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  • Nanomeasurement is a Matter of the Utmost Precision | JILA-PFC
    could measure more diminutive forces of half an attoNewton 0 5 x 10 18 N Their new system consists of a tiny oscillating mechanical wire embedded in a microwave cavity with an integrated microwave interferometer two amplifiers one of them virtually noiseless and a signal detector The system is so sensitive that at milliKelvin temperatures it could weigh a cube of carbon atoms with 140 atoms on a side or 2 5 x 10 6 atoms According to Italian physicist Amedeo Avogadro 1776 1856 this cube should weigh about 5 x 10 17 grams Of course Teufel and Lehnert haven t actually weighed any atom cubes yet What they have done is measure the nanomechanical motion of a thin aluminum wire inside the microwave cavity with precision beyond that at the standard quantum limit which is a limit on the minimum noise at quantum scales Im precision is one of two fundamental sources of noise whose sum must exceed that standard limit The researchers managed to make a measurement with precision beyond that at the standard quantum limit by measuring the motion of the wire with the microwave interferometer built into the cavity housing the beam This amazing interferometer operates near the shot noise limit which is a measure of the inherent randomness from the microwave photons scattering off the wire during the measurement process Since the interferometer operates at cryogenic temperatures motion of the wire is fairly subdued In fact thanks in part to the reduced thermal motion of the wire at these low temperatures it is an excellent force detector with a sensitivity of 0 51 aN Hz Research associate Tobias Donner graduate students Manuel Castellanos Beltran and Jennifer Harlow and new JILA Associate Fellow Cindy Regal provided valuable assistance in the creation of the new force detector

    Original URL path: http://jila-pfc.colorado.edu/highlights/nanomeasurement-matter-utmost-precision (2016-04-29)
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  • Radical Changes | JILA-PFC
    1 the experimental observation of the oxyallyl diradical a key intermediate in a series of important chemical reactions and 2 the posting of an abstract of the Angewandte Chemie cover story reporting this achievement on Facebook While the Lineberger group is responsible for the clever design of the photoelectron spectroscopy experiments that led to the observation of oxyallyl diradical Lineberger was astonished that his work got on Facebook He speculated that the journal s publisher Wiley VCH was responsible Wiley had also marketed the article with refrigerator magnets of the cover shown here reprints of the article high resolution copies of the cover art designed by JILA s own Greg Kuebler wall calendars and notebooks with the cover art on the front A follow up discussion of the story appeared weeks after the article was first published in October 2009 Welcome to the new world of marketing for research publications Wiley couldn t have picked a more interesting topic for its marketing blitz For more than 50 years the oxyallyl diradical has been postulated to be a key intermediate step in important organic chemical reactions However it hadn t been observed until the Lineberger group s negative ion experiments supplied the first direct evidence for its existence The group s photoelectron spectroscopy studies also provided detailed information on the molecule s electronic states and geometrical structure The secret of the group s transition state spectroscopy is quite ingenious Before attempting to observe the very unstable states of oxyallyl diradical the researchers added an electron to the molecule creating a stable negative ion Then after carefully setting up their spectroscopy experiment they ripped off the extra electron then quickly looked for and found the molecule that chemists have predicted for so many years Perhaps that s why the Angewandte Chemie s

    Original URL path: http://jila-pfc.colorado.edu/highlights/radical-changes (2016-04-29)
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  • Buried Treasure | JILA-PFC
    is necessary for obtaining quantitative information about the behavior of an ultracold gas under different experimental conditions Until now the preferred method has been to find a shape such as a Gaussian that looks like the results and write an image fitting routine to probe a series of photographs The drawback is that information extracted this way will be biased by the model chosen The two groups recently employed model free analysis techniques to extract results from interferometry experiments on Bose Einstein condensates BECs The statistical processing techniques were able to rapidly pinpoint correlations in large image sets helping the researchers uncover unbiased experimental results Using the techniques graduate student Steve Segal former graduate student Quentin Diot Fellows Eric Cornell and Dana Anderson and a colleague from Worcester Polytechnic Institute calibrated their interferometer identified and mitigated some noise sources and unearthed signal information partially buried in the noise generated during the BEC experiment By looking for correlations and relationships between pixels in a series of images a the researchers were able to clearly see changes in the overall number of atoms d changes in the vertical positions of three peaks in a momentum distribution c and changes in the fraction of atoms in the central peak b which was the primary experimental signal The results were obtained with principal component analysis PCA and independent component analysis ICA PCA identified simple pixel correlations and looked for areas of maximum variance Such areas provided an idea about where to look for changes in size structure or position of the ultracold atom cloud The PCA analysis was sufficient for calibrating the interferometer and debugging the experiment It also provided an idea of size changes in one or more features of the experiment However the PCA analysis alone wasn t perfect ICA was required

    Original URL path: http://jila-pfc.colorado.edu/highlights/buried-treasure (2016-04-29)
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  • Extreme "Sheep" Herding | JILA-PFC
    ghostly quantum mechanical force field with the energy of about 100 billionths of an electron volt These strange diatomic rubidium Rb molecules are the world s first long range Rydberg molecules They were recently formed in Tilman Pfau s laboratory at the University of Stuttgart from an ultracold cloud of Rb atoms One neat aspect of the new experiment is that in 2000 Fellow Chris Greene s collaboration with Hossein Sadeghpour ITAMP Harvard and Alan Dickinson Newcastle predicted the novel chemical bonding process that would give rise to Rydberg molecules in an ultracold gas To make a Rydberg molecule you need a Rydberg atom an atom in an excited state in which at least one electron roams far from its parent nucleus in an elongated elliptical orbit Lasers are a good tool for making some Rydberg atoms inside a cloud of ground state Rb atoms Next comes the exciting part If a roaming Rydberg electron moves close enough to an ordinary ground state atom the electron can capture and hold onto the ordinary atom forming a Rydberg molecule The electron captures the ordinary atom when the latter wanders inside its orbit which can occur at interatomic distances of 100 nm or more The Rydberg electron then binds the molecule much like a sheep dog keeps its flock together by running around the perimeter of its territory and continually nudging strays back toward the center In other words once an energetic Rydberg pup captures a ground state atom it races around its orbit keeping the second atom from drifting away The molecule will stay bound for about 18 µs if the environment around it remains ultracold Warm things up just a tiny bit and the weakly bound Rydberg molecule falls apart which is why there aren t any already hanging out

    Original URL path: http://jila-pfc.colorado.edu/highlights/extreme-sheep-herding (2016-04-29)
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  • Rave Reviews for the Efimov Quartet | JILA-PFC
    additional atom to form daughter molecules which inherit many of their mother s characteristics What s strange is that the atoms in a BEC mostly feel no force of attraction to each other In fact the atoms only feel attracted to one another when they are right on top of each other Even so any three of them can still stick together in an infinite number of quantum states This strange behavior is due to a kind of memory ghost created by the attraction that the atoms experience when stacked on top of each other This eerie memory allows three but not two atoms to form an infinite number of fragile molecules or bound states even when they are relatively far apart Curiously weakly bound triatomic Efimov molecules are quite different from garden variety molecules They form very floppy triangles in which the three atoms can have virtually any geometric relationship with one other Vitaly Efimov predicted these bound states in 1970 During the late 1990s Fellow Chris Greene s group with J P Burke Jr and Brett Esry and others explored and expanded a theory of Efimov physics Greene s group was eventually able to predict the conditions under which triatomic Efimov molecules could be observed experimentally their efforts were rewarded in 2006 when Rudi Grimm s group at the Universität Innsbruck found them in the laboratory A year or so afterwards graduate student Javier von Stecher now a postdoc with Fellow Ana Maria Rey began to wonder what would happen if you added another atom to the system In other words would an Efimov quartet form What would it look like How would it behave It took von Stecher senior research associate José D Incao graduate student Seth Rittenhouse former postdoc Nirav Mehta now at Grinnell College and

    Original URL path: http://jila-pfc.colorado.edu/highlights/rave-reviews-efimov-quartet (2016-04-29)
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  • Holy Monodromy! | JILA-PFC
    as well as atoms and molecules Fellow Heather Lewandowski s group recently decided to do an experiment to see whether a pendulum on a spring does in fact have monodromy as predicted in 2004 Even though the theory of monodromy has been around for almost 30 years nobody had actually tested the classical prediction in the lab before she said Lewandowski was assisted by graduate students Noah Fitch and Paul Parazzoli undergraduate student Carrie Weidner and visiting mathematician H R Dullin University of Sydney The researchers focused on the behavior of the pendulum on a spring when the swinging and bouncing frequencies were in a ratio of 1 2 This frequency ratio facilitated energy transfer between the swinging and bouncing modes and resulted in the evolution of pure bouncing into pure swinging then back into pure bouncing over and over again until damping stopped the cycle The ellipses traced by the swinging pendulum precessed at a constant step angle between successive swinging episodes To see whether this system had monodromy Lewandowski s group performed two sets of experiments Each one had a different set of initial conditions corresponding to different initial positions of the pendulum bob These sets of initial conditions formed two loops One loop enclosed a singularity and the other did not The researchers measured the step angles at the beginning and at the end of the loops They found the net change was zero only for the loop that did not enclose the singularity The observation that the change in the step angle of the singularity enclosing loop was not zero was experimental proof that monodromy existed in this system In this simple classical system monodromy was easily detected Consequently the group s experiments can now provide a foundation for a deeper understanding of quantum mechanical monodromy

    Original URL path: http://jila-pfc.colorado.edu/highlights/holy-monodromy (2016-04-29)
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  • A Light Changing Experience | JILA-PFC
    important step toward gaining a detailed understanding of the molecular processes responsible for the UV induced DNA damage that results in mutations and can lead to cancer or cell death Graduate student Jesse Marcum student assistant Amit Halevi and Fellow J Mathias Weber recently studied the UV photodissociation of DNA subunits called nucleotides Nucleotides contain one of the four DNA bases adenine cytosine guanine or thymine linked to a sugar molecule which in turn is linked to a phosphate group In DNA strands the phosphate and sugar groups of many individual nucleotides are chemically linked together to form the DNA backbone The researchers found that the UV light which was absorbed by the four bases causes chemical reactions inside the molecule that can break chemical bonds in two places in the nucleotides First the break can occur in the link between the phosphate and sugar groups In an extended DNA chain this sort of damage would lead to breaking of the DNA strands Second the bond can break between the sugar and the base this breakage can be followed by additional reactions and lead to the loss of genetic information from DNA Both types of UV damage can occur in living tissue and require enzymes for repair However the processes responsible for this damage inside molecules are not completely understood Interestingly the molecules break apart at the same two places following collisions between nucleotides and gas atoms However the likelihood of each process occurring was quite different than in UV photodissociation A comparison of breakage caused by collisions with that caused by UV light suggested that both processes lead to strongly vibrating i e hot ground state ions These ions then fall apart at one of two vulnerable bonds after the vibrational energy gets distributed throughout the molecule However because

    Original URL path: http://jila-pfc.colorado.edu/highlights/light-changing-experience (2016-04-29)
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  • Free Association Tunes | JILA-PFC
    coherent superpositions of atoms and molecules Fellow Carl Wieman and others have done exactly this Recently the Jin group wondered if it would be possible to accomplish the same thing starting with a normal gas cloud of atoms To spice up the experiment they included two kinds of atoms neighborly bosons 87 Rb that readily pile up in the same state and more independent minded fermions 40 K no two of which are ever willing to occupy the same quantum state Would it be possible for free atoms just ambling along through a gas cloud to enter a quantum superposition of both being free atoms and being in a single well defined state known as a Feshbach molecule Graduate student Michele Olsen research associate John Perreault graduate student Tyler Cumby and Fellow Debbie Jin decided to see If they were successful they d not only gain a new tool for probing the behavior of strongly interacting mixtures of bosons and fermions but also the means for investigating the detailed physics of Feshbach resonances which play a key role in Fermi gas superfluidity To ensure that their ambling gas atoms comprised a distribution of energy states Olsen and her colleagues kept the temperature of their ultracold gas cloud above the temperature where the 87 Rb atoms could form a condensate Then they created KRb molecules by slowly ramping down a magnetic field across an interspecies Feshbach resonance Under the best conditions they were able to form molecules from about a third of the 87 Rb atoms in the cloud Then they met the challenge of creating coherent atom molecule superpositions and measuring their oscillation frequency The atoms oscillated between being free atoms and being a weakly bound molecule at a frequency that corresponded to the predicted binding energy of the Feshbach

    Original URL path: http://jila-pfc.colorado.edu/highlights/free-association-tunes (2016-04-29)
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