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  • Curling Up in a Nanobathtub | JILA-PFC
    useful to be able to precisely control the temperature around the sample Until now heating has required electric currents that warm up microscope stages slides and optics in addition to the specimen under study Such methods are slow and hard to control not to mention capable of accidentally altering the chemistry or structure of the sample Now there is a better solution for keeping samples nice and warm The nanobathtub Graduate student Erik Holstrom and Fellow David Nesbitt have come up with a way to precisely control the temperature of tiny bathtubs of water on a glass slide The column shaped bathtubs contain only 35 trillionths of a liter of water which is easily warmed with gently focused laser light The heating laser is aimed at the samples from above and forms a spot size of about 20 micrometers Its near infrared light is the perfect wavelength for inducing the oxygen hydrogen OH bonds in water to start vibrating These vibrations are responsible for warming up the water in the nanobathtub As the water warms the researchers can monitor any changes in their sample with a fl uorescence microscope Such laser induced fl uorescencebased microscopy techniques have been used extensively by the Nesbitt group to study single molecules of RNA What s new is that if a nanobathtub containing a single molecule of RNA is attached to the slide the laser can warm the RNA molecule to exactly any temperature between 20 to 90 ºC 68 to 194 ºF This capability means that researchers can now perform experiments that use sudden controlled jumps in temperature to activate specific molecular processes and observe them in real time Before attempting these new experiments however Holstrom and Nesbitt decided to compare observations of RNA folding that occurred in the nanobathtubs with folding that

    Original URL path: http://jila-pfc.colorado.edu/highlights/curling-nanobathtub (2016-04-29)
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  • The Mysterious Fermi Gap | JILA-PFC
    amount of energy into an ideal Fermi gas you can excite a fermionic atom and make it move faster If the system has an energy gap however then amounts of energy smaller than the gap cannot excite one of the atoms You need energy equal to or larger than the gap to excite atoms The gap exists because you have to put in enough energy to break apart a pair of fermions before you can excite either one of them That s why finding and measuring the gap was so exciting back in 2008 This experiment was conducted at a temperature known as Tc which is the point at which a superfl uid forms The observation of a gap fi t with conventional theory This theory predicted that pairs of Fermi atoms would act in synchrony below Tc creating an energy gap The same theory predicted that above Tc no atom pairs would form and thus no energy gap would exist Similar relationships were predicted to hold true for superconductivity in solid materials Interestingly the prediction that the gap must disappear above Tc held true for all superconducting materials except high temperature superconductors In high temperature superconductors researchers do see a gap in the region above Tc This anomaly recently piqued the curiosity of the Jin group and their theorist colleagues from Italy s Universitá di Camerino They began to wonder what would happen to the gap in an ultracold atom gas at temperatures above Tc After all conventional theory predicts that pairing disappears along with the gap So the Jin group team led by graduate student John Gaebler repeated its photoemission spectroscopy experiment with a gas of 40K atoms above Tc and sure enough they observed a gap Gaebler was assisted in this unexpected discovery by former graduate student

    Original URL path: http://jila-pfc.colorado.edu/highlights/mysterious-fermi-gap (2016-04-29)
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  • An Occurence at the Solvent Bridge | JILA-PFC
    molecules get involved when an electron hops from one solute molecule to another For example in liquids which do most of the dissolving solvent molecules move constantly making it very challenging to see what they re doing when charge transfer events occur The Lineberger group recently met this challenge using a simple prototype gas phase system In this system a single solvent molecule of carbon dioxide CO2 interacts with an IBr molecule as it is broken apart by a laser pulse A second or probe laser pulse is used to watch what happens as the IBr molecule falls apart The group discovered the ways in which the CO2 molecule affected the dissociation process The experiments were performed by research associate Lenny Sheps and graduate student Elisa Miller under the guidance of Fellow Carl Lineberger The experimentalists collaborated with theorists Robert Parson former graduate student Matt Thompson Anne McCoy the Ohio State University and McCoy s student Samantha Horvath to unravel the role of CO2 in the dissociation process When there was no solvent CO2 present the laser pulse moved the IBr into a specifi c electronic state that then fell apart producing only I and Br atoms However with a single CO2 molecule present things got very interesting About a third of the time the breakup still produced only I and Br atoms The CO2 molecule basically flew off into space Then a little less than two thirds of the time the breakup produced an I CO2 complex and a Br atom In this case the CO2 molecule kind of snuggled up to the I atom during the dissociation and just kept vibrating against it The most interesting chain of events occurred only about 3 of the time In this case right after the IBr was hit by the fi

    Original URL path: http://jila-pfc.colorado.edu/highlights/occurence-solvent-bridge (2016-04-29)
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  • Them's the Brakes | JILA-PFC
    and his colleagues Such an experiment could also demonstrate the presence of a roton A roton is the quantum of energy that may represent the link between superfluid helium and a yet to be observed supersolid phase of helium In helium it is also the excitation or quasi particle that determines the fluid velocity at which friction sets in The analog of the roton in a dipolar BEC has been often discussed but never seen Wilson hopes this situation will change soon once his new theoretical analysis becomes widely known He believes that dipolar BECs provide an amazing opportunity to explore the relationship between roton behavior and superfluidity This is the reason he decided to model an experiment with a dipolar BEC similar to an actual experiment done 15 years ago at MIT on a BEC of sodium atoms This experiment unfortunately was somewhat inconclusive In the new model a blue laser beam sweeps through a dipolar BEC of chromium Cr atoms at constant speed As this speed reaches a critical velocity it excites roton modes friction develops and the condensate begins to slosh The onset of sloshing is linked to a critical velocity which in turn depends on the density of the Cr atoms making up the BEC and their dipole moment According to the model the critical velocity is somewhat smaller than expected from studies of denser materials However Wilson and his colleagues believe this fi nding is related to the role that the roton plays in the mechanical stability of a dipolar BEC Wilson and his colleagues hope that their proposed experiment will soon come into reality They d like to see an unequivocal measurement of the critical velocity in a dipolar BEC and fi nd out whether dipolar BECs are similar to superfl uid helium Plus

    Original URL path: http://jila-pfc.colorado.edu/highlights/thems-brakes (2016-04-29)
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  • Redefining Chemistry at JILA | JILA-PFC
    even more challenging to move all the molecules into the lowest of 36 possible nuclear spin states However the team eventually developed a method that allowed them to prepare molecules either in the lowest energy nuclear spin state or in a coherent superposition of selected spin states The secret was figuring out how to use an interaction in an excited rotational state of the polar molecules to couple the molecules nuclear spins with their rotations Then by zapping the molecules with two different wavelengths of microwave radiation the team could move all the molecules into their quantum mechanical ground state This accomplishment was reported in the January 22 2010 issue of Physical Review Letters The ability to create ultracold KRb molecules in their lowest quantum mechanical state made it possible for the team to observe the behavior of the molecules colliding as well as breaking and forming chemical bonds This achievement was reported by Ospelkaus and colleagues in the February 12 2010 issue of Science where the researchers described the first ever study of the chemistry of ultralow temperature KRb molecules At ultralow temperatures the molecules manifest themselves mostly in quantum mechanical waves instead of behaving like ordinary particles The molecular waves extend long distances inside a gaseous cloud The behavior of molecules at ultralow temperatures includes chemistry but chemistry in a strange world where the laws of quantum mechanics prevail The team observed molecular interactions that led to the breaking and formation of chemical bonds between atoms These observations were possible because the researchers were able to control every aspect of the energy and motion of the molecules What controls ultracold collisions is the nature of the molecules themselves Ye said It depends on whether the molecules are fermions or bosons Neighborly bosons happily pile up in the same place at ultralow temperatures When bosons get close to each other they collide forming new chemical bonds or breaking old ones In contrast the independently minded fermions cannot share the same piece of real estate So when these standoffish molecules approach each other they can only get so close before they start warily circling around each other But even so some pairs of these molecules can still manage to slowly form new chemical bonds At some point while fermionic molecules are dancing around each other the molecules may quantum mechanically tunnel through the barrier between them and undergo a chemical reaction Jin explained She added that her work with Ye and Bohn has shown that the chemistry of ultracold molecules is far richer than anticipated For instance the team was able to adjust its experiment to allow collisions between KRb molecules all of which are fermions The secret was preparing two groups of KRb molecules that were different from each other in terms of the energy state of their nuclei Both sets of molecules were still fermions but they were no longer identical In this system the identical fermions that got close together still circled around each other as before

    Original URL path: http://jila-pfc.colorado.edu/highlights/redefining-chemistry-jila (2016-04-29)
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  • Freeze Frame | JILA-PFC
    the electric field and keep the magnetic field at a fixed value during the imaging process However the team recently began to probe the influence of changing electric and magnetic fields on the behavior of ultralow temperature KRb molecules Consequently the researchers wanted to directly image ultralow temperature KRb molecules in the ground state However the complex energy level structure of molecules made the task of directly imaging molecules much more challenging than for atoms A collaboration team led by research associate Dajun Wang met this challenge To do so Wang had to find a molecular transition sensitive to a particular frequency of laser light Then he had to conduct experiments to determine how the molecules and photons interacted including determining the laser intensity to use The laser had to be intense enough so that most of the molecules in a ultracold molecular gas would absorb at least one photon Then by counting the photons missing from the laser beam the team could determine the number of molecules in the cloud But the laser couldn t shine too brightly or it would create noise due to the extra photons and the molecular signal would get lost It took Wang months to solve these two problems He had help from graduate students Brian Neyenhuis and Marcio de Miranda former graduate student Kang Kuen Ni former research associate Silke Ospelkaus and Fellows Deborah Jin and Jun Ye Finally the team found the right combination of frequency and intensity to get direct images of the ground state molecules To image the molecules Wang shined a 658 nm laser at a cloud of KRb molecules in their ground state Molecules absorbed photons from this pulse creating a shadow image Then to reduce background noise Wang shined a second pulse of the same wavelength on

    Original URL path: http://jila-pfc.colorado.edu/highlights/freeze-frame (2016-04-29)
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  • Good Vibrations | JILA-PFC
    the April 1 2010 cover of the Journal of Physical Chemistry A shows an artist s conception of the process from start to finish The figure includes two photoelectron spectroscopic images that clearly distinguish between the loss of the extra electron due to nitro group vibrations versus an ordinary chemical reaction Graduate student Chris Adams and former graduate student Holger Schneider now a postdoc at the Paul Scherrer Institute in Switzerland worked with Weber on this novel experiment The experiment is a molecular analog of heat conduction and molecular level understanding of this kind of process is important because knowing the way in which energy flows through and gets redistributed in molecules is necessary for understanding and predicting chemical reactions Even before doing the experiment the researchers suspected that the anion would end up emitting its extra electron The other possible ways for getting rid of the excess energy were much less likely For instance the molecule could have fallen apart but that route would have required more energy than the laser delivered to the molecule in the first place The molecule could also have stopped vibrating by simply radiating its extra heat into the environment in a process known as radiative cooling However radiative cooling occurs far more slowly than the vibrational detachment of the extra electron Consequently the group opted to look for and study the vibrational detachment of the electron due to laser heating of the methyl end of the molecule However for heat to travel through nitromethane anion the vibrations initiated by the laser in the methyl group had to couple into the nitro group This end of the molecule is where the extra electron spends most of its time Adams and his colleagues realized that it wouldn t take a lot of energy to dislodge

    Original URL path: http://jila-pfc.colorado.edu/highlights/good-vibrations (2016-04-29)
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  • The BEC Transporter | JILA-PFC
    working system easily fits on an average sized rolling cart This technology opens the door to using ultracold matter in gravity sensors atomic clocks inertial sensors as well as in electric and magnetic field sensing Research associate Dan Farkas demonstrated the new system at the American Physical Society s March 2010 meeting held in Portland Oregon March 15 19 To perfect the new compact BEC transporter Farkas worked closely with Fellow Dana Z Anderson graduate students Kai Hudek Evan Salim and Stephen Segal and Matthew Squires who received his Ph D from CU in 2008 The Anderson group has been working on different aspects of this new technology for more than a decade Key components of the new system include the two chamber vacuum cell and an innovative atom chip design The new vacuum cell took the Anderson group more than a decade to perfect Researchers built and tested more than 70 different prototypes before coming up with a design that provides the ultrahigh vacuum quality needed in the new portable system The new vacuum cell is 10 20 times smaller than its conventional counterparts It also serves as the platform for the atom chip where the BECs are made Plus the cell is now standardized making it a good candidate for commercialization The atom chip was developed in 5 year collaboration between Anderson and Victor Bright of CU s Department of Mechanical Engineering Teledyne Technologies Inc the Sarnoff Corporation and Vescent Photonics Although the collaboration s microchip was not the first to incorporate a BEC it makes a BEC faster than any comparable technology in the world It can transform hot atoms at room temperature into a BEC in 3 seconds about 10 times faster than traditional BEC apparatus Such speed is important for such applications as atomic clocks

    Original URL path: http://jila-pfc.colorado.edu/highlights/bec-transporter (2016-04-29)
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