UMD CMNS Physics S1 Color

Trapped ions and superconductors face off in quantum benchmark

debnath nature conceptAn artist's rendering of many linked trapped-ion modules. Researchers at JQI put one of their modules to the test against an IBM superconducting device. (Credit: E. Edwards/JQI)

The race to build larger and larger quantum computers is heating up, with several technologies competing for a role in future devices. Each potential platform has strengths and weaknesses, but little has been done to directly compare the performance of early prototypes. Now, researchers at the JQI have performed a first-of-its-kind benchmark test of two small quantum computers built from different technologies.

The team, working with JQI Fellow Christopher Monroe and led by postdoctoral researcher Norbert Linke, sized up their own small-scale quantum computer against a device built by IBM. Both machines use five qubits—the fundamental units of information in a quantum computer—and both machines have similar error rates. But while the JQI device relies on chains of trapped atomic ions, IBM Q uses coupled regions of superconducting material.

To make their comparison, the JQI team ran several quantum programs on the devices, each of which solved a simple problem using a series of logic gates to manipulate one or two qubits at a time. Researchers accessed the IBM device using an online interface, which allows anyone to try their hand at programming IBM Q.

Both computers have strengths and weaknesses. For example, the superconducting platform has quicker gates and may be easier to mass produce, but its man-made qubits are all slightly different and have shorter lifetimes. Monroe says that the slower gates of ions might not be a major hurdle, though. "Because there is time," Monroe says. "Trapped ion qubit lifetimes are way longer than any other type of qubit. Moreover, the ion qubits are identical, and they can be better replicated without error."

When put to the test, researchers found that the trapped-ion module was more accurate for programs that involved many pairs of qubits. Linke and Monroe attribute this to the simple fact that every qubit in their device is connected to every other—meaning that a logic gate can connect any pair of qubits. IBM Q has fewer than half the connections of its JQI counterpart, and in order to run some programs it had to shuffle information between qubits—a step that introduced errors into the calculation. When this shuffling wasn't necessary, the two computers had similar performance. "As we build larger systems, connectivity between qubits will become even more important," Monroe says.

The new study, which was recently published in Proceedings of the National Academy of Sciences, provides an important benchmark for researchers studying quantum computing. And such head-to-head comparisons will become increasingly important in the future. "If you want to buy a quantum computer, you'll need to know which one is best for your application," Linke says. "You'll need to test them in some way, and this is the first of this kind of comparison."

By Erin Marshall

"Experimental comparison of two quantum computing architectures," N.M. Linke, D. Maslov, M. Roetteler, S. Debnath, C. Figgatt, K.A. Landsman, K. Wright, C. Monroe, Proceedings of the National Academy of Sciences, 114, 3305-3310 (2017)
Norbert Linke|This email address is being protected from spambots. You need JavaScript enabled to view it.

Christopher Monroe|This email address is being protected from spambots. You need JavaScript enabled to view it.

Programmable ions set the stage for general-purpose quantum computers

The latest on HAWC and the search for high-energy gamma rays

In our own galaxy and beyond, violent collisions fling a never-ending stream of stuff at the earth, and astrophysicists are eager to learn more about the processes that produce this cosmic barrage.

Researchers from around the world have teamed up to build the High-Altitude Water Cherenkov (HAWC) gammy-ray observatory, an array of hundreds of huge water tanks on a mountain in Mexico. HAWC helps astrophysicists spot active cosmic neighborhoods by capturing the shower of particles created when high-energy packets of light smash into the earth's atmosphere.

Jordan Goodman, HAWC's lead investigator, and Dan Fiorino, a postdoctoral researcher at UMD, tell Chris Cesare about the details of the HAWC experiment and how it promises to fill some gaps in our understanding of the universe. To learn more about HAWC, please visit The collaboration is preparing to publish the first results of its search, and you can read about the details in an upcoming source catalog or a paper about high-energy gamma rays from the Crab Nebula.

This episode of Relatively Certain was produced by Chris Cesare, Sean Kelley and Emily Edwards and edited by Chris Cesare and Kate Delossantos, featuring music by Dave Depper, Podington Bear, Kevin MacLeod and Chris Zabriskie. Relatively Certain is a production of the Joint Quantum Institute and the University of Maryland, and you can find it on iTunes, Google Play or Soundcloud. 

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



Ions sync up into world's first time crystal

Consider, for a moment, the humble puddle of water. If you dive down to nearly the scale of molecules, it will be hard to tell one spot in the puddle from any other. You can shift your gaze to the left or right, or tilt your head, and the microscopic bustle will be identical—a situation that physicists call highly symmetric.

High-flying Experiments Tackle the Mysteries of Cosmic Rays

Cosmic rays are not rays at all, but highly energetic particles that zoom through space at nearly the speed of light.  The particles range in size, from subatomic protons to the atomic nuclei of elements such as carbon and boron. Scientists suspect that the particles are bits of subatomic shrapnel produced by supernovae, but could also be signatures of other cataclysmic phenomena.

Destabilized solitons perform a disappearing act

When your heart beats, blood courses through your veins in waves of pressure. These pressure waves manifest as your pulse, a regular rhythm unperturbed by the complex internal structure of the body. Scientists call such robust waves solitons, and in many ways they behave more like discrete particles than waves. Soliton theory may aid in the understanding of tsunamis, which—unlike other water waves—can sustain themselves over vast oceanic distances.