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 ©

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 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 Linked contents

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 -Fundamental particle Photon -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

 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 Particle diffraction

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. Relative graphical distribution of particle hits Screen has a single-slit opening Light source "Single-slit“ pattern forms

Double-slit diffraction Distances to the same point are different  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. Relative graphical distribution of particle hits Screen has a double-slit opening Light source “Double-slit“ pattern forms

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. Relative graphical distribution of particle hits Screen has a double-slit opening Light source 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. 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. Screen has a double-slit opening Light source Particles suffer a random "collapse“ to one set of two flight paths for each of the three particles. Range of probable flight paths. Three particle hits.

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. A B Detectors register which path the photon took Light source 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 A B ???? Detectors can now find which slit the photon transited for its entangled partner that hit the Main screen T1T1 Crystals do not detect anything. They simply create two entangled photons from one initial photon. At time T 1, neither photon has been detected. Given no information has been gathered before impact occurs, particle P should be able to hit anywhere for a double-slit pattern. P AB PAPA PBPB DBDB DADA T2T2 There is a time difference between T 1 and T 2. Particle P AB hits way before its entangled partner is detected at either D A or D B. Main Test

“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… A B However Single-slit patterns have formed without detecting which slit the photon transited. ? At this point in time, neither photon has been detected. ? Experiment therefore reveals the double-slit pattern IS NOT formed although we have not yet determined which slit the photon transited T1T1 PAPBPAPB 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

“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 Double-slit patterns will form on both screens given no "which way“ information has been acquired in entire experiment. A B P AB Detectors now blocked T1T1 DBDB DADA T2T2

“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”. 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”