Tyler O'Neal, Staff Editor HEALTH

Dutch researchers show how to build a two-dimensional array of qubits to function as a quantum processor

The heart of any computer, its central processing unit, is built using semiconductor technology, which is capable of putting billions of transistors onto a single chip. Now, researchers from the group of Menno Veldhorst at QuTech, a collaboration between TU Delft and TNO, have shown that this technology can be used to build a two-dimensional array of qubits to function as a quantum processor. Their work, a crucial milestone for scalable quantum technology, was published today in an academic journal.

Quantum supercomputers have the potential to solve problems that are impossible to address with classical computers. Whereas current quantum devices hold tens of qubits – the basic building block of quantum technology – a future universal quantum supercomputer capable of running any quantum algorithm will likely consist of millions to billions of qubits. Quantum dot qubits hold the promise to be a scalable approach as they can be defined using standard semiconductor manufacturing techniques. Veldhorst said, "By putting four such qubits in a two-by-two grid, demonstrating universal control over all qubits, and operating a quantum circuit that entangles all qubits, we have made an important step forward in realizing a scalable approach for quantum computation."  Menno Veldhorst and Nico Hendrickx standing next to the setup hosting the germanium quantum processor.

An entire quantum processor

Electrons trapped in quantum dots, semiconductor structures of only a few tens of nanometres in size, have been studied for more than two decades as a platform for quantum information. Despite all promises, scaling beyond two-qubit logic has remained elusive. To break this barrier, the groups of Menno Veldhorst and Giordano Scappucci decided to take an entirely different approach and started to work with holes (i.e. missing electrons) in germanium. Using this approach, the same electrodes needed to define the qubits could also be used to control and entangle them. ‘No large additional structures have to be added next to each qubit such that our qubits are almost identical to the transistors in a computer chip,’ says Nico Hendrickx, a graduate student in the group of Menno Veldhorst and first author of the article. ‘Furthermore, we have obtained excellent control and can couple qubits at will, allowing us to program one, two, three, and four-qubit gates, promising highly compact quantum circuits." 

2D is key

After successfully creating the first germanium quantum dot qubit in 2019, the number of qubits on their chips has doubled every year. "Four qubits by no means make a universal quantum computer, of course," Veldhorst commented. "But by putting the qubits in a two-by-two grid we now know how to control and couple qubits along with different directions." Any realistic architecture for integrating large numbers of qubits requires them to be interconnected along two dimensions.

Germanium as a highly versatile platform

Demonstrating four-qubit logic in germanium defines the state-of-the-art for the field of quantum dots and marks an important step toward dense, and extended two-dimensional semiconductor qubit grids. Next to its compatibility with advanced semiconductor manufacturing, germanium is also a highly versatile material. It has exciting physics properties such as spin-orbit coupling and it can make contact with materials like superconductors. Germanium is therefore considered an excellent platform in several quantum technologies. Veldhorst said, "Now that we know how to manufacture germanium and operate an array of qubits, the germanium quantum information route can truly begin."

Event Horizon Telescope reveals magnetic structures near supermassive black hole

Tyler O'Neal, Staff Editor HEALTH

Work gives clues about how powerful jets are driven

A new view of the region closest to the supermassive black hole at the center of the galaxy Messier 87 (M87) has shown important details of the magnetic fields close to the black hole and hints about how powerful jets of material can originate in that region.

A worldwide team of astronomers using the Event Horizon Telescope, a collection of eight telescopes, including the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, measured a signature of magnetic fields -- called polarization -- around the black hole. Polarization is the orientation of the electric fields in light and radio waves and it can indicate the presence and alignment of magnetic fields.

"We are now seeing the next crucial piece of evidence to understand how magnetic fields behave around black holes, and how activity in this very compact region of space can drive powerful jets," said Monika Mościbrodzka, Coordinator of the EHT Polarimetry Working Group and Assistant Professor at Radboud University in the Netherlands.

New images with the EHT and ALMA allowed scientists to map magnetic field lines near the edge of M87's black hole. That same black hole is the first ever to be imaged -- by the EHT in 2019. That image revealed a bright ring-like structure with a dark central region -- the black hole's shadow. The newest images are a key to explaining how M87, 50 million light-years from Earth, can launch energetic jets from its core. This composite image shows three radio-telescope views of the central region of the galaxy Messier 87 (M87), where a jet of fast-moving particles is ejected from the galaxy's core. In these images, the lines indicate polarization -- the alignment of the electric fields in the radio waves coming from the object. The polarization is a signature of the magnetic fields. The ALMA image shows the inner 6000 light-years of the jet. The image from the National Science Foundation's Very Long Baseline Array (VLBA) zooms down to show the inner one light-year of the jet, and the EHT image shows the region closest to the supermassive black hole at the galaxy's core. Labels indicate the observing frequency in GigaHertz (GHz) and the distance indicated by the scale bar below the frequency. Combined, these images allow astronomers to study the structure of magnetic fields from very close to the black hole to thousands of light-years outward from it. Credit: EHT Collaboration; Goddi et al., ALMA (ESO/NAOJ/NRAO); Kravchenko et al.; J. C. Algaba, I. Martí-Vidal, NRAO/AUI/NSF.

The black hole at M87's center is more than 6 billion times more massive than the Sun. Material drawn inward forms a rotating disk -- called an accretion disk -- closely orbiting the black hole. Most of the material in the disk falls into the black hole, but some surrounding particles escape and are ejected far out into space in jets moving at nearly the speed of light.

"The newly published polarized images are key to understanding how the magnetic field allows the black hole to 'eat' matter and launch powerful jets," said Andrew Chael, a NASA Hubble Fellow at the Princeton Center for Theoretical Science and the Princeton Gravity Initiative in the U.S.

The scientists compared the new images that showed the magnetic field structure just outside the black hole with supercomputer simulations based on different theoretical models. They found that only models featuring strongly magnetized gas can explain what they are seeing at the event horizon.

"The observations suggest that the magnetic fields at the black hole's edge are strong enough to push back on the hot gas and help it resist gravity's pull. Only the gas that slips through the field can spiral inwards to the event horizon," explained Jason Dexter, Assistant Professor at the University of Colorado Boulder and Coordinator of the EHT Theory Working Group.

To make the new observations, the scientists linked eight telescopes around the world -- including ALMA -- to create a virtual Earth-sized telescope, the EHT. The impressive resolution obtained with the EHT is equivalent to that needed to measure the length of a credit card on the surface of the Moon.

This resolution allowed the team to directly observe the black hole shadow and the ring of light around it, with the new image clearly showing that the ring is magnetized. The results are published in two papers in the Astrophysical Journal Letters by the EHT collaboration. The research involved more than 300 researchers from multiple organizations and universities worldwide.

A third paper also was published in the same volume of The Astrophysical Journal Letters, based on data from ALMA, lead by Ciriaco Goddi, a scientist at Radboud University and Leiden Observatory, the Netherlands.

"The combined information from the EHT and ALMA allowed scientists to investigate the role of magnetic fields from the vicinity of the event horizon to far beyond the core of the galaxy, along its powerful jets extending thousands of light-years," Goddi said.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

The EHT collaboration involves more than 300 researchers from Africa, Asia, Europe, North and South America. The international collaboration is working to capture the most detailed black hole images ever obtained by creating a virtual Earth-sized telescope. Supported by considerable international investment, the EHT links existing telescopes using novel systems -- creating a fundamentally new instrument with the highest angular resolving power that has yet been achieved.

The individual telescopes involved are ALMA, APEX, the Institut de Radioastronomie Millimetrique (IRAM) 30-meter Telescope, the IRAM NOEMA Observatory, the James Clerk Maxwell Telescope (JCMT), the Large Millimeter Telescope (LMT), the Submillimeter Array (SMA), the Submillimeter Telescope (SMT), the South Pole Telescope (SPT), the Kitt Peak Telescope, and the Greenland Telescope (GLT).

The EHT consortium consists of 13 stakeholder institutes: the Academia Sinica Institute of Astronomy and Astrophysics, the University of Arizona, the University of Chicago, the East Asian Observatory, Goethe-Universitaet Frankfurt, Institut de Radioastronomie Millimétrique, Large Millimeter Telescope, Max Planck Institute for Radio Astronomy, MIT Haystack Observatory, National Astronomical Observatory of Japan, Perimeter Institute for Theoretical Physics, Radboud University and the Smithsonian Astrophysical Observatory.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning, and operation of ALMA.

Using Facebook built AI, University of Rochester prof maps how the brain understands sentences

Tyler O'Neal, Staff Editor HEALTH

Have you ever wondered why you are able to hear a sentence and understand its meaning - given that the same words in a different order would have an entirely different meaning? New research involving neuroimaging and A.I., describes the complex network within the brain that comprehends the meaning of a spoken sentence.

"It has been unclear whether the integration of this meaning is represented in a particular site in the brain, such as the anterior temporal lobes, or reflects a more network-level operation that engages multiple brain regions," said Andrew Anderson, Ph.D., research assistant professor in the University of Rochester Del Monte Institute for Neuroscience and lead author on of the study which was published in the Journal of Neuroscience. "The meaning of a sentence is more than the sum of its parts. Take a very simple example - 'the car ran over the cat' and 'the cat ran over the car' - each sentence has exactly the same words, but those words have a totally different meaning when reordered."

The study is an example of how the application of artificial neural networks, or A.I., is enabling researchers to unlock the extremely complex signaling in the brain that underlies functions such as processing language. The researchers gather brain activity data from study participants who read sentences while undergoing fMRI. These scans showed activity in the brain spanning across a network of different regions - anterior and posterior temporal lobes, inferior parietal cortex, and inferior frontal cortex. Using the computational model InferSent - an A.I. model developed by Facebook trained to produce unified semantic representations of sentences - the researchers were able to predict patterns of fMRI activity reflecting the encoding of sentence meaning across those brain regions. Say what you see in this picture out loud - "The cat ran over the car." A.I. is helping researchers unlock how your brain knows that sentence is different than - "The car ran over the cat."

"It's the first time that we've applied this model to predict brain activity within these regions, and that provides new evidence that contextualized semantic representations are encoded throughout a distributed language network, rather than at a single site in the brain."

Anderson and his team believe the findings could be helpful in understanding clinical conditions. "We're deploying similar methods to try to understand how language comprehension breaks down in early Alzheimer's disease. We are also interested in moving the models forward to predict brain activity elicited as language is produced. The current study had people read sentences, in the future we're interested in moving forward to predict brain activity as people might speak sentences."