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  • richardmitnick 11:17 am on May 23, 2018 Permalink | Reply
    Tags: A quantum internet promises completely secure communication, Engineering diamond strings that can be tuned to quiet a qubit’s environment and improve memory, John A Paulson School of Engineering and Applied Sciences at Harvard, Quantum Memory, , Tunable diamond string may hold key to quantum memory,   

    From John A Paulson School of Engineering and Applied Sciences: “Tunable diamond string may hold key to quantum memory” 

    Harvard School of Engineering and Applied Sciences
    From John A Paulson School of Engineering and Applied Sciences

    May 22, 2018

    Leah Burrows
    lburrows@seas.harvard.edu
    (617) 496-1351

    A process similar to guitar tuning improves storage time of quantum memory.

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    Electrodes stretch diamond strings to increase the frequency of atomic vibrations to which an electron is sensitive, just like tightening a guitar string increases the frequency or pitch of the string. The tension quiets a qubit’s environment and improves memory from tens to several hundred nanoseconds, enough time to do many operations on a quantum chip. (Second Bay Studios/Harvard SEAS)

    A quantum internet promises completely secure communication. But using quantum bits or qubits to carry information requires a radically new piece of hardware – a quantum memory. This atomic-scale device needs to store quantum information and convert it into light to transmit across the network.

    A major challenge to this vision is that qubits are extremely sensitive to their environment, even the vibrations of nearby atoms can disrupt their ability to remember information. So far, researchers have relied on extremely low temperatures to quiet vibrations but, achieving those temperatures for large-scale quantum networks is prohibitively expensive.

    Now, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the University of Cambridge have developed a quantum memory solution that is as simple as tuning a guitar.

    The researchers engineered diamond strings that can be tuned to quiet a qubit’s environment and improve memory from tens to several hundred nanoseconds, enough time to do many operations on a quantum chip.

    “Impurities in diamond have emerged as promising nodes for quantum networks,” said Marko Loncar, the Tiantsai Lin Professor of Electrical Engineering at SEAS and senior author of the research. “However, they are not perfect. Some kinds of impurities are really good at retaining information but have a hard time communicating, while others are really good communicators but suffer from memory loss. In this work, we took the latter kind, and improved the memory by ten times.”

    The research is published in Nature Communications.

    Impurities in diamond, known as silicon-vacancy color centers, are powerful qubits. An electron trapped in the center acts as a memory bit and can emit single photons of red light, which would in turn act as long-distance information carriers of a quantum internet. But with the nearby atoms in the diamond crystal vibrating randomly, the electron in the center quickly forgets any quantum information it is asked to remember.

    “Being an electron in a color center is like trying to study at a loud marketplace,” said Srujan Meesala, a graduate student at SEAS and co-first author of the paper. “There is all this noise around you. If you want to remember anything, you need to either ask the crowds to stay quiet or find a way to focus over the noise. We did the latter.”

    To improve memory in a noisy environment, the researchers carved the diamond crystal housing the color center into a thin string, about one micron wide — a hundred times thinner than a strand of hair — and attached electrodes to either side. By applying a voltage, the diamond string stretches and increases the frequency of vibrations the electron is sensitive to, just like tightening a guitar string increases the frequency or pitch of the string.

    “By creating tension in the string, we increase the energy scale of vibrations that the electron is sensitive to, meaning it can now only feel very high energy vibrations,” said Meesala. “This process effectively turns the surrounding vibrations in the crystal to an irrelevant background hum, allowing the electron inside the vacancy to comfortably hold information for hundreds of nanoseconds, which can be a really long time on the quantum scale. A symphony of these tunable diamond strings could serve as the backbone of a future quantum internet.”

    Next, the researchers hope to extend the memory of the qubits to the millisecond, which would enable hundreds of thousands of operations and long-distance quantum communication.

    The Harvard Office of Technology Development has protected the intellectual property relating to this project and is exploring commercialization opportunities.

    The research was co-first authored by Young-Ik Sohn and Srujan Meesala from Marko Loncar’s group at Harvard, and Benjamin Pingault from Mete Atature’s group at the University of Cambridge. Researchers from Harvard SEAS, Harvard Physics, Sandia National Laboratories also contributed to the manuscript.

    The research was supported by the National Science Foundation-sponsored Center for Integrated Quantum Materials, Office of Naval Research Multidisciplinary University Research Initiative on Quantum Optomechanics, NSF Emerging Frontiers in Research and Innovation ACQUIRE, the University of Cambridge, the ERC Consolidator Grant PHOENICS, and the EPSRC Quantum Technology Hub NQIT.

    See the full article here .


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    Please help promote STEM in your local schools.
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    Stem Education Coalition

    Through research and scholarship, the Harvard School of Engineering and Applied Sciences (SEAS) will create collaborative bridges across Harvard and educate the next generation of global leaders. By harnessing the power of engineering and applied sciences we will address the greatest challenges facing our society.

    Specifically, that means that SEAS will provide to all Harvard College students an introduction to and familiarity with engineering and technology as this is essential knowledge in the 21st century.

    Moreover, our concentrators will be immersed in the liberal arts environment and be able to understand the societal context for their problem solving, capable of working seamlessly withothers, including those in the arts, the sciences, and the professional schools. They will focus on the fundamental engineering and applied science disciplines for the 21st century; as we will not teach legacy 20th century engineering disciplines.

    Instead, our curriculum will be rigorous but inviting to students, and be infused with active learning, interdisciplinary research, entrepreneurship and engineering design experiences. For our concentrators and graduate students, we will educate “T-shaped” individuals – with depth in one discipline but capable of working seamlessly with others, including arts, humanities, natural science and social science.

    To address current and future societal challenges, knowledge from fundamental science, art, and the humanities must all be linked through the application of engineering principles with the professions of law, medicine, public policy, design and business practice.

    In other words, solving important issues requires a multidisciplinary approach.

    With the combined strengths of SEAS, the Faculty of Arts and Sciences, and the professional schools, Harvard is ideally positioned to both broadly educate the next generation of leaders who understand the complexities of technology and society and to use its intellectual resources and innovative thinking to meet the challenges of the 21st century.

    Ultimately, we will provide to our graduates a rigorous quantitative liberal arts education that is an excellent launching point for any career and profession.

     
  • richardmitnick 4:17 pm on January 28, 2015 Permalink | Reply
    Tags: , , Quantum Memory   

    From BNL: “Nanoscale Mirrored Cavities Amplify, Connect Quantum Memories” 

    Brookhaven Lab

    January 28, 2015
    Karen McNulty Walsh, (631) 344-8350 or Peter Genzer, (631) 344-3174

    Advance could lead to quantum computing and the secure transfer of information over long-distance fiber optic networks

    1
    Members of the MIT team (l to r): Luozhou Li, Dirk Englund, Michael Walsh, Edward Chen, and Tim Schroder. Photo credit: MIT

    The idea of computing systems based on controlling atomic spins just got a boost from new research performed at the Massachusetts Institute of Technology (MIT) and the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory. By constructing tiny “mirrors” to trap light around impurity atoms in diamond crystals, the team dramatically increased the efficiency with which photons transmit information about those atoms’ electronic spin states, which can be used to store quantum information. Such spin-photon interfaces are thought to be essential for connecting distant quantum memories, which could open the door to quantum computers and long-distance cryptographic systems.

    Crucially, the team demonstrated a spin-coherence time (how long the memory encoded in the electron spin state lasts) of more than 200 microseconds—a long time in the context of the rate at which computational operations take place. A long coherence time is essential for quantum computing systems and long-range cryptographic networks.

    “Our research demonstrates a technique to extend the storage time of quantum memories in solids that are efficiently coupled to photons, which is essential to scaling up such quantum memories for functional quantum computing systems and networks,” said MIT’s Dirk Englund, who led the research, now published in Nature Communications. Scientists at the Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility at Brookhaven Lab, helped to fabricate and characterize the materials.

    2
    A scanning electron micrograph of one of the one-dimensional diamond crystal cavities. Photo credit: MIT

    The memory elements described in this research are the spin states of electrons in nitrogen-vacancy (NV) centers in diamond. The NV consists of a nitrogen atom in the place of a carbon atom, adjacent to a crystal vacancy inside the carbon lattice of diamond. The up or down orientation of the electron spins on these NV centers can be used to encode information in a way that is somewhat analogous to how the charge of many electrons is used to encode the “0”s and “1”s in a classical computer.

    The scientists preferentially orient the NV’s spin, whose direction is naturally randomly oriented, along a particular direction. This step prepares a quantum state of “0”. From there, scientists can manipulate the electron spins into “1” or back into “0” using microwaves. The “0” state has brighter fluorescence than the “1” state, allowing scientists to measure the state in an optical microscope.

    The trick is getting the electron spins in the NV centers to hold onto the stable spin states long enough to perform these logic-gate operations—and being able to transfer information among the individual memory elements to create actual computing networks.

    “It is already possible to transfer information about the electron spin state via photons, but we have to make the interface between the photons and electrons more efficient. The trouble is that photons and electrons normally interact only very weakly. To increase the interaction between photons and the NV, we build an optical cavity—a trap for photons—around the NV,” Englund said.
    Light and mirrors

    3
    Building quantum memories on a chip: Diamond photonic crystal cavities (ladder-like structures) are integrated on a silicon substrate. Green laser light (green arrow) excites electrons on impurity atoms trapped within the cavities, picking up information about their spin states, which can then be read out as red light (red arrow) emitted by photoluminescence from the cavity. The inset shows the nitrogen-vacancy (NV)-nanocavity system, where a nitrogen atom (N) is substituted into the diamond crystal lattice in place of a carbon atom (gray balls) adjacent to a vacancy (V). Layers of diamond and air keep light trapped within these cavities long enough to interact with the nitrogen atom’s spin state and transfer that information via the emitted light. Photo credit: MIT

    These cavities, nanofabricated at Brookhaven by MIT graduate student Luozhou Li with the help of staff scientist Ming Lu of the CFN, consist of layers of diamond and air tightly spaced around the impurity atom of an NV center. At each interface between the layers there’s a little bit of reflection—like the reflections from a glass surface. With each layer, the reflections add up—like the reflections in a funhouse filled with mirrors. Photons that enter these nanoscale funhouses bounce back and forth up to 10,000 times, greatly enhancing their chance of interacting with the electrons in the NV center. This increases the efficiency of information transfer between photons and the NV center’s electron spin state.

    The devices’ performance was characterized in part using optical microscopy in a magnetic field at the CFN, performed by CFN staff scientist Mircea Cotlet, Luozhou Li, and Edward Chen, who is also a graduate student studying under the guidance of Englund at MIT.

    4
    Brookhaven scientist Mircea Cotlet at the CFN, where he and the MIT graduate students performed optical measurements of the quantum memory devices.

    “Coupling the NV centers with these optical resonator cavities seemed to preserve the NV spin coherence time—the duration of the memory,” Cotlet said.

    Added Englund: “These methods have given us a great starting point for translating information between the spin states of the electrons among multiple NV centers. These results are an important part of validating the scientific promise of NV-cavity systems for quantum networking.”

    In addition, said Li, “The transferred hard mask lithography technique that we have developed in this work would benefit most unconventional substrates that aren’t suitable for typical high-resolution patterning by electron beam lithography. In our case, we overcame the problem that hundred-nanometer-thick diamond membranes are too small and too uneven. ”
    Ming Lu

    6
    CFN staff scientist Ming Lu helped to fabricate diamond-and-air layered nanoscale “funhouses” that trap light so it can interact with atomic spin states.

    The methods may also enable the long-distance transfer of quantum-encoded information over fiber optic cables. Such information could be made completely secure, Englund said, because any attempt to intercept or measure the transferred information would alter the photons’ properties, thus alerting the sender and the recipient to the possible presence of an eavesdropper.

    Fabrication and experiments were supported in part by the Air Force Office of Scientific Research. The CFN at Brookhaven Lab is supported by the DOE Office of Science. Additional funding for individual researchers came from the Alexander von Humboldt Foundation, the NASA Office of the Chief Technologist’s Space Technology Research Fellowship, and the National Science Foundation.

    Working Together: Benefits for Facility Users, Students, and CFN

    “At the CFN,” said longtime facility user Dirk Englund of MIT, “we can do things that are very difficult or impossible in a normal university setting. Developing a radically new process, like our processing of diamond quantum memories, has been so successful at the CFN because of the consistency in the fabrication tools, the wide range of characterization tools, and the expert knowledge.”

    His students agree: “We got a lot of technical support and scientific guidance from CFN research scientists, who are willing to help early-year students start their research careers,” said MIT graduate student Luozhou Li. In addition, he said, “CFN has all the advanced nanofabrication and confocal facilities centralized in one place. It is convenient and efficient to step from one room to another, finish the device fabrication in a clean-room environment and measure optical properties quickly.”

    Edward Chen, the other MIT grad student involved in this work, appreciated the chance to see first-hand the benefits of working in an interdisciplinary atmosphere at Brookhaven Lab, where state-of-the-art facilities like the CFN and the new National Synchrotron Light Source II (NSLS-II) can be found side-by-side. “I hope to continue finding ways to improve the nanofabrication process we developed for this research so that I can potentially take advantage of other unique facilities available at Brookhaven Lab,” he said.

    The benefits go both ways, said CFN staff scientist, Mircea Cotlet. “We now have a new method we can use and pass on to future users,” he said, referring to the electron spin resonance microscopy techniques used to measure the spin-dependent fluorescence of the NV centers and resonators explored in this study.

    On a more personal note, Cotlet added, “I have never worked with such challenging students.” The collaboration, he said, helped invigorate his work. “I learned a lot from them. They make you realize you don’t have all the answers.”

    Continuing to stimulate that kind of intellectual interaction for the benefit of science and society is what research at DOE user facilities like the CFN is all about.

    See the full article here.

    BNL Center for Functional Nanomaterials
    BNL Center for Functional Nanomaterials

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    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

     
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