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  • Tunnel Vision | JILA-PFC
    measure its performance To make the displacement detector the researchers used lithography tools to create a gold structure with a freely suspended nanomechanical beam 100 nm thick connected initially to an atomic point contact as shown below Then the researchers ran a current through the point creating an electron wind that shoved atoms aside creating a tiny gap between the point and the beam During this process they measured the resistance of the point contact looking for a characteristic increase in resistance indicating that electrons had started to hop tunnel across the gap An artist s conception of the atom sized gap between the atomic point contact and the freely suspended nanomechanical beam is shown at the right Once the device was up and running the researchers monitored the size of the atom sized gap by measuring the current that flowed through the atomic point contact However there was also shot noise in the current This noise arises from the fact that current across the gap is composed of individual discreet tunneling electrons subject to the laws of quantum mechanics i e tunneling is a random probabilistic event Even though the researchers could easily determine the average current the nature of a tunneling current meant there would always be fluctuations around this average or shot noise The shot noise limited how accurately the position of the freely suspended beam could be determined However when more electrons traveled across the gap per second less noise affected the displacement measurement If shot noise were the only issue in measuring tunneling current then Flowers Jacobs and his colleagues could simply have increased the average current through their device until the displacement noise became as small as desired Unfortunately there was also a random force acting on the freely suspended beam due to the

    Original URL path: http://jila-pfc.colorado.edu/highlights/tunnel-vision (2016-04-29)
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  • Spin City | JILA-PFC
    in the wells increases the strength of the light electron interaction and allows the electrons to be isolated In the process of probing spin transport and coherence time the researchers are also gaining new insights into optical spin control Although the Cundiff group currently has no plans to actually build a spintronic device it seeks a better understanding of the fundamental physics that will make such devices possible Transport Sam Carter s studies of spin transport in semiconductor quantum wells have shown that the optical pulses he uses to manipulate and probe electron spin also affect the transport of spin packets The figure above displays the optical excitation of a spin packet and how the spins move and spread out in an electric field Carter believes that with further study it may even be possible to use lasers to control spin transport Optical control could well play a role in the design of spin based quantum computers However other spintronic devices such as the spin transistor will likely not rely on lasers Carter recently performed systematic studies of spin diffusion using transient spin gratings In this technique two laser pulses interfere on the semiconductor to generate a spin grating alternating regions of spin up and spin down electrons separated by a few microns Spin diffusion causes this grating to wash out so measuring how long the grating lasts determines how fast diffusion occurs Carter has shown that increasing the power of the lasers used to excite the electrons increases spin diffusion Stronger laser excitation can free electrons from their local environment allowing them to move more freely about the quantum well Raising the temperature of the semiconductor had a similar effect The difference between diffusion of electron spins was also compared to diffusion of bound electron hole pairs called excitons

    Original URL path: http://jila-pfc.colorado.edu/highlights/spin-city (2016-04-29)
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  • JILA Physicists Investigating Atomtronics | JILA-PFC
    3 coherent flow With such characteristics atomtronics could play a key role in quantum computing nanoscale amplifiers and precision sensors A recent analysis by graduate student Brian Seaman research associate Meret Krämer and Fellows Dana Anderson and Murray Holland describes the operation of atomtronic batteries circuits diodes and transistors These devices are based on strongly interacting ultracold Bose atomic gases in lattices The researchers show how the behavior of ultracold atoms in such systems is analogous to that of electrons in a doped semiconductor Their study lays the theoretical groundwork for more advanced atomtronic devices including amplifiers oscillators and logic gates Atomtronic devices use atom analogs of currents batteries and resistors Atom flux or current plays the role of electric current Atom currents appear when atoms can flow from a high density region to a lower density region The difference in atom density creates a chemical potential analogous to the electrical potential created inside a battery If two optical lattices are connected by a waveguide this wire will allow atoms to flow from a lattice with lots of atoms to another that contains just a few atoms In this way the optical lattices connected by a waveguide function as a battery as shown in the schematic at right In atomtronic circuits increasing the height of an optical lattice will slow atom currents as a resistor does in an electronic circuit However higher lattices don t dissipate heat and cause power loss as do resistors In addition precisely adjusting the height of adjacent optical lattices and changing the number of atoms in the lattices can create a diode which allows current flow in only one direction Such atomtronic diodes are analogous to semiconductor diodes created by ajoining N type and P type semiconductors Similarly atomtronic transistors can be created by aligning

    Original URL path: http://jila-pfc.colorado.edu/highlights/jila-physicists-investigating-atomtronics (2016-04-29)
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  • Imaging the Nanoworld | JILA-PFC
    structure of the atoms molecules and surfaces populating this nanoworld you just might have to invent a new microscope In fact that s exactly what Fellow David Nesbitt s group recently accomplished Oliver Monti a former JILA postdoc currently at the University of Arizona graduate student Tom Baker and Nesbitt have invented a microscope capable of analyzing the make up and properties of nanoscale electronics and nanoparticles The group s new scanning photoionization microscope SPIM is shown above It includes an optical microscope in a vacuum chamber and an ultrafast laser which appears blue in the foreground It combines the high spatial resolution of optical microscopy with the ability to detect low energy electrons emitted by a material illuminated with laser pulses The ability to monitor photoelectron emission should make it possible for the microscope to detect electronic patterns in devices such as nano scale transistors or electrode sensors and to identify their chemical constituents At the same time the new microscope can make a physical picture of the tiny structures You make images by virtue of how readily electrons are photoejected from a material Nesbitt explains The method is in its infancy but nevertheless it really does have the

    Original URL path: http://jila-pfc.colorado.edu/highlights/imaging-nanoworld (2016-04-29)
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  • Running Backwards | JILA-PFC
    one On the other hand various extensions of the standard model predict a much larger eEDM that might be just within reach of a cleverly designed experiment That tantalizing idea has induced Fellow Eric Cornell to collaborate with Bohn on a multiyear project to try to measure the eEDM in ultracold trapped molecular ions If the researchers succeed in detecting an eEDM they will show that running time forward or backward at the quantum level makes a difference in the behavior of individual particles Recently Bohn a theorist and graduate students Ed Meyer and Mike Deskevich decided to try and figure out good candidates for the proposed experiment which will use high precision spectroscopy to search for an eEDM signal in ultracold trapped molecular ions Before they started their analysis the theorists knew they needed to find ions consisting of two atoms capable of creating a huge effective electric field on the ions valence electrons a much bigger field than would be possible to apply in the lab This criterion meant that one atom in a candidate ion had to be large and heavy The researchers also knew the experimentalists would need to be able to use a small applied electric field to precisely align the internal electric fields of their trapped ions This requirement meant that the unpaired or valence electron in a candidate ion had to have a high angular momentum around the molecular axis However such a high angular momentum would naturally keep that electron far away from the nucleus But a valence electron has to be fairly close to the nucleus to experience the big electric field between the ion s atomic constituents At this point the theorists muttered So now what Undaunted they decided to look for molecular ions with two unpaired electrons one with

    Original URL path: http://jila-pfc.colorado.edu/highlights/running-backwards (2016-04-29)
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  • Team Photon | JILA-PFC
    going on here than the ordinary photoelectric effect which Albert Einstein explained more than a century ago In the photoelectric effect electrons escape from a solid after absorbing a single photon or bundle of light energy What happens when two laser beams simultaneously hit a surface is called the laser assisted photoelectric effect The laser assisted photoelectric effect was recently observed for the first time in a solid by research associate Guido Saathoff graduate student Luis Miaja Avila Fellows Margaret Murnane and Henry Kapteyn former post doc Chi Fong Lei and former Visiting Fellows Martin Aeschlimann Technische Universität Kaiserlautern and John Gland University of Michigan Their apparatus is shown at right A platinum sample the disk at the left of center is simultaneously illuminated by X ray and infrared IR laser beams In addition to absorbing the X ray photon energy necessary for escaping from the surface the electrons escaping from the surface can simultaneously either grab or hurl away an infrared photon This complex interaction changes the characteristic energies of the newly freed electrons The laser assisted photoelectric effect works the same way on a surface as it does in a cloud of atoms energetic X rays eject electrons from a surface or a cloud of atoms The liberated electrons would normally have a fixed energy given by the absorbed photon energy minus the energy needed to escape the surface barrier This is simply Einstein s photoelectric effect However when an intense IR pulse hits the surface at the same time as an X ray pulse the liberated electrons are either sped up or slowed down as they escape the surface barrier Which way it goes depends on the exact moment in the IR light wave when it encounters a particular free electron What s interesting is that the

    Original URL path: http://jila-pfc.colorado.edu/highlights/team-photon (2016-04-29)
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  • Universal Attractions | JILA-PFC
    s now hard evidence that this is true thanks to graduate students Jayson Stewart and John Gaebler Cindy Regal who received her Ph D in physics in November and Fellow Debbie Jin Jin says that many of us might expect the behavior of an ultracold trapped gas of fermions to depend on the interactions between the fermions or how they feel each other But ironically if these interactions are extremely strong then they no longer matter under such conditions the behavior of the gas depends only on temperature and density In a recent experiment the Jin group measured the potential energy of an ultracold trapped gas of 40 K atoms in the crossover region between Bose Einstein condensation and superconductivity superfluidity The researchers used a magnetic Feshbach resonance to maximize the intensity of the interatomic interactions and found that an attraction between the atoms caused them to become more tightly packed They then studied the effect of temperature on the ratio of the potential energy of their strongly interacting gas to that of a noninteracting gas By extrapolating the ratio to a temperature of 0 K they were able to extract a universal many body parameter ß and determine its

    Original URL path: http://jila-pfc.colorado.edu/highlights/universal-attractions (2016-04-29)
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  • The South Broadway Shootout | JILA-PFC
    Marty Boyd Andrew Ludlow Seth Foreman and Sebastian Blatt postdoc Tanya Zelevinsky former postdoc Tetsuya Ido and Fellow Jun Ye There are two key reasons why the Ye group s lattice based strontium clock is so precise 1 Its ultrastable clock laser has a short term laser linewidth of 0 2 Hz NIST s experimental mercury ion clock s laser is the only laser in the world that s more stable and 2 Its optical lattice holds the strontium atoms in place for a relatively long time but doesn t perturb the critical optical atomic clock transitions Taken together the ultrastable laser and perturbation free atomic sample produce the world s highest quality resonance profile a measure of the clock s precision Q 2 5 x 10 14 Aided by unprecedented spectral resolution the group s clock can achieve the highest precision ever measured with coherent spectroscopy Its precision is much greater than the NIST F1 cesium fountain atomic clock the nation s primary time and frequency standard Boyd says that the precision of his group s clock is potentially superior to the mercury ion clock under development by Jim Bergquist s group at NIST But Boyd and his colleagues must still prove this claim in a direct comparison of the two optical atomic clocks The mercury ion clock has already proven itself to be at least five times more precise than the NIST F1 Then there s the question of accuracy The current NIST F1 clock neither gains nor loses a second in about 70 million years For the mercury ion clock which is the most accurate clock in the world the figure is 400 million years Ye and his group recently showed that the current version of their Sr clock has an accuracy similar to that of the

    Original URL path: http://jila-pfc.colorado.edu/highlights/south-broadway-shootout (2016-04-29)
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