Quantum Communication and Entanglement Techniques

Quantum communication exploits the counterintuitive properties of quantum mechanics—most notably entanglement—to transmit information with unrivalled security and to link distant quantum processors. By preparing pairs or multiparty systems in entangled states, it becomes possible to perform protocols such as quantum teleportation, superdense coding and device-independent key distribution. Long-distance transmission faces inevitable losses and decoherence, which degrade entanglement fidelity. To counteract these effects, researchers employ entanglement purification and distillation protocols, together with quantum repeaters that segment channels into shorter links and perform local error correction. Advances in hyperentanglement—simultaneous entanglement in multiple degrees of freedom—and in robust quantum memories have further enhanced channel capacity and network reliability. Underpinning these developments are novel coding techniques, including graph codes and quantum low-density parity-check codes, which allow scalable error correction and efficient resource trade-offs. Collectively, these techniques aim to lay the foundations of a global quantum internet, enabling secure communications, distributed quantum computing and metrology applications.

Research from Nature Portfolio

Superdense teleportation using hyperentangled photons has demonstrated that photon pairs entangled in both polarisation and orbital angular momentum can convey higher-dimensional quantum states with fewer resources. This approach achieved near-unit fidelity for a constrained set of ququart states, effectively doubling classical channel capacity. Experimental realisation of entanglement in multiple degrees of freedom between two quantum memories established hyper- and hybrid entanglement across separate atomic ensembles. By storing and retrieving path and orbital angular momentum information, this work showcased high-capacity quantum storage compatible with heterogeneous network nodes. A complete nondestructive analysis of two-photon six-qubit hyperentangled Bell states employed cross-Kerr nonlinearity to perform parity checks across three degrees of freedom without destroying the photons. This scheme paves the way for deterministic Bell-state measurements in high-dimensional quantum communication and advanced repeater protocols.

Quantum Communication and Entanglement Techniques publication trend

The graph below shows the total number of articles in quantum communication and entanglement techniques across all publications each year (not limited to Nature Index journals).

Technical terms

Entanglement distillation: A process that converts multiple noisy entangled pairs into fewer pairs of higher fidelity through local operations and classical communication.

Quantum repeater: A device that subdivides long channels into shorter links, performing entanglement swapping, purification and error correction to extend communication distances.

Hyperentanglement: Simultaneous entanglement of quantum systems in more than one degree of freedom, such as polarisation and spatial mode, to increase channel capacity.

Graph code: An error-correcting code derived from a mathematical graph, used to design optimal entanglement distillation or error-correction circuits with minimal gate depth.

Quantum low-density parity-check (QLDPC) code: A sparse-matrix quantum error-correcting code that offers favourable scaling of logical qubits and distance, suitable for distributed purification and error correction.

References

1. Superdense teleportation using hyperentangled photons. Nature Communications (2015).
2. Experimental realization of entanglement in multiple degrees of freedom between two quantum memories. Nature Communications (2016).
3. Complete nondestructive analysis of two-photon six-qubit hyperentangled Bell states assisted by cross-Kerr nonlinearity. Scientific Reports (2016).
4. Near-Term n to k Distillation Protocols Using Graph Codes. IEEE Journal on Selected Areas in Communications (2024).
5. Quantum Repeater for W States. PRX Quantum (2023).
6. Entanglement Purification with Quantum LDPC Codes and Iterative Decoding. Quantum (2024).