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  • Reactions on Demand | JILA-PFC
    we can also make the atom not see them Ranitovic said This a novel way of doing coherent control He explained that if the atom sees the pulses it ionizes But the atom can t ionize if it doesn t see the pulses The process of keeping the atom from seeing ionizing pulses is called electromagnetically induced transparency To create electromagnetically induced transparency the researchers modified the electronic structure of helium with the IR pulse that controls the amplitude of the XUV harmonics and the relative phase between the XUV and IR pulses In so doing they were able to create a quantum double slit situation in which they could control the probability of ionization by interfering two electron waves constructively or destructively If the interference was constructive the IR enhanced XUV pulses could knock an electron out of a helium atom even though neither of the pulses was energetic enough by itself to remove one of helium s two electrons In contrast if the interference was destructive the XUV pulses sailed through the helium atoms as if they weren t even there Another way to think about helium ionization is that three colors of light influence a helium electron The three colors none of which is visible to the human eye are IR photons red in the figure and two higher energy XUV photons blue and purple in the figure By adjusting the three colors Ranitovic and his colleagues showed that they can launch an electron wave in a helium atom along two different quantum pathways The wave traveling the different quantum pathways has the same amplitude but opposite phases It cancels itself out on the way out of the helium atom thus controlling the likelihood that an electron will separate from its parent atom This new technique has

    Original URL path: http://jila-pfc.colorado.edu/highlights/reactions-demand (2016-04-29)
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  • The Secrets of the Resonant Lattice | JILA-PFC
    lattice has led to a powerful new mathematical model capable of shedding light on the fundamental physics of the quantum behavior of these systems The creators of the new model included senior research associate Javier von Stecher Fellow Ana Maria Rey and their colleagues Victor Gurarie and Leo Radzihovsky from the University of Colorado Von Stecher and his colleagues found that atoms in an optical lattice couldn t move at any speed they want to Rather the atoms were confined to hundreds of discrete energy bands However at ultracold temperatures the atoms moved so slowly the could only move in the lowest energy band This restriction made it easier for the researchers to understand their behavior as they interacted with one another However things changed at a Feshbach resonance which made the atoms interact more strongly Now the two atoms could collide and form a molecule And each of the atoms in the new molecule could end up in hundreds of different energy bands Interestingly von Stecher and his colleagues discovered that it was not necessary to describe the molecule as made up of two atoms in different energy bands Rather they looked at the molecule as if it were a new particle that could only move in its own energy bands These molecular bands were different from those of the atoms There were as many molecular energy bands as atomic bands But there was a key difference A molecular band would move in response to changes in the magnetic field The atom bands would not Tuning the magnetic field turned out to be the control knob for making things really interesting in a resonant lattice As a molecule band moved in response to changes in the magnetic field it inevitably ran into touched an atom band When this happened

    Original URL path: http://jila-pfc.colorado.edu/highlights/secrets-resonant-lattice (2016-04-29)
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  • Laws of Attraction | JILA-PFC
    formation of an endless sea of three bound quantum states even when individual atoms are far apart Now the Greene group has shown that dipolar Efimov trimers can also form in an ultracold system The dipolar Efimov states are even more peculiar than ordinary Efimov molecules The strangest thing is that they exist at all Theorists including senior research associate José D Incao and Fellow Chris Greene once thought the Efimov effect would not occur with atoms and molecules in a strong electric field However the JILA researchers have just proved that they were mistaken Even though 1 the atoms in a dipolar Efimov trimer are normally very far apart and extremely weakly bound and even though 2 an electric field exerts a twist on the dipolar trimers to align with the field the Efimov effect persists in dipolar systems In fact in a dipole system the stronger the electric field the longer the Efimov molecules live Dipolar Efimov states can survive long enough inside a dipolar gas that experimental physicists should be able to create and manipulate them in the laboratory according to the JILA theorists This kind of survival is stunning when you consider that Efimov physics in an ultracold dipolar BEC is constrained by an electric field However the major constraint is not if the molecules can form Rather it is that Efimov trimers can only form inside a well defined band of energy that looks a little like the hatband on a Mexican sombrero Chalk one up for the laws of attraction and the utter weirdness of the quantum world The quantum world we study looks crazy but it s actually real says research associate Yujun Wang who worked with D Incao and Greene to probe the nature of the Efimov effect in an ultracold dipolar

    Original URL path: http://jila-pfc.colorado.edu/highlights/laws-attraction (2016-04-29)
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  • Quantum CT Scans | JILA-PFC
    angles of this quantum state as it was wiggling around Because they only viewed the quantum state from one angle at a time they were able to circumvent quantum uncertainties to make virtually noiseless measurements of amplitude changes in their tiny microwave signals Multiple precision measurements of the same quantum state yielded a full quantum picture of the microwave field What we did was a quantum version of the CT scan for light at microwave frequencies says Lehnert Since we can represent information as a state of a microwave field this is a lively topic in the field of quantum information processing Lehnert adds that measuring microwave fields and manipulating information with them already works fairly well with microwaves trapped inside a box or cavity However the Lehnert group and its NIST collaborators have taken the plunge of measuring a single quantum state outside the box The JILA team includes research associate François Mallet graduate student Hsiang Sheng Ku former graduate student Manuel Castellanos Beltran and Fellow Konrad Lehnert Their NIST Boulder collaborators include Scott Glancy Emanuel Knill Kent Irwin Gene Hilton and Leila Vale The eventual goal of the joint research is the creation of quantum entanglement of different quantum states of a microwave field outside of a cavity Quantum entanglement is a kind of spooky shared quantum state superposition that extends across space and time It is an essential ingredient for high speed quantum computing The key ingredient in creating quantum entanglement as well as in measuring the quantum state of a microwave field is a Josephson parametric amplifier or JPA The best ever design of such a device was created in 2008 by the JILA NIST collaboration This JPA not only functioned as a virtually noiseless amplifier See JILA Light Matter Fall 2008 but also had ability

    Original URL path: http://jila-pfc.colorado.edu/highlights/quantum-ct-scans (2016-04-29)
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  • JILA MONSTR and the Chamber of Secrets | JILA-PFC
    the bell vibrate The second creates an interference pattern in the original vibration enhancing some frequencies and damping out others The third interacts with the remaining frequencies and the resulting ring tone pattern contains information about the dynamics of the bell Similarly the signals produced by interactions with a series of laser pulses reveal information about the dynamics of the strange world inside the GaAs quantum dots When particles there interact with one or more pulses of laser light they radiate light of different colors frequencies Researchers use a spectrometer and computer to convert these signals into multidimensional frequency spectra that make it easier for them to look for evidence of particle interactions Recently a team led by graduate student Galan Moody used the MONSTR to not only learn more about GaAs quantum dots but also the interactions of particles inside the dots with the GaAs quantum well that surrounds them The experimenters used samples arranged like Oreo cookies The cookies correspond to the barriers of aluminum gallium arsenide AlGaAs that surround the GaAs on the sample wafer The filling corresponds to a two dimensional quantum well and lumpy islands in the filling correspond to the zero dimensional GaAs quantum dots Inside both quantum dots and the quantum well the laws of quantum mechanics determine behavior of electrons Gaining a better understanding of how those laws affect the behavior of particles in the quantum dots was one goal of Moody s experiments Moody was assisted by research associates Mark Siemens now at the University of Denver Alan Bristow now at West Virginia University Xingcan Dai now at Tsinghua University in China and Denis Karaiskaj now at the University of South Florida researchers from the Naval Research Laboratory and Fellow Steve Cundiff The researchers studied excitons both inside the quantum dots

    Original URL path: http://jila-pfc.colorado.edu/highlights/jila-monstr-and-chamber-secrets (2016-04-29)
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  • I Sing the Body Electric | JILA-PFC
    to see what would happen if it could get cold molecules 1K 1mK and ultracold 3 molecules and ultracold 600 microK rubidium Rb atoms The researchers hoped their experiment would help elucidate the role of quantum mechanics in molecular collisions Their novel experimental setup is shown in the top picture Figure 1 The researchers cool and trap Rb atoms at the intersection of the red laser cooling beams Then a pulsed valve lower right creates a beam of cold ND 3 molecules The metallic rods and rings create electric fields that slow and trap the molecular beam To combine the cold molecules and ultracold atoms the researchers physically move the coils forming the atom trap across the table until the atom trap overlays the molecule trap With the traps superimposed atom molecule collisions are likely to occur according to theory These collisions will have very little effect on an ND 3 molecule An ND 3 molecule will usually remain in the same quantum state after a collision as it was in before anything happened To liven up their experiment the researchers decided to see how electric fields would affect these unusual collisions They quickly discovered that electric fields have a major effect on ultracold atom cold molecule collisions Even though electric fields affect only the orientations of the molecules they increase the likelihood that a given atom molecule collision will change the quantum state of the ND 3 molecule And collisions occurred faster than expected The JILA researchers enlisted the help of theorist colleagues from the University of Durham UK to explain what was happening New theory showed that electric fields strongly influence atom molecule collisions even if there are no dipole dipole interactions Figure 2 Dipole dipole interactions occur between atoms or molecules that have slight differences in charge

    Original URL path: http://jila-pfc.colorado.edu/highlights/i-sing-body-electric (2016-04-29)
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  • The Long Goodbye | JILA-PFC
    group and explained theoretically by senior research associate Agnieszka Jaroń Becker of the Becker group Graduate student Craig Hogle former research associates Vandana Sharma and Xibin Zhou and Fellows Andreas Becker Henry Kapteyn and Margaret Murnane contributed to this seminal work Li and his colleagues initiated the dissociation of a Br 2 molecule with a violet 400 nm ultrafast laser pulse If a Br 2 molecule absorbs only a single photon at this wavelength the molecule gets excited into a dissociative state where it begins to break apart into its constituent atoms The researchers then used an infrared laser pulse to ionize the dissociating molecule and probe the progression of the dissociation at varying times after the molecule began to fall apart The series of probe pulses allowed Li and his colleagues to follow the motions of all ten valence electrons as the molecular bond was breaking This is the first experiment to capture the coordinated dance of multiple electrons at once What surprised the team was that the change from a molecule to two atoms could be observed over such a surprisingly long time and distance While times of 140 millionths of a billionth of a second and distances of 55 billionths of a meter may seem very small they are much longer than would normally be expected in the exceedingly fast and small world where individual atoms interact To explain these unexpected results the laboratory scientists turned to their theorist colleagues With the help of Jaroń Becker the laboratory scientists realized they were observing all 10 valence electrons evolving in time as the molecular bond was breaking Jaroń Becker s analysis showed that the researchers were not likely to see two separate atoms until 140 160 fs after the initial dissociative laser pulse a prediction that dovetailed nicely

    Original URL path: http://jila-pfc.colorado.edu/highlights/long-goodbye (2016-04-29)
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  • The Quantum Control Room | JILA-PFC
    in all three dimensions ultracold KRb molecules were so chemically reactive they disappeared almost as soon as they were formed Then with help from their theorist colleagues in the Bohn group the researchers found out that when an electric field is present the KRb molecules would get even more reactive In an electric field the fast chemical reactions started looking like explosions Explosions are pretty cool for chemists But they re a nightmare for experimental physicists especially if their goal is to cool a gas of polar KRb molecules down to the temperature where all their quantum states occupy the lowest possible energy levels This state of affairs is called quantum degeneracy To get there the KRb molecules have to collide but not react Fortunately research associate Goulven Quéméner and Fellow John L Bohn developed a theory for seriously suppressing the reaction rate of KRb molecules Then a team from the Ye and Jin groups proved the method worked The experimental team was led by Marcio de Miranda now at the Universidade de São Paulo research associate Amodsen Chotia graduate student Brian Neyenhuis and former research associate Dajun Wang now at the Chinese University of Hong Kong The team also included former research associate Silke Ospelkaus now at the University of Hanover in Germany as well as Fellows Jun Ye and Debbie Jin Here s what the experimental team did to slow down the chemical reactions First the researchers squeezed ultracold KRb molecules into a two dimensional pancake trap This trap forced the molecules to line up side by side with identical ends of the molecules next to each other This step mostly prevents the molecules from aligning head to tail which enhances chemical reactions in a major way because opposite ends of dipoles attract one another Second the experimentalists

    Original URL path: http://jila-pfc.colorado.edu/highlights/quantum-control-room (2016-04-29)
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