a) Gravitons are very theoretically

b) you must differ between quantum teleportation and classical communication channels

c) entangled particles always show the corresponding property 

d) Gravitons belong to masses and their gravitation-fields

e) never heard till now, that mass has a corresponding property  

In quantum computation Alice usually transmit her measurement result to Bob over a classical communication channel. Classical channel is limited to the speed of light. If we could transmit quantum states faster than light (e.g. using zero mass gravitons) then my question is could we send information backwards in time? Since we lack of appropriate technology this is only a theoretical question.

Don't understand your question.

Quantum states can be transmitted faster than light to the entangled particle - that's OK. If you measure the state of one particle the corresponding second particle is changing his state too to the corresponding value. (electron A spin-up - electron B spin-down).

So you know the information about the state of the entangled particle.

Till now nobody wrote about any information coming back in any way. That would be a new physical effect. 

Please have a look at M. Nielsen and I. Chuang: Quantum Computation and Quantum Information Cambridge Uni. Press. book 10th an. ed. page 26, chapter 1.3.7  this is the source of my question

Dear Franz,

thank you very much for your comments. My question can be discussed as follows:

The main protocol of quantum teleportation is the following:

My question is related to step 6. If Alice is using a massless spin-2 boson particle (aka. graviton) and create a gravitational wave (using an advanced non-thermal graviton generator) that can be detected by Bob (using a gravitational wave detector, like the Advanced LIGO system) and she can code the two bit information to the waves, then Bob can decode it immediately and we can eliminate the time consuming classical channel and probably can send information back in spacetime (since even the light hasn't yet had time to travel the distance between location A and location B)?

Dear Attila,

I am no Physicist, I am Information Scientist interested in real Quantum Computing, so I may not know all. 

From my point of view not possibility is:

 mix of QuBits and classical bits and

I don't know if gravitation-waves have corresponding properties for entanglement. 

You think about three systems : the entangled pair of particles by Bob and Alice, the gravitation-wave-system and the classical 2 bits.

Of course Alice could send back information, but only gravitational-waves or 2 bits in classical way. 

Gravitation-waves would act in speed of light, the classical 2 bits depend on the system which Alice uses for it - if light then its the same speed.

I hope I could help you - I wouldn't mix up all these 3 systems - so you get a possible answer by your own.

.

Dear Franz,

thank you for your comment, I agree with you, there seems to be no benefit using graviton for superluminal communication due to the limit of the speed of gravitational-waves.

There is another particle that could be interesting in this case and this is the Tachyon (if you are still interested, you can get more information here: https://en.wikipedia.org/wiki/Tachyonic_antitelephone ).

Best regards,

Attila

Dear Mohamed,

thanks, but I am more curious than greedy :-)

It seems that the real problem is not how to get an answer to a particular question, but the fact that every answer leads us to another question.

What would you prefer:

• a universe that is fully understandable after answering lots, but finite number of questions, or
• a universe that always keeps us far from fully understanding, but provides us enough question not to be bored?

No, because it's not known how to describe ``graviton shot noise'', nor is it known how to sum over intermediate configurations of gravitons. Only coherent superpositions of a macroscopic number of gravitons, I.e. classical gravitational waves, can be described quantitatively. For quantum teleportation studies, where the spacetime geometry is classical, this isn't a problem.

I would be more empirical

Before speculation on such matters, first wait till they directly detect

a gravitational wave, let alone a graviton.