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  • richardmitnick 12:51 pm on December 18, 2019 Permalink | Reply
    Tags: "Remote Quantum Systems Produce Interfering Photons", , , , , , , , Quantum internet,   

    From Joint Quantum Institute: “Remote Quantum Systems Produce Interfering Photons” 

    JQI bloc

    From Joint Quantum Institute

    December 17, 2019

    Research Contact
    Steve Rolston

    Story by Jillian Kunze

    A schematic showing the paths taken by photons from two different sources in neighboring buildings. (Credit: S. Kelley/NIST)

    Scientists at the Joint Quantum Institute (JQI) have observed, for the first time, interference between particles of light created using a trapped ion and a collection of neutral atoms. Their results could be an essential step toward the realization of a distributed network of quantum computers capable of processing information in novel ways.

    In the new experiment, atoms in neighboring buildings produced photons—the quantum particles of light—in two distinct ways. Several hundred feet of optical cables then brought the photons together, and the research team, which included scientists from JQI as well as the Army Research Lab, measured a telltale interference pattern. It was the first time that photons from these two particular quantum systems were manipulated into having the same wavelength, energy and polarization—a feat that made the particles indistinguishable. The result, which may prove vital for communicating over quantum networks of the future, was published recently in the journal Physical Review Letters.

    “If we want to build a quantum internet, we need to be able to connect nodes of different types and functions,” says JQI Fellow Steve Rolston, a co-author of the paper and a professor of physics at the University of Maryland. “Quantum interference between photons generated by the different systems is necessary to eventually entangle the nodes, making the network truly quantum.”

    The first source of photons was a single trapped ion—an atom that is missing an electron—held in place by electric fields. Collections of these ions, trapped in a chain, are leading candidates for the construction of quantum computers due to their long lifetimes and ease of control. The second source of photons was a collection of very cold atoms, still in possession of all their electrons. These uncharged, or neutral, atomic ensembles are excellent interfaces between light and matter, as they easily convert photons into atomic excitations and vice versa. The photons produced by each of these two systems are typically different, limiting their ability to work together.

    In one building, researchers used a laser to excite a trapped barium ion to a higher energy. When it transitioned back to a lower energy, it emitted a photon at a known wavelength but in a random direction. When scientists captured a photon, they stretched its wavelength to match photons from the other source.

    In an adjacent building, a cloud of tens of thousands of neutral rubidium atoms generated the photons. Lasers were again used to pump up the energy of these atoms, and that procedure imprinted a single excitation across the whole cloud through a phenomenon called the Rydberg blockade. When the excitation shed its energy as photons, they traveled in a well-defined direction, making it easy for researchers to collect them.

    The team used an interferometer to measure the degree to which two photons were identical. A single photon entering the interferometer is equally likely to take either of two possible exits. And two distinguishable photons entering the interferometer at the same time don’t notice each other, acting like two independent single photons.

    But when researchers brought together the photons from their two sources, they almost always took the same exit—a result of quantum interference and an indication that they were nearly identical. This was precisely what the research team had hoped for: the first demonstration of interference between photons from these two very different quantum systems.

    In this experiment, photons traveled from the first building to the second via hundreds of feet of optical fiber. Due to this distance, sending photons from both systems to meet at the interferometer simultaneously was a feat of precise timing. Detectors were placed at the exits of the interferometer to detect where the photons came out, but the team often had to wait—gathering all the data took 24 hours over a period of 3 days.

    Further experimental upgrades could be used to generate a special quantum connection called entanglement between the ion and the neutral atoms. In entanglement, two quantum objects become so closely linked that the results from measuring one are correlated with the results from measuring the other, even if the objects are separated by a huge distance. Entanglement is necessary for the speedy algorithms that scientists hope to run on quantum computers in the future.

    Generating entanglement between different quantum systems usually requires identical photons, which the researchers were able to create. Unfortunately, trapped ions emit photons in a random direction, making the probability of catching them low. This meant that only about eight photons from the trapped ion made it to the interferometer each second. If the researchers attempted to perform more intricate experiments with that rate, the data could take months to collect. However, future work may increase how frequently the ion emits photons and allow for a useful rate of entanglement production.

    “This is a stepping-stone on the way to being able to entangle these two systems,” says Alexander Craddock, a graduate student at JQI and the lead author of this study. “And that would be fantastic, because you can then take advantage of all the different weird and wonderful properties of both of them.”

    In addition to Rolston and Craddock, co-authors of the paper include JQI graduate students John Hannegan, Dalia Ornelas-Huerta, and Andrew Hachtel, JQI postdoctoral researcher James Siverns, Army Research Laboratory scientists and JQI Affiliates Elizabeth Goldschmidt (now an Assistant Professor of Physics at the University of Illinois) and Qudsia Quraishi, and JQI Fellow Trey Porto.

    See the full article here .


    Please help promote STEM in your local schools.

    Stem Education Coalition

    JQI supported by Gordon and Betty Moore Foundation

    We are on the verge of a new technological revolution as the strange and unique properties of quantum physics become relevant and exploitable in the context of information science and technology.

    The Joint Quantum Institute (JQI) is pursuing that goal through the work of leading quantum scientists from the Department of Physics of the University of Maryland (UMD), the National Institute of Standards and Technology (NIST) and the Laboratory for Physical Sciences (LPS). Each institution brings to JQI major experimental and theoretical research programs that are dedicated to the goals of controlling and exploiting quantum systems.

  • richardmitnick 11:24 am on February 4, 2019 Permalink | Reply
    Tags: A prototype for a key element of all-photonic quantum repeaters, Quantum internet,   

    From University of Toronto: “Towards a Quantum Internet” 

    U Toronto Bloc

    From University of Toronto

    January 31, 2019
    Jessica MacInnis

    U of T’s Hoi-Kwong Lo is among a group of quantum experts who are helping to develop a more secure and stable quantum internet. Photo by Jessica MacInnis

    A University of Toronto researcher is among a global group of experts who have demonstrated, in principle, a device that could serve as the backbone of a quantum internet.

    Hoi-Kwong Lo, a professor in the department of electrical and computer engineering in the Faculty of Applied Science & Engineering, and his collaborators have developed a prototype for a key element of all-photonic quantum repeaters, a critical step in long-distance quantum communication.

    “An all-optical network is a promising form of infrastructure for fast and energy-efficient communication that is required for a future quantum internet,” says Lo, who is cross-appointed to the department of physics in the Faculty of Arts & Science.

    A quantum internet is considered the Holy Grail of quantum information processing, enabling many novel applications including information-theoretic secure communication. By contrast, today’s internet was not specifically designed for security, and it shows: breaches, break-ins and computer espionage are common challenges. Nefarious hackers are constantly poking holes in sophisticated layers of defence erected by individuals, corporations and governments.

    In light of this, researchers have proposed other ways of transmitting data that would leverage key features of quantum physics to provide virtually unbreakable encryption. One of the most promising technologies involves a technique known as quantum key distribution, or QKD. QKD exploits the fact that the simple act of sensing or measuring the state of a quantum system disturbs that system. Because of this, eavesdropping by a third party would leave behind a detectable trace, and the communication could be aborted before sensitive information is lost.

    Until now, this type of quantum security has been only demonstrated in small-scale systems. Lo and his team are among a group of global researchers who are laying the groundwork for a future quantum internet by addressing some of the challenges of transmitting quantum information over great distances using optical fibre communication.

    Because light signals lose potency as they travel long distances through fibre-optic cables, devices called repeaters are inserted at regular intervals along the line. The repeaters boost and amplify the signals to help transmit the information.

    But existing repeaters for quantum information are highly problematic. They require storage of the quantum state at the repeater sites, making the repeaters error prone, difficult to build, and very expensive because they often operate at cryogenic temperatures.

    Lo and his team have proposed a different approach. They are working on the development of the next generation of repeaters, called all-photonic quantum repeaters, that would eliminate or reduce many of the shortcomings of standard quantum repeaters. With collaborators at Osaka University, Toyama University and NTT Corporation in Japan, Lo and his team have demonstrated proof-of-concept of their work in a paper recently published in Nature Communications.

    “We have developed all-photonic repeaters that allow time-reversed adaptive Bell measurement,” says Lo.

    “Because these repeaters are all-optical, they offer advantages that traditional – quantum-memory-based matter – repeaters do not. For example, this method could work at room temperature.”

    A quantum Internet could offer applications that are impossible to implement in the conventional Internet, such as impenetrable security and quantum teleportation, which takes advantage of the phenomenon of quantum entanglement to transmit information between atoms separated by large distances.

    “Our work helps pave the way toward this future,” Lo says.

    The research was funded by the Natural Sciences and Engineering Research Council of Canada, among others.

    See the full article here.


    Please help promote STEM in your local schools.

    Stem Education Coalition

    Founded in 1827, the University of Toronto has evolved into Canada’s leading institution of learning, discovery and knowledge creation. We are proud to be one of the world’s top research-intensive universities, driven to invent and innovate.

    Our students have the opportunity to learn from and work with preeminent thought leaders through our multidisciplinary network of teaching and research faculty, alumni and partners.

    The ideas, innovations and actions of more than 560,000 graduates continue to have a positive impact on the world.

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