From Columbia University Fu Foundation School of Engineering and Applied Science (US) via : “Shrinking qubits for quantum computing with atom-thin materials” 

From Columbia University Fu Foundation School of Engineering and Applied Science (US)

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At Columbia University (US)


November 30, 2021

Optical micrograph of the team’s superconducting qubit chip that is 1000 times smaller than others made with conventional fabrication techniques. Credit: Abhinandan Antony / Columbia Engineering.

For quantum computers to surpass their classical counterparts in speed and capacity, their qubits—which are superconducting circuits that can exist in an infinite combination of binary states—need to be on the same wavelength. Achieving this, however, has come at the cost of size. Whereas the transistors used in classical computers have been shrunk down to nanometer scales, superconducting qubits these days are still measured in millimeters—one millimeter is one million nanometers.

Combine qubits together into larger and larger circuit chips, and you end up with, relatively speaking, a big physical footprint, which means quantum computers take up a lot of physical space. These are not yet devices we can carry in our backpacks or wear on our wrists.

To shrink qubits down while maintaining their performance the field needs a new way to build the capacitors that store the energy that “powers” the qubits. In collaboration with Raytheon BBN Technologies, Wang Fong-Jen Professor James Hone’s lab at Columbia Engineering recently demonstrated a superconducting qubit capacitor built with 2D materials that’s a fraction of previous sizes.

To build qubit chips previously, engineers have had to use planar capacitors, which set the necessary charged plates side by side. Stacking those plates would save space, but the metals used in conventional parallel capacitors interfere with qubit information storage. In the current work, published on November 18 in Nano Letters, Hone’s Ph.D. students Abhinandan Antony and Anjaly Rajendra sandwiched an insulating layer of boron nitride between two charged plates of superconducting niobium dieselenide. These layers are each just a single atom thick and held together by van der Waals forces, the weak interaction between electrons. The team then combined their capacitors with aluminum circuits to create a chip containing two qubits with an area of 109 square micrometers and just 35 nanometers thick—that’s 1000 times smaller than chips produced under conventional approaches.

When they cooled their qubit chip down to just above absolute zero, the qubits found the same wavelength. The team also observed key characteristics that showed that the two qubits were becoming entangled and acting as a single unit-a phenomenon known as quantum coherence; that would mean the qubit’s quantum state could be manipulated and read out via electrical pulses, said Hone. The coherence time was short—a little over 1 microsecond, compared to about 10 microseconds for a conventionally built coplanar capacitor, but this is only a first step in exploring the use of 2D materials in this area, he said.

Separate work published in August from researchers at The Massachusetts Institute of Technology (US) also took advantage of niobium diselenide and boron nitride to build parallel-plate capacitors for qubits. The devices studied by the MIT team showed even longer coherence times—up to 25 microseconds—indicating that there is still room to further improve performance.

From here, Hone and his team will continue refining their fabrication techniques and test other types of 2D materials to increase coherence times, which reflect how long the qubit is storing information. New device designs should be able to shrink things down even further, said Hone, by combining the elements into a single van der Waals stack or by deploying 2D materials for other parts of the circuit.

“We now know that 2D materials may hold the key to making quantum computers possible,” Hone said. “It is still very early days, but findings like these will spur researchers worldwide to consider novel applications of 2D materials. We hope to see a lot more work in this direction going forward.”

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The Fu Foundation School of Engineering and Applied Science (US) is the engineering and applied science school of Columbia University (US). It was founded as the School of Mines in 1863 and then the School of Mines, Engineering and Chemistry before becoming the School of Engineering and Applied Science. On October 1, 1997, the school was renamed in honor of Chinese businessman Z.Y. Fu, who had donated $26 million to the school.

The Fu Foundation School of Engineering and Applied Science maintains a close research tie with other institutions including National Aeronautics and Space Administration(US), IBM, Massachusetts Institute of Technology(US), and The Earth Institute. Patents owned by the school generate over $100 million annually for the university. Faculty and alumni are responsible for technological achievements including the developments of FM radio and the maser.

The School’s applied mathematics, biomedical engineering, computer science and the financial engineering program in operations research are very famous and ranked high. The current faculty include 27 members of the National Academy of Engineering (US) and one Nobel laureate. In all, the faculty and alumni of Columbia Engineering have won 10 Nobel Prizes in physics, chemistry, medicine, and economics.

The school consists of approximately 300 undergraduates in each graduating class and maintains close links with its undergraduate liberal arts sister school Columbia College which shares housing with SEAS students.

Original charter of 1754

Included in the original charter for Columbia College was the direction to teach “the arts of Number and Measuring, of Surveying and Navigation […] the knowledge of […] various kinds of Meteors, Stones, Mines and Minerals, Plants and Animals, and everything useful for the Comfort, the Convenience and Elegance of Life.” Engineering has always been a part of Columbia, even before the establishment of any separate school of engineering.

An early and influential graduate from the school was John Stevens, Class of 1768. Instrumental in the establishment of U.S. patent law. Stevens procured many patents in early steamboat technology; operated the first steam ferry between New York and New Jersey; received the first railroad charter in the U.S.; built a pioneer locomotive; and amassed a fortune, which allowed his sons to found the Stevens Institute of Technology.

When Columbia University first resided on Wall Street, engineering did not have a school under the Columbia umbrella. After Columbia outgrew its space on Wall Street, it relocated to what is now Midtown Manhattan in 1857. Then President Barnard and the Trustees of the University, with the urging of Professor Thomas Egleston and General Vinton, approved the School of Mines in 1863. The intention was to establish a School of Mines and Metallurgy with a three-year program open to professionally motivated students with or without prior undergraduate training. It was officially founded in 1864 under the leadership of its first dean, Columbia professor Charles F. Chandler, and specialized in mining and mineralogical engineering. An example of work from a student at the School of Mines was William Barclay Parsons, Class of 1882. He was an engineer on the Chinese railway and the Cape Cod and Panama Canals. Most importantly he worked for New York, as a chief engineer of the city’s first subway system, the Interborough Rapid Transit Company. Opened in 1904, the subway’s electric cars took passengers from City Hall to Brooklyn, the Bronx, and the newly renamed and relocated Columbia University in Morningside Heights, its present location on the Upper West Side of Manhattan.

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Columbia University was founded in 1754 as King’s College by royal charter of King George II of England. It is the oldest institution of higher learning in the state of New York and the fifth oldest in the United States.

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Columbia University is one of the world’s most important centers of research and at the same time a distinctive and distinguished learning environment for undergraduates and graduate students in many scholarly and professional fields. The University recognizes the importance of its location in New York City and seeks to link its research and teaching to the vast resources of a great metropolis. It seeks to attract a diverse and international faculty and student body, to support research and teaching on global issues, and to create academic relationships with many countries and regions. It expects all areas of the University to advance knowledge and learning at the highest level and to convey the products of its efforts to the world.

Columbia University is a private Ivy League research university in New York City. Established in 1754 on the grounds of Trinity Church in Manhattan Columbia is the oldest institution of higher education in New York and the fifth-oldest institution of higher learning in the United States. It is one of nine colonial colleges founded prior to the Declaration of Independence, seven of which belong to the Ivy League. Columbia is ranked among the top universities in the world by major education publications.

Columbia was established as King’s College by royal charter from King George II of Great Britain in reaction to the founding of Princeton College. It was renamed Columbia College in 1784 following the American Revolution, and in 1787 was placed under a private board of trustees headed by former students Alexander Hamilton and John Jay. In 1896, the campus was moved to its current location in Morningside Heights and renamed Columbia University.

Columbia scientists and scholars have played an important role in scientific breakthroughs including brain-computer interface; the laser and maser; nuclear magnetic resonance; the first nuclear pile; the first nuclear fission reaction in the Americas; the first evidence for plate tectonics and continental drift; and much of the initial research and planning for the Manhattan Project during World War II. Columbia is organized into twenty schools, including four undergraduate schools and 15 graduate schools. The university’s research efforts include the Lamont–Doherty Earth Observatory, the Goddard Institute for Space Studies, and accelerator laboratories with major technology firms such as IBM. Columbia is a founding member of the Association of American Universities and was the first school in the United States to grant the M.D. degree. With over 14 million volumes, Columbia University Library is the third largest private research library in the United States.

The university’s endowment stands at $11.26 billion in 2020, among the largest of any academic institution. As of October 2020, Columbia’s alumni, faculty, and staff have included: five Founding Fathers of the United States—among them a co-author of the United States Constitution and a co-author of the Declaration of Independence; three U.S. presidents; 29 foreign heads of state; ten justices of the United States Supreme Court, one of whom currently serves; 96 Nobel laureates; five Fields Medalists; 122 National Academy of Sciences members; 53 living billionaires; eleven Olympic medalists; 33 Academy Award winners; and 125 Pulitzer Prize recipients.