New research from the University of Chicago shows a theoretical way to link quantum computers over much greater distances than before. The paper in Nature Communications, led by Assistant Professor Tian Zhong, suggests a range increase to 2,000 km (1,243 miles). Previously, fiber links between quantum machines reached only a few kilometres.
The advance comes from longer quantum coherence of individual erbium atoms. Zhong and his team raised coherence from about 0.1 milliseconds to longer than 10 milliseconds, and in one experiment they demonstrated up to 24 milliseconds. That longer coherence could, in theory, allow links as far as 4,000 km, the distance cited from UChicago PME to Ocaña, Colombia.
Rather than new materials, the group changed how they make crystals. They used molecular-beam epitaxy (MBE) to build rare-earth doped crystals instead of the usual Czochralski melting method. The MBE material showed very high purity. The team will now test connectivity by linking two qubits in separate dilution refrigerators through 1,000 kilometres of spooled cable and by building a third fridge to simulate a longer link. Outside experts praised the work as an innovative, scalable route for networkable qubits.
Difficult words
- coherence — The time a quantum state stays unchanged
- qubit — A basic quantum computer unit of informationqubits
- molecular-beam epitaxy — A method to grow crystals one layer at a time
- dope — To add small amounts of impurities to materialdoped
- dilution refrigerator — A very cold machine for experiments at low temperaturesdilution refrigerators
- connectivity — Ability to connect devices or systems for data transfer
- purity — The absence of unwanted particles or chemical impurities
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- How could linking quantum computers over thousands of kilometres change communication or technology?
- What practical problems might scientists face when using 1,000 kilometres of spooled cable in experiments?
- Do you think changing the crystal growth method is a good approach to improve devices? Why or why not?
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