Do you know what quantum entanglement and quantum teleportation are? Most people are confused with quantum teleportation. In 2016-17, Chinese researchers announced that they had succeeded in teleporting photons to a satellite in Earth’s lower orbit. At that time the news spread rapidly throughout the world and people felt that teleportation in the Star Tracks Hollywood movie has now become a reality but in reality, it was something else. Whenever we talk about teleportation we mean that to d-materialize an object from one place to another, to materialize again, i.e. to physically transfer a body from one place to another, that isn’t true. If we call quantum teleportation as quantum communication then it will not be wrong. But what China achieved was quantum teleportation. The concept of which is completely different from classical teleportation. In this, we teleport quantum information to the place of an object or say that quantum information teleport from one place to another without any medium. So what China did was that it succeeded in teleportation quantum information of a photon from a Gobi Desert on Earth to a satellite in space without any medium. It was not that quantum teleportation was not tested by anyone else. There were already tests done on Earth, but before that, no country had done this on space from Earth and the satellite that China tested was orbiting at an altitude of 500 km above the Earth. For the first time, this test was conducted between such distances, so China gained fame for this work. Quantum teleportation is important for us because it can make future communication networks hacking proof. So let’s know what quantum teleportation is and how it can make our communication network hacking proof.
What is Quantum Teleportation?
In quantum teleportation, we already know that it teleport quantum information, not an object and that too without any medium and instantly. “No cloning, No deleting” theorem tells us that quantum information can neither be copied nor destroyed. When quantum information is teleported to the satellite from the earth, then the information of the entangled particles present on the earth changes to another information. It appears to us that all the information of the entangled particles present on Earth has been teleported to the entangled particle present on the satellite. Hence it is called quantum teleportation. Now we know how it works.
Before understanding it’s working principle, you have to understand quantum entanglement. So let’s know what is quantum entanglement?
What is Quantum Entanglement?
Until quantum particles are not observed, they do not exist in any one state but are present in all their possible states simultaneously. Which we know as the Superposition States. Let us understand this by example. Subatomic particles such as electrons have an intrinsic property called spin. The spin here does not mean that they are rotating particles. Spin is a form of angular momentum. There are two states of such spin. These occur either in the up states or in the down states. If we talk about the superposition theorem, then they exist simultaneously in both of their possible states and not in any one state. That is, they occur simultaneously in the up states and in the down states. We call this state the superposition state.
The point to note here is that superposition states are not like a coin-tossing case. If we talk about a coin, it has two faces, one head, and the other tail, i.e. a coin has two possible states. When we toss the coin in the air, we do not know which states will come after the fall, i.e. as long as the coin is in the air, we do not know which states it is in. Although to a large extent it resembles the superposition states, it is not. Actually, as long as the coin is in the air, we don’t know if the head is coming or the tail, but on the coin already the head is hidden on one side and the tail on the other side, but if we talk about superposition states, then nothing is fixed on this already. Superposition only means that quantum particles are present in all possible states and not in one of their states. That is, they are together in their up states at the same time also in the down states. Now you must have understood the superposition principle.
Unless we are obeying quantum particles, they are in superposition states, and as soon as we start observing them. Similarly, their wave function collapses and only one of the possible states is selected and in the end, we get similar states.
Entangled particles are used in quantum entanglement. In some special circumstances, when two particles are created simultaneously by dividing a photon, then the properties of both those particles are linked in such a way that they start working like a combined system. If one spin is up, the other will be down. If we talk about a photon as an example, then the photon has no spin of its own, but electrons and positrons have their own spin. If the spin of the electron is up, then the spin of the positron will always be down, and if the spin of both the electron and the positron are combined, the total spin will be zero which is that of the photon because both are made up of one photon, i.e., it is certain that if one of these two is spin up, the other will be down, but we cannot tell which of them will be whose spin. From the perspective of quantum theory superposition states, until we observe them, they are simultaneously in their up states as well as in the down states.
Now, if we talk about entangled states, then it is a state in which two particles are linked to each other in such a way that both of them exist only in combined states. That is, we can’t tell the states of either one without knowing the states of both the particles. Therefore, we call them entangled particles. These particles instantly affect each other in a system. Such behavior of these particles was strange to Einstein, so he called it “Spooky Action at a Distance“.
Before proceeding further, I would like to tell you that qubits are used in quantum computing and quantum teleportation, just as bits are used for computing in a computer. I have explained, what is the difference between bits and qubits, in my previous blog “What is Quantum Computer? ”.
How to work Quantum Teleportation?
Suppose there are two persons named Alice and Bob who are quite far from each other. Alice has a photon named C that he wants to transport to Bob. So how will he do it? For this, he will need a pair of entangled particles. One of which he will keep the entangled particle with him and will send the other entangled particle to Bob because entangled particles affect each other. If after measuring, Alice entangled particles come up spin, then it is certain that Bob’s entangled particle will be spin-down and if the spin-down of Alice’s entangled particle comes, then it is certain that Bob’s entangled particle will also spin up. Since we are talking about quantum particles here, we cannot ignore the superposition theorem either. The superposition theorem tells us that they exist in all possible states until we observe or measure quantum particles and as soon as we start observing them. Similarly, their wave function collapses and only one of the possible states is selected and in the end, we get similar states. Until Alice measures both of her nearby photons, they will remain in the superposition states. If Alice measures both his photons i.e. A and C, then their wave function collapses and both photons move to a particular state, which causes Alice don’t be able to teleport photon C to Bob so instead of measuring both photons individually, one will measure the combined states of both. We call this particular measurement of “Bell measurement“. This does not allow us to know which photos are in which states. But it is definitely known what is the relationship between the two photons. In the measurement rule, we saw that as we measure the quantum particle, its wave function collapses and it moves to one of the particular states of all possible states. Therefore, as Alice measures the combined photons near him, both photons will interact with each other. Since particle A was already entangled, the quantum of particle C would reach particle B through particle A and that too instantly. Since particle B now contains all the quantum information of particle C, we can make the correct clone of particle C. But Bob is not yet known that he has got Quantum Information. Therefore Bob cannot currently create particle C by manipulating particle B and at the same time. He does not know how to manipulate particle B to create particle C. So Alice must send the information to Bob using the classical communication channel, telling him what his result was when he measured both of the combined photons with the Bell measurement. We send this information through 2 classical bits. When Bob gets this information, then he will know what action to perform on particle B to get quantum information of particle C. After manipulates particle B by Bob, the bond between particles A and B will break, and as we do so, we’ll say that Alice teleported photon C and transmit to Bob. “No cloning, No deleting” theorem tells us that quantum information can neither be copied nor destroyed. As Bob extracts the information of particle C through particle B, the states of particle C are converted to other states, i.e., now all the properties of photon C have been transferred to photon B. Therefore we call it teleportation.
Hacking proof Communication Network:
Now let us know how our current communication network can become hacking proof in the future with Quantum Teleportation. Suppose Alice wants to send secret information to Bob. If they send the encoded information through classical communication systems like telephone, email, fax then the information can also be changed by the hackers. If Alice sends the same information through the entangled particles, then the encoded information will instantly reach to Bob without any medium, which Bob can decode and get the information. Since such communication will use qubits instead of bits and quantum computers instead of classical computers. It will be faster and secure than the existing communication system. To stabilize such a communication system, not one but a lot of entangled particles would be required because only one qubit can be teleported from a photon. If you want to understand quantum bits practically, then you can go down and use the Quantum-Kit (a graphical quantum circuit simulator.