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  • richardmitnick 10:22 am on February 23, 2019 Permalink | Reply
    Tags: , , , , , , Semiconductor quantum dots, University of Cambridge   

    From University of Cambridge: “Physicists get thousands of semiconductor nuclei to do ‘quantum dances’ in unison” 

    U Cambridge bloc

    From University of Cambridge

    22 Feb 2019
    Communications office

    1
    Theoretical ESR spectrum buildup as a function of two-photon detuning δ and drive time τ, for a Rabi frequency of Ω = 3.3 MHz on the central transition. Credit: University of Cambridge.

    A team of Cambridge researchers have found a way to control the sea of nuclei in semiconductor quantum dots so they can operate as a quantum memory device.

    Quantum dots are crystals made up of thousands of atoms, and each of these atoms interacts magnetically with the trapped electron. If left alone to its own devices, this interaction of the electron with the nuclear spins, limits the usefulness of the electron as a quantum bit – a qubit.

    Led by Professor Mete Atatüre from Cambridge’s Cavendish Laboratory, the researchers are exploiting the laws of quantum physics and optics to investigate computing, sensing or communication applications.

    “Quantum dots offer an ideal interface, as mediated by light, to a system where the dynamics of individual interacting spins could be controlled and exploited,” said Atatüre, who is a Fellow of St John’s College. “Because the nuclei randomly ‘steal’ information from the electron they have traditionally been an annoyance, but we have shown we can harness them as a resource.”

    The Cambridge team found a way to exploit the interaction between the electron and the thousands of nuclei using lasers to ‘cool’ the nuclei to less than 1 milliKelvin, or a thousandth of a degree above the absolute zero temperature. They then showed they can control and manipulate the thousands of nuclei as if they form a single body in unison, like a second qubit. This proves the nuclei in the quantum dot can exchange information with the electron qubit and can be used to store quantum information as a memory device. The results are reported in the journal Science.

    Quantum computing aims to harness fundamental concepts of quantum physics, such as entanglement and superposition principle, to outperform current approaches to computing and could revolutionise technology, business and research. Just like classical computers, quantum computers need a processor, memory, and a bus to transport the information backwards and forwards. The processor is a qubit which can be an electron trapped in a quantum dot, the bus is a single photon that these quantum dots generate and are ideal for exchanging information. But the missing link for quantum dots is quantum memory.

    Atatüre said: “Instead of talking to individual nuclear spins, we worked on accessing collective spin waves by lasers. This is like a stadium where you don’t need to worry about who raises their hands in the Mexican wave going round, as long as there is one collective wave because they all dance in unison.

    “We then went on to show that these spin waves have quantum coherence. This was the missing piece of the jigsaw and we now have everything needed to build a dedicated quantum memory for every qubit.”

    In quantum technologies, the photon, the qubit and the memory need to interact with each other in a controlled way. This is mostly realised by interfacing different physical systems to form a single hybrid unit which can be inefficient. The researchers have been able to show that in quantum dots, the memory element is automatically there with every single qubit.

    Dr Dorian Gangloff, one of the first authors of the paper [Science] and a Fellow at St John’s, said the discovery will renew interest in these types of semiconductor quantum dots. Dr Gangloff explained: “This is a Holy Grail breakthrough for quantum dot research – both for quantum memory and fundamental research; we now have the tools to study dynamics of complex systems in the spirit of quantum simulation.”

    The long term opportunities of this work could be seen in the field of quantum computing. Last month, IBM launched the world’s first commercial quantum computer, and the Chief Executive of Microsoft has said quantum computing has the potential to ‘radically reshape the world’.

    Gangloff said: “The impact of the qubit could be half a century away but the power of disruptive technology is that it is hard to conceive of the problems we might open up – you can try to think of it as known unknowns but at some point you get into new territory. We don’t yet know the kind of problems it will help to solve which is very exciting.”

    See the full article here .

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    Please help promote STEM in your local schools.

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    U Cambridge Campus

    The University of Cambridge (abbreviated as Cantab in post-nominal letters) is a collegiate public research university in Cambridge, England. Founded in 1209, Cambridge is the second-oldest university in the English-speaking world and the world’s fourth-oldest surviving university. It grew out of an association of scholars who left the University of Oxford after a dispute with townsfolk. The two ancient universities share many common features and are often jointly referred to as “Oxbridge”.

    Cambridge is formed from a variety of institutions which include 31 constituent colleges and over 100 academic departments organised into six schools. The university occupies buildings throughout the town, many of which are of historical importance. The colleges are self-governing institutions founded as integral parts of the university. In the year ended 31 July 2014, the university had a total income of £1.51 billion, of which £371 million was from research grants and contracts. The central university and colleges have a combined endowment of around £4.9 billion, the largest of any university outside the United States. Cambridge is a member of many associations and forms part of the “golden triangle” of leading English universities and Cambridge University Health Partners, an academic health science centre. The university is closely linked with the development of the high-tech business cluster known as “Silicon Fen”.

     
  • richardmitnick 11:13 am on January 21, 2019 Permalink | Reply
    Tags: American University of Beirut, , , , , Kuiper Belt objects - A few objects are orbiting differently from everything else and we don't know why., , , University of Cambridge   

    From Science Alert: “Something Else Instead of Planet Nine Could Be Hiding in The Outer Solar System” 

    ScienceAlert

    From Science Alert

    21 JAN 2019
    MICHELLE STARR

    1
    Dwarf planet Sedna, one of the detached TNOs. (NASA/JPL-Caltech)

    Somewhere in the outer reaches of the Solar System, beyond the orbit of Neptune, something wonky is happening. A few objects are orbiting differently from everything else, and we don’t know why.

    A popular hypothesis is that an unseen object called Planet Nine could be messing with these orbits; astronomers are avidly searching for this planet. But now physicists have come up with an alternative explanation they think is more plausible.

    Instead of one big object, the orbital wobblies could be caused by the combined gravitational force of a number of smaller Kuiper Belt or trans-Neptunian objects (TNOs). That’s according to astrophysicists Antranik Sefilian of the University of Cambridge in the UK and Jihad Touma of the American University of Beirut in Lebanon.

    If it sounds familiar, that’s because Sefilian and Touma are not the first to think of this idea – but their calculations are the first to explain significant features of the strange orbits of these objects, while taking into account the other eight planets in the Solar System.

    A hypothesis for Planet Nine was first announced in a 2016 study [The Astronomical Journal]. Astronomers studying a dwarf planet in the Kuiper Belt noticed that several TNOs were “detached” from the strong gravitational influence of the Solar System’s gas giants, and had weird looping orbits that were different from the rest of the Kuiper Belt.

    But the orbits of these six objects were also clustered together in a way that didn’t appear random; something seemed to have tugged them into that position. According to modelling, a giant, heretofore unseen planet could do so.

    So far, this planet has remained elusive – not necessarily odd, since there are considerable technical challenges to seeing a dark object that far away, especially when we don’t know where it is. But its evasiveness is prompting scientists to seek alternative explanations.

    “The Planet Nine hypothesis is a fascinating one, but if the hypothesised ninth planet exists, it has so far avoided detection,” Sefilian said, adding that the team wanted to see if there was a less dramatic explanation of the weird TNO orbits.

    “We thought, rather than allowing for a ninth planet, and then worry about its formation and unusual orbit, why not simply account for the gravity of small objects constituting a disk beyond the orbit of Neptune and see what it does for us?”

    The researchers created a computer model of the detached TNOs, as well as the planets of the Solar System (and their gravity), and a huge disc of debris past Neptune’s orbit.

    By applying tweaks to elements such as the mass, eccentricity and orientation of the disc, the researchers were able to recreate the clustered looping orbits of the detached TNOs.

    “If you remove Planet Nine from the model, and instead allow for lots of small objects scattered across a wide area, collective attractions between those objects could just as easily account for the eccentric orbits we see in some TNOs,” Sefilian said.

    This solves a problem that scientists from the University of Colorado Boulder had when they first floated the collective gravity hypothesis last year. Although their calculations were able to account for the gravitational effect on the detached TNOs, they couldn’t explain why their orbits were all tilting the same way.

    And there’s still another problem with both models: in order to produce the observed effect, the Kuiper Belt needs a collective gravity of at least a few Earth masses.

    Current estimates, however, put the mass of the Kuiper Belt at just 4 to 10 percent of Earth’s mass.

    But, according to Solar System formation models, it should be much higher; and, Sefilian notes, it’s hard to view the entirety of a debris disc around a star when you’re inside it, so it’s possible that there’s a lot more to the Kuiper Belt than we’re able to see.

    “While we don’t have direct observational evidence for the disc, neither do we have it for Planet Nine, which is why we’re investigating other possibilities,” Sefilian said.

    “It’s also possible that both things could be true – there could be a massive disk and a ninth planet. With the discovery of each new TNO, we gather more evidence that might help explain their behaviour.”

    The team’s research is due to appear in the Astronomical Journal and you can find the pre-print on arXiv.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

     
  • 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, , , Tunable diamond string may hold key to quantum memory, University of Cambridge   

    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.

    1
    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.
    stem
    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.

     
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