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May 23, 2016 | PFC | Research News

Quantum cycles power cold-atom pump

The idea of a pump is at least as old as the ancient Greek philosopher and scientist Archimedes. More than 2000 years ago, Archimedes allegedly invented a corkscrew pump that could lift water up an incline with the turn of a handle. Versions of the ancient invention still bear his name and are used today in agriculture and industry.Modern pumps have achieved loftier feats. For instance, in the late 1990s, NIST developed a device that could pump individual electrons, part of a potential new standard for measuring capacitance.While pumps can be operated mechanically, electrically or via any other source of energy, they all share the common feature of being driven by a periodic action. In the Archimedean pump, that action is a full rotation of the handle, which draws up a certain volume of water. For the NIST electron pump, it is a repeating pattern of voltage signals, which causes electrons to hop one at a time between metallic islands.But physicists have sought for decades to build a different kind of pump—one driven by the same kind of periodic action but made possible only by the bizarre rules of quantum mechanics. Owing to their physics, these pumps would be immune to certain imperfections in their fabrication.Now, a team of physicists working in collaboration with JQI Fellow Ian Spielman and NIST postdoctoral researcher Hsin-I Lu has created just such a pump. By periodically jostling many individual atoms, the researchers were able to shift an entire atomic cloud without any apparent overall motion by its constituents. The team is the first to test this predicted behavior, which arises in what they call a geometric charge pump. The work follows close on the heels of two recent papers that examined topological charge pumps, which demonstrate a distinct but related effect. The new result was published May 20 in Physical Review Letters.
May 10, 2016 | Research News

Novel gate may enhance power of Majorana-based quantum computers

Quantum computers hold great potential, but they remain hard to build because their basic components—individual quantum systems like atoms, electrons or photons—are fragile. A relentless and noisy background constantly bombards the computer’s data. One promising theoretical approach, known as topological quantum computing, uses groups of special particles confined to a plane to combat this environmental onslaught. The particles, which arise only in carefully crafted materials, are held apart from each other so that the information they store is spread out in space. In this way, information is hidden from its noisy environment, which tends to disrupt small regions at a time. Such a computer would perform calculations by moving the particles around one another in a plane, creating intricate braids with the paths they trace in space and time. Although evidence for these particles has been found in experiments, the most useful variety found so far appear only at the ends of tiny wires and cannot easily be braided around one another. Perhaps worse for the prospect of quantum computing is that these particles don’t support the full power of a general quantum computer—even in theory. Now, researchers at JQI and the Condensed Matter Theory Center (CMTC) at the University of Maryland, including JQI Fellows Sankar Das Sarma and Jay Deep Sau, have proposed a way to dispense with both of these problems. By adding an extra process beyond ordinary braiding, they discovered a way to give a certain breed of topological particles all the tools needed to run any quantum calculation, all while circumventing the need for actual braiding. The team described their proposal last month in Physical Review X.
May 3, 2016 | People News

Christopher Monroe elected to National Academy of Sciences

University of Maryland Physics Professor Christopher Monroe has been elected to the National Academy of Sciences. Monroe, who is also a Distinguished University Professor, the Bice Zorn Professor of Physics, and a fellow of the Joint Quantum Institute and the Joint Center for Quantum Information and Computer Science, is one of 84 new members and 21 foreign associates elected in 2016. He joins a select group of 2,291 scientists around the country elected by their peers and recognized for their influential research. He is a scientific leader in trapping atomic ions and studying how to use their quantum properties for information processing. 
April 25, 2016 | People News

Gretchen Campbell named new JQI Co-Director

JQI Fellow Gretchen Campbell has been named the new NIST Co-Director of the Joint Quantum Institute, effective April 1, 2016. Campbell joined the JQI in 2009 and is also a UMD Adjunct Associate Professor and APS Fellow. In recent years she has received various accolades for her atomtronics research, including the APS Maria Goeppert-Mayer award. Campbell succeeds JQI Fellow Charles Clark, who has held the position since 2011. JQI Fellow Steven Rolston will continue as the UMD Co-Director. Rolston, on behalf of JQI, would like to thank Clark for his service. "I would particularly like to highlight Charles’ leadership and active engagement with the public in the promotion of quantum physics. The JQI will continue to benefit from his dedication." Rolston continues, "Gretchen is an outstanding research colleague and I look forward to working with her in her new role as Co-Director."
April 22, 2016 | Research News

Oscillating currents point to practical application for topological insulators

Scientists studying an exotic material have found a potential application for its unusual properties, a discovery that could improve devices found in most digital electronics.Under the right conditions the material, a compound called samarium hexaboride, is a topological insulator—something that conducts electricity on its surface but not through its interior. The first topological insulators were only recently created and demonstrated in labs.Now, a team of physicists at JQI and the University of California, Irvine, may have found a use for tiny crystals of samarium hexaboride. When pumped with a small but constant electric current and cooled to near absolute zero, the crystals can produce a current that oscillates. The frequency of that oscillation can be tuned by changing the amount of pump current or the crystal size.
March 30, 2016 | PFC | Research News

Measuring the magnetization of wandering spins

The swirling field of a magnet—rendered visible by a sprinkling of iron filings—emerges from the microscopic behavior of atoms and their electrons. In permanent magnets, neighboring atoms align and lock into place to create inseparable north and south poles. For other materials, magnetism can be induced by a field strong enough to coax atoms into alignment.In both cases, atoms are typically arranged in the rigid structure of a solid, glued into a grid and prevented from moving. But the team of JQI Fellow Ian Spielman has been studying the magnetic properties of systems whose tiny constituents are free to roam around—a phenomenon called “itinerant magnetism." “When we think of magnets, we usually think of some lattice,” says graduate student Ana Valdés-Curiel. Now, in a new experiment, Valdés-Curiel and her colleagues have seen the signatures of itinerant magnetism arise in a cold cloud of rubidium atoms.
March 16, 2016 | PFC | Research News

Rogue rubidium leads to atomic anomaly

The behavior of a few rubidium atoms in a cloud of 40,000 hardly seems important. But a handful of the tiny particles with the wrong energy may cause a cascade of effects that could impact future quantum computers. Some proposals for quantum devices use Rydberg atoms—atoms with highly excited electrons that roam far from the nucleus—because they interact strongly with each other and offer easy handles for controlling their individual and collective behavior. Rubidium is one of the most popular elements for experimenting with Rydberg physics. Now, a team of researchers led by JQI Fellows Trey Porto, Steven Rolston and Alexey Gorshkov have discovered an unwanted side effect of trying to manipulate strongly interacting rubidium atoms: When they used lasers to drive some of the atoms into Rydberg states, they excited a much larger fraction than expected. The creation of too many of these high-energy atoms may result from overlooked “contaminant” states and could be problematic for proposals that rely on the controlled manipulation of Rydberg atoms to create quantum computers.
February 26, 2016 | PFC | Research News

Characterizing quantum Hall light zooming around a photonic chip

When it comes to quantum physics, light and matter are not so different. Under certain circumstances, negatively charged electrons can fall into a coordinated dance that allows them to carry a current through a material laced with imperfections. That motion, which can only occur if electrons are confined to a two-dimensional plane, arises due to a phenomenon known as the quantum Hall effect.Researchers, led by Mohammad Hafezi, a JQI Fellow and assistant professor in the Department of Electrical and Computer Engineering at the University of Maryland, have made the first direct measurement that characterizes this exotic physics in a photonic platform. The research was published online Feb. 22 in Nature Photonics. These techniques may be extended to more complex systems, such as one in which strong interactions and long-range quantum correlations play a role.
February 24, 2016 | People News

Waks Elevated to Fellow of the Optical Society of America

Professor Edo Waks was named a 2016 fellow of the Optical Society of America (OSA). The OSA Fellow Members Committee and Board of Directors honored Professor Waks specifically for outstanding contributions to optical quantum information processing using quantum dots coupled to nanophotonic devices.