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Delayed - choice quantum eraser

Delayed - choice quantum eraser  


we all know are present affect the future what we do today it's affect the future , but in the quantum world the future affect the past in quantum physics we learn very tiny particles .... according to quantum physics theory Delayed - choice quantum eraser ,  future affect the past  .....



 delayed choice quantum eraser theory ?

A delayed quantum eraser experiment first performed by  YOON-HO KIM and other reported in early 1999 is an elaboration on the quantum eraser experiment that incorporates concept considered in wheeler's delayed - choice experiment . the experiment was designed to investigate peculiar consequence of the well- known double slit experiment in quantum mechanics as well as the consequence of quantum entanglement .....




what does quantum eraser experiment tell us ?

when you measure the photons it is finally possible to think its properties classically and the wave function allows one to calculate all probabilities that outcomes will be something or something else , in the case of the quantum eraser , we store the interference pattern . 


Does quantum eraser break causality ?

The delayed choice quantum eraser is no refutation of the principle of causality . 


what is the delayed measurement experiment ?

In the delayed choice quantum eraser experiment that would mean quantum doesn't become real until you measure it , which could be billion of years after its origin in the case of quasar light , quantum objects are real , but simply have indefinite properties these properties are defined by the experiment we do .



How does  a quantum eraser work ?

The quantum eraser experiment is a variation of Thomas Young's classic double -slit experiment . it establishes that when action is taken to determine which of 2 slits a photons has passed through , the photons cannot   interfere with itself. When a stream of photons is marked in this way, then the interference fringes characteristic of the Young experiment will not be seen. The experiment also creates situations in which a photon that has been "marked" to reveal through which slit it has passed can later be "unmarked." A photon that has been "marked" cannot interfere with itself and will not produce fringe patterns, but a photon that has been "marked" and then "unmarked" will interfere with itself and produce the fringes characteristic of Young's experiment



EXPERIMENT 

This experiment involves an apparatus with two main sections. After two entangled photons are created, each is directed into its own section of the apparatus. Anything done to learn the path of the entangled partner of the photon being examined in the double-slit part of the apparatus will influence the second photon, and vice versa. The advantage of manipulating the entangled partners of the photons in the double-slit part of the experimental apparatus is that experimenters can destroy or restore the interference pattern in the latter without changing anything in that part of the apparatus. Experimenters do so by manipulating the entangled photon, and they can do so before or after its partner has passed through the slits and other elements of experimental apparatus between the photon emitter and the detection screen. Under conditions where the double-slit part of the experiment has been set up to prevent the appearance of interference phenomena (because there is definitive "which path" information present), the quantum eraser can be used to effectively erase that information. In doing so, the experimenter restores interference without altering the double-slit part of the experimental apparatus.



A variation of this experiment, delayed choice quantum eraser , allows the decision whether to measure or destroy the "which path" information to be delayed until after the entangled particle partner (the one going through the slits) has either interfered with itself or not. In delayed-choice experiments quantum effects can mimic an influence of future actions on past events. However, the temporal order of measurement actions is not relevant. 

First, a photons is shot through a specialized nonlinear optical device: a  (BBO) crystal. This crystal converts the single photon into two entangled photons of lower frequency, a process known as  (SPDC). These entangled photons follow separate paths. One photon goes directly to a polarization-resolving detector, while the second photon passes through the double-slit mask to a second polarization-resolving detector. Both detectors are connected to a coincidence circuit , ensuring that only entangled photon pairs are counted. A stepper motor moves the second detector to scan across the target area, producing an intensity map. This configuration yields the familiar interference pattern.Next, a circular polarizer  is placed in front of each slit in the double-slit mask, producing clockwise circular polarization in light passing through one slit, and counter-clockwise circular polarization in the other slit . (Which slit corresponds to which polarization depends on the polarization reported by the first detector.) This polarization is measured at the second detector, thus "marking" the photons and destroying the interference pattern...

Finally,linear polarizer   as introduced in the path of the first photon of the entangled pair, giving this photon a diagonal polarization . Entanglement ensures a complementary diagonal polarization in its partner, which passes through the double-slit mask. This alters the effect of the circular polarizers: each will produce a mix of clockwise and counter-clockwise polarized light. Thus the second detector can no longer determine which path was taken, and the interference fringes are restored.

A double slit with rotating polarizers can also be accounted for by considering the light to be a classical wave.However this experiment uses entangled photons, which are not compatible with classical mechanics.



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