Synopsis

Distant Memories Entangled

Physics 15, s101
On the road to a quantum internet, researchers demonstrate entanglement of two memory elements located 12.5 km apart in an urban environment.
Terrametrics/Maxar Technologies/CNES Airbus

The quantum internet promises secure communications, precise sensing, and distributed quantum computing. Progress toward this dream is often measured by the distance that quantum information is shared over optical fibers or satellite connections. Researchers have now demonstrated an optically connected pair of entangled quantum memories separated by 12.5 km; the longest physical separation so far achieved [1].

Regular readers may recall longer distances of quantum connections (see for example Synopsis: Demonstrating Quantum Communication Under Realistic Conditions). Those experiments involved sending entangled photons; the new experiments establish entanglement between two atom-based memory elements. “In the previous realization of entanglement distribution using satellites or fibers, further connectivity with other links is challenging,” says Xiao-Hui Bao from the University of Science and Technology of China. By contrast, storing information in quantum memories provides a “buffer” for distributing entanglement over a network of links.

In the experiment of Bao and colleagues, the memory elements are both atomic gases that store information in the form of spin waves for relatively long times (around 100 𝜇s). The first element’s information is “written” onto a photon that is downconverted in frequency and sent over 20 km of a commercial fiber network to the second memory element. The researchers overcame several challenges, including the synchronization of the pump lasers in the two distant labs.

The next step will be to include a “heralding” signal that tells researchers when entanglement is established (the current method involves “postselection” in which entanglement is verified with measurements). In another work, a separate group demonstrated heralded entanglement between memories connected by 33 km of fiber [2]. But for that study the experiment was performed in a lab setting over spooled fiber rather than the urban environment of Bao and colleagues’ demonstration.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics Magazine based in Lyon, France.

References

  1. Xi-Yu Luo et al., “Postselected entanglement between two atomic ensembles separated by 12.5 km,” Phys. Rev. Lett. 129, 050503 (2022).
  2. Tim van Leent et al., “Entangling single atoms over 33 km telecom fibre,” Nature 607, 69 (2022).

Subject Areas

Quantum Information

Related Articles

Hiding Secrets Using Quantum Entanglement
Quantum Information

Hiding Secrets Using Quantum Entanglement

Three experiments demonstrate the key elements of a quantum cryptographic scheme that predictions indicate should be unhackable, bringing the promise of quantum encryption technologies a step closer to reality. Read More »

Quantum-Aided Machine Learning Shows Its Value
Quantum Information

Quantum-Aided Machine Learning Shows Its Value

A machine-learning algorithm that includes a quantum circuit generates realistic handwritten digits and performs better than its classical counterpart. Read More »

Error-Correcting Surface Codes Get Experimental Vetting
Quantum Information

Error-Correcting Surface Codes Get Experimental Vetting

Two independent groups have experimentally demonstrated surface-code quantum error correction—an approach for remedying errors in quantum computations. Read More »

More Articles