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  • richardmitnick 8:30 pm on September 9, 2014 Permalink | Reply
    Tags: , , , Quantum Computing   

    From Kavli: “Tiny Graphene Drum Could Form Future Quantum Memory” 

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    The Kavli Foundation

    09/09/2014
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    Scientists from TU Delft’s Kavli Institute of Nanoscience have demonstrated that they can detect extremely small changes in position and forces on very small drums of graphene. Graphene drums have great potential to be used as sensors in devices such as mobile phones. Using their unique mechanical properties, these drums could also act as memory chips in a quantum computer. The researchers present their findings in an article in the August 24th edition of Nature Nanotechnology. The research was funded by the FOM Foundation, the EU Marie-Curie program, and NWO.

    Graphene drums

    drum
    Graphene Drum

    Graphene is famous for its special electrical properties, but research on the one-layer thin graphite was recently expanded to explore graphene as a mechanical object. Thanks to their extreme low mass, tiny sheets of graphene can be used the same was as the drumhead of a musician. In the experiment, scientists use microwave-frequency light to ‘play’ the graphene drums, to listen to its ‘nano sound’, and to explore the way graphene in these drums moves.

    Optomechanics

    Dr. Vibhor Singh and his colleagues did this by using a 2D crystal membrane as a mirror in an ‘optomechanical cavity’. “In optomechanics you use the interference pattern of light to detect tiny changes in the position of an object. In this experiment, we shot microwave photons at a tiny graphene drum. The drum acts as a mirror: by looking at the interference of the microwave photons bouncing off of the drum, we are able to sense minute changes in the position of the graphene sheet of only 17 femtometers, nearly 1/10000th of the diameter of an atom.”, Singh explains.

    Amplifier

    The microwave ‘light’ in the experiment is not only good for detecting the position of the drum, but can also push on the drum with a force. This force from light is extremely small, but the small mass of the graphene sheet and the tiny displacements they can detect mean that the scientist can use these forces to ‘beat the drum’: the scientists can shake the graphene drum with the momentum of light. Using this radiation pressure, they made an amplifier in which microwave signals, such as those in your mobile phone, are amplified by the mechanical motion of the drum.

    Memory

    The scientists also show you can use these drums as ‘memory chips’ for microwave photons, converting photons into mechanical vibrations and storing them for up to 10 milliseconds. Although that is not long by human standards, it is a long time for a computer chip. “One of the long-term goals of the project is explore 2D crystal drums to study quantum motion. If you hit a classical drum with a stick, the drumhead will start oscillating, shaking up and down. With a quantum drum, however, you can not only make the drumhead move up and then down, but also make it into a ‘quantum superposition’, in which the drum head is both moving up and moving down at the same time ”, says research group leader Dr. Gary Steele. “This ‘strange’ quantum motion is not only of scientific relevance, but also could have very practical applications in a quantum computer as a quantum ‘memory chip’”.

    In a quantum computer, the fact that quantum ‘bits’ that can be both in the state 0 and 1 at the same time allow it to potentially perform computations much faster than a classical computer like those used today. Quantum graphene drums that are ‘shaking up and down at the same time’ could be used to store quantum information in the same way as RAM chips in your computer, allowing you to store your quantum computation result and retrieve it at a later time by listening to its quantum sound.

    See the full article, with video, here.

    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

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  • richardmitnick 6:41 pm on April 9, 2014 Permalink | Reply
    Tags: , , , , Quantum Computing   

    From M.I.T.: “New ‘switch’ could power quantum computing” 

    April 9, 2014
    Peter Dizikes | MIT News Office

    A light lattice that traps atoms may help scientists build networks of quantum information transmitters.

    Using a laser to place individual rubidium atoms near the surface of a lattice of light, scientists at MIT and Harvard University have developed a new method for connecting particles — one that could help in the development of powerful quantum computing systems.

    qc

    The new technique, described in a paper published today in the journal Nature, allows researchers to couple a lone atom of rubidium, a metal, with a single photon, or light particle. This allows both the atom and photon to switch the quantum state of the other particle, providing a mechanism through which quantum-level computing operations could take place.

    Moreover, the scientists believe their technique will allow them to increase the number of useful interactions occurring within a small space, thus scaling up the amount of quantum computing processing available.

    “This is a major advance of this system,” says Vladan Vuletić, a professor in MIT’s Department of Physics and Research Laboratory for Electronics (RLE), and a co-author of the paper. “We have demonstrated basically an atom can switch the phase of a photon. And the photon can switch the phase of an atom.”

    That is, photons can have two polarization states, and interaction with the atom can change the photon from one state to another; conversely, interaction with the photon can change the atom’s phase, which is equivalent to changing the quantum state of the atom from its “ground” state to its “excited” state. In this way the atom-photon coupling can serve as a quantum switch to transmit information — the equivalent of a transistor in a classical computing system. And by placing many atoms within the same field of light, the researchers may be able to build networks that can process quantum information more effectively.

    “You can now imagine having several atoms placed there, to make several of these devices — which are only a few hundred nanometers thick, 1,000 times thinner than a human hair — and couple them together to make them exchange information,” Vuletić adds.

    Using a photonic cavity

    Quantum computing could enable the rapid performance of calculations by taking advantage of the distinctive quantum-level properties of particles. Some particles can be in a condition of superposition, appearing to exist in two places at the same time. Particles in superposition, known as qubits, could thus contain more information than particles at classical scales, and allow for faster computing.

    However, researchers are in the early stages of determining which materials best allow for quantum-scale computing. The MIT and Harvard researchers have been examining photons as a candidate material, since photons rarely interact with other particles. For this reason, an optical quantum computing system, using photons, could be harder to knock out of its delicate alignment. But since photons rarely interact with other bits of matter, they are difficult to manipulate in the first place.

    In this case, the researchers used a laser to place a rubidium atom very close to the surface of a photonic crystal cavity, a structure of light. The atoms were placed no more than 100 or 200 nanometers — less than a wavelength of light — from the edge of the cavity. At such small distances, there is a strong attractive force between the atom and the surface of the light field, which the researchers used to trap the atom in place.

    Other methods of producing a similar outcome have been considered before — such as, in effect, dropping atoms into the light and then finding and trapping them. But the researchers found that they had greater control over the particles this way.

    “In some sense, it was a big surprise how simple this solution was compared to the different techniques you might envision of getting the atoms there,” Vuletić says.

    The result is what he calls a “hybrid quantum system,” where individual atoms are coupled to microscopic fabricated devices, and in which atoms and photons can be controlled in productive ways. The researchers also found that the new device serves as a kind of router separating photons from each other.

    “The idea is to combine different things that have different strengths and weaknesses in such a way to generate something new,” Vuletić says, adding: “This is an advance in technology. Of course, whether this will be the technology remains to be seen.”

    ‘Still amazing’ to hold onto one atom

    The paper, Nanophotonic quantum phase switch with a single atom, is co-authored by Vuletić; Tobias Tiecke, a postdoc affiliated with both RLE and Harvard; Harvard professor of physics Mikhail Lukin; Harvard postdoc Nathalie de Leon; and Harvard graduate students Jeff Thompson and Bo Liu.

    The collaboration between the MIT and Harvard researchers is one of two advances in the field described in the current issue of Nature. Researchers at the Max Planck Institute of Quantum Optics in Germany have concurrently developed a new method of producing atom-photon interactions using mirrors, forming quantum gates, which change the direction of motion or polarization of photons.

    “The Harvard/MIT experiment is a masterpiece of quantum nonlinear optics, demonstrating impressively the preponderance of single atoms over many atoms for the control of quantum light fields,” says Gerhard Rempe, a professor at the Max Planck Institute of Quantum Optics who helped lead the German team’s new research, and who has read the paper by the U.S.-based team. “The coherent manipulation of an atom coupled to a photonic crystal resonator constitutes a breakthrough and complements our own work … with an atom in a dielectric mirror resonator.”

    Rempe adds that he thinks both techniques will be regarded as notable “achievements on our way toward a robust quantum technology with stationary atoms and flying photons.”

    If the research techniques seem a bit futuristic, Vuletić says that even as an experienced researcher in the field, he remains slightly awed by the tools at his disposal.

    “For me what is still amazing, after working in this for 20 years,” Vuletić reflects, “is that we can hold onto a single atom, we can see it, we can move it around, we can prepare quantum superpositions of atoms, we can detect them one by one.”

    Funding for the research was provided in part by the National Science Foundation, the MIT-Harvard Center for Ultracold Atoms, the Natural Sciences and Engineering Research Council of Canada, the Air Force Office of Scientific Research, and the Packard Foundation.

    See the full article here.


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  • richardmitnick 3:44 pm on December 5, 2013 Permalink | Reply
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    From Berkeley Lab: “Berkeley Lab Researchers Create a Nonlinear Light-generating Zero-Index MetaMaterial” 


    Berkeley Lab

    Holds Promise for Future Quantum Networks and Light Sources

    December 05, 2013
    Lynn Yarris (510) 486-5375 lcyarris@lbl.gov

    The Information Age will get a major upgrade with the arrival of quantum processors many times faster and more powerful than today’s supercomputers. For the benefits of this new Information Age 2.0 to be fully realized, however, quantum computers will need fast and efficient multi-directional light sources. While quantum technologies remain grist for science fiction, a team of researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have taken an important step towards efficient light generation, the foundation for future quantum networks.

    graph
    In this graphic showing four-wave mixing in a positive/negative-index (upper) and zero-index (lower) metamaterial, forward-propagating FWM is much stronger than backward FWM for the positive/negative-index material but about the same in both directions for the zero-index metamaterial. (Image courtesy of Zhang group)

    In a study led by Xiang Zhang, a faculty scientist with Berkeley Lab’s Materials Sciences Division, the research team used a unique optical metamaterial with a refractive index of zero to generate phase mismatch–free nonlinear light, meaning the generated light waves move through the material gaining strength in all directions. This phase mismatch-free quality holds promise for quantum computing and networking, and future light sources based on nonlinear optics – the phenomena that occur when interactions with light modify a material’s properties.

    “In our demonstration of nonlinear dynamics in an optical metamaterial with zero-index refraction, equal amounts of nonlinearly generated waves are observed in both forward and backward propagation directions,” says Zhang. “The removal of phase matching in nonlinear optical metamaterials may lead to applications such as efficient multidirectional light emissions for novel light sources and the generation of entangled photons for quantum networking.”

    Zhang is the corresponding author of a paper in Science that describes this research. The paper is titled Phase Mismatch–Free Nonlinear Propagation in Optical Zero-Index Materials. Co-authors are Haim Suchowski, Kevin O’Brien, Zi Jing Wong, Alessandro Salandrino and Xiaobo Yin.

    team
    From left Xiang Zhang, Haim Suchowski, Zi Jing Wong, Kevin O’Brien and Alessandro Salandrino have created a nonlinear light-generating zero-index metamaterial that holds promise for future quantum networks and light sources. (Photo by Roy Kaltschmidt)

    Zhang, who holds the Ernest S. Kuh Endowed Chair Professor of Mechanical Engineering at the University of California (UC) Berkeley, where he also directs the National Science Foundation’s Nano-scale Science and Engineering Center, is one of the world’s foremost authorities in metamaterials research.

    See the full article here.

    A U.S. Department of Energy National Laboratory Operated by the University of California

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  • richardmitnick 6:46 pm on November 4, 2013 Permalink | Reply
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    From Berkeley Lab: “Diamond Imperfections Pave the Way to Technology Gold” 


    Berkeley Lab

    November 04, 2013
    Lynn Yarris (510) 486-5375 lcyarris@lbl.gov

    From supersensitive detections of magnetic fields to quantum information processing, the key to a number of highly promising advanced technologies may lie in one of the most common defects in diamonds. Researchers at the Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have taken an important step towards unlocking this key with the first ever detailed look at critical ultrafast processes in these diamond defects.

    Using two-dimensional electronic spectroscopy on pico- and femto-second time-scales, a research team led by Graham Fleming, Vice Chancellor for Research at UC Berkeley and faculty scientist with Berkeley Lab’s Physical Biosciences Division, has recorded unprecedented observations of energy moving through the atom-sized diamond impurities known as nitrogen-vacancy (NV) centers. An NV center is created when two adjacent carbon atoms in a diamond crystal are replaced by a nitrogen atom and an empty gap.

    “Our use of 2D electronic spectroscopy allowed us to essentially map the flow of energy through the NV center in real time and observe critical quantum mechanical effects,” Fleming says. “The results hold broad implications for magnetometry, quantum information, nanophotonics, sensing and ultrafast spectroscopy.”

    lab
    Vanessa Huxter, former member of Graham Fleming’s research group and now a professor at the University of Arizona, was a key member of the research team that provided unprecedented observations of ultrafast processes in diamond NV centers. (Photo by Beatriz Verdugo, University of Arizona)

    See the full article here.

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  • richardmitnick 6:39 pm on September 16, 2013 Permalink | Reply
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    From Berkeley Lab: “On the Road to Fault-Tolerant Quantum Computing” 


    Berkeley Lab

    Collaboration at Berkeley Lab’s Advanced Light Source Induces High Temperature Superconductivity in a Toplogical Insulator

    September 16, 2013
    Lynn Yarris (510) 486-5375 lcyarris@lbl.gov

    Reliable quantum computing would make it possible to solve certain types of extremely complex technological problems millions of times faster than today’s most powerful supercomputers. Other types of problems that quantum computing could tackle would not even be feasible with today’s fastest machines. The key word is “reliable.” If the enormous potential of quantum computing is to be fully realized, scientists must learn to create “fault-tolerant” quantum computers. A small but important step toward this goal has been achieved by an international collaboration of researchers from China’s Tsinghua University and the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) working at the Advanced Light Source (ALS).

    Using premier beams of ultraviolet light at the ALS, a DOE national user facility for synchrotron radiation, the collaboration has reported the first demonstration of high-temperature superconductivity in the surface of a topological insulator – a unique class of advanced materials that are electrically insulating on the inside but conducting on the surface. Inducing high-temperature superconductivity on the surface of a topological insulator opens the door to the creation of a pre-requisite for fault-tolerant quantum computing, a mysterious quasiparticle known as the “Majorana zero mode.”

    “We have shown that by interfacing a topological insulator, bismuth selenide, with a high temperature superconductor, BSCCO (bismuth strontium calcium copper oxide), it is possible to induce superconductivity in the topological surface state,” says Alexei Fedorov, a staff scientist for ALS beamline 12.0.1, where the induced high temperature superconductivity of the topological insulator heterostructure was confirmed. “This is the first reported demonstration of induced high temperature superconductivity in a topological surface state.”

    state
    This schematic of a bismuth selenide/BSCCO cuprate (Bi2212) heterostructure shows a proximity-induced high-temperature superconducting gap on the surface states of the bismuth selenide topological insulator. No image credit.

    See the full article here.

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  • richardmitnick 3:07 pm on February 8, 2013 Permalink | Reply
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    From Caltech: “Creating New Quantum Building Blocks” 

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    Caltech

    “Scientists have long dreamed of creating a quantum computer—a device rooted in the bizarre phenomena that transpire at the level of the very small, where quantum mechanics rules the scene. It is believed that such new computers could process currently unsolvable problems in seconds.

    Researchers have tried using various quantum systems, such as atoms or ions, as the basic, transistor-like units in simple quantum computation devices. Now, laying the groundwork for an on-chip optical quantum network, a team of researchers, including Andrei Faraon from the California Institute of Technology (Caltech), has shown that defects in diamond can be used as quantum building blocks that interact with one another via photons, the basic units of light.

    photon

    The device is simple enough—it involves a tiny ring resonator and a tunnel-like optical waveguide, which both funnel light. Both structures, each only a few hundred nanometers wide, are etched in a diamond membrane and positioned close together atop a glass substrate. Within the resonator lies a nitrogen-vacancy center (NV center)—a defect in the structure of diamond in which a nitrogen atom replaces a carbon atom, and in which a nearby spot usually reserved for another carbon atom is simply empty. Such NV centers are photoluminescent, meaning they absorb and emit photons.

    ‘These NV centers are like the building blocks of the network, and we need to make them interact—like having an electrical current connecting one transistor to another,’ explains Faraon, lead author on a paper describing the work in the New Journal of Physics. “In this case, photons do that job.'”

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 2:07 pm on November 27, 2012 Permalink | Reply
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    From MIT: “Proving quantum computers feasible” 

    With a new contribution to probability theory, researchers show that relatively simple physical systems could yield powerful quantum computers.

    November 27, 2012
    Larry Hardesty

    Quantum computers are devices — still largely theoretical — that could perform certain types of computations much faster than classical computers; one way they might do that is by exploiting spin, a property of tiny particles of matter. A ‘spin chain,’ in turn, is a standard model that physicists use to describe systems of quantum particles, including some that could be the basis for quantum computers.

    ch
    The possible quantum states of a chain of particles can be represented as points in space, with lines connecting states that can be swapped with no change in the chain’s total energy. MIT researchers and their colleagues showed that such networks are densely interconnected, with heavily trafficked pathways between points. Graphic: Christine Daniloff

    Many quantum algorithms require that particles’ spins be ‘entangled,’ meaning that they’re all dependent on each other. The more entanglement a physical system offers, the greater its computational power. Until now, theoreticians have demonstrated the possibility of high entanglement only in a very complex spin chain, which would be difficult to realize experimentally. In simpler systems, the degree of entanglement appeared to be capped: Beyond a certain point, adding more particles to the chain didn’t seem to increase the entanglement.

    This month, however, in the journal Physical Review Letters, a group of researchers at MIT, IBM, Masaryk University in the Czech Republic, the Slovak Academy of Sciences and Northeastern University proved that even in simple spin chains, the degree of entanglement scales with the length of the chain. The research thus offers strong evidence that relatively simple quantum systems could offer considerable computational resources.”

    See the full article here.


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  • richardmitnick 11:42 am on August 31, 2012 Permalink | Reply
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    From MIT News: “A one-way street for spinning atoms” 

    Work correlating ultracold atoms’ spin with their direction of motion may help physicists model new circuit devices and unusual phases of matter.

    August 30, 2012
    News Office

    Elementary particles have a property called spin that can be thought of as rotation around their axes. In work reported this week in the journal Physical Review Letters, MIT physicists have imposed a stringent set of traffic rules on atomic particles in a gas: Those spinning clockwise can move in only one direction, while those spinning counterclockwise can move only in the other direction.

    image
    Elementary particles have a fundamental property called ‘spin’ that determines how they align in a magnetic field. MIT researchers have created a new physical system in which atoms with clockwise spin move in only one direction, while atoms with counterclockwise spin move in the opposite direction.
    Graphic: Christine Daniloff

    Physical materials with this distinctive property could be used in “spintronic” circuit devices that rely on spin rather than electrical current for transferring information. The correlation between spin and direction of motion is crucial to creating a so-called topological superfluid, a key ingredient of some quantum-computing proposals.

    The MIT team, led by Martin Zwierlein, an associate professor of physics and a principal investigator in the Research Laboratory of Electronics (RLE), produced this spin-velocity correlation in an ultracold, dilute gas of atoms.

    The MIT research was funded in part by the National Science Foundation, the Air Force Office of Scientific Research, the Office of Naval Research, the Army Research Office with funding from the DARPA Optical Lattice Emulator program, and the David and Lucile Packard Foundation.

    See the full and important article here.


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  • richardmitnick 2:54 pm on July 25, 2012 Permalink | Reply
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    From MIT News: “Single-photon transmitter could enable new quantum devices” 

    July 25, 2012
    David L. Chandler

    Long-sought goal for quantum devices — the ability to transmit single photons while blocking multiple photons — is finally achieved.

    In theory, quantum computers should be able to perform certain kinds of complex calculations much faster than conventional computers, and quantum-based communication could be invulnerable to eavesdropping. But producing quantum components for real-world devices has proved to be fraught with daunting challenges.

    cloud
    An artist’s conception shows how any number of incoming photons (top) can be absorbed by a cloud of ultra-cold atoms (center), tuned so that only one single photon can pass through at a time. Being able to produce a controlled beam of single photons has been a goal of research toward creating quantum devices. Graphic: Christine Daniloff

    Now, a team of researchers at MIT and Harvard University has achieved a crucial long-term goal of such efforts: the ability to convert a laser beam into a stream of single photons, or particles of light, in a controlled way. The successful demonstration of this achievement is detailed in a paper published this week in the journal Nature by MIT doctoral student Thibault Peyronel and colleagues.

    See the full article here.

     
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