Novel Atomic Device Facilitates a Simplified Approach to Link Quantum Computers
Innovative Quantum Device Allows for Easier Quantum Computer Interconnectivity
Princeton researchers have introduced an innovative technique for constructing quantum repeaters by utilizing telecom-ready light emitted from a single ion, with calcium tungstate emerging as the most effective material. The researchers aim to enhance the duration of quantum state storage in future endeavors.
A groundbreaking atomic device is now capable of transmitting high-fidelity quantum information through fiber optic networks.
A new methodology for linking quantum devices across extensive distances has been revealed by researchers, representing a pivotal step towards integrating this technology into future communication systems.
Presently, conventional data signals can be amplified over large distances, spanning cities or oceans. However, this is not the case with quantum signals. These signals must be repeated at intervals—essentially halted, duplicated, and relayed through specialized machines known as quantum repeaters. Many experts anticipate that quantum repeaters will be instrumental in forthcoming communication networks, fostering heightened security and enabling connections among remote quantum computers.
Revolutionary Approach to Quantum Repeaters
Published in the journal Nature on August 30th, the Princeton study outlines a fresh approach to constructing quantum repeaters. It leverages telecom-ready light emitted from a solitary ion implanted within a crystal. The principal author of the study, Jeff Thompson, explains that this endeavor was the culmination of several years of effort, amalgamating advancements in photonic design and materials science.
While other prominent quantum repeater designs emit light within the visible spectrum—a medium that degrades rapidly over optical fiber and necessitates conversion for long-distance travel—the new device is predicated on a singular rare earth ion implanted within a host crystal. This ion emits light at an optimal infrared wavelength, obviating the need for signal conversion. As a result, this approach promises more straightforward and resilient networks.
Structural Design and Operational Mechanism
The device comprises two core components: a calcium tungstate crystal infused with a small quantity of erbium ions, and a minuscule silicon piece etched into a J-shaped channel. Under the influence of a specialized laser, the ion emits light upward through the crystal. Simultaneously, the silicon piece, a delicate semiconductor layer affixed to the crystal’s apex, captures and guides individual photons into the fiber optic cable.
The ideal scenario involves encoding the photon with information from the ion, specifically pertaining to a quantum property known as spin. In the context of a quantum repeater, collecting and interfering with signals from distant nodes generates entanglement between their spins. This facilitates end-to-end transmission of quantum states, even in the presence of losses along the transmission path.
Material Selection and Rigorous Testing
Thompson’s team embarked on their journey with erbium ions several years ago. However, initial versions employed different crystals that introduced excessive noise. This noise led to erratic fluctuations in the frequency of emitted photons—a phenomenon referred to as spectral diffusion. This disrupted the delicate quantum interference essential for quantum network operations. To surmount this challenge, Thompson’s lab collaborated with Nathalie de Leon, an associate professor of electrical and computer engineering, and Robert Cava, a preeminent solid-state materials scientist and Princeton’s Russell Wellman Moore Professor of Chemistry. Together, they explored new materials capable of accommodating single erbium ions with significantly reduced noise.
The team methodically narrowed down a vast pool of candidate materials, ultimately identifying calcium tungstate as the ideal choice. The material selection process entailed rigorous testing over several months, with the final three contenders undergoing comprehensive evaluation. The first material exhibited inadequate clarity, the second compromised the quantum properties of erbium, while the third—calcium tungstate—proved to be the optimal candidate.
Validation of the New Material’s Potential
To substantiate the suitability of the new material for quantum networks, the researchers devised an interferometer in which photons randomly traverse either of two paths: a short path spanning several feet or a lengthy path extending 22 miles (comprising coiled optical fiber). Photons emitted from the ion can traverse either the long or short path, and approximately half the time, consecutive photons follow opposing paths before converging at the output simultaneously.
When such collisions occur, quantum interference prompts the photons to exit the output in pairs only if they are inherently indistinguishable—possessing identical characteristics in terms of shape and frequency. Alternatively, if they are distinguishable, they exit the interferometer individually. Through observing a marked suppression—up to 80 percent—of individual photons at the interferometer output, the research team definitively demonstrated that the erbium ions within the new material emit indistinguishable photons. According to Salim Ourari, a co-leading graduate student on the project, this achievement surpasses the high-fidelity threshold.
Future Prospects
While this breakthrough marks a significant milestone, further efforts are necessary to enhance the duration of quantum state storage within the spin of the erbium ion. The team is presently engrossed in refining calcium tungstate with greater precision, aiming to reduce impurities that disrupt quantum spin states.
Reference: “Indistinguishable telecom band photons from a single erbium ion in the solid state” Salim Ourari, Łukasz Dusanowski, Sebastian P. Horvath, Mehmet T. Uysal, Christopher M. Phenicie, Paul Stevenson, Mouktik Raha, Songtao Chen, Robert J. Cava, Nathalie P. de Leon and Jeff D. Thompson, 30 August 2023, Nature.
DOI: 10.1038/s41586-023-06281-4
The research was published in the esteemed journal Nature with the backing of the U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, and the Co-design Center for Quantum Advantage (C2QA). Beyond Thompson, Cava, and Ourari, the list of authors includes Łukasz Dusanowski, Sebastian P. Horvath, Mehmet T. Uysal, Christopher M. Phenicie, Paul Stevenson, Mouktik Raha, Songtao Chen, and Nathalie de Leon. Ourari, Dusanowski, Horvath, and Uysal all made equal contributions to the study.
