March 4, 2024

Research team takes fundamental step towards a working quantum Internet

Informative summary

  • A research team at Stony Brook University demonstrated a network of quantum memories that show identical performance at room temperature.

  • The team believes this is a fundamental step towards the development of quantum repeaters, a process necessary for quantum communication.
  • Not only did they achieve the same quantum memory performance, but they also received two US patents, one for room temperature quantum storage and another for high repetition rate quantum repeaters.

  • Image: At his Stony Brook Quantum Information Laboratory, principal investigator Eden Figueroa, left, with his research collaborators investigating the Internet’s quantum capabilities, Sonali Gera and Chase Wallace. Credit: John Griffin, Stony Brook University

PRESS RELEASE: Research with quantum computing and quantum networks is being carried out around the world in hopes of developing a quantum Internet in the future. A quantum Internet would be a network of quantum computers, sensors and communication devices that will create, process and transmit quantum states and entanglements and is expected to improve society’s Internet system and provide certain services and securities that the current Internet does not have. A team of Stony Brook University physicists and their collaborators have taken a significant step toward building a quantum Internet testbed by demonstrating a fundamental quantum network measurement using room-temperature quantum memories. Their findings are described in an article published in the journal Nature Quantum Information.

The field of quantum information essentially combines aspects of physics, mathematics, and classical computing to use quantum mechanics to solve complex problems much faster than classical computing and transmit information in an unhackable way. While the vision of a quantum Internet system is growing and the field has seen a surge in interest from researchers and the general public, accompanied by a sharp increase in invested capital, a quantum Internet prototype has not been built. real.

According to the Stony Brook research team, the key obstacle to achieving the potential of making communication networks more secure, measurement systems more precise, and algorithms for certain scientific analyzes more powerful lies in the development of systems capable of transmit quantum information and entanglement across many nodes. and long distances. These systems are called quantum repeaters and represent one of the most complex challenges in current physics research.

Researchers have advanced quantum repeater capabilities in their latest experiment. They built and characterized quantum memories that operate at room temperature and showed that these memories have identical performance, an essential characteristic when the goal is to build large-scale quantum repeater networks comprising several of these memories.

They tested how identical these memories are in their functionality by sending identical quantum states to each of the memories and performing a process called Hong-Ou-Mandel Interference on the outputs of the memories, a standard test for quantifying the indistinguishability of photon properties. . They demonstrated that the process of storing and retrieving optical qubits in their room-temperature quantum memories does not significantly distort the joint interference process and enables memory-assisted entanglement sharing, a protocol for distributing entanglements over long distances and the key to building systems. operational quantum. repeaters.

“We believe this is an extraordinary step toward the development of viable quantum repeaters and the quantum Internet,” says senior author Eden Figueroa, PhD, Stony Brook Presidential Innovation Endowed Professor and director of the Center for Distributed Quantum Processing, who holds a position set. at the US Department of Energy’s Brookhaven National Laboratory.

Additionally, the quantum hardware developed by the team operates at room temperature, which significantly reduces the cost of operation and makes the system much faster. Much quantum research is not done at room temperature, but at temperatures close to absolute zero, which are more expensive, slower, and technically more difficult to network. Therefore, room temperature technology is promising for building large-scale quantum networks.

The team has not only achieved room temperature quantum memory and communication results, but has also patented their approach. They received US patents on room temperature quantum storage and high repetition rate quantum repeaters.

“Getting these fleets of quantum memories to work together at the quantum level and in a room temperature state is essential for any quantum Internet at any scale. To our knowledge, this feat has not been demonstrated before and we hope to continue this research,” emphasizes Figueroa, noting that their patented technology allows them to further test the quantum network.

Co-authors Sonali Gera, a postdoctoral researcher, and Chase Wallace, a doctoral student, both in the Department of Physics and Astronomy, worked closely with Figueroa, along with other colleagues, during the experimentation that in a sense aims to “amplify” effectively “Entanglement at distances, the essential function of a quantum repeater.

“Because the memories are capable of storing photons with a user-defined storage time, we were also able to show the time synchronization of photon retrieval even though the photons arrive at the memories at random times, which is another characteristic necessary to operate a quantum system”. repeater system,” explains Gera.

She and Wallace add that some of the next steps in the team’s research are to construct and characterize entanglement sources compatible with quantum memories and to design mechanisms to “announce” the presence of photons stored in many quantum memories.

The research was conducted in collaboration with scientists at Qunnect, Inc., a Brooklyn, New York-based quantum technology affiliate of Stony Brook University, and with international colleagues at the University of Padua in Italy.

How a network of quantum repeaters works (see image below):

A quantum repeater jump requires two sources of entangled photon pairs separated by a distance L (infinity symbols in the bottom box). One photon from each pair is sent toward a central measurement node (middle shaded area in the figure), where they are stored in quantum memories. Their associated photons are sent in opposite directions and are also stored in quantum memories separated by a distance of 2L. A measurement that quantifies the indistinguishability of the two photons arriving at the central node, similar to that demonstrated by Figueroa’s team, can be used to entangle distantly located photons.

This protocol amounts to effectively “amplifying” entanglement, as it distributes it over a distance that is twice the distance (2L) that a single source of entangled photons could reach (L). By joining several of these repeater hops, it is possible to extend the entanglement over hundreds of kilometers.

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