What Is The Quantum Eraser Experiment?

By Antonia Čirjak on June 10 2020 in Science

The quantum eraser experiment is a concept in quantum theory.
The quantum eraser experiment is a concept in quantum theory.
  • The quantum eraser experiment is a variation of older experiments in quantum theory, dealing mostly with the double-slit experimention.
  • The double-slit apparatus helps us experiment on the interference patterns between the photons with the changes being reversible.
  • This experiment proves the concept of complementarity, which states that all objects have certain complementary properties that can’t be observed or measured simultaneously.

The quantum eraser experiment is a concept in quantum theory. It is exhibited via an experiment through which we can actually witness several important aspects of quantum mechanics. Some of these aspects include complementarity and quantum entanglement. The experiment itself is actually a variation of older experiments in quantum theory, mostly the double-slit experiment.

It is based on the fact that when we use an action to try and figure out which of the two slits a photon passed through, the photon can’t intervene with itself anymore. It is actually an incredibly complex experiment that helps us mark photons, but they can also be unmarked afterward. Once we mark the photons we can’t see the fringes they create.

We mark the photons by interacting with them, and they can’t produce fringe patterns anymore because of this. To produce fringe patterns they need to be able to interfere with themselves. However, when unmarked, they can continue to produce fringes.

Setting Up The Experiment

The quantum eraser experiment is performed using a special apparatus which has two sections. We create two entangled photons and separate them in the different parts of the apparatus. However, if we do anything to examine one photon, or interact with it in any way, it will actually influence the other photon. This works both ways.

We can manipulate these photon partners this way because of this double-slit apparatus. It helps us experiment on the interference patterns between the photons, even destroy them, but the change will not be permanent. The photon that is entangled can be manipulated in different parts of the experiment, before or after passing through the slit. There is also a variation of the experiment called the delayed choice quantum eraser, which allows us to measure the chosen path of information that will be delayed until the photon that is going through the slits manages to interfere with itself.

A Simplified Explanation

The quantum eraser experiment started out as just an idea, but eventually, we managed to actually perform it. It was first performed in 1999. We start things off by letting light photons travel through a double slit. Once the light exits it will hit a prism that will split a photon into a pair of photons. After this, the next course of action is determined by the slit the single photon passed through. There are the top and bottom slits in the apparatus. 

If it passes through the slit that is placed on top, it will go to the half-silvered mirror beam splitter. If it passes through the bottom slit it will be directed by the prism to a different half-silvered beam splitter. It changes its direction. These half-silvered beam splitters reflect exactly one half of the photon while allowing the other half to pass through.

The thing with this experiment is that it is incredibly complex to everyone but people well versed in quantum theory. Well, one could say the same about anything related to quantum theory. Still, the point of the experiment is this: in a way, this experiment “erases” the past in a way that makes it impossible for us to know which slit the photon passed through. This experiment proves the concept of complementarity, which states that all objects have certain complementary properties that can’t be observed or measured simultaneously. The concepts of time and space really don’t mean a lot in quantum theory.

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