# What happens when we insert detectors in a delayed choice experiment?

• entropy15
In summary, the conversation discusses an experiment involving an electron gun emitting electrons through two slits onto a screen. By adding detectors in between the slits and the screen, the interference pattern disappears and the electron is detected at either of the telescopes with a 50:50 chance. The question is whether there would be any difference in the detection pattern at the detector array depending on whether the screen is up or down. The usual rule is that the pattern changes according to whether or not which-slit information is available.
entropy15
Consider the below (figure 1), an electron gun is made to emit electrons one by one through two slits S1 and S2.
There is a screen at the other side and a pair of telescopes (with electron detectors inside them) T1 and T2 trained on the slits S1 and S2 respectively.
We can choose to bring down the screen even after the electron has crossed the slits.

If we choose to keep the screen up, we get an interference pattern as more and more electrons move through the slits.
But if we choose to remove the screen the electron is always detected either at T1 or T2 with a 50:50 chance.

Now if we choose to insert an array of detectors in between the slits and the screen/telescopes (figure 2), the electron will be detected in only one of the detectors in the array as it moves from the slits to the screen.

How does the detector affect the entire set up?

Consider that we have the screen up. Since we have the detectors the interference pattern should disappear.
If we have the screen down, then the electron shows up only at either of the telescopes.
So wouldn't the electron be detected at the detectors which are in line with the telescopes T1 and T2.

The question is whether there would be any difference in the detection pattern (at the detector array) depending on whether the screen is up or down?

#### Attachments

• fig1.jpg
6.3 KB · Views: 470
• fig2.jpg
8.2 KB · Views: 461
Welcome to PhysicsForums, entropy15!

The setup you propose is not clear to me as to what you are varying that is of significance.

The usual rule is the pattern changes according to whether or not which-slit information is available (in principle, regardless of whether the observer actually obtains it). So I am not sure I see where this element is being varied. Raising or lowering the screen doesn't change that.

## What is a delayed choice experiment?

A delayed choice experiment is a thought experiment in quantum mechanics that explores the concept of wave-particle duality. It involves a setup where a particle's behavior can be observed as either a wave or a particle, depending on the choices made by the observer after the particle has already passed through the setup. This challenges our traditional understanding of cause and effect, as the choice made by the observer seems to retroactively determine the particle's behavior.

## What is the significance of delayed choice experiments?

Delayed choice experiments have significant implications for our understanding of reality and the nature of time. They suggest that the act of observation can affect the behavior of particles in the past, which challenges our traditional understanding of causality. This has led to debates and discussions about the true nature of reality and the role of consciousness in the universe.

## How are delayed choice experiments conducted?

Delayed choice experiments are typically conducted using a setup called the Mach-Zehnder interferometer, which splits a beam of particles into two paths. One path leads to a detector that measures the particle's behavior as a wave, while the other path leads to a detector that measures the particle's behavior as a particle. The choice of which detector to use is made after the particle has passed through the setup, and the results of the experiment can be observed and analyzed.

## What are some real-life applications of delayed choice experiments?

While delayed choice experiments are primarily thought experiments used to explore the fundamentals of quantum mechanics, they have also been applied in practical applications such as quantum cryptography and quantum computing. These experiments have also sparked new ideas and theories about the nature of time and the role of consciousness in the universe.

## What are some criticisms of delayed choice experiments?

Some critics argue that delayed choice experiments are purely theoretical and do not have any real-world implications. Others argue that these experiments do not actually challenge our understanding of causality and are simply a result of our limited knowledge and understanding of quantum mechanics. Additionally, there are debates about the interpretation and implications of the results of these experiments, which continue to be a topic of discussion among scientists and philosophers.

• Quantum Physics
Replies
2
Views
536
• Quantum Physics
Replies
28
Views
860
• Quantum Physics
Replies
33
Views
3K
• Quantum Physics
Replies
2
Views
848
• Quantum Physics
Replies
5
Views
881
• Quantum Physics
Replies
16
Views
1K
• Quantum Physics
Replies
8
Views
1K
• Quantum Physics
Replies
4
Views
1K
• Quantum Physics
Replies
18
Views
1K
• Quantum Physics
Replies
32
Views
2K