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Since quantum entangled particles can transfer the data of their spin properties faster than the speed of light and without any problem of weak signal, can we use quantum entanglement to transfer phone calls and internet connection? Why are we not building up a telecommunication structure based on this technology? What is stopping us? What are the practical difficulties in this process?

Ramji Gupta
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The assumptions you're making in your first sentence are incorrect.

Since quantum entangled particles can transfer the data of their spin properties faster than the speed of light

There is no "data transfer" when one of two entangled particles is measured. The no-communication theorem states that you can't use a measurement of entangled particles alone to communicate information. In order to use entangled particles to communicate, you must also communicate via classical channels at the same time, with all of the limitations that implies.

and without any problem of weak signal

In order to use entangled particles at a distance, you have to physically carry them from one place to another. During their travel, they have the opportunity to interact with everything in their environment, which can alter their state along the way. Correcting this kind of "noise" is a difficult problem, and a substantial amount of research is being dedicated to developing workable techniques to deal with it.

The rest of your question depends on these two assumptions, so since they're incorrect, the question is moot.

probably_someone
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Because quantum entanglement is not a communication technology.

Your question is similar to asking "Why don't we build a communication technology based on the principle of randomly shuffling a deck of cards and distributing it to everyone?"

Randomly shuffling a deck of cards is an example of a classical correlation -- if you check your card and see you got a king of clubs, you know nobody else got that king of clubs, so you now have this extra information. However, there is no actual transfer of information between the two cards, no causal link, only a correlation. Another example: predictions about the future. You make predictions about the future based on what has already happened, based on correlations you already know of between past and future events. This doesn't mean the future has a causal effect on your present.

The standard statement is "information cannot pass faster than light" (to understand the significance of this statement, you need to adopt positivism or Bayesian rationality as your philosophy).

Abhimanyu Pallavi Sudhir
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If you have two entanged qubits, each placed in different area, you can use them for sending another qubit from one place to the other one. This is called quantum teleportation. However, to do so, you firstly have to measure some properties on one side, then send this information classically and on other side to change qubits placed there with this information to get teleported qubit.

Since there is a classical channel for submitting results of measurement, a speed of communication cannot exceed that of light.

Martin Vesely
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