UMD CMNS Physics S1 Color

Proximity Effect Realized in Topological Kondo Insulator

Superconductivity in the topologically protected surface states of a three-dimensional topological insulator has been predicted to be a promising platform for exploring exotic quantum states such as Majorana fermion excitations. Although previous efforts have focused on the superconducting proximity effect in bilayer structures between a superconductor and a chalcogenide topological insulator, suppressing the conducting bulk contribution and securing high interfacial transparency between a superconductor and a topological insulator have been major experimental bottlenecks to demonstrating induced superconductivity. Researchers from the Center for Nanophysics and Advanced Materials led by Ichiro Takeuchi, in collaboration with Richard Greene and Johnpierre Paglione, have now demonstrated a supercurrent to flow through the surface layer of the topological Kondo insulator material samarium hexaboride (SmB6) via in situ deposition of a superconducting layer on SmB6 thin films. Published in Physical Review X, this study provides a unique insight into the surface state of SmB6, and marks an important stepping stone for pursuing novel quantum phenomena using thin-film topological insulator devices.

Programmable ions set the stage for general-purpose quantum computers

Quantum computers promise speedy solutions to some difficult problems, but building large-scale, general-purpose quantum devices is a problem fraught with technical challenges.

To date, many research groups have created small but functional quantum computers. By combining a handful of atoms, electrons or superconducting junctions, researchers now regularly demonstrate quantum effects and run simple quantum algorithms—small programs dedicated to solving particular problems.

But these laboratory devices are often hard-wired to run one program or limited to fixed patterns of interactions between their quantum constituents. Making a quantum computer that can run arbitrary algorithms requires the right kind of physical system and a suite of programming tools. Atomic ions, confined by fields from nearby electrodes, are among the most promising platforms for meeting these needs.

In a paper published as the cover story in Nature on August 4, researchers working with Christopher Monroe, a Fellow of the Joint Quantum Institute and the Joint Center for Quantum Information and Computer Science (link is external) at the University of Maryland, introduced the first fully programmable and reconfigurable quantum computer module (link is external). The new device, dubbed a module because of its potential to connect with copies of itself, takes advantage of the unique properties offered by trapped ions to run any algorithm on five quantum bits, or qubits—the fundamental unit of information in a quantum computer.

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Trailing the Photons from Neutron Decay

A high-precision measurement of the photons emitted by neutron decays brings researchers closer to a new test of the standard model. The research, with contributions from UMD Researchers including, Research Scientist and UMD lead  Herbert Breuer, Professor Elizabeth Beise, Alumna Kristin Kiriluk and Affiliate Professors Jeff Nico and Pieter Mumm, was highlighted in APS Physics and is published in Physical Review Letters.

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Ultra-cold atoms may wade through quantum friction

Theoretical physicists studying the behavior of ultra-cold atoms have discovered a new source of friction, dispensing with a century-old paradox in the process. Their prediction, which experimenters may soon try to verify, was reported recently in Physical Review Letters.

The friction afflicts certain arrangements of atoms in a Bose-Einstein Condensate (BEC), a quantum state of matter in which the atoms behave in lockstep. In this state, well-tuned magnetic fields can cause the atoms to attract one another and even bunch together, forming a single composite particle known as a soliton.

Solitons appear in many areas of physics and are exceptionally stable. They can travel freely, without losing energy or dispersing, allowing theorists to treat them like everyday, non-quantum objects. Solitons composed of photons—rather than atoms—are even used for communication over optical fibers.

Studying the theoretical properties of solitons can be a fruitful avenue of research, notes Dmitry Efimkin, the lead author of the paper and a former JQI postdoctoral researcher now at the University of Texas at Austin. “Friction is very fundamental, and quantum mechanics is now quite a well-tested theory,” Efimkin says. “This work investigates the problem of quantum friction for solitons and marries these two fundamental areas of research.”

Efimkin, along with JQI Fellow Victor Galitski and Johannes Hofmann, a physicist at the University of Cambridge, sought to answer a basic question about soliton BECs: Does an idealized model of a soliton have any intrinsic friction?

Prior studies seemed to say no. Friction arising from billiard-ball-like collisions between a soliton and stray quantum particles was a possibility, but the mathematics prohibited it. For a long time, then, theorists believed that the soliton moved through its cloudy quantum surroundings essentially untouched.

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Dormant Black Hole Eats Star, Becomes X-ray Flashlight

A team of University of Michigan and University of Maryland researchers, including Physics' Lixin Dai, is the first to catch x-ray echoes of a tidal disruption event. Their paper, “Relativistic Reverberation in the Accretion Flow of a Tidal Disruption Event,” is published in  Nature.

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