A Glimpse of the Next Generation Internet – Harvard Gazette

It’s one thing to imagine a next-generation quantum internet capable of transmitting highly complex, hacker-proof information around the world at ultra-high speeds. It’s another thing to physically show that it’s possible.

That’s exactly what Harvard physicists have done, using existing telecommunications fibers in the Boston area, in a demonstration of the world’s longest fiber distance between two quantum memory nodes. Think of it as a simple, closed internet that carries a signal that is not encoded by classical pieces like the existing internet, but by perfectly secure, individual particles of light.

The groundbreaking workpublished in Nature, was led by Mikhail Lukin, Joshua and Beth Friedman University Professor in the Department of Physics, in collaboration with Harvard professors Marko Loncar And Hongkun Parkwho are all members of the Harvard Quantum Initiative. Nature There was collaboration with researchers from Amazon Web Services.

The Harvard team has laid the practical foundation for the first quantum internet by intertwining two quantum memory nodes separated by an optical fiber link, deployed over a roughly 22-mile loop through Cambridge, Somerville, Watertown and Boston. The two nodes were located one floor apart in the Harvard Laboratory for Integrated Science and Engineering.

Quantum memory, analogous to classical computer memory, is an important part of the future of quantum computers because it enables complex network operations and the storage and retrieval of information. Although other quantum networks have been created in the past, the Harvard team’s is the longest fiber-optic network between devices that can store, process and move information.

Each node is a very small quantum computer, made from a piece of diamond with a defect in the atomic structure called a silicon vacancy center. In the diamond, cut structures smaller than one-hundredth the width of a human hair enhance the interaction between the silicon vacancy center and light.

The silicon vacancy center contains two qubits, or pieces of quantum information: one in the form of an electron spin used for communication, and the other in a longer-lived nuclear spin used as a memory qubit to store entanglement, the quantum mechanical property that allows information over any distance can be perfectly correlated.

(In classical computing, information is stored and transmitted as a series of discrete binary signals, say on/off, forming a kind of decision tree. Quantum computers are more fluid, because information can exist in phases between on and off, and stored and transmitted as shifting patterns of particle motion across two entangled points.)

The use of silicon voids as quantum memory devices for single photons is a multi-year research program at Harvard. The technology solves a major problem in the theoretical quantum internet: signal loss that cannot be amplified in traditional ways.

A quantum network cannot use standard optical fiber signal amplifiers because simply copying quantum information as individual bits is impossible – making the information secure, but also very difficult to transport over long distances.

Silicon void-based network nodes can capture, store and scramble bits of quantum information while correcting signal loss. After the nodes cool to near absolute zero, light is sent through the first node and, due to the nature of the atomic structure of the silicon vacancy center, becomes entangled with it, allowing it to transmit the information.

“Because the light is already entangled at the first node, it can transfer this entanglement to the second node,” explains first author Can Knaut, a student from the Kenneth C. Griffin Graduate School of Arts and Sciences in Lukin’s lab. “We call this photon-mediated entanglement.”

In recent years, the researchers rented fiber optic from a Boston company to conduct their experiments, placing their demonstration network on top of existing fiber to indicate that creating a quantum internet with similar network lines would be possible.

“Showing that quantum network nodes can become entangled in the real world of a very busy urban area is an important step toward practical networking among quantum computers,” Lukin said.

A two-node quantum network is just the beginning. The researchers are working hard to expand the performance of their network by adding nodes and experimenting with more network protocols.

The article is titled “Entanglement of nanophotonic quantum memory nodes in a telecom network.” The work was supported by the AWS Center for Quantum Networking research alliance with the Harvard Quantum Initiative, the National Science Foundation, the Center for Ultracold Atoms (an NSF Physics Frontiers Center), the Center for Quantum Networks (an NSF Engineering Research Center) , the Air Force Office of Scientific Research and other sources.