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Experiments at the LHC are once again recording collisions at extraordinary energies

After months of winter hibernation the world’s most powerful particle accelerator is once again smashing protons and taking data. The Large Hadron Collider will run around the clock for the next six months and produce roughly 2 quadrillion high-quality proton collisions, six times more than in 2015 and just shy of the total number of collisions recorded during the nearly three years of the collider’s first run.

Between 2010 and 2013 the LHC produced proton-proton collisions with 8 teraelectronvolts of energy. In the spring of 2015, after a two-year shutdown, LHC operators ramped up the collision energy to 13 TeV. This increase in energy enables scientists to explore a new realm of physics that was previously inaccessible. Run II collisions also produce Higgs bosons – the groundbreaking particle discovered in LHC Run I – 25 percent faster than Run I collisions and increase the chances of finding new massive particles by more than 40 percent.

During this run, University of Maryland physicists will continue looking for new particles, including those that make up dark matter. Although the nature of dark matter and its counterpart, dark energy, remain a complete mystery, taken together they make up a total of around 95 percent of the universe.

The signature that will indicate the dark matter particle is known as missing transverse energy. UMD physicists are very familiar with this measurement, as they are a leading institution in the missing transverse energy group of the LHC’s Compact Muon Solenoid (CMS) detector.

Members of the Maryland group will also study collisions of nuclei with the CMS detector as well as the details of the interactions of the particles responsible for the sun’s energy. UMD physicists will also harness the LHC to investigate the origin of matter-antimatter asymmetry in the universe. When the Big Bang created matter, it also created an equal quantity of antimatter, made up of particles with identical mass but an opposite electrical charge. For as-yet unknown reasons, antimatter is no longer common in the universe, but can be recreated in particle accelerators such as the LHC.

UMD’s Hassan Jawahery leads a group that will use the LHCb detector to study the “beauty” or “bottom” quark— hence the “b” in the detector’s name. The collider will also produce the antimatter counterpart to the beauty quark. Comparing the properties of these two complementary particles could reveal laws of nature that treat matter and antimatter differently.

Key members of the University of Maryland LHC Team are available to comment on their work:
Drew Baden, Chair and Professor
Alberto Belloni, Assistant Professor
Sarah Eno, Professor
Nicholas Hadley, Professor
Hassan Jawahery, Distinguished University Professor and Gus T. Zorn Professor
Alice Mignery, Professor
Andris Skuja, Professor


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.

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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 examples of topological insulators were only recently created in the lab, and their discovery has sparked a great deal of theoretical and experimental interest.

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. Read More

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.

The team mapped out the magnetic properties of their atomic cloud, probing the transition between unmagnetized and magnetized phases. Using interfering lasers, the researchers dialed in magnetic fields and observed the atoms’ responses. The experiment, which was the first to directly observe magnetic properties that result from the particles’ motion, was reported March 30 in Nature Communications. Read More