Quantum teleportation

Moreover, the location of the recipient can be unknown, but to complete the quantum teleportation, classical information needs to be sent from sender to receiver.

Entanglement imposes statistical correlations between otherwise distinct physical systems by creating or placing two or more separate particles into a single, shared quantum state.

These correlations hold even when measurements are chosen and performed independently, out of causal contact from one another, as verified in Bell test experiments.

The main advantage with this is that Bell states can be shared using photons from lasers, making teleportation achievable through open space, as there is no need to send information through physical cables or optical fibers.

[9] Understanding quantum teleportation requires a good grounding in finite-dimensional linear algebra, Hilbert spaces and projection matrices.

Nevertheless, a teleportation protocol analogous to that described above can still be (conditionally) implemented by exploiting two independently prepared qubits, with no need of an initial Bell state.

[11] Work in 1998 verified the initial predictions,[2] and the distance of teleportation was increased in August 2004 to 600 meters, using optical fiber.

[14] There has been a recent record set (as of September 2015[update]) using superconducting nanowire detectors that reached the distance of 102 km (63 mi) over optical fiber.

[18] In April 2011, experimenters reported that they had demonstrated teleportation of wave packets of light up to a bandwidth of 10 MHz while preserving strongly nonclassical superposition states.

[22][23] On 26 February 2015, scientists at the University of Science and Technology of China in Hefei, led by Chao-yang Lu and Jian-Wei Pan carried out the first experiment teleporting multiple degrees of freedom of a quantum particle.

[24][25][26] In 2016, researchers demonstrated quantum teleportation with two independent sources which are separated by 6.5 km (4.0 mi) in Hefei optical fiber network.

[28] In December 2020, as part of the INQNET collaboration, researchers achieved quantum teleportation over a total distance of 44 km (27.3 mi) with fidelities exceeding 90%.

[3] Zeilinger's group developed an experiment using active feed-forward in real time and two free-space optical links, quantum and classical, between the Canary Islands of La Palma and Tenerife, a distance of over 143 kilometers.

In order to achieve teleportation, a frequency-uncorrelated polarization-entangled photon pair source, ultra-low-noise single-photon detectors and entanglement assisted clock synchronization were implemented.

The two locations were entangled to share the auxiliary state:[14] La Palma and Tenerife can be compared to the quantum characters Alice and Bob.

Alice will perform a Bell-state measurement (BSM) that randomly projects the two photons onto one of the four Bell states with each one having a probability of 25%.

[14] The results of Zeilinger's group concluded that the average fidelity (overlap of the ideal teleported state with the measured density matrix) was 0.863 with a standard deviation of 0.038.

An 800-meter-long optical fiber wire was installed in a public sewer system underneath the Danube River, and it was exposed to temperature changes and other environmental influences.

The goal was to teleport the quantum information of the qubit to the Micius satellite that was launched on August 16, 2016, at an altitude of around 500 km.

[6] Quantum teleportation has been demonstrated over fiber optic cables simultaneously carrying regular telecommunications traffic.

A less crowded wavelength of light was used for the quantum signal and special filters were required to reduce noise from other traffic.

The above-mentioned three gates correspond to rotations of π radians (180°) about appropriate axes (X, Y and Z) in the Bloch sphere picture of a qubit.

Some remarks: When implementing the quantum teleportation protocol, different experimental noises may arise affecting the state transference.

where the integration is performed over the Haar measure defined by assuming maximal uncertainty over the initial quantum states

A detailed diagrammatic derivation of entanglement swapping has been given by Bob Coecke,[49] presented in terms of categorical quantum mechanics.

[50] The generalization to infinite-dimensional so-called continuous-variable systems was proposed by Braunstein and Kimble[51] and led to the first teleportation experiment that worked unconditionally.

In general, mixed states ρ may be transported, and a linear transformation ω applied during teleportation, thus allowing data processing of quantum information.

Their paper asserts that the two bits that Alice sends Bob contain "locally inaccessible information" resulting in the teleportation of the quantum state.

Experiments by D. Gottesman and I. L. Chuang have determined that a "Clifford hierarchy"[57] gate arrangement which acts to enhance protection against environmental errors.

Overall, a higher threshold of error is allowed with the Clifford hierarchy as the sequence of gates requires less resources that are needed for computation.