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Entangle, swap, purify, repeat: Enhancing connections between distant nodes

American Association for the Advancement of Science

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IMAGE: Art image illustrating the concept of entanglement distillation between spins in diamond. This material relates to a paper that appeared in the June 2, 2017, issue of Science, published by... view more 

Credit: Cheyenne Hensgens

Scientists have developed a protocol that enhances quantum entanglement, confirming its effectiveness across a distance of two meters. The advancement marks the first successful demonstration of a technique called entanglement distillation, which was developed nearly 20 years ago. Quantum entanglement, a physical phenomenon in which particles are correlated, or "linked" together, across a distance, holds important implications for secure communication, quantum computation and simulation, and enhanced metrology. Yet unavoidable interactions between particles and environment can disrupt entanglement and must be accounted for and corrected. To overcome this challenge, Norbert Kalb et al. employed two diamond chips, each featuring two types of spin - a nitrogen-vacancy electron spin, which was used as a "communication" qubit, and a nearby carbon-13 nuclear spin, which was used as a "memory" qubit. In the researchers' approach, the communication qubits are subjected to a raw entangled state, which is then swapped on to the memory qubits. Once the raw state of the communication qubit is projected onto the memory qubit, the communication qubit is free to take on another raw state. The memory qubit is vulnerable to losing the state given by the communication qubit, and so the researchers developed a way to monitor the memory particle in real time. The team of scientists was able to account and adjust for any errors between the communicating qubits, thus enhancing the entanglement on each iteration.

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