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  • richardmitnick 5:01 pm on May 10, 2021 Permalink | Reply
    Tags: "JQI Researchers Generate Tunable Twin Particles of Light", A new technique sees two distinct particles of light enter a chip and two identical twin particles of light leave it., , Identical twins might seem “indistinguishable” but in the quantum world the word takes on a new level of meaning., Inside a resonator a photon from each of the beams spontaneously combine. The researchers then observed how the photons reformed into two indistinguishable photons., Joint Quantum Institute (US), , , Quantum interference— needed for quantum computers., , The resulting combination of being indistinguishable and entangled is essential for many potential uses of photons in quantum technologies.   

    From Joint Quantum Institute (US): “JQI Researchers Generate Tunable Twin Particles of Light” 

    JQI bloc

    At


    University of Maryland (US)

    May 10, 2021

    Story by Bailey Bedford

    Mohammad Hafezi
    hafezi@umd.edu

    1
    A new technique sees two distinct particles of light enter a chip and two identical twin particles of light leave it. The image artistically combines the journey of twin particles of light along the outer edge of a checkerboard of rings with the abstract shape of its topological underpinnings. Credit: Kaveh Haerian.

    Identical twins might seem “indistinguishable” but in the quantum world the word takes on a new level of meaning. While identical twins share many traits, the universe treats two indistinguishable quantum particles as intrinsically interchangeable. This opens the door for indistinguishable particles to interact in unique ways—such as in quantum interference—that are needed for quantum computers.

    While generating a crowd of photons—particles of light—is as easy as flipping a light switch, it’s trickier to make a pair of indistinguishable photons. And it takes yet more work to endow that pair with a quantum mechanical link known as entanglement. In a paper published May 10, 2021 in the journal Nature Photonics, JQI researchers and their colleagues describe a new way to make entangled twin particles of light and to tune their properties using a method conveniently housed on a chip, a potential boon for quantum technologies that require a reliable source of well-tailored photon pairs.

    The researchers, led by JQI fellow Mohammad Hafezi, designed the method to harness the advantages of topological physics. Topological physics explores previously untapped physical phenomena using the mathematical field of topology, which describes common traits shared by different shapes. (Where geometry concerns angles and sizes, topology is more about holes and punctures—all-encompassing characteristics that don’t depend on local details.) Researchers have made several major discoveries by applying this approach, which describes how quantum particles—like electrons or, in this case, photons—can move in a particular material or device by analyzing its broad characteristics through the lens of topological features that correspond to abstract shapes (such as the donut in the image above). The topological phenomena that have been revealed are directly tied to the general nature of the material; they must exist even in the presence of material impurities that would upset the smooth movement of photons or electrons in most other circumstances.

    Their new method builds on previous work, including the generation of a series of distinguishable photon pairs. In both the new and old experiments, the team created a checkerboard of rings on a silicon chip. Each ring is a resonator that acts like a tiny race track designed to keep certain photons traveling round and round for a long time. But since individual photons in a resonator live by quantum rules, the racecars (photons) can sometimes just pass unchanged through an intervening wall and proceed to speed along a neighboring track.

    The repeating grid of rings mimics the repeating grid of atoms that electrons travel through in a solid, allowing the researchers to design situations for light that mirror well known topological effects in electronics. By creating and exploring different topological environments, the team has developed new ways to manipulate photons.

    “It’s exactly the same mathematics that applies to electrons and photons,” says Sunil Mittal, a JQI postdoctoral researcher and the first author of the paper. “So you get more or less all the same topological features. All the mathematics that you do with electrons, you can simply carry to photonic systems.”

    In the current work, they recreated an electronic phenomenon called the anomalous quantum Hall effect that opens up paths for electrons on the edge of a material. These edge paths, which are called topological edge states, exist because of topological effects, and they can reliably transport electrons while leaving routes through the interior easily disrupted and impassable. Achieving this particular topological effect requires that localized magnetic fields push on electrons and that the total magnetic field when averaged over larger sections of the material cancels out to zero.

    But photons lack the electrical charge that makes electrons susceptible to magnetic shoves, so the team had to recreate the magnetic push in some other way. To achieve this, they laid out the tracks so that it is easier for the photons to quantum mechanically jump between rings in certain directions. This simulates the missing magnetic influence and creates an environment with a photonic version of the anomalous quantum Hall effect and its stable edge paths.

    For this experiment, the team sent two laser beams of two different colors (frequencies) of light into this carefully designed environment. Inside a resonator a photon from each of the beams spontaneously combine. The researchers then observed how the photons reformed into two indistinguishable photons, travelled through the topological edge paths and were eventually ejected from the chip.

    Since the new photons formed inside a resonator ring, they took on the traits (polarization and spatial mode) of the photons that the resonators are designed to hold. The only trait left that the team needed to worry about was their frequencies.

    The researchers matched the frequencies of the photons by selecting the appropriate input frequencies for the two lasers based on how they would combine inside the silicon resonators. With the appropriate theoretical understanding of the experiment, they can produce photons that are quantum mechanically indistinguishable.

    The nature of the formation of the new photons provides the desired quantum characteristics. The photons are quantum mechanically entangled due to the way they were generated as pairs; their combined properties—like the total energy of the pair—are constrained by what the original photons brought into the mix, so observing the property of one instantly reveals the equivalent fact about the other. Until they are observed—that is, detected by the researchers—they don’t exist as two individual particles with distinct quantum states for their frequencies. Rather, they are identical mixtures of possible frequency states called a superposition. The two photons being indistinguishable means they can quantum mechanically interfere with each other

    The resulting combination of being indistinguishable and entangled is essential for many potential uses of photons in quantum technologies. An additional lucky side effect of the researcher’s topological approach is that it gives them a greater ability to adjust the frequencies of the twin photons based on the frequencies they pump into the chip and how well the frequencies match with the topological states on the edge of the device.

    “This is not the only way to generate entangled photon pairs—there are many other devices—but they are not tunable,” Mittal says. “So once you fabricate your device, it is what it is. If you want to change the bandwidth of the photons or do something else, it’s not possible. But in our case, we don’t have to design a new device. We showed that, just by tuning the pump frequencies, we could tune the interference properties. So, that was very exciting.”

    The combination of the devices being tunable and robust against manufacturing imperfections make them an appealing option for practical applications, the authors say. The team plans to continue exploring the potential of this technique and related topological devices and possible ways to further improve the devices such as using other materials to make them.

    In addition to Hafezi and Mittal, former JQI graduate student Venkata Vikram Orre and former JQI postdoctoral researcher and current assistant professor at the University of Illinois Urbana-Champaign (US) Elizabeth Goldschmidt were also co-authors of the paper.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    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) (US) is pursuing that goal through the work of leading quantum scientists from the Department of Physics of the University of Maryland (UMD (US)), 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.

    U Maryland Campus

    Driven by the pursuit of excellence, the University of Maryland (US) has enjoyed a remarkable rise in accomplishment and reputation over the past two decades. By any measure, Maryland is now one of the nation’s preeminent public research universities and on a path to become one of the world’s best. To fulfill this promise, we must capitalize on our momentum, fully exploit our competitive advantages, and pursue ambitious goals with great discipline and entrepreneurial spirit. This promise is within reach. This strategic plan is our working agenda.

    The plan is comprehensive, bold, and action oriented. It sets forth a vision of the University as an institution unmatched in its capacity to attract talent, address the most important issues of our time, and produce the leaders of tomorrow. The plan will guide the investment of our human and material resources as we strengthen our undergraduate and graduate programs and expand research, outreach and partnerships, become a truly international center, and enhance our surrounding community.

    Our success will benefit Maryland in the near and long term, strengthen the State’s competitive capacity in a challenging and changing environment and enrich the economic, social and cultural life of the region. We will be a catalyst for progress, the State’s most valuable asset, and an indispensable contributor to the nation’s well-being. Achieving the goals of Transforming Maryland requires broad-based and sustained support from our extended community. We ask our stakeholders to join with us to make the University an institution of world-class quality with world-wide reach and unparalleled impact as it serves the people and the state of Maryland.

     
  • richardmitnick 9:58 pm on May 2, 2021 Permalink | Reply
    Tags: "Two (Photons) is Company- Three’s a Crowd", Joint Quantum Institute (US),   

    From Joint Quantum Institute (US) at University of Maryland (US) : “Two (Photons) is Company- Three’s a Crowd” 

    JQI bloc

    From Joint Quantum Institute (US)

    At


    University of Maryland (US)

    April 26, 2021

    S. Rolston
    rolston@umd.edu

    Written by Bailey Bedford

    1
    Researchers have engineered a cloud of atoms (blue circles) to create exotic interactions that selectively whittle down a beam of light made of bunches of one, two or three photons (red circles). In the animation above, the ideal case is presented: All groups of three photons interact with each other and are knocked out of the beam, while the smaller bunches pass through unaffected. (Credit: Chris Cesare/JQI)

    Photons—the quantum particles of light—normally don’t have any sense of personal space. A laser crams tons of photons into a tight beam, and they couldn’t care less that they are packed on top of each other. Two beams can even pass through each other without noticing. This is all well and good when making an extravagant laser light show or using a laser level to hang a picture frame straight, but for researchers looking to develop quantum technologies that require precise control over just one or two photons, this lack of interaction often makes life difficult.

    Now, a group of UMD researchers has come together to create tailored interactions between photons in an experiment where, at least for photons, two’s company but three’s a crowd. The technique builds on many previous experiments that use atoms as intermediaries to form connections between photons that are akin to the bonds between protons, electrons and other kinds of matter. These interactions, along with the ability to control them, promises new opportunities for researchers to study the physics of exotic interactions and develop light-based quantum technologies.

    “With a laser you cannot really say ‘I only want one photon or two photons or three photons,’ or ‘I only want one and two photons, but not three photons,’” says Dalia Ornelas-Huerta, a former JQI graduate student and the lead experimental author on the paper. “So, with the system, it could lead to a degree of freedom of saying, ‘I want one photon or two photons, but not three.’”

    In a paper published today in the journal Physical Review Letters, the researchers described how they created a venue for influencing a beam of photons, with several experimental knobs for adjusting the subtle interactions between them. In their experiment, they dialed up the interactions among three photons to be stronger than the interactions between two photons—a fact that allowed them to selectively remove three photons at a time from the beam. When they sent in a beam of light that generally contains no more than three photons, they got out just one or two photons at a time.

    The effort to keep photons from congregating brought together several research groups at the University of Maryland (UMD). Ornelas-Huerta, JQI Fellow Steven Rolston, a Fellow of the Quantum Technology Center and a physics professor at UMD, and JQI Fellow and NIST physicist Trey Porto, together with other team members, carried out the experiment. JQI Fellow Alexey Gorshkov and Michael Gullans, both National Institute of Standards and Technology(US) physicists and Fellows of the Joint Center for Quantum Information and Computer Science (UMD) (US), and colleagues focused on the theoretical explanation.

    “We thought we had a simple idea,” says Gullans, who began working on this line of research in 2017 when he was a JQI postdoctoral researcher. “And then we tried the experiment. And we had to invent a bunch of new ideas for how to calculate three-body physics and we also spent a huge amount of time learning how to analyze the data and interpret the data to see evidence for this effect.”

    That seemingly simple idea was to use Rydberg atoms as an intermediary between the normally non-communicative photons to create just the right conditions so that three photons traveling together would experience an interaction that would knock them out of the beam. These atoms are useful because they are sensitive to the influence of nearby photons and other atoms. The sensitivity arises because Rydberg atoms have electrons that roam far from the center of the atom, leaving them open to external influences—influences that can produce strong, adjustable interactions.

    The interactions between the Rydberg atoms and a passing photon can form a polariton—a hybrid of the quantum states of the photon and the atoms that behaves like a new distinct particle. Polaritons have been used in many past experiments, and researchers know how to manipulate them (and their component photons) using lasers. The ability to manipulate these states inspired the researchers to try to craft a new sort of interaction where three polaritons interact in a distinctly different way than just two.

    These sorts of interactions, called three-body interactions, aren’t very common in day-to-day life or even in a physics lab. Most interactions that happen at a scale bigger than an atom (no matter how many objects are involved) are two-body interactions, like the gravitational attraction between planets or the repulsion of electrons in a conductor. Being a two-body interactions simply means that the interactions between each possible pairing of objects is the same as if that pair existed in isolation. So the overall behavior of the collection is just the result of adding together the interactions between the pairs.

    But in certain situations, like protons and neutrons binding together into atomic nuclei, three-body interactions occur and the total interaction is more than just the sum of interactions between pairs. These more complex relationships can arise when the particles that mediate the interaction (in nuclei, these particles are called gluons) can impact each other. So photons communicating through intermediary atoms have the potential for strong three-body interactions since the atoms can interact with each other and can change during the process.

    “You have a feedback in the sense that the involved polaritons change because of the interaction,” says JQI postdoctoral researcher Przemyslaw Bienias, who was the theoretical lead author on the paper. So, you not only get an interaction but the interaction changes the polaritons’ internal structure and this leads to those strong multi-body effects.”

    You can think of the collection of Rydberg atoms in the experiment like a restaurant set up for Valentine’s Day with only intimate tables for two. Photons entering as couple or a single customer can happily enjoy a meal at a small, cozy table, but if you crowd three people around one, they are probably going to bump elbows and irritate each other. They will probably quickly leave the restaurant before getting to dessert.

    For the photons (dressed up as polaritons), this change to the venue isn’t really about the physical space they share but about the abstract quantum space in which they exchange energy and momentum. In the abstract space, two photons can easily share a table without knocking each other into new states, but three will most likely elbow each other into new states and away from the table through an interaction.

    The experiment’s success lies in the team determining how to orchestrate the necessary relationships between polaritons. They had to set the laser used to manipulate the atoms to a precise frequency, related to how the Rydberg atoms shuffle energy between quantum energy states that the outermost electron can inhabit. The team successfully created conditions where the possible interactions depended on the number of polaritons present. Just one or two and they were unlikely to scatter. But if three were available to exchange energy and momentum the chance of them interacting and being knocked out of the beam shot up. So after leaving the Rydberg atoms behind, the uncluttered stream of light is left containing just individual or pairs of photons.

    The whole thing is the result of a carefully choreographed juggling act, with the atoms using energy from photons to move their electrons between low-, intermediate- and high-energy quantum states—all while simultaneously dancing with each other.

    “It was challenging, both in theory and experiment,” Ornelas-Huerta says. “We needed to go into this experimental regime where we had strong interactions and we had a strong coupling between the light and the atoms and also we have to try to minimize the losses from the intermediate state.”

    The theorists identified what laser frequencies to use and the signatures of three-photon losses that experimentalists looked for. Then they were able to closely match the experimental data to mathematical descriptions of how the interactions affected the photons traveling in bunches of various sizes and how the polaritons states exchanged energy and momentum during the interactions.

    “There are still efforts in theory and experiment to keep studying different regimes of few-body interactions.” Ornelas-Huerta says. “And to study how we can tune them or how we can add other states to even have more degrees of freedom and make these interactions more tunable. There’s still room to do much more research and interesting experiments on these systems.”

    Understanding and being able to create many-body interactions opens opportunities to simulate the physics of other many-body interactions and to develop new technologies, like photonic gates that serve as the basic building blocks of quantum computers and quantum networks that can send messages between quantum devices.

    “We now have a much clearer picture of the few-body physics in these Rydberg systems,” Gullans says. “And, I think where we want to go now is starting to put the pieces together—making photonic gates and quantum networks. We understand the fundamental physics well enough that we can start to get into those questions.”

    In addition to Rolston, Porto, Gullans, Gorshkov, Ornelas-Huerta and Bienias, co-authors of the research paper include JQI graduate students Alexander Craddock and Andrew Hachtel; JQI postdoctoral researcher Mary E. Lyon; and JQI undergraduate summer researcher Marcin Kalinowski.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    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.

    U Maryland Campus

    Driven by the pursuit of excellence, the University of Maryland has enjoyed a remarkable rise in accomplishment and reputation over the past two decades. By any measure, Maryland is now one of the nation’s preeminent public research universities and on a path to become one of the world’s best. To fulfill this promise, we must capitalize on our momentum, fully exploit our competitive advantages, and pursue ambitious goals with great discipline and entrepreneurial spirit. This promise is within reach. This strategic plan is our working agenda.

    The plan is comprehensive, bold, and action oriented. It sets forth a vision of the University as an institution unmatched in its capacity to attract talent, address the most important issues of our time, and produce the leaders of tomorrow. The plan will guide the investment of our human and material resources as we strengthen our undergraduate and graduate programs and expand research, outreach and partnerships, become a truly international center, and enhance our surrounding community.

    Our success will benefit Maryland in the near and long term, strengthen the State’s competitive capacity in a challenging and changing environment and enrich the economic, social and cultural life of the region. We will be a catalyst for progress, the State’s most valuable asset, and an indispensable contributor to the nation’s well-being. Achieving the goals of Transforming Maryland requires broad-based and sustained support from our extended community. We ask our stakeholders to join with us to make the University an institution of world-class quality with world-wide reach and unparalleled impact as it serves the people and the state of Maryland.

     
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