UMD CMNS Physics S1 Color

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. The new results were published online March 16 in Physical Review Letters.

Read More

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, have made the first direct measurement that characterizes this exotic physics in a photonic platform. The research was published online Feb. 22 and featured on the cover of the March 2016 issue of 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. Read More

Gravitational Waves Detected 100 Years After Einstein’s Prediction

An international team of scientists that includes UMD physicists has opened an unprecedented new window on the universe with the first observation of ripples in the fabric of space-time. These ripples, known as gravitational waves, were generated by the colliding of two massive black holes a billion light-years away from Earth. Though such black hole collisions have long been predicted, they had never before been observed. Read More

New Material Becomes Invisible to Microwave Radiation with the Flip of a Switch

University of Maryland physicists have developed a new cloaking material that can become transparent to microwave radiation with the flip of a switch. Because many wireless communication devices rely on microwaves, the new material could be used to design more efficient communications networks. Additionally, the material has unique properties that could help bridge the gap between modern digital computers and next-generation “quantum” computers.

The new material can be selectively tuned to respond to a wide range of microwave wavelengths, making it more versatile than many previous attempts at cloaking technology. The achievement is described in a paper published on December 18, 2015 in the journal Physical Review X. The UMD researchers teamed with HYPRES, an advanced electronics company based in Elmsford, NY, on the project.

“Prior to this work, other cloaking materials were only effective at a single wavelength, which is not realistically useful,” said Daimeng Zhang, lead author of the study and a graduate student in electrical and computer engineering at UMD. “Our material is transparent across a broad range of microwave wavelengths. Also, we can turn the microwave transparency on and off. This hasn’t been explored before.”

This schematic illustrates a new self-cloaking metamaterial developed by University of Maryland physicists in collaboration with HYPRES, Inc. An array of miniature devices (circular structures) called rf-SQUIDs can become transparent to microwave radiation with the flip of a switch. At left, the material is in transparent mode and allows microwaves to travel freely. At right, the material is in opaque mode and prevents microwaves from traversing the barrier. Image credit: Sean Kelley/JQI (Click image to download hi-res version.)

This schematic illustrates a new self-cloaking metamaterial developed by University of Maryland physicists in collaboration with HYPRES, Inc. An array of miniature devices (circular structures) called rf-SQUIDs can become transparent to microwave radiation with the flip of a switch. At left, the material is in transparent mode and allows microwaves to travel freely. At right, the material is in opaque mode and prevents microwaves from traversing the barrier. Image credit: Sean Kelley/JQI (Click image to download hi-res version.)

The cloaking material developed at UMD cannot make other objects (or people) disappear. Instead, by selectively becoming transparent to microwave radiation, it can either shield or expose a target to incoming microwaves. For this reason, the researchers use the terms “auto-cloaking” or “self-cloaking” to describe the material.

“In that sense, our material could be said to work in reverse. When the transparency is turned on, any object behind it is visible to microwave detection,” said Steven Anlage, senior author of the study and a professor of physics at UMD. “But when the transparency is turned off, the material becomes a barrier and conceals anything behind it. It’s a good hider.”

The cloaking material is considered a metamaterial, or a “smart” material engineered to have properties not found in nature. Metamaterials are made of an array of “meta-atoms,” which are not atoms in the true chemical sense, but rather the smallest component parts of a metamaterial. The meta-atoms used in the UMD cloaking material are tiny devices—not much wider than a human hair—called Radio Frequency Superconducting QUantum Interference Devices (rf-SQUIDs). Each rf-SQUID exhibits the same properties as the metamaterial, meaning that the technology theoretically can be scaled up to any size.

“Previous attempts at cloaking technology could only respond to one wavelength,” said Melissa Trepanier, a co-author of the study and a graduate student in physics at UMD. “Perhaps more importantly, the wavelength could not be changed after the material was created. This meant that engineers needed to decide on—and commit to—a target wavelength prior to the design and construction phase.”

The UMD researchers solved this problem by designing the rf-SQUIDs with properties that can be tuned by varying the magnetic field applied to the material and/or the temperature of the material.

Zhang, Trepanier and Anlage co-authored the study with Oleg Mukhanov, chief technology officer of HYPRES. The research was supported by the National Science Foundation’s Grant Opportunities for Academic Liaison with Industry (GOALI) program. The GOALI program is designed to fund high-risk/high-reward research projects and enhance collaborations between academic scientists and industry.

Beyond its use for cloaking, the rf-SQUID-based metamaterial might help solve other technological challenges, including the implementation of quantum computers.

“HYPRES is very interested in the interface between quantum computing and classical digital computing, so we are looking for new technology capable of connecting the two,” Mukhanov said. “This new metamaterial has properties that are sensitive to both quantum processes and superconducting digital logic, so it would most likely be cross-compatible.”

“We’re working on the edges of what anyone has done before,” Anlage added. “It’s wild stuff, but there is a lot of potential to help develop cool new technology.”

###

This work was supported by the National Science Foundation through the Grant Opportunities for Academic Liaison with Industry (GOALI) program (Award No. ECCS-1158644). The content of this article does not necessarily reflect the views of this organization.

The research paper, “Tunable Broadband Transparency of Macroscopic Quantum Superconducting Metamaterials,” Daimeng Zhang, Melissa Trepanier, Oleg Mukhanov and Steven Anlage, was published on December 18, 2015 in the journal Physical Review X.

Media Relations Contact: Matthew Wright, 301-405-9267, This email address is being protected from spambots. You need JavaScript enabled to view it.

Sensitivity of World’s Most Sensitive Dark Matter Detector Improves

A new set of calibration techniques has once again dramatically improved the sensitivity of the Large Underground Xenon (LUX) dark matter experiment, which operates nearly a mile underground at the Sanford Underground Research Facility (SURF) in the Black Hills of South Dakota. Read More