Delayed choice quantum communication - "Berlin riddle"

In summary, a sender in Berlin and a recipient on the moon were expecting a specific event to occur at 12:00h. The sender sent a photon through a double slit towards the moon 0.8 seconds before 12:00h, with the expectation that it would miss the detector on the moon and indicate that the event had not occurred. However, at 12:00h, it was discovered that the event had not occurred and the double slit was immediately removed at the sender's location. This was done in the belief that it would cause the photon to follow the wave function and miss the detector on the moon. As a result, no signal was measured on the moon 0.2 seconds after 12:00h
  • #1
Bob Ziegler
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At 12.00h a specific event is being expected in Berlin, whether the wall ist teared down, or not. The sender is in Berlin and wants to send the information about the event to the recipient on the moon. Both sides know about the possibly upcoming event. As the light takes 1 second to the moon, the sender sends 0.8 seconds before 12:00h a photon through a double slit in direction of the moon. The photon (slit inormation) is being measured and stored at the double slit, through what slit it went, that's why it is assumed the photon goes straight towards the moon, without effect of the wave-function. The recipient expects 0.2 seconds after 12:00h an incoming photon or no signal, and knows before: incoming photon means, that the "wall was teared" down, a missing photon means "wall still standing". At 12:00h it turns out, that the wall is still standing. The double-slit is immediately being removed at the sender in Berlin, so that the path-information is being destroyed, in expectation, that the photon in superposition does not longer fly straight, but now corresponding to the wave function, so that it misses the detector on the moon very likely. On the moon no signal is measured 0.2 after 12:00, with the interpretation that the wall is still standing. That is how the moon knew whithin 0.2 seconds about the event on earth, whereas a usual communication would have taken 1 second.

This idea of communication requires prior information (how to act) at both spots, and the light goes in usual speed towards the moon. So it appears to be no ftl communication.

But does it work that way?
 
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  • #2
Your scenario is very difficult to understand. Can you state clearly what is the expected result in all cases?

Bob Ziegler said:
The double-slit is immediately being removed at the sender in Berlin, so that the path-information is being destroyed, in expectation, that the photon in superposition does not longer fly straight, but now corresponding to the wave function, so that it misses the detector on the moon very likely.
There is nothing you can do to the double-slit setup after the photon has passed through the slits that will affect that photon.

Note also that one photon does not give an interference pattern. It is the cumulative effect of many photons that will do that.
 

What is delayed choice quantum communication?

Delayed choice quantum communication is a form of quantum communication where the sender and receiver can choose to either send or not send a message after the communication channel has been established. This means that the sender can decide to send a message or not based on the measurement of a quantum system, even after the communication has started.

How does delayed choice quantum communication work?

In delayed choice quantum communication, the sender and receiver share an entangled quantum state. The sender then performs a measurement on their part of the entangled state, which affects the receiver's part of the state. Based on the measurement outcome, the sender can choose to either send or not send a message to the receiver.

What is the "Berlin riddle" in delayed choice quantum communication?

The "Berlin riddle" is a thought experiment proposed by physicist John Wheeler to illustrate the concept of delayed choice quantum communication. It involves a sender in Berlin and a receiver in New York, sharing an entangled quantum state. The sender can choose to measure their part of the state and send a message to the receiver, or not measure and not send a message, even after the communication has started.

What are the potential applications of delayed choice quantum communication?

Delayed choice quantum communication has potential applications in secure communication, quantum teleportation, and quantum computing. By allowing the sender to make a decision after the communication has started, it can improve the efficiency and security of these processes.

What are the current challenges and limitations of delayed choice quantum communication?

One of the main challenges of delayed choice quantum communication is the difficulty in maintaining and controlling entangled quantum states. Additionally, the practical implementation of this concept is still in its early stages, and more research is needed to fully understand its potential and limitations.

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