Tyler O'Neal, Staff Editor APPLICATIONS

Johns Hopkins physicist discovers material that could be a game-changer for supercomputing

Quantum supercomputers with the ability to perform complex calculations, encrypt data more securely and more quickly predict the spread of viruses, maybe within closer reach thanks to a discovery by Johns Hopkins researchers.

"We've found that a certain superconducting material contains special properties that could be the building blocks for the technology of the future," says Yufan Li, a postdoctoral fellow in the Department of Physics & Astronomy at The Johns Hopkins University and the paper's first author.

The findings will be published on October 11 in Science. CAPTION A visual representation of a qubit, which can exist simultaneously between two states. A famous example of a qubit is Schrodinger's cat, a hypothetical cat that can be both dead and alive. Similarly, a flux qubit, or a ring made of a superconducting material, can have electric current flowing both clockwise and counterclockwise at the same time. CREDIT Yufan Li{module In-article}

Today's supercomputers use bits, represented by an electrical voltage or current pulse, to store information. Bits exist in two states, either "0" or "1." Quantum supercomputers, based on the laws of quantum mechanics, use quantum bits, or qubits, which do not only use two states but a superposition of two states.

This ability to use such qubits makes quantum supercomputers much more powerful than existing supercomputers when solving certain types of problems, such as those relating to artificial intelligence, drug development, cryptography, financial modeling, and weather forecasting.

A famous example of a qubit is Schrodinger's cat, a hypothetical cat that may be simultaneously dead and alive.

"A more realistic, tangible implementation of the qubit can be a ring made of superconducting material, known as flux qubit, where two states with clockwise- and counterclockwise-flowing electric currents may exist simultaneously," says Chia-Ling Chien, Professor of Physics at The Johns Hopkins University and another author on the paper. To exist between two states, qubits using traditional superconductors require a very precise external magnetic field to be applied to each qubit, thus making it difficult to operate practically.

In the new study, Li and colleagues found that a ring of β-Bi2Pd already naturally exists between two states in the absence of an external magnetic field. Current can inherently circulate both clockwise and counterclockwise, simultaneously, through a ring of β-Bi2Pd.

Adds Li: "A ring of β-Bi2Pd already exists in the ideal state and doesn't require any additional modifications to work. This could be a game-changer."

The next step, says Li, is to look for Majorana fermions within β-Bi2Pd; Majorana fermions are particles that are also anti-particles of themselves and are needed for the next level of disruption-resistant quantum supercomputers: topological quantum supercomputers.

Majorana fermions depend on a special type of superconducting material--a so-called spin-triplet superconductor with two electrons in each pair aligning their spins in a parallel fashion--that has thus far been elusive to scientists. Now, through a series of experiments, Li and colleagues found that thin films of β-Bi2Pd have the special properties necessary for the future of quantum computing.

Scientists have yet to discover the intrinsic spin-triplet superconductor needed to advance quantum supercomputing forward, but Li is hopeful that the discovery of β-Bi2Pd's special properties, will lead to finding Majorana fermions in the material next.

"Ultimately, the goal is to find and then manipulate Majorana fermions, which is key to achieving fault-tolerant quantum computing for truly unleashing the power of quantum mechanics," says Li.

Iowa State engineers solve 50-year-old puzzle in signal processing

Tyler O'Neal, Staff Editor APPLICATIONS

Something called the fast Fourier transform is running on your cell phone right now. The FFT, as it is known, is a signal-processing algorithm that you use more than you realize. It is, according to the title of one research paper, "An algorithm the whole family can use."

Alexander Stoytchev - an associate professor of electrical and computer engineering at Iowa State University who's also affiliated with the university's Virtual Reality Applications Center, its Human-Computer Interaction graduate program and the department of computer science - says the FFT algorithm and its inverse (known as the IFFT) are at the heart of signal processing.

And, as such, "These are algorithms that made the digital revolution possible," he said. CAPTION Vladimir Sukhoy and Alexander Stoytchev, left to right, with the derivation for the ICZT algorithm in structured matrix notation -- the answer to a 50-year-old puzzle in signal processing. CREDIT Photo by Paul Easker{module In-article}

They're a part of streaming music, making a cell phone call, browsing the internet or taking a selfie.

The FFT algorithm was published in 1965. Four years later, researchers developed a more versatile, generalized version called the chirp z-transform (CZT). But a similar generalization of the inverse FFT algorithm has gone unsolved for 50 years.

Until that is, Stoytchev and Vladimir Sukhoy - an Iowa State doctoral student co-majoring in electrical and computer engineering, and human-computer interaction - worked together to come up with the long-sought algorithm, called the inverse chirp z-transform (ICZT).

Like all algorithms, it's a step-by-step process that solves a problem. In this case, it maps the output of the CZT algorithm back to its input. The two algorithms are a little like a series of two prisms - the first separates the wavelengths of white light into a spectrum of colors and the second reverses the process by combining the spectrum back into white light, Stoytchev explained.

Stoytchev and Sukhoy describe their new algorithm in a paper recently published online by Scientific Reports. Their paper shows that the algorithm matches the computational complexity or speed of its counterpart, that it can be used with exponentially decaying or growing frequency components (unlike the IFFT) and that it has been tested for numerical accuracy.

Stoytchev said he stumbled on the idea to attempt to formulate the missing algorithm while looking for analogies to help the graduate students in his "Computational Perception" course understand the fast Fourier transform. He read a lot of the signal-processing literature and couldn't find anything about the inverse to the related chirp z-transform.

"I got curious," he said. "Is that because they couldn't explain it, or is it because it doesn't exist? It turned out it didn't exist."

And so he decided to try to find a fast inverse algorithm.

Sukhoy said the inverse algorithm is a harder problem than the original, forward algorithm and so "we needed better precision and more powerful computers to attack it." He also said a key was seeing the algorithm within the mathematical framework of structured matrices.

Even then, there were lots of computer test runs "to show everything was working - we had to convince ourselves that this could be done."

It took courage to keep attacking the problem, said James Oliver, director of Iowa State's Student Innovation Center and former director of the university's Virtual Reality Applications Center. Stoytchev and Sukhoy acknowledge Oliver in their paper "for creating the research environment in which we could pursue this work over the past three years."

Oliver said Stoytchev earned his support for a mathematical and computational challenge that hadn't been solved for 50 years: "Alex has always impressed me with his passion and commitment to take on big research challenges. There is always a risk in research and it takes courage to devote years of hard work to a fundamental problem. Alex is a gifted and fearless researcher."

How do the strongest magnets in the universe form?

Tyler O'Neal, Staff Editor APPLICATIONS

German-British research team simulates basic conditions for the formation of magnetic stars

How do some neutron stars become the strongest magnets in the Universe? A German-British team of astrophysicists has found a possible answer to the question of how these so-called magnetars form. The researchers used large supercomputer simulations to demonstrate how the merger of two stars creates strong magnetic fields. If such stars explode in supernovae, magnetars could result. Scientists from Heidelberg University, the Max Planck Society, the Heidelberg Institute for Theoretical Studies, and the University of Oxford were involved in the research. The simulation marks the birth of a magnetic star such as Tau Scorpii. The image is a cut through the orbital plane where the colouring indicates the strength of the magnetic field and the light hatching reflects the direction of the magnetic field line. | © Ohlmann/Schneider/Röpke{module In-article}

Our Universe is threaded by magnetic fields. The Sun, for example, has an envelope in which convection continuously generates magnetic fields. "Even though massive stars have no such envelopes, we still observe a strong, large-scale magnetic field at the surface of about ten percent of them," explains Dr Fabian Schneider from the Centre for Astronomy of Heidelberg University, who is the first author of the study in "Nature". Although such fields were already discovered in 1947, their origin has remained elusive so far.

Over a decade ago, scientists suggested that strong magnetic fields are produced when two stars collide. "But until now, we weren't able to test this hypothesis because we didn't have the necessary computational tools," says Dr. Sebastian Ohlmann from the supercomputing center of the Max Planck Society in Garching near Munich. This time, the researchers used the AREPO code, a highly dynamic simulation code running on compute clusters of the Heidelberg Institute for Theoretical Studies (HITS), to explain the properties of Tau Scorpii (τ Sco), a magnetic star located 500 light-years from Earth.

Already in 2016, Fabian Schneider and Philipp Podsiadlowski from the University of Oxford realized that τ Sco is a so-called blue straggler. Blue stragglers are the product of merged stars. "We assume that Tau Scorpii obtained its strong magnetic field during the merger process," explains Prof. Dr Philipp Podsiadlowski. Through its supercomputer simulations of τ Sco, the German-British research team has now demonstrated that strong turbulence during the merger of two stars can create such a field.

Stellar mergers are relatively frequent: Scientists assume that about ten percent of all massive stars in the Milky Way are the products of such processes. This is in good agreement with the occurrence rate of magnetic massive stars, according to Dr Schneider. Astronomers think that these very stars could form magnetars when they explode in supernovae.

This may also happen to τ Sco when it explodes at the end of its life. The supercomputer simulations suggest that the magnetic field generated would be sufficient to explain the exceptionally strong magnetic fields in magnetars. "Magnetars are thought to have the strongest magnetic fields in the Universe - up to one hundred million times stronger than the strongest magnetic field ever produced by humans," says Prof. Dr Friedrich Röpke from HITS. The results were published in "Nature".