Quantum Teleportation is a technique to transfer quantum information of a particle from one place to another without any medium.
Has Quantum Teleportation been done?
Yes many successful experiments have been done on quantum teleportation. But the first successful longest distance teleportation was done by china.
Quantum Teleportation China:
In 2017, China’s researchers reported that they have succeeded in teleporting a photon to a satellite present somewhere on the lower orbit of the universe. This news spread like a fire in the whole world. Commoners started presuming that china has teleported a person from one place to the other as shown in movies. But, this is not true.
Whenever, we talk about term teleportation. That means to dematerialize a matter from one place and materialize it again at some other place. Simply, to transfer a body from one place to another.
The thing that China achieved was Quantum Teleportation that’s totally different from classical teleportation. In quantum teleportation, instead of transferring any object, we teleport quantum information from one place to the other. Or we can say that quantum information is transferred without using a medium. China was succeeded in transmitting the quantum information of a photon from a desert on earth to a satellite without using any medium. And for your information let me tell you, this was not the first time when teleportation was made successful. Many successful experiments have already been performed on teleportation by different countries. But, for the first time teleportation was done through such a long distance. The satellite to which china teleported the photon was 500km away from the earth. This was the first successful longest distance teleportation.
Misconceptions about quantum teleportation
The term quantum teleportation is quite confusing for many. People have misconception that teleportation means to transfer an object physically from one place to the other. But in actual, only quantum information is transmitted. It can also be called quantum communication.
Applications of Quantum Teleportation
Quantum teleportation is more beneficial for us because it can make our communication network fully secure or hacking proof in future.
Quantum teleportation can be used to quickly transfer information from one place to another without any medium. No Cloning and No Deleting theorem tells us that quantum information can neither be copied nor destroyed. When quantum information is transferred from position A to B, than the original information changes into some other form. Since, the information is totally transferred, we can say that it has teleported.
To understand Quantum teleportation, one should be aware of quantum entanglement .
In specific circumstances when a particle is subdivided into two particles. The properties of these two particles are linked in such a way that these start working as combined system. For example, if one of these particles has up spin the other must have down spin and vice versa. These particles are called entangled particles. These entangled particles effect each other no matter how far these are placed form each other. Now, I hope you have an idea of quantum entanglement .
Difference Between Classical Bits and Qubits:
In classical bits there are only two possible states ‘0’ or ‘1’. Bit can exist in one of these states at a time. But, qubit can exist in these two states at the same time. Because of this factor, the memory of quantum computer thousands of time higher then classical computer.
How Quantum Teleportation works:
Let’s say John at position A has a photon which he wants to transfer to Mike at position B. Here, It’s necessary to know that as Bits are used in computers similarly, Qubits(quantum bits) are used in quantum computing or quantum teleportation. Coming to the point, John needs a pair of entangled particle. He will keep one entangled particle with him and send the other particle to Mike. As entangled particles effect each other. So, by measuring, we’ll get to know that if spin of John’s particle is up, than its certain that Mike’s particle exhibits down spin and vice versa.
As we are taking about quantum particles, we cannot neglect the superposition principle.
Superposition principle tells us that quantum particles exists in all possible states unless we observe them, this state of particle is called superposition state. When we start observing or measuring a particle’s state, its wave functions collapse and at the end we get only one state of all the possible states of that particle.
For Example, when a quantum particle is unobserved , it possesses both up and down spin. But, when we start observing it, its wave functions collapse and at the end we get only one state either up or down. Until John measures or observe his pair of photons(A and C), these remain in superposition state.
But, when he measures these particles individually, their wave function collapse and both photons will go in some particular state and John will not be able to teleport C in this way. So, instead of measuring individually, he will have to measure to the combined state of both photons(A and C) .This kind of measurement is called ‘Bell Measurement’. Though Bell measurement does not tell us about the individual state of each photon, but it tells us about the relation between the states of two photons.
In Measurement rule we studied that, when we measure a quantum particle, its wave functions collapse and it goes to a single state of all the possible states. That’s why, when John measures the combined state of A and C. These two photons interact with each other. As photon ‘A’ was entangled. So, the quantum state of photon ‘C’ will also reach ‘B’. Now, photon ‘B’ have all the information of quantum state of ‘C’. Now, a perfect colon of ‘C’ can be formed by manipulating it. But, Mike is not aware that he has the quantum information of ‘C’ also he does not know that what action should he take to manipulate it to get photon ‘C’. To make this teleportation successful, John needs to send information to Mike through some classical communication system (e.g: Telephone, Telegram or mail etc) .
This information includes the result that John concluded when he measured the combined state of ‘A’ and ‘C’ by ‘Bell measurement’. We send this information through 2 classical bits. By this information Mike will be able to take the action to manipulate the photon so that photon B will get the quantum state of photon C. By this action, quantum entanglement between A and B will break. And now B has the quantum state of photon C. Now, We can say that photon C has been teleported from John to Mike.
we need classical communication channels to make quantum teleportation successful because it does not break the laws of special theory of relativity. But wait! John still has photon C, than how can we say that photon has been teleported to Mike. Actually, No Cloning and No Deleting theorem tells us that quantum information can neither be copied perfectly nor it can be deleted or destroyed completely. As quantum information can not be copied or cloned. So, when Mike manipulates the photon B and extracts the quantum state of photon C, The C photon at John’s place will change to some other quantum state. It’s properties are not same as before teleportation. All of its properties have been transferred to photon at Mike’s place. That’s why it is called teleportation. So, now you have seen that in quantum teleportation the object itself is not transferred but it’s quantum information is transmitted.
To increase the understandability, let me give you a practical example of quantum teleportation. You’ll be able to understand how quantum teleportation can make the communication system hacking proof.
Let’s suppose that John has some sensitive information which he has encoded in the spin state of his quantum particle. For example, if there’s up spin than encoder binary number is 1 and if there’s down than encoder binary number is 0. Let say he wants to tell Mike who is at some distant place, that he has binary number 1. He can transfer this information through fax, mail or any classical media, but none of these communication channel is safe. It means that anyone can hack this information. But, through quantum teleportation any third party can not hack this information. Let us see how it works.
John already has a quantum particle which exhibits some encoded message. To transfer this message to Mike securely, John needs a pair of entangled particles. He’ll keep one and give the other particle to Mike. Now, John will calculate the combined state of these particles by Bell measurement. By this measurement he will not be able to know the quantum state of individual particle. But, he will get to know the relationship between these two particles. For example, he got to know that the state of these two particles are opposite to each other. When John measured the state of particles A and C, these two particles interacted with each other that caused any interaction between the quantum state of these two particles. As particle A was entangled with particle B. So, the interaction between A and C means that at the same time A also interacted with B. And the quantum state of C reached B through A. This caused the breakage of entanglement between A and B. Now A and C are entangled with each other. Here, You need to know that the quantum state of C has now changed. Mike has received the information that John wanted to send him and now Mike only needs to extract this information. But Mike still does not know what information he has received. Now, John will send an information through some classical communication channel(e.g: Fax, Mail, Telephone etc) in which he tells that the state of two particles is opposite to each other. If a third person hacks this information, he’ll only get to know that the measured state is opposite. As this information makes no sense So, it’s useless for him. Any ways, when Mike will get this information. He’ll measure the state of particle he has. As this particle was entangled so its state was changed when John did some measurement with its partner particle. If Mike find that the spin state of this particle is up, he will understand that at the time when John measured, the state of its partner particle was up. Now, Mike will concentrate on the information that John sent him in which he told that the measured states are opposite. As, Mike already knows that the spin of entangled particle A is down it means that the opposite particle has an opposite spin. From this it’s certain that particle C had Up spin. On the basis of this data, if Mike manipulates quantum particle B, he can get the exact state of particle C that was at John’s place. Means information has been safely transmitted to Mike. As the state of original particle C at John’s place has now been changed. We can say that information has teleported.
As in this kind of communication system, Qubits are used instead of Bits and quantum computers are used instead of normal computers. So, this system will be faster and safer then current communication system. To make this kind of communication system we need a lot of entangled pairs. As with one pair of entangled particles we can teleport only one Qubit.
In this article I have tried to teach the protocol of quantum teleportation in simple words. But there’s a complex mathematics behind it. To understand that you need to know the concept of quantum spin and mathematics of bell states quantum mathematics and Quantum logics.
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