Quantum teleportation of a 2 qubit entangled state
Teleportation — the transfer of a quantum state from one place to another — is one of the most intriguing phenomena quantum physics has to offer. It is central to quantum communication, and plays an important role in a number of quantum computation protocols. Single bits of quantum information have been teleported before, for example for Photons and Atoms (Ions). However, teleportation of single qubits is insufficient for a large-scale realization of quantum communication and computation. Recently, for the first time, we could realize teleportation for a more complex quantum state, a two qubit composite system: A general entangled state of two photons. In the experiment, we develop and exploit a six-photon interferometer to teleport an arbitrary polarization state of two photons. The observed teleportation fidelities for different initial states are all well beyond the state estimation limit of 0.40 for a two-qubit system. Not only does our six-photon interferometer provide an important step towards teleportation of a complex system, it will also enable future experimental investigations on a number of fundamental quantum communication and computation protocols.
Schematic diagram showing the principle of two-qubit quantum teleportation. Alice wants to teleport an unknown state of a system composed of photons 1 and 2 to Bob. To do so, Alice and Bob first share two entangled photon pairs (EPR source), photon pairs 3–5 and 4–6. Alice then carries out a joint Bell-state measurement (BSM) both on photons 1 and 3 and on photons 2 and 4, respectively. On receiving Alice’s BSM results via classical communication, Bob can then carry out a corresponding unitary transformation (U) on both photons 5 and 6 to covert them in to the original state of photons 1 and 2.
Schematic diagram of the experimental setup. The ultraviolet pulse passes through a BBO crystal to generate a polarization-entangled photon pairs in modes 1-2 and 3-5 and 4-6. The photons are all detected by silicon avalanche single-photon detectors.