Quantum computing may still be in its infancy, but scientists around the world have already begun building the quantum internet. Studies conducted independently by researchers at institutes in three different countries have shown that sending quantum bits over long distances over a fiber optic cable is possible.
Even as the biggest names in the tech industry race to create fault-tolerant quantum computers, the transition from binary to quantum can only be completed with a reliable internet connection to transmit the data.
Unlike binary bits transported as light signals in a fiber optic cable that can be read, amplified and transmitted over long distances, quantum bits (qubits) are fragile and even trying to read them changes their state.
Because light signals cannot be amplified, they cannot travel long distances, making them unsuitable for long-distance transmission.
Still, for the quantum internet to scale rapidly, it needs to use the existing network of fiber optic cables.
Three approaches to a quantum internet
Researchers in the Netherlands, China and the US have separately demonstrated how qubits can be stored in “quantum memory” and transmitted over the optical network.
Ronald Henson and his team at Delft University of Technology in the Netherlands encoded qubits in the electron states of the nitrogen atoms and the nuclear states of the carbon atoms of the tiny diamond crystals that contain them.
A fiber-optic cable ran 25 miles from the university to another lab in The Hague to establish a connection with similarly embedded nitrogen atoms in diamond crystals.
At the University of Science and Technology of China (USTC), qubits were encoded in clouds of rubidium atoms. The quantum states were set using a photon, and the research team led by Pan Jian-Wei demonstrated entanglement in three separate laboratories located at least six miles apart.
In the US, Mikhail Lukin of Harvard University uses diamond-based devices with silicon atoms in them and uses quantum states of both the electrons and the nucleus, similar to Henson’s lab.
The devices were used to demonstrate entanglement in two quantum memory nodes separated by a fiber-optic link deployed over a distance of more than 22 miles (35 km), setting a record for the storage, processing and movement of quantum information.
The way forward
While the Chinese and Dutch teams’ approach required photons to arrive at a server with precise timing, the one used by the American scientists is relatively easier to implement.
The two quantum nodes must be maintained at super-cold temperatures, but instead of making the qubits emit entanglement photons, the researchers sent a single photon that entangled with silicon in the first node, then traveled through the optical cable to graze a silicon atom in the second node and achieved entanglement with the first.
“Because the light is already entangled in the first node, it can transfer this entanglement to the second node,” explained Kahn Knauth, a graduate student in Lukin’s lab, in a statement. “We call this photon-mediated entanglement.”
USTC’s Pan Jian-Wei said Nature that at this rate of progress his lab would be able to achieve entanglement over 600 miles (1,000 km) by the end of the decade.
Such a system would help transfer sensitive information using cryptographic keys, connect individual quantum computers to build a powerful one, or unify a vast network of optical telescopes spread hundreds of miles into one large antenna.
The results of the Pan and Lukin lab study were published in the journal Nature and can be accessed below
Lukin’s lab paper
Pan Lab Paper.
FOR THE EDITOR
Ameya Palezha Ameya is a science writer based in Hyderabad, India. A molecular biologist at heart, he swapped micropipettes to write about science during the pandemic, and he doesn’t want to go back. He enjoys writing about genetics, microbes, technology and public policy.
