Sensing Atoms Caught in Ripples of Light

Optical fibers are ubiquitous, carrying light wherever it is needed. These glass tunnels are the high-speed railway of information transit, moving data at incredible speeds over tremendous distances.  

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Space-based Experiment Will Tackle the Mysteries of Cosmic Rays

On August 14, 2017, a groundbreaking University of Maryland-designed cosmic ray detector will travel to the International Space Station (ISS) aboard the SpaceX-12 Commercial Resupply Service mission. The instrument, named ISS Cosmic Ray Energetics and Mass (ISS-CREAM), is roughly the size of a refrigerator and will remain installed on the ISS’ Japanese Experiment Module for at least three years. The massive amounts of data ISS-CREAM will collect could reveal new details about the origin and diversity of cosmic rays.

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Simulating the Quantum World with Electron Traps

Quantum behavior plays a crucial role in novel and emergent material properties, such as superconductivity and magnetism. Unfortunately, it is still impossible to calculate the underlying quantum behavior, let alone fully understand it. Scientists of QuTech, the Kavli Institute of Nanoscience in Delft and TNO, in collaboration with ETH Zurich and the University of Maryland, have now succeeded in building an "artificial material" that mimics this type of quantum behavior on a small scale. In doing so, they have laid the foundations for new insights and potential applications. Their work is published today in Nature.

Over the past century, an increased understanding of semiconductor materials has led to many technological improvements, such as computer chips becoming ever faster and smaller. We are, however, gradually reaching the limits of Moore's Law, the trend that predicts a doubling in computing power for half the price every two years. But this prediction ignores the possibility that computers might harness quantum physics.

"There is so much physics left to discover if we truly want to understand materials on the very smallest scale," says Lieven Vandersypen, a professor at TU Delft in the Netherlands and the lead experimentalist on the new paper. And that new physics is set to bring even more new technology with it. "The difficulty is that, at this scale, quantum theory determines the behavior of electrons and it is virtually impossible to calculate this behavior accurately even for just a handful of electrons, using even the most powerful supercomputers," Vandersypen says.

Scientists are now combining the power of the semiconductor industry with their knowledge of quantum technology in order to mimic the behavior of electrons in materials—a technique known as quantum simulation. "I hope that, in the near future, this will enable us to learn so much about materials that we can open some important doors in technology, such as the design of superconductors at room temperature, to make possible loss-free energy transport over long distances, for example," Vandersypen says.

qchipcredMicrograph image of semiconductor quantum chip with lattice visualization above. By applying voltages on "gates" (white lines), electrons (red and blue spheres) can be captured in quantum dots. The potential landscape (white wave) determines the locations where the electrons are captured. (Credit: Graphic by E. Edwards/JQI, micrograph courtesy of the authors.)

Mimicking nature

It has long been known that individual electrons can be confined to small regions on a chip, known as quantum dots. There are, in principle, suitable for researching the behavior and interactions of electrons in materials. The captured electrons can move, or tunnel, between the quantum dots in a controlled way, while they interact through the repulsion of their negative charges. "Processes like these in quantum dots, cooled to a fraction of a degree above absolute zero, are perfectly suitable for simulating the electronic properties of new materials," says Toivo Hensgens, a graduate student at TU Delft and the lead author of the paper.

In practice, it is a major challenge to control the electrons in quantum dots so precisely that the underlying physics becomes visible. Imperfections in the quantum chips and inefficient methods of controlling the electrons in the dots have made this a particularly hard nut to crack.

Quantum equipment

Researchers have now demonstrated a method that is both effective and can be scaled up to larger numbers of quantum dots. The number of electrons in each quantum dot can be set from 0 to 4 and the chance of tunnelling between neighbouring dots can be varied from negligible to the point at which neighbouring dots actually become one large dot. "We use voltages to distort the (potential) landscape that the electrons sense," explains Hensgens. "That voltage determines the number of electrons in the dots and the relative interactions between them."

In a quantum chip with three quantum dots, the QuTech team has demonstrated that they are capable of simulating a series of material processes experimentally. But the most important result is the method that they have demonstrated. "We are now easily able to  add more quantum dots with electrons and control the potential landscape in such a way that we can ultimately simulate very large and interesting quantum processes," Hensgens says.

The Vandersypen team aims to progress towards more quantum dots as soon as possible. To achieve that, he and his colleagues have entered a close collaboration with chipmaker Intel. "Their knowledge and expertise in semiconductor manufacturing combined with our deep understanding of quantum control offers opportunities that are now set to bear fruit," he says.

This story was prepared by the Delft University of Technology (TU Delft) and adapted with permission. The experiments described were performed at TU Delft, with theoretical and numerical contributions from JQI Fellow and Condensed Matter Theory Center Director Sankar Das Sarma and JQI postdoctoral researcher Xiao Li.


Research Contacts:

Professor Lieven Vandersypen
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Dr. Xiao Li
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Proposed LHC Experiment Would Spot Invisible, Long-lived Particles

More than 300 feet underground, looping underneath both France and Switzerland on the outskirts of Geneva, a 16-mile-long ring called the Large Hadron Collider (LHC) smashes protons together at nearly the speed of light. Sifting through the wreckage, scientists have made some profound discoveries about the fundamental nature of our universe.

CERNcredThe Large Hadron Collider (Credit: Maximilien Brice/CERN/CC BY-SA 4.0)

But what if all that chaos underground is shrouding subtle hints of new physics? David Curtin, a postdoctoral researcher at the Maryland Center for Fundamental Physics here at UMD, has an idea for a detector that could be built at the surface—far away from the noise and shrapnel of the main LHC experiments. The project, which he and his collaborators call MATHUSLA, may resolve some of the mysteries that are lingering behind our best theories.

This episode of the Relatively Certain podcast was produced by Chris Cesare, Emily Edwards, Sean Kelley and Kate Delossantos. It features music by Dave Depper, Podington Bear, Broke for Free, Chris Zabriskie and the LHCsound project. Relatively Certain is a production of the Joint Quantum Institute, a research partnership between the University of Maryland and the National Institute of Standards and Technology, and you can find it on iTunes, Google Play or Soundcloud.


To listen now, click here and a player will open.

For more on this topic, read this Quanta Magazine article. 


Atomic cousins team up in early quantum networking node

Large-scale quantum computers, which are an active pursuit of many university labs and tech giants, remain years away. But that hasn’t stopped some scientists from thinking ahead, to a time when quantum computers might be linked together in a network or a single quantum computer might be split up across many interconnected nodes.

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