How does Quantum Teleportation work?
Carlos Mirabelli was a Brazilian physical medium and spiritualist from Sao Paulo, Brazil. He was pretty well-known for his ability to perform various seemingly supernatural feats, such as levitation and telekinesis. Mirabelli showed his most impressive ability in 1926.
In 1926, Mirabelli was about to board a train travelling from Sao Paulo to the port of Santos with some friends when one of his companions saw Mirabelli walk towards the platform and vanish into thin air. In the middle of the day and in front of dozens of witnesses, he faded in a foggy haze without the possibility to be seen anymore.
Mirabelli’s friends were surprised without understanding where he was at that moment.
Everything was solved when 15 minutes later, a station master approached them, telling them that they had a call from Mirabelli himself. Mirabelli claimed that he was suddenly in the town of Sao Vincente, which was 56 miles away from the train’s destination. He also claimed that he practically immediately transported there, realising after his supposed materialisation that only 2 minutes had passed when he disappeared at the train station in Sao Paulo.
Mirabelli story has been told for decades until another teleportation happened.
The Quantum Case
In 1993, Bennett and other physicists discovered a genuine type of quantum teleportation, enabling a quantum state to be transported across long distances without directly sending the quantum state.
Quantum teleportation is the transfer of quantum states from one qubit to one another. It’s not about transferring the information physically, but it’s focused on transferring the information state.
Many physicists followed Bennett, demonstrating this effect even more. For instance, it’s led to essential ideas about reducing the impact of noise on quantum computers and new hardware ideas for building quantum computers. Teleportation is today viewed as a core primitive in quantum information science.
Overview
imagine if there is a physicist, Alice wants to send quantum information to Bob, a researcher in Quantum Biology. Specifically, suppose she wants to send the qubit state |ψ⟩= α|0⟩+β|1⟩. One general idea is to pass the information of α and β to Bob.
However, you can’t do that because once you measure a qubit, a circumstance called decoherence can’t make you achieve so.
No-cloning theorem
you cannot simply make an exact copy of an unknown quantum state.
This is known as the no-cloning theorem. As a result, we can see that Alice can’t simply generate a copy of |ψ⟩ and give the copy to Bob. We can only copy classical states (not superpositions).
However, by taking advantage of two classical bits and an entangled qubit pair, Alice can transfer her state |ψ⟩ to Bob. We call this teleportation because, in the end, Bob will have |ψ⟩ and Alice won’t anymore.
Process
So what can Alice and Bob do (apart from changing their job)?
Part 1: Alice and Bob need to begin by sharing a special two-qubit state to start the teleportation. That qubit state is (∣00⟩+∣11⟩)/√2
Currently, we have 3 qubits, and we want to send 1 qubit.
Part 2: Alice creates Bell pair on her qubits, followed by measuring both of her qubits on the computational basis, with outcomes z and x. These are just conventional classical bits, each taking the value 0 or 1. In quantum circuit language, the way to create a Bell pair between two qubits is first to transfer one of them to the X-basis (|+⟩ and |−⟩ using a Hadamard gate, and then to apply a CNOT gate onto the other qubit controlled by the one in the X-basis.
Part 3: Alice then sends the classical bits z and x to Bob. Sending bits is far easier than sending qubits. Indeed, it can happen on the internet, with a mail Pigeon or any other means. In any case, the information won’t be faster than light because Alice has to send 2 classical bits. In other words, Quantum Teleportation can’t be faster than light.
Part 4: Bob received those qubits.
- If x=1, Bob then applies the Pauli X gate (i.e., the quantum NOT gate) to his qubit
- If z = 1, Bob then applies the Pauli Z gate (i.e., the quantum NOT gate) to his qubit
- If x = 0 or z = 0, Bob can drink a soda.
Bob’s qubit is now in the same state |ψ⟩ that Alice started with.
Mission Compete!
The great main idea to remember is that Alice didn’t know anything about her qubits bust sending 2 classical bits, and Bob could recover (not receive) the information.
Explanation
Bob should be happy always because even if he finds some states such as X |ψ⟩ rather than |ψ⟩, he can use other Pauli gates to make reach |ψ⟩, again!
(Remember that XX=I and ZZ=I)
Experimental results
Work in 1998 verified the initial predictions, and the distance of teleportation was increased in August 2004 to 600 meters, using optical fiber.
Subsequently, the record distance for quantum teleportation has been gradually increased to 16 kilometres and is now 143 km.
A variant of teleportation is called “open-destination” teleportation, with receivers located at multiple locations using five-photon entanglement.
Researchers have also successfully used quantum teleportation to transmit information between clouds of gas atoms, notable because gas clouds are macroscopic atomic ensembles.
Conclusion
In this article, we have seen how quantum teleportation works.
Indeed, we noticed that the ability of quantum information to flow through a classical channel surviving decoherence is the basis of quantum teleportation to be done.
Indeed, a way to transfer the qubit was to transform another qubit’s state after the decoherence of 2 qubits.
There will be many applications in the future following that system. The most interesting ones are in the field of privacy. However, who knows if biology may work in that way, even if we may not be aware of it.
