
90°
Pentaprism
90°
Pentaprism
810 nm
Horizontal
Polarization
810 nm
Vertical
Polarization
ʘ
Polarizing
Splitter
ppKTP Crystal
Longpass
Filter
Lens
Half-Wave
Plate
ʘ
405 nm
Pump Laser
Sacher TEC100-0405-040
Hot
Mirror
Aperture
f
Pump
Beam
Monitor
The Far-Fetching Implications
of Nonlocal Communication:
Faster than Light &
Backwards in Time
Faster-Than-Light Signaling
4
In this test, we would string equal lengths of fiber optics cables
to separate the two ends of the experiment by a line-of-sight
distance of ~1.4 km.
We would then send bits
1
3
at a photon rate of 10 MHz
over this link. Assuming a 102
90°
90°
Splitter
Pentaprism
Pentaprism
Splitter
photon decoding “latency”,
In/Out
this would demonstrate a
signal transmission speed of
Send
Receive
about 5 times the speed of
Mirror
Mirror
light.
90°
Pentaprism
90°
Pentaprism
90°
Pentaprism
1.0 km
1.0 km
Crystal Oven
ppKTP Crystal
Mirror
D-mirror
Mirror
810 nm
Horizontal
Polarization
Half-Wave
Plate
ʘ
405 nm
Pump Laser
Sacher TEC100-0405-040
Mirror
D-mirror
ʘ
810 nm
Vertical
Polarization
Longpass
Filter
Lens
Hot
Mirror
Mirror
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Polarizing
Splitter
Aperture
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Back-In-Time Signaling
We would use 10 km of high-quality optical fiber coiled in the corner
of the laboratory. We split the horizontally polarized entangled photon
beam with a D-mirror and pass each of the two paths through 10 km of
fiber coils.
The vertically polarized
3
4
90°
Pentaprism
Splitter
In/Out
90°
Pentaprism
1
APD
Detectors
2
Send
Splitter
Receive
Mirror
90°
Pentaprism
10 km
D-mirror
entangled photons have no optical
delay, and the signal is received
as soon as these photons are
detected at D1,2, which is about
50 ms before the signal is
transmitted, when the twin
entangled photons arrive at D3,4.
Back-in-time signaling!
90°
Pentaprism
10 km
Crystal Oven
Mirror
D-mirror
810 nm
Horizontal
Polarization
810 nm
Vertical
Polarization
ʘ
ppKTP Crystal
Longpass
Filter
Lens
Half-Wave
Plate
ʘ
405 nm
Pump Laser
Sacher TEC100-0405-040
Hot
Mirror
Mirror
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Polarizing
Splitter
Aperture
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Time-Travel
Paradoxes
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The Bilking Paradox
Suppose that we constructed a million
connected retrocausal links of the type just
shown (or used 107 km of fiber optics). Then the
transmitted message would be received 50
seconds before it was sent.
Now suppose that a tricky observer receives
a message from himself 50 seconds in the future,
but then he decides not to send it. This
produces an inconsistent timelike loop, which has
come to be known as a “bilking paradox”. Could
this happen? If not, what would prevent it?
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Chronology Protection:
The Hawking Bomb
“The Chronology Protection Hypothesis”, suggested by Steven
Hawking, asserts that, in the context of timelike loops made with
wormholes, the quantum fluctuations of the vacuum should rise without
limit as the timelike loop was about to be produced, smiting the
experimenter and his apparatus and preventing the formation of the
timelike loop. In quantum field theory there are equations that appear
to support this idea.
Thus, retrocausal communication could in principle lead to the
creation of a “Hawking Bomb”, a device that, by approaching the creation
of a timelike loop, causes disruption of molecules, atoms, and
fundamental particles due to excessive vacuum fluctuations. This has
interesting implications - both for hard SF and for the military.
As a working hypothesis in thisa work, we assume that this will not be
a problem, since we see Nature doing retrocausal things all the time in
the quantum domain.
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Anti-Bilking
Discussions of bilking paradoxes have been published
in the physics literature from the 1940s by Wheeler and
Feynman (advanced waves) to the 1990s by Kip Thorne and
his colleagues (timelike wormholes).
The consensus of such discussions is that Nature will
forbid inconsistent timelike loops and will instead require
a consistent set of conditions. Thorn and coworkers
showed that for any inconsistent paradoxical situation
involving a timelike wormhole, there is a “nearby” selfconsistent situation that does not involve a paradox.
As Sherlock Holmes told us several times, “When
the impossible is eliminated, whatever remains, however
improbable, must be the truth.”
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Bilking &
Probability Control
These speculations suggest that equipment failure
producing a consistent sequence of events is more likely
than equipment operation producing an inconsistency
between the send and receive events. The implications of
this are that bilking itself is impossible, but that very
improbable events could be forced into existence in order
to avoid it.
Thus, using the threat of producing an inconsistent
timelike loop, one might “bilk” Nature into producing an
improbable event. For example, you might set up a highly
redundant and reliable system that would produce an
inconsistent timelike loop unless the number for the
lottery ticket you had purchased was the winning number.
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The “Immaculate
Conception” Paradox
The other issue raised by retrocausal signaling might be called the
“immaculate conception” paradox. Suppose that you are using the setup
described above, and you receive from yourself in the future a .pdf file
of a wonderful novel with your name listed as the author. You sell it to
Tor Books, it is published, it becomes a best-seller, you become rich and
famous, and are the Writer Guest of Honor at Norwescon 38.
When the time subsequently comes for transmission, you duly send
the .pdf file back to yourself, thereby closing the timelike loop and
producing a completely consistent set of events. But the question is,
just who actually wrote the novel?
Clearly, you did not; you merely passed it along to yourself. Yet
highly structured information (the novel) has been created out of
nothing. And in this case, Nature should not object, because there are
no inconsistent timelike loops.
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Present Status

The experiment has been in testing phases since midJanuary, 2007. Our initial attempt to produce downconverted photons with LiIO3 and BBO and detect them
with a cooled CCD camera or APDs did not work. We
have demonstrated that the production rate is too low
and the detectors too noisy. In 2009-10 we have
substituted a new crystal, laser, and interferometers.

The experiment was recently moved from the basement
UW Laser Physics Facility to the 2nd Floor Optics Lab,
where we can turn off the lights without interfering with
other experimenters.

We are now testing the Mark III configuration. Our
main problem seems to be the small quantity of entangled
photons produced. (Zeilinger in Vienna makes 106 pairs
per second with a crystal and laser similar to ours.)
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Conclusions
 There are no obvious “show stoppers” that
would seem to prevent our proposed
measurements. Nevertheless, because of
their implications, the experiment has a low
probability of success.
 We have so far received about $46k in
contributions from foundations and individuals
in support of this work . We have spent most
of this on the Mark III system.
 This experiment is a rare opportunity to
push the boundaries of physics with a simple
tabletop measurement. We are pushing hard.
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The
End
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