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  • Scratching the Surface | JILA-PFC
    type of abstract surface in a gas of ultracold atoms that had been predicted in 1926 but not previously observed Jin and her colleagues are leading researchers in the field of ultracold Fermi gases made up of thousands to millions of fermions Fermions including electrons and some types of atoms such as potassium 40 K cannot occupy exactly the same quantum state This property leads to a unique distribution of the energy or speed of a collection of fermions at low temperature The distribution has a sharp boundary called a Fermi surface Figure 1 And under the right conditions an ultracold gas of fermions should exhibit a sharp step or boundary in the distribution of speeds Famous physicists Enrico Fermi and Paul Dirac predicted the existence of this step nearly 100 years ago For most of a century physicists were unable to directly see the Fermi surface by looking at the speeds of a bunch of fermions One difficulty was that fermions interact in virtually all systems except for ultracold gases where interactions can be controlled by adjusting the magnetic field However confining ultracold gas clouds in traps using light or magnetic fields does cause variations in the density of the gas in different parts of the cloud These density variations wash out the sharp Fermi surface when speed distributions are averaged over an entire ultracold gas cloud So although physicists were sure that a Fermi surface was present in small sections of the clouds of ultracold fermions they were unable to see it experimentally However seeing it experimentally was exactly what the Jin group wanted to do So research associate Yoav Sagi graduate students Tara Drake and Rabin Paudel former graduate students Jayson Stewart and John Gaebler and Fellow Jin devised a clever strategy that allowed them to see

    Original URL path: http://jila-pfc.colorado.edu/highlights/scratching-surface (2016-04-29)
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  • New Silicon Cavity Silences Laser Noise | JILA-PFC
    interferometers Interferometers are widely used measurement tools in optical atomic clocks astronomy and spectroscopy Their thermal noise is due to incoherent collective motions of atoms and molecules inside them and other material systems Motion related noise increases as the temperature goes up To reduce this noise researchers designed an optical cavity made from a single crystal of silicon An ultrastable laser system using such a cavity could theoretically have nearly ten times less heat related noise than other ultrastable optical cavities used to stabilize laser frequencies Since 2008 graduate student Mike Martin former graduate student Marty Boyd Chen and Ye have all worked with PTB on testing and comparing a laser using the new silicon crystal cavity with one of the best Ye group lasers which uses a spacer made of ultralow expansion glass and mirror substrates made from fused silica glass The new cavity s spacer and mirrors are made of single crystal silicon and operated at 124 K a special temperature at which a silicon crystal s heat related expansion is at a minimum The cavity itself is mounted vertically in a way that is immune to additional vibrations in the surrounding environment Only the mirror coatings contribute in a significant way to the thermal noise of the new silicon cavity system Recently a laser using the new cavity was tested and compared with two ultrastable lasers including one Martin brought to Germany from the Ye labs All three lasers are extremely stable For instance both the new silicon cavity laser and the laser from JILA can remain coherent in sync for distances of up to three million kilometers The three lasers were tested in a three cornered hat comparison In this kind of comparison performance differences are measured between laser 1 and 2 laser 2 and 3

    Original URL path: http://jila-pfc.colorado.edu/highlights/new-silicon-cavity-silences-laser-noise (2016-04-29)
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  • New Flavors of Quantum Magnetism | JILA-PFC
    things are never so simple and straightforward in the quantum world It s as if in addition to spin up and spin down in alkaline earth atoms there were also eight more unique spin directions such as spin forwards spin backwards or spin diagonal Of course in this case the spin directions are just a convenient analogy for quantum spin states The multi flavored alkaline earth atoms have some real advantages in quantum simulation Inside a simulator a set number of alkaline earth atoms with ten flavors can actually make the whole system get five times colder than the same number of atoms with only two flavors This result was entirely unexpected Conventional wisdom said that a higher number of magnetic flavors in the atomic nuclei would cause the lowest possible temperature of the system to be higher than that of a system with a lower number of magnetic flavors I was so shocked when we first saw this I spent a whole day trying to find the error in my calculation said Kaden Hazzard an NRC National Research Council postdoc with the Rey group But Hazzard hadn t made a mistake The Rey group has proved conventional wisdom wrong and opened the door to some novel experiments with the quantum simulator in the Ye lab Since the simulator is already kept at ultracold temperatures the newly discovered relationship of cooling to an increased number of spin states means that it should theoretically be possible to cool highly controlled atoms down to nano Kelvin temperatures Such temperatures are needed to directly observe quantum magnetism in action When you get alkaline earth atoms really cold that s when you can see the most interesting physics Hazzard said Because of the unique properties of alkaline earth atoms scientists will soon be able

    Original URL path: http://jila-pfc.colorado.edu/highlights/new-flavors-quantum-magnetism (2016-04-29)
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  • The Laser with Perfect Pitch | JILA-PFC
    normal laser s pitch or frequency will wander around spoiling a perfectly good night at the lab The new superradiant laser avoids the echo chamber distortions because emitted light quickly leaks out of its mirrors much faster than the choir of atoms loses track of the note it is singing But there is more involved in building a laser with nearly perfect pitch For instance it s critical to avoid bad singers To accomplish this the Thompson group hired a pretty talented choir composed of a million laser cooled and trapped Rubidium atoms Because of its talented choir and its much smaller echo the new laser s pitch is ten thousand times less likely to be altered by rippling mirrors than is the pitch in a normal laser As a result its pitch is a hundred times sharper than the best normal lasers The new laser was built by Fellow James Thompson and graduate students Justin Bohnet Zilong Chen and Josh Weiner Former postdoctoral researcher Dominic Meiser of the Holland group provided theory support Naturally there are tradeoffs for getting perfect pitch The leaky mirrors mean that the laser operates in a strange regime where an average of less than one photon of light bounces between the mirrors This small amount of light acts like a very weak telephone line between the atoms allowing them to agree to sing the same note The atoms are trapped in stacks of 5000 by a one dimensional crystal of light Not only do the atoms in each crystal sing the same note but they also sing in just the right way Consequently the rate at which the light is emitted increases as the square of the number of atoms making the laser much brighter A similar effect can occur when crickets start chirping

    Original URL path: http://jila-pfc.colorado.edu/highlights/laser-perfect-pitch (2016-04-29)
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  • The Secret Life of Magnets | JILA-PFC
    Mathias and Mark Siemens graduate student Emrah Turgut Fellows Henry Kapteyn and Margaret Murnane NIST Boulder s Tom Silva and colleagues from the University of Kaiserslautern Peter Grünberg Institute and University of Denver Metals like iron and nickel get magnetized because the spins of all their individual atoms get lined up and point in the same direction Figure 1 Since every spin is like a tiny bar magnet with a north and south pole when trillions and trillions of spins get lined up the resulting magnet is large enough for people to see which is why it s possible to explore how magnetism works in the everyday world Many scientists including those who did this experiment investigated magnets when they were children That s one reason they were interested in figuring out exactly what was going on with the individual atoms inside a magnetized metal In the magnetized alloy of iron and nickel both kinds of atoms act like members of a marching band moving in unison across a football field Imagine that the spins of the iron atoms are the brass section and the spins of the nickel atoms are the woodwinds When a laser strikes this marching band at first something very strange happens The brass players iron spins start walking off in random directions but the woodwinds nickel spins keep marching in unison Soon however the nickel spins also start walking off in random directions and the entire magnetic band is in disarray The whole process takes about 240 quadrillionths of a second Here s what happens in detail The iron spins likely see the ultrafast light more readily than the nickel spins for reasons that are not yet completely understood The light quickly heats up and randomizes the iron spins which is why the brass players

    Original URL path: http://jila-pfc.colorado.edu/highlights/secret-life-magnets (2016-04-29)
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  • The Quantum Drum Song | JILA-PFC
    The Regal group and Brad Baxley JILA Fellows Konrad Lehnert and Cindy Regal are collaborating on an ambitious undertaking to explore the quantum behavior of tiny mechanical systems that are large enough to be visible to the naked eye as opposed to systems exhibiting quantum behavior that are no bigger than a few tens of atoms At the same time they have been looking for ways to prolong vibrations in mechanical objects such as drums or strings Prolonging vibrations makes it possible to laser cool objects to temperatures where it is possible to observe quantum mechanical motion The Regal lab has recently completed a set of experiments that increased its understanding of the properties of tiny drums that influence the lifetime of their vibrations The group made and characterized a series of microscopic two layer drums of aluminum metal and silicon nitride Si 3 N 4 that are 100 nm thick and approximately 1 mm long The aluminum layer was important because it represents a class of materials that offers some advantages for use in tiny drums but which are also bad materials in the sense they often suppress vibrations The studies were conducted by graduate student Pen Li Ben Yu research associate Tom Purdy and Fellow Regal At first the researchers observed that layering aluminum metal on a Si 3 N 4 membrane made drum vibrations disappear more quickly This effect was not unexpected However it opened the door to discovering exactly how the vibrations were disappearing for different vibrational patterns Many tiny mechanical objects vibrate like bridges but the Si 3 N 4 membranes studied by Yu and his colleagues pulsate more like drums So the researchers modeled the vibrations and their disappearance for drums Figure 1 The model showed that the behavior of the vibrating drum at

    Original URL path: http://jila-pfc.colorado.edu/highlights/quantum-drum-song (2016-04-29)
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  • Variation on an Infinity of Triangles | JILA-PFC
    states of ultracold fermions that are also dipoles Dipoles are particles with small positively and negatively charged ends Atoms or molecules that are fermions cannot occupy the same quantum state unlike the neighborly bosons that readily occupy the same state and form Bose Einstein condensates at ultracold temperatures The new theoretical study was interesting because it explored what would happen to dipolar fermions under the same conditions that cause dipolar bosons to form infinitely many three atom molecules even though no two bosons ever form a molecule under these conditions The physics underlying the formation of the triatomic molecules is called Efimov physics after Russian theoretical physicist Vitaly Efimov who predicted the strange states in 1970 The Greene group has made major contributions to the study of Efimov physics since the 1990s including those described in Laws of Attraction and Rave Reviews for the Efimov Quartet The new study is the first to investigate what would happen to dipolar fermions under the same conditions that cause dipolar bosons to form triatomic Efimov molecules The study was performed by research associate Yujun Wang senior research associate Jose D Incao and Fellow Chris Greene What the researchers found was that three dipolar fermions should not form an Efimov state However as the attraction among the dipolar fermions reached the magic point where an Efimov state would have formed with bosons the fermions formed only one kind of triangular molecule the one shown in the picture Figure 1 This picture appeared on the cover of Physical Review Letters the week ending with Dec 2 2011 This triangular cluster always had the same shape unlike a true Efimov state in which the three particles can have almost any configuration However as with the previously studied Efimov states the attraction between the dipolar fermions could

    Original URL path: http://jila-pfc.colorado.edu/highlights/variation-infinity-triangles (2016-04-29)
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  • The Indomitable Ruler of Light | JILA-PFC
    XUV comb It has also opened the door to exploring the internal quantum states of many different atoms and molecules With the XUV ruler scientists will be able to look at exactly how electrons arrange themselves in high energy states inside molecules The new ruler may also make it possible to develop new clocks based on the behavior of nuclei of atoms The team responsible for these exciting prospects includes research associates Arman Cingöz and Tom Allison graduate student Dylan Yost Fellow Jun Ye and their colleagues who provided the infrared laser used to make the XUV comb from IMRA America The creation of the XUV comb was a major milestone in the goal of designing frequency combs that span the entire electromagnetic spectrum The invention of the XUV comb s famous cousin the optical frequency comb earned its creators a Nobel Prize The optical frequency comb is a stable pulsed laser that can create millions of equally spaced colors of visible light Unfortunately it s impossible to build a pulsed XUV laser stable enough to be a frequency comb To make an XUV comb the scientists had to come up with a method to transfer visible or infrared comb lines up to XUV frequencies without losing the delicate and coherent comb structure The Ye group has done just that In a nutshell here s how it works First the Ye group commissioned the high power infrared ytterbium fiber frequency comb developed by their collaborators at IMRA America Second the researchers optically coupled the laser into an enhancement cavity that was carefully engineered to add laser pulses constructively After 200 round trips through the enhancement cavity the original laser pulse still had the same coherent structure but it had reached a high enough intensity to initiate high harmonic generation or

    Original URL path: http://jila-pfc.colorado.edu/highlights/indomitable-ruler-light (2016-04-29)
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