User:Djobes/SDC

Copied from Superdense coding

[here we're working on the suggested change of having the lead relate more to the body of the article by adding in more detail of the procedure and the utilization of SDC for secure communication]

In quantum information theory, superdense coding is a quantum communication protocol to transmit two classical bits of information (i.e., either 00, 01, 10 or 11) from a sender (often called Alice) to a receiver (often called Bob), by sending only one qubit from Alice to Bob, under the assumption of Alice and Bob pre-sharing an entangled state. By performing one of four quantum gate operations on the (entangled) qubit she possesses, Alice can prearrange the measurement Bob makes. After receiving Alice's qubit, operating on the pair and measuring both, Bob has two classical bits of information. If Alice and Bob do not already share entanglement before the protocol begins, then it is impossible to send two classical bits using 1 qubit, as this would violate Holevo's theorem.

Superdense coding is a the underlying principle of secure quantum secret coding. The necessity of having both qubits to decode the information being sent eliminates the risk of eavesdroppers intercepting messages.

It can be thought of as the opposite of quantum teleportation, in which one transfers one qubit from Alice to Bob by communicating two classical bits, as long as Alice and Bob have a pre-shared Bell pair.

Security
Superdense coding is a form of secure quantum communication. If an eavesdropper, which may be referred to as Eve, intercepts Alice's qubit en route to Bob, all that is obtained by Eve is part of an entangled state. Without Access to Bob's qubit, Eve is unable to get any information from Alice's qubit. A third party is unable to eavesdrop on information being communicated through superdense coding and an attempt to measure either qubit would collapse that qubit's state and alert Bob and Alice.

Experimental
The protocol of superdense coding has been actualized in several experiments using different systems to varying levels of channel capacity and fidelities. In 2004, trapped beryllium 9 ions were used in a maximally entangled state to achieve a channel capacity of 1.16 with a fidelity of 0.85. In 2017, a channel capacity of 1.665 was achieved with a fidelity of 0.87 through optical fibers. High dimensional ququarts were used to exceed a channel capacity of 2, at 2.09 with a fidelity of 0.98. Nuclear Magnetic Resonance (NMR) has also been used to share among three parties.

Working references:

Information on secure communication: Farouk, A. "et al. A generalized architecture of quantum secure direct communication for N disjointed users with authentication. Sci. Rep. 5, 16080

This is a dense review article on super dense coding and secure quantum communication with many references that can be looked into for details.

Capacity of superdense coding: Bowen, G. (2001). Classical information capacity of superdense coding. Physical Review A, 63(2).