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  • Breaking Up Is Hard To Do | JILA-PFC
    apart so easily even when an X ray knocks out one of its electrons and superexcites the molecule during a process called photoionization In this process the X ray first removes an electron from deep inside the molecule leaving a hole in O 2 Then an outer electron can fall into the hole and a second outer electron gets ejected carrying away any excess energy The loss of the second electron is known as autoionization or Auger decay Surprisingly in superexcited O 2 the second electron can take a really long time to be ejected up to 300 fs During this time the pieces of the oxygen molecule consisting of an excited O atom and a positively charged O ion move at least 25 times farther apart than in a normal O 2 molecule before the second electron is ejected When the second electron is ejected the molecule falls apart The basic sequence of events is shown in the figure So what s happening inside superexcited O 2 molecules that keeps them intact for so long A very complicated process according to former JILAns Etienne Gagnon Arvinder Sandu and Robin Santra research associate Wen Li Fellows Margaret Murnane and Henry Kapteyn and their colleagues from Kansas State University The scientists recently monitored the breakup of molecular oxygen after zapping the molecule with a fast burst of soft X rays They found that the molecule itself suppressed ejection of the second electron until the fragments of the molecule were separated by 30 Å 3 nm or more Essentially the second electron felt an attraction to each of the O fragments that kept it bound between the two ions until they were so far apart they hardly interacted at all Even after this separation the researchers found that the electron did not

    Original URL path: http://jila-pfc.colorado.edu/highlights/breaking-hard-do (2016-04-29)
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  • Fortune’s Bubbles Rise and Fall | JILA-PFC
    Rb and 87 Rb atoms dominated interactions between the same kinds of atoms Under these conditions 85 Rb and 87 Rb stopped happily being part of the ultracold atom gas mixture Instead they began to repel each other so strongly that they became immiscible like oil and water As they grew increasingly incapable of being mixed the condensate bubbles appeared Pino said that watching the bubbles form was like seeing chunks of ice suddenly emerge in a pool of water The researchers were fairly sure that the bubbles were excited states and not the ground state condensates they had anticipated However there was no theory available at the time to explain what they d observed However now there is a theoretical explanation thanks to research associate Shai Ronen Fellow John Bohn and their colleagues from Georgia Southern University Ronen and his colleagues were able to simulate the formation of the bubbles during evaporative cooling of a mixture of ultracold 85 Rb and 87 Rb atoms They also verified that the ground state of a dual condensate of 85 Rb and 87 Rb would either be a mixed atom condensate under conditions where the atoms mixed well or two spatially separated condensates one consisting of 85 Rb and the other consisting of 87 Rb under conditions where mixing could not occur The simulations showed that when condensates form in a rapidly cooled immiscible mixture of atoms in a cigar trap they create multiple alternating bubbles of the different atoms And the bubbles are far from the system s true ground state Even so the bubble pattern is quite stable The repulsive interactions between the different atoms are responsible for this behavior When a condensate first begins to form the interactions between 85 Rb and 87 Rb atoms don t affect the

    Original URL path: http://jila-pfc.colorado.edu/highlights/fortune%E2%80%99s-bubbles-rise-and-fall (2016-04-29)
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  • Exotic Probes | JILA-PFC
    CO 2 and other molecules The researchers use two innovative tools 1 coherent electrons knocked out of the CO 2 molecules by a laser and 2 the X rays produced by these electrons when they recollide with the same molecules The coherent electrons and X rays are produced in a process known as high harmonic generation The process involves four steps First an intense laser pulse kicks the CO 2 molecules to set them spinning in such a way that they become aligned with each other Second a high intensity laser pulse plucks the outermost electron out of a CO 2 molecule Third the laser s electric field accelerates the free electron Finally if the free electron comes anywhere near its ionized parent molecule it crashes back into it and stays there This high energy collision causes the reconstituted molecule to emit an X ray photon Zhou and his colleagues showed that the intensity and phase of the emitted X ray photons depend on the orientation of the CO 2 molecules when electrons recollide with them This means that measurements of the orientation dependence of the intensity of the emitted X ray beam can provide information about the molecular structure of CO 2 To understand why this is true it s useful to consider the graphic on the left which shows an electron wave function colliding with a CO 2 ion step 4 of high harmonic generation The grey ball in the center represents a carbon atom and the two red balls represent oxygen atoms The red and blue areas are the molecule s electron clouds which center on the oxygen atoms In this figure a recolliding electron wave function arrives at an obtuse angle to the molecule making it possible for the crests and troughs of the wave function

    Original URL path: http://jila-pfc.colorado.edu/highlights/exotic-probes (2016-04-29)
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  • The Oldest Trick in the Book | JILA-PFC
    theory world by storm in 2006 when they devised a simple and straightforward method for the evaluation of molecular candidates for an eEDM search See JILA Light Matter Fall 2006 In their initial effort the theorists used simple physics ideas in lieu of complex analytical techniques Two years ago their method was able to replicate all previous complex and painstaking analyses within a factor of 2 Missed it by THAT much Agent 86 noted recently inside this reporter s cone of silence In an unexpected turn of events the JILA theorists were recently asked by the ACME collaboration from Yale and Harvard the evil competition to provide similar eEDM theory work Bohn and Meyer said yes No matter who wins JILA wins Agent 86 explained seemingly oblivious to the possibility that ACME might be an arm of KAOS Chief Cornell saw it differently at least in public Both recalled the terse conversation that ensued Chief Please don t tell me you re actually doing theory for the forces of ACME Agent 86 Chief we re doing theory for the forces of ACME Chief slaps forehead I asked you not to tell me that Agent 86 Sorry about that Chief Well maybe not all that sorry After all Meyer and Bohn discovered that thorium oxide ThO has the strongest internal electric field they d ever evaluated So as they reported to ACME ThO is perhaps the best candidate yet identified for an eEDM experiment More importantly for JILA a similar molecule ThF was found to be just as good as ThO And ThF would work in the Chief s ion experiment In their work for ACME agents 13 and 86 coaxed a more realistic wave function out of their MOLPRO software As a result their method has become competitive with those

    Original URL path: http://jila-pfc.colorado.edu/highlights/oldest-trick-book (2016-04-29)
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  • All Quiet on the Amplifier Front | JILA-PFC
    he invented one Working with graduate student Manuel Castellanos Beltran and NIST scientists Kent Irwin Gene Hilton and Leila Vale he conceived a tunable device that operates in frequencies ranging from 4 to 8 GHz This device has the lowest system noise ever measured for an amplifier In fact it produces 80 times less noise than the best commercial amplifier More importantly it adds no noise to a measurement system a critical feature for a system probing the quantum limits of measurement In addition to its tunability and low noise the new amplifier exhibits the largest squeezing of quantum fluctuations 10 dB ever measured for this kind of amplifier Lehnert says squeezing is a devilishly nonintuitive process in which the quantum uncertainties associated with measuring phase and amplitude are circumvented to allow virtually noiseless measurement of just the amplitude changes in a tiny microwave signal The amplifier will be a key addition to experiments that map information onto microwave fields including those that probe the electronic states of qubits quantum computing or the position of nanomechanical oscillators For instance the Lehnert group will use their amplifier in future experiments to detect minute forces such as those produced in a nanomechanical beam by quantum fluctuations see JILA Light Matter Summer 2008 The Lehnert group s new amplifier is not the first device of this kind However it is the best design ever for a parametric device employing Josephson junctions which are superfast switches made of thin layers of insulating material sandwiched between layers of superconducting material The Lehnert amplifier consists of a series array of 960 Josephson junctions split into parallel pairs that form SQUIDS s uperconducting q uantum i nterference d evices The SQUIDs are exquisitely sensitive to tiny changes in electric current The SQUID array forms a composite metamaterial

    Original URL path: http://jila-pfc.colorado.edu/highlights/all-quiet-amplifier-front (2016-04-29)
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  • From Mental to Experimental? | JILA-PFC
    recently piqued the interest of a couple of intrepid theoretical physicists at JILA who just happened to be ardent Colorado Rockies fans They already knew that other researchers had shown that humidified balls are less bouncy so they don t get as much speed off the bat traveling about 6 feet less far on average However was this effect enough to explain why humidifying the baseballs has obliterated hitter s heaven in Denver The truth is the Bohn lab didn t know What they did know was that it s hard to ascribe a big change in homeruns to a single cause So they decided to look around for others Bohn s graduate student Ed Meyer chose to study the effects of humidity on baseball aerodynamics an obvious option for his Comps II project A quick consultation with advisor Bohn led a plan to gather real data to plug into Ed s model describing baseball aerodynamics The Bohn lab at the PIs own expense soon acquired three plastic boxes humidors and the means to keep five baseballs inside each of them either dry 32 relative humidity RH moist 56 RH or wet 74 RH The moist balls in their experiment were similar to the 10 12 dozen balls stored in the humidified room at Coors Field Meyer carefully measured changes in the diameter and mass of the baseballs as a function of relative humidity Then the researchers modeled trajectories for pitched and batted baseballs to see whether there were any differences between balls stored at 30 RH versus 50 RH The results were clear Drier baseballs should curve slightly more than humidified ones And more important for the analysis of home run behavior drier balls are likely to travel about 2 feet less far when batted From the perspective of

    Original URL path: http://jila-pfc.colorado.edu/highlights/mental-experimental (2016-04-29)
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  • Missing Link | JILA-PFC
    atoms To perform photoemission spectroscopy on ultracold atoms Stewart and his colleagues first cooled a gas of potassium atoms 40 K in a laser trap to the crossover point connecting superconductivity and Bose Einstein condensation BEC Under these conditions the atom gas became a superfluid with nearly all the 40 K atoms paired up one spin up and one spin down and dancing in sync Next the researchers sent an rf pulse into the ultracold atom cloud and at the same time turned off the laser trap The low momentum photons in the rf pulse transferred a small percentage of the atoms into another spin state Even though these atoms were in the same exact place and traveling at the same velocity they suddenly became completely invisible to their dance partners The invisible dance partners flew out of the trap and were easily imaged The remaining correlated atom pairs continued to dance in sync but in movements governed by the very complicated physics of the system In a very cool move Stewart and his colleagues were able to use the energy and velocity of the escaping spin flipped invisible atoms to determine their energy and velocity when they had been dancing in sync with a partner inside the atom cloud Likewise condensed matter physicists have been able to figure out what an electron has been doing near the surface of a metal superconductor before it gets knocked out by a uv photon Suddenly Stewart and his colleagues had a powerful new tool at their disposal They decided to use it to compare the physics of their superfluid gas with the physics of superconductivity Before they focused on comparing superfluidity and superconductivity they wanted to test their spectroscopy technique on molecules To do this the researchers adjusted the magnetic field in

    Original URL path: http://jila-pfc.colorado.edu/highlights/missing-link (2016-04-29)
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  • Bragging Rites | JILA-PFC
    of superfluid liquids and ultracold atoms Whatever happens there s a whole lot of ultracool physics to explore in BECs with strong atomic interactions JILA s BEC collaboration recently embarked on this exciting search Newly minted CU Ph D Scott Papp Wieman group and graduate students Juan Pino Jin group and Robert Wild Cornell group have used Feshbach physics to create a strongly interacting BEC and probe it with Bragg spectroscopy To prepare for Bragg spectroscopy researchers change the magnetic field around an ordinary everyday BEC Until the magnetic field changes the atoms in the condensate have been pretty much ignoring each other even though they have been singing a single pure very large tone With the change in magnetic field the atoms suddenly start talking with each other via a large scattering length Once the BEC becomes strongly interacting researchers can perform Bragg spectroscopy They quickly direct two red laser beams into the BEC from opposite sides of condensate They have to work fast because a strongly interacting BEC will melt as collisions rapidly warm it up sending hot atoms flying away Luckily lasers are fast The counter propagating beams impart energy and momentum to a small fraction 10 of the atoms in the condensate This energy and momentum spread throughout the condensate via collisions Then the scientists take a picture of the whole condensate to see how its momentum has grown The picture gives them enough information to determine the BEC s available energy and momentum states When the experiment was finished Papp and his colleagues enlisted the aid of theorist Shai Ronen a postdoc in the Bohn group Ronen helped them adapt several different theoretical descriptions of interacting BECs for direct comparison with the new experimental data This comparison underscored the need for a better theory describing

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