Wave, photon, or particle sources can send collimated beams through one or two slits, to a measuring surface {slit experiment, quantum mechanics} {two-slit experiment}. For one slit, beam makes medium intensity line across from slit. For two slits, beam makes line with four times medium intensity across from slit. It makes alternating intense and clear lines on both sides. First intense line to side has two times medium intensity. Second intense line has medium intensity. Third intense line has lower intensity, and so on. Beam waves constructively and destructively interfere.
quanta
Particles sent through two consecutive pinholes create concentric rings on screen, as waves do. Particles sent through two adjacent pinholes make stripes perpendicular to line between pinholes on far screen, as waves do. If one slit closes, ring pattern appears. If slits alternate between closed and open, two ring patterns appear. If detector is at one slit, ring pattern appears. If detectors are poor, feeble stripe pattern appears. If half-silvered mirror is after one slit in particle-stream path, and both paths reflect from mirrors, stripe pattern appears.
wave
Particle motions are not single trajectories but diffract, as waves do. Wave theory accounts for all results. Matrix theory can account for results if slits act together to make periodicity.
Paths entangle, so electrons that pass through beam splitter and go past solenoid coil have quantum interference {Aharonov-Bohm effect}, though no electromagnetic field is outside solenoid coil.
Detectors can be after location at which particles must choose which path to take and can turn on after particles pass decision point {delayed-choice experiment} (Wheeler) [1980].
In two-slit experiments (Scully and Drühl) [1982], tagger {quantum eraser} can be in front of each slit to make spin clockwise or counterclockwise along axis. Screen can detect particle location and spin. There is no interference. Waves are present, but they cancel. Before screen, place spin tagger that always results in same spin. There is interference. Waves do not cancel.
down conversion
A photon can become two photons, each with half the energy {down-converter}. In beam-splitter experiments (Scully and Drühl) [1982], a down-converter can be on each path, to make one photon that continues on that path {signal photon} and one photon {idler photon} that is detected {delayed-choice quantum eraser}. Waves do not interfere.
When information about idler photon is random, because idler photon splits and goes on ambiguous paths, waves interfere. Instruments can receive the information before or after signal photons hit, by any amount of time or space. Waves are always present, but they can cancel.
detector
In two-slit experiments, particles make interference pattern when observed. If detector capable of knowing if particle went through left, right, none, or both slits is after slits, and it indicates that each particle goes only through either left or right slit, never both or none, there is no interference pattern.
If detector can operate without affecting particle in any way, and observer observes it, there is still no interference pattern.
If observer does not observe detector, there is interference pattern, even if detector puts the information in memory awhile and then deletes memory. This suggests that just gaining information is enough to end interference [Seager, 1999].
5-Physics-Quantum Mechanics-Waves
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Date Modified: 2022.0225