Harvard, MIT Scientists Make Quantum Leap Toward New Internet

Researchers from Harvard and MIT have pioneered a device that could improve quantum communication and may be the key to developing a quantum internet, according to an article published Monday in the scientific journal Nature.

Quantum signals lose information when traveling over long distances. To solve this problem, the researchers’ new technology catches and stores quantum bits — known as qubits — thus preventing information loss. The physicists hope this breakthrough will open the door to a quantum internet that can communicate unhackable messages.

“This is the first system-level demonstration, combining major advances in nanofabrication, photonics and quantum control, that shows a clear quantum advantage to communicating information using quantum repeater nodes,” Mikhail D. Lukin — a Harvard physics professor who lead the research team — said in a press release published Monday. “We look forward to starting to explore new, unique applications using these techniques.”

Other researchers on the project include electrical engineering professor Marko Loncar, chemistry professor Hongkun Park, and Dirk R. Englund, a professor of electrical engineering and computer science at MIT.

Given recent restrictions on laboratory research in response to the novel coronavirus outbreak, the team’s experiments have come to a temporary standstill. However, the researchers are still meeting through Zoom and other online platforms in order to “continue applying for grants, writing review articles, and designing new ideas,” according to Loncar.

Mihir K. Bhaskar, a graduate student in the Lukin group and an author of the paper, said the quantum internet is innovative because it enhances the security of transmitted messages. Qubits cannot be copied because they change state when measured, Bhaskar said.

A quantum internet, therefore, makes it impossible for hackers to intercept or steal data before it reaches the intended recipient.

“If we can share quantum information between two parties, this information is unique and kind of fragile,” Bhaskar said. “So when people measure it they will change the state of it a little bit, so we can say that the information is secured by the laws of physics, since you know no one has measured your bit since it would be corrupted otherwise.”

The main roadblock to inventing a quantum internet is information loss over long distances. Traditional communication networks use repeaters to amplify signals, fix errors, and account for losses. But those repeaters would not work for a quantum internet, because simply by observing the qubits, they would corrupt the information being transmitted, Bhaskar said.

Another hurdle is that quantum information is hard to process and store over long periods of time.

To address both challenges, Lukin’s group fabricated a nano-scale diamond cavity containing a color center — a crystal defect that absorbs a specific kind of light. When cooled to a temperature of absolute zero, the device’s color center can capture and store quantum information for milliseconds — long enough to transmit information across thousands of kilometers.

“Originally, in order to exchange one bit of information, a single photon would have to go all the way from Alice to Bob, and that can become exponentially unlikely the more Alice and Bob move further and further apart,” Bhaskar said.

The new quantum node that the team has developed can store these photons mid-journey, improving the quality of signal transmission.

—Staff writer Meera S. Nair can be reached at meera.nair@thecrimson.com.