Quantum entanglement in communications possible?

Is it possible to move an entangled particle, without disrupting the wave function, to create a communication signal?
 
14
0
Is it possible to move an entangled particle, without disrupting the wave function, to create a communication signal?
well surely if a particle is entangled it's already displaying signs of 'communication' since what happens to one paticle will instantaniously affect the other???
 
227
0
There is no way to send information FTL if that's what you're wondering. Any interaction with a particle in an entangled states tends to break the entanglement, but even then there is no possible way for the two particles to exchange information, so you can't use them for communication. You can however do some very cool things like secure signaling, teleportation, dense coding and stuff, but nothing that violates relativity in any way.
 
14
0
There is no way to send information FTL if that's what you're wondering. Any interaction with a particle in an entangled states tends to break the entanglement, but even then there is no possible way for the two particles to exchange information, so you can't use them for communication. You can however do some very cool things like secure signaling, teleportation, dense coding and stuff, but nothing that violates relativity in any way.
Hold on a sec, why is interaction with a particle that is entangled, breaks the entanglement?
 
227
0
When you just look at one particle in an entangled pair (Bell state), it appears to be in something called a maximally mixed state, which means it has a 50/50 chance of being found spin up or down along ANY axis. But a measurement projects it into a pure state, and in a pure state you can always find an axis along which the probabilities are 1 and 0 or 0 and 1 for spin up/down. So after a measurement, the particle can no longer be in a mixed state, so the entanglement is broken.
 
14
0
Can you simplify by what you mean a mixed state? Are you refering to particle-wave-function property or something else?
 

vanhees71

Science Advisor
Insights Author
Gold Member
13,210
5,186
A mixed state is used to describe a system whose state is not completely determined. A mixed state is described by a positive semidefinite self-adjoint operator [tex]\hat{R}[/tex] with [tex]\text{Tr} \hat{R}=1[/tex], the Statistical operator of the system.

A pure state is a particular case of this more general situation. [tex]\hat{R}[/tex] describes a pure state if it is a projection operator with [tex]\hat{R}^2=\hat{R}[/tex]. Then there exists a normalized state ket [tex]|\psi \rangle[/tex] such that [tex]\hat{R}=|\psi \rangle \langle \psi |[/tex].

Now take a two-spin system in the entangled pure state

[tex]|\Psi \rangle=\frac{1}{\sqrt{2}} [|\mathrm{up},\mathrm{down} \rangle - \mathrm{down},\mathrm{up} \rangle][/tex].

Then the spin of particle 1 is described by the reduced Statistical operator

[tex]\hat{R}=\text{Tr}_2 |\Psi \rangle \langle \Psi |=\frac{1}{2} \hat{1}[/tex]

which is the state of maximal ignorance with respect to the von Neumann entropy as the information measure.
 
Last edited:

Related Threads for: Quantum entanglement in communications possible?

Replies
2
Views
1K
Replies
5
Views
2K
Replies
21
Views
5K
Replies
8
Views
4K
Replies
18
Views
2K
Replies
1
Views
2K
Replies
5
Views
5K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top