Quantum Entanglement Nonlocality and BackInTime Messages John G

Quantum Entanglement, Nonlocality, and Back-In-Time Messages John G. Cramer Professor Emeritus of Physics University of Washington Norwescon 33 April 3, 2010

Causality & Retrocausality The Law of Causality: A cause must precede its effects in all reference frames. In quantum mechanics, there 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. April 3, 2010 Norwescon 33 2/28

Evidence for Retrocausality: Publicity Precedes the Experiment April 3, 2010 New Scientist September 30, 2006 Norwescon 33 Seattle Post Intelligencer November 15, 2006 3/28

… and Even More Evidence Men’s Journal October, 2007 April 3, 2010 Seattle Metropolitan Magazine October, 2007 Norwescon 33 4/28

Quantum Entanglement and Nonlocality “Spooky Actions-at-a-Distance” Albert Einstein April 3, 2010 Norwescon 33 /28

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 M 2 depend of the results of measurement M 1, 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. ” April 3, 2010 Norwescon 33 Measurement 1 M 1 Entangled photon 1 Nonlocal Connection Entangled photon 2 Measurement 1 /28

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. April 3, 2010 Norwescon 33 7/28

One-Slit Diffraction April 3, 2010 Norwescon 33 8/28

Two-Slit Interference April 3, 2010 Norwescon 33 9/28

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. April 3, 2010 Norwescon 33 10/28

Shih Ghost Interference Experiment (1995) Note the use of coincidence April 3, 2010 Norwescon 33 /28

Klyshko Reflection April 3, 2010 Norwescon 33 /28

Dopfer Position-Momentum EPR Experiment (1998) Li. IO 3 Down-Conversion Crystal UV Las Bea er m “Heisenberg” Lens f = 86 cm 28. 2 o o . 2 28 Laser Beam Stop Auxiliary Lens Double Slit System a = 75 mm, d = 255 mm Birgit Dopfer Ph. D Thesis U. Innsbruck, 1998. April 3, 2010 “Heisenberg” Detector D 1 f Momentum 2 f Position Double-Slit Detector D 2 Coincidence Circuit or f 2 f Norwescon 33 Note the use of coincidence. /28

Detecting Interference Cramer Half-Slit Interferometer 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. April 3, 2010 Norwescon 33 /28

Periodically Poled Nonlinear Crystal pp. KTP = periodically poled KTi. OPO 4 (potassium titanyl phosphate) Phase Matching: k. P = k. S + k. I + 2 p/L April 3, 2010 Norwescon 33 /28

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 90° Pentaprism 1 Receive APD Detectors Splitter Half-Slit Interferometer V D-mirror Send Splitter In/Out Half-Slit Interferometer H D-mirror 90° Pentaprism April 3, 2010 2 90° Pentaprism Crystal Oven Mirror 810 nm Horizontal Polarization The D-mirrors intercept and deflect one-half of each of the beams of entangled photons. 810 nm Vertical Polarization ʘ Polarizing Splitter pp. KTP Crystal Longpass Filter Lens Half-Wave Plate ʘ 405 nm Pump Laser Sacher TEC 100 -0405 -040 Hot Mirror Aperture f Norwescon 33 Pump Beam Monitor /28

The Far-Fetching Implications of Nonlocal Communication: Faster than Light & Backwards in Time April 3, 2010 Norwescon 33 /28

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° Splitter Pentaprism Splitter photon decoding “latency”, In/Out this would demonstrate a signal transmission speed of Send Receive about 5 times the speed of Mirror light. 90° Pentaprism 1. 0 km Crystal Oven pp. KTP Crystal Mirror D-mirror Mirror 810 nm Horizontal Polarization D-mirror Half-Wave Plate ʘ 405 nm Pump Laser Sacher TEC 100 -0405 -040 Mirror ʘ 810 nm Vertical Polarization Longpass Filter Lens Hot Mirror April 3, 2010 Polarizing Splitter Aperture Norwescon 33 18/28

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 D 1, 2, which is about 50 ms before the signal is transmitted, when the twin entangled photons arrive at D 3, 4. Back-in-time signaling! 90° Pentaprism Crystal Oven Mirror D-mirror 810 nm Horizontal Polarization 810 nm Vertical Polarization ʘ pp. KTP Crystal Longpass Filter Lens Half-Wave Plate ʘ 405 nm Pump Laser Sacher TEC 100 -0405 -040 Hot Mirror April 3, 2010 Polarizing Splitter Aperture Norwescon 33 19/28

Time-Travel Paradoxes April 3, 2010 Norwescon 33 20/28

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? April 3, 2010 Norwescon 33 21/28

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. April 3, 2010 Norwescon 33 22/28

Anti-Bilking Discussions of bilking paradoxes have been published in the physics literature from the 1940 s by Wheeler and Feynman (advanced waves) to the 1990 s 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. ” April 3, 2010 Norwescon 33 23/28

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. April 3, 2010 Norwescon 33 24/28

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. April 3, 2010 Norwescon 33 25/28

Present Status l The experiment has been in testing phases since mid. January, 2007. Our initial attempt to produce downconverted photons with Li. IO 3 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. l The experiment was recently moved from the basement UW Laser Physics Facility to the 2 nd Floor Optics Lab, where we can turn off the lights without interfering with other experimenters. l 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. ) April 3, 2010 Norwescon 33 26/28

Conclusions l 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. l We have so far received about $46 k in contributions from foundations and individuals in support of this work. We have spent most of this on the Mark III system. l This experiment is a rare opportunity to push the boundaries of physics with a simple tabletop measurement. We are pushing hard. April 3, 2010 Norwescon 33 27/28

The End April 3, 2010 Norwescon 33 28/28