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  • Altered States | JILA-PFC
    Fellow John Bohn recently decided to investigate the general collision behavior of polar molecules in low temperature gases He wanted to see whether knowing the molecule s dipole moment and mass would be sufficient to predict the size of its sphere of influence a k a the scattering cross section Think of it as a cage surrounding a polar molecule that delineates the boundaries of its interactions with other polar molecules To figure all this out Bohn collaborated with two former JILAns Mike Cavagnero University of Kentucky and Chris Ticknor a postdoc at Australia s Swinburne University of Technology Bohn s analysis yielded some interesting results At ultracold temperatures the molecular dipole system could be readily modeled using some simplifying assumptions in quantum mechanics He found that all polar molecules would behave in pretty much the same predictable way under ultracold conditions He also discovered that the size of the sphere of influence was indeed determined mostly by the dipole moment Moreover the sphere of influence would be large Even weak distant forces could have a large effect on individual molecules Since molecules move very slowly at ultracold temperatures there would be plenty of time for interactions too Even so it isn t clear whether chemical reactions would take place because the kinetic energies of ultracold polar molecules are so low At merely cold temperatures the system could also be readily modeled this time with semiclassical approximations Again any polar molecule would behave pretty much the same way as any other under the same circumstances once allowances for different dipole moments were taken into account However the spheres of influence would be much smaller and the molecules would move quite a lot faster Because they are traveling faster the molecules would interact weakly and head on collisions would be rare

    Original URL path: http://jila-pfc.colorado.edu/highlights/altered-states (2016-04-29)
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  • It Takes Two to Tango | JILA-PFC
    terms of quantum mechanics this confinement means that the wavelengths of the wave functions of both the electron and the hole are forced to be significantly smaller and more on top of each other inside a quantum dot than they would be in ordinary semiconductor material When electron hole pairs recombine they can release energy as light When continuously illuminated by a laser quantum dots blink on and off randomly These on and off periods can last from a microsecond to several minutes i e on time scales as short or as long as an experimentalist decides to observe In 2001 Fellow David Nesbitt and his co workers caught the attention of others in this field when they reported that the probabilities of the on and off times follow a power law Power law behavior typically indicates that something fairly complicated is going on Recently Nesbitt and former research associate Jeff Peterson now on the faculty at the State University of New York at Geneseo figured out what first turns blinking off and then back on again In this work the researchers used quantum dots made of cadmium selenide CdSe surrounded by a coating of zinc sulfide ZnS The CdSe dots are similar to those that are responsible for the beautiful orange colors in 12 th century stained glass The researchers wanted to understand why their modern orange quantum dots blink on and off like Christmas tree lights The key to solving the mystery was a paradox The amount of time it takes an on quantum dot to blink off seems to depend on when it was observed and for how long The longer a dot has been on the more likely it is to decay exponentially rather than follow power law behavior In addition the use of higher power

    Original URL path: http://jila-pfc.colorado.edu/highlights/it-takes-two-tango (2016-04-29)
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  • How to Marry a Microscope | JILA-PFC
    of ordinary AFMs a hundredfold Credit Greg Kuebler The most important step for a microscope wanting to marry another microscope is finding the right partner A professional matchmaker such as the Perkins lab might be just the ticket The group recently presided over the nuptials of atomic force microscopy and optical trapping microscopy Research associate Gavin King graduate students Ashley Carter and Allison Churnside CU freshman Louisa Eberle and Fellow Tom Perkins officiated The marriage produced an ultrastable atomic force microscope AFM capable of precisely studying proteins in real world ambient conditions The recently married AFM is a hundred times more stable than other state of the art AFMs one of the most widely used tools in nanoscience However using just AFM technology to probe a protein under ambient conditions is a lot like trying to write a letter while careening along a back country road in a jeep There s just a whole lot of movement happening at room temperature in either the air or liquids where biomolecules are found By adopting techniques developed in the Perkins lab King and his colleagues are now in a position to secure a protein to a laser stabilized surface then hold an AFM tip above specific parts of that protein as a second laser measures the motion of the tip This procedure is expected to allow the researchers to monitor a biomolecule s conformational dynamics in real time while canceling out the unwanted motion that obscures such measurements in conventional instruments The new microscope is analogous to the noise canceling headphones popular on noisy airplane flights In a recent proof of concept experiment the Perkins group demonstrated a hundredfold improvement in the stability of AFM measurements of test targets consisting of 5 mm gold balls which have a geometry and size similar

    Original URL path: http://jila-pfc.colorado.edu/highlights/how-marry-microscope (2016-04-29)
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  • Fermions in Collision? | JILA-PFC
    in the Ye lab considered this unneighborly behavior a big advantage in designing a new optical atomic clock based on an ensemble of identical 87 Sr atoms They along with every other physicist in the world assumed that using fermions meant they wouldn t have to worry about atomic collisions causing frequency shifts when these atoms were cooled to sufficiently low temperatures Of course things are never as simple as you expect them to be In 2008 the Ye group s optical atomic clock team identified tiny frequency shifts in their clock caused by colliding fermions In response Andrew Ludlow the graduate student who was leading the project did the smart thing and graduated The job of figuring out why some 87 Sr atoms were colliding fell to research associate Gretchen Campbell graduate students Mike Martin Sebastian Blatt and Travis Nicholson research associate Matt Swallows Fellow Jun Ye and their colleagues from NIST now including Ludlow Former JILAn Marty Boyd and Visiting Fellow Jan Thomsen also helped out The good news the researchers found no violations of the laws of quantum mechanics The interaction of their laser based precision measurement technique with the optical lattice confining the 87 Sr atoms was responsible for the frequency shifts Here s what Campbell and her colleagues discovered Their frequency measurements required focusing a laser beam on a 87 Sr atom filled lattice However because the lattice is actually slightly curved the atoms moving around inside it transitioned to their excited states at slightly different rates During the transition from their ground to excited states the atoms evolved differently And fermions in different superpositions of their ground and excited states are no longer identical Pairs of atoms that can be distinguished from one another can and do collide Once they understood what was happening

    Original URL path: http://jila-pfc.colorado.edu/highlights/fermions-collision (2016-04-29)
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  • Collision Course | JILA-PFC
    body corresponds to two fermions at the point where they form a molecule Credit Greg Kuebler and Seth Rittenhouse The Greene group just figured out everything you theoretically might want to know about four fermions crashing into each other at low energies Low energies in this context mean ultracold temperatures under conditions where large floppy Feshbach molecules form The group decided to investigate four fermions because this number makes up the smallest ultracold few body system exhibiting behaviors characteristic of the transition between Bose Einstein condensation and superfluidity Senior research associate José D Incao graduate student Seth Rittenhouse former research associate Nirav Mehta and Fellow Chris Greene participated in the study The researchers found that inelastic collisions can occur between two Feshbach molecules One of two things will happen either 1 one of the Feshbach molecules falls apart or 2 one of the molecules gets knocked into a lower energy state and releases enough energy to send everything else flying out of the trap In the latter case the new theory is able to predict the rate at which the molecules relax into lower energy states The rate curve arcs nicely through experimental data on Feshbach molecules from the Jin group In very very low energy collisions the size of the Feshbach molecules determines the efficiency with which they bounce off each other during a collision In other words the strength of the intermolecular interaction is proportional to the size of the molecules This relationship confirmed an earlier prediction by research associate Javier von Stecher when he was a graduate student in the Greene group The group had previously confirmed and improved upon earlier predictions by other theorists To showcase what happened during collisions of four fermions Rittenhouse created a projection of what occurs when they interact The projection shown

    Original URL path: http://jila-pfc.colorado.edu/highlights/collision-course (2016-04-29)
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  • Qubits in Action | JILA-PFC
    of the firm via a communication system Each office or local processor would be a quantum register Each register would contain one pair of employees a configuration analogous to a single Sr atom Each office register would not only work in perfect harmony but also create less resonance demand on the company computer than if every office had to always be in sync Imagine that John and Mary run the company s communications office they are also a single Sr atom John s communication function is analogous to a specific electronic transition or qubit in a Sr atom Mary is responsible for information storage which is mapped on the nuclear spin states of the same Sr atom John and Mary are in a mind meld superposition They re working on a company newsletter article about the theory behind the new light saber under development at the company Ricardo and Lisa are the lead engineers on the project and just happen to be discussing it in Ricardo s office The two engineers are also a single Sr atom in a mind meld superposition Lisa contains the information storage qubits and Ricardo is the communication qubit When the communications office has a draft of the article and a great picture to show to Lisa and Ricardo it activates a communication link to Ricardo s office First a precision laser moves the communications office a short distance and sets it down next to Ricardo s office Second a magic room partition i e a quantum gate opens up between the two offices Now John Mary Ricardo and Lisa enter a gigantic mind meld 4 party entanglement to swap information about the newsletter and recommend changes What s really neat is that if the company had a really big project like building a commercial

    Original URL path: http://jila-pfc.colorado.edu/highlights/qubits-action (2016-04-29)
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  • Explosive Evidence | JILA-PFC
    Dagdikian of Johns Hopkins University and Fellow David Nesbitt have taken this kind of study into a whole different arena They recently probed the molecules that form when the surface of a liquid is bombarded with a very reactive gas The liquid surface is an oily compound called squalane a large natural molecule containing hydrogen H and carbon C atoms It is purified from shark liver oil and sometimes used in cosmetics The gas is fluorine F the most chemically reactive of all the elements The resulting molecules are hydrogen fluoride HF They form when F atoms striking the liquid surface pluck a hydrogen atom from it and form a chemical bond This particular chemical reaction releases lots of heat and energy In fact inside the vacuum chamber where the reaction takes place there s a small explosion happening After the molecules form and leave the liquid surface Zolot and his colleagues examine them with an infrared laser beam aimed across the reaction chamber a little above the surface The laser s interactions with the molecules allow the researchers to determine not only the density of the molecules but also any patterns in their velocities vibrations or rotations This information in turn makes it possible to figure out how the molecules interact with the liquid surface after they are formed For instance some new molecules fly off of the surface right away They are vibrating intensely and spinning very fast b in the figure above They are also traveling very fast when probed by the laser beam Their speed suggests they are likely very hot in the range of 600 2800 F In other words the fast spinning molecules are also traveling very fast away from the surface The longer a molecule stays on the surface the more its vibrations

    Original URL path: http://jila-pfc.colorado.edu/highlights/explosive-evidence (2016-04-29)
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  • Beams In Collision | JILA-PFC
    Last year the Ye group conducted an actual laboratory astrophysics experiment Graduate students Brian Sawyer Ben Stuhl and Mark Yeo research associate Dajun Wang and Fellow Jun Ye fired cold hydroxyl OH radicals into a linear decelerator equipped with an array of highly charged electrodes and slowed the OH molecules to a standstill These molecules were then loaded into a permanent magnetic trap where they became the stationary target for collision studies Next Sawyer and his colleagues aimed supersonic beams of either helium He atoms or deuterium molecules D 2 at the OH molecules They then studied the resulting low energy collisions which took place at temperatures of 80 300 K With respect to the D 2 collisions they wanted to see if their findings would shed light on the action of OH masers See JILA Light Matter Spring 2008 Some theorists posit that OH masers emit coherent radio wavelength photons after being excited by collisions with H 2 molecules at temperatures only a few tens of degrees K lower than those in the laboratory experiment For this reason the researchers planned to use H 2 supersonic beams in their collision studies However their turbo pumps didn t work with H 2 Luckily D 2 molecules are chemically similar to H 2 and their collision behavior was expected to be very similar to that of H 2 The D 2 molecules also had the advantage of being as massive as the He atoms so the pumps worked The results of the experiments depended on whether the molecular beam contained He atoms or D 2 molecules In a He OH collision the billiard ball like He atom would either start an OH molecule spinning in an inelastic collision or it would bounce off the OH molecule without rotating the molecule elastic

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