The ability to exploit entanglement is seen as a key step towards a quantum internet, and promises a way to generate random cryptographic keys for encoded information so quickly that it can become nearly unbreakable. Masu. It could also be used to connect quantum computers, expanding their operational capabilities.
The Chinese-American team's feat was detailed in the journal Nature, but the Dutch researchers' paper was uploaded as a preprint to repository website arXiv in April and has not been peer-reviewed.
“A step from the lab to the field has actually been taken,” said lead author of the Dutch paper and physicist Ronald Hanson of Delft University of Technology, according to a Nature news release.
A Harvard University team led by physicist Mikhail Lukin says that among the “key challenges” to achieving practical long-distance quantum communications is “robust entanglement between quantum memory nodes connected by fiber optic infrastructure. included.”
Each node contains a qubit (a quantum version of a computer bit, the fundamental unit of information represented by a 0 or 1 and can also exist in a third coupled state) and communicates through a “photonic channel”. US researchers said.
Each team demonstrated quantum entanglement by using fiber optic cables to create a secure connection between receiving node devices, but their approaches differed.
US researchers used a 35km (22 mile) fiber loop that stretched all the way to Boston to connect two nodes placed side by side in a Harvard University lab in Cambridge, Massachusetts.
The Chinese team set up three nodes, Alice, Bob, and Charlie, in a triangular network around Hefei, the capital of Anhui province and home to the USTC, with a central server lab in the middle, all approximately 10 kilometers apart. It was installed in ).
In the Netherlands, a total of 25 km (15 miles) of fiber stretches from Delft to The Hague, connecting the server and two nodes at the halfway point.
According to the paper, Pan and the researchers operated a single-photon scheme using qubits encoded in collections of rubidium atoms, sending one photon from each node to a server for entanglement. That's what it means.
According to Chinese researchers, an entangled state is achieved when two photons arrive at the server at exactly the same time.
“Our work provides a metropolitan-scale testbed for the evaluation and exploration of multi-node quantum network protocols and begins a phase of quantum internet research,” the paper says.
Pan told Nature that his team expects to be able to establish entanglement across 1,000 km (621 miles) of optical fiber using about 10 nodes by the end of this decade.
Instead of relying on clusters of atoms, the US team used a diamond device that replaced carbon atoms with silicon atoms. “Essentially, we intertwined two of his small quantum computers,” Lukin says.
In the US experiment, a single photon was sent to the first node, where it became entangled with a silicon atom, and then sent down a fiber loop to graze a second silicon atom at another node, enabling the entanglement. Ta.
In a similar approach to the American researchers, Dutch researchers used nitrogen atoms embedded in diamond crystals.
The Nature report says the Chinese and Dutch methods rely on very precise timing of photons arriving at a central server and require a level of fine-tuning that the US researchers' method does not. It pointed out.
Although the single-atom method is less efficient than the Chinese team's ensemble method, it is more adaptable because it can be used to perform basic calculations, according to Nature.
The Chinese researchers' method achieved “two orders of magnitude” higher entanglement efficiency than the US researchers' method, according to a USTC press release.
While demonstrating entanglement between nodes located within a city is a major achievement, Hanson told Nature, “It's not commercially useful yet, but it's a big step.”
Tracy Northup, a physicist at the University of Innsbruck in Austria who was not involved in any of the research, said the experiment was “the most advanced demonstration yet” of the technology needed to develop a quantum internet, according to Nature magazine. He said that.
