From The Harvard Gazette: “Unlocking potential of quantum technologies”
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March 23, 2022
Yahya Chaudhry
Harvard Researcher Unlocks Potential of Quantum Technologies
Chemical biology professor works to crack secrets of new states of matter.
Throughout human history, most of our efforts to store information, from knots and oracle bones to bamboo markings and the written word, boil down to two techniques: using characters or shapes to represent information. Today, huge amounts of information are stored on silicon wafers with zeros and ones, but a new material at the border of quantum chemistry and quantum physics could enable vast improvements in storage.
Suyang Xu, assistant professor of chemical biology, is tying quantum mechanical “knots” in topological materials, which may be the key to unlocking the potential of quantum technologies to store and process vast arrays of information and bring game-changing advances in a variety of fields.
“Imagine a rope identified by a number of knots,” Xu said. “No matter how much the shape of the rope is changed, the number of knots — known as the topological number — cannot be changed without altering its fundamental identity by adding or undoing knots.” It is this robustness that potentially makes topological materials particularly useful.
Xu, who took his undergraduate degree in China, first encountered topological materials when he started graduate school in physics at Princeton University in 2008 when the materials were first being created. Xu’s research interests involve electronic and optical properties in quantum matters, such as topological and broken symmetry states.
Topological materials move electrons along their surfaces and edges without any friction or loss making them promising materials for super-high-speed electronics like quantum computers. Such devices have the potential to be more powerful than existing computers because their quantum bits, referred to as “qubits,” take advantage of two properties of quantum states —superposition and entanglement — to encode information.
However, quantum states are delicate and when they are perturbed can lead to decoherence, falling out of sync and losing stored information. Because topological materials are robust and resist perturbation they could be used to build more resilient and longer-lasting qubits.
Xu’s physics background and experimental chemistry experience enable him to test quantum theories in the real world. “Even though physicists and chemists both study materials, physicists tend to look at them more as abstract equations, while chemists engage with their emergent properties,” Xu said. “Since I have a pure physics background and speak the language of chemistry, I can translate difficult theories into real space.”
With a few well-reasoned assumptions and some innovative techniques, Xu and his team bridge the gap the between quantum physics and chemistry, testing theories with materials. First, they predict which materials may realize topological properties. The chemical formulas for the elements in such materials do not provide adequate insight; Xu is also interested in their macroscopic properties.
“If I were to study water, steam, and ice only by looking at their H20 equation, I would learn nothing about their different properties.” Xu said. “As a chemist, I am trying to find certain elements and organize them microscopically, so that they can produce a topological property.”
Xu’s lab then tests current theories about chemical reactions against experimental data to expand the map of topological materials. Using specialized refrigerators in which atoms and molecules are cooled to temperatures just above absolute zero, at which they become highly controllable and more visible, Xu and his team test the flow of electrons through materials with currents.
They are also interested in the optical properties of materials, testing to see their interaction with light. The team fires photons at the materials and gathers quantum mechanical topological data based on how light scatters, reflects, and transmits. Xu has already yielded strong evidence for theoretical particles that answers one of the most vexing problems in quantum science.
In a study reported last year in Nature, Xu and his team set out to study the properties of axions, a theoretical elementary particle proposed by physicist Frank Wilczek. The Nobel Prize winner named it after a brand of laundry detergent because it “cleaned up” the complex, highly technical Strong Charge Parity problem in quantum chromodynamics by filling in a gap between theory and observation.
In addition one of the most enticing predictions about axion states is that we may be able to use them to control magnetization, which could revolutionize all kinds of technology as magnetism and magnetic materials are at the heart of many, many applications.
In a class of topological materials called axion insulators, Xu’s team sought to simulate the behavior of the axion. They fabricated a dual-gated MnBi2Te4 device in an argon environment, and measured its electrical and optical properties, uncovering new pathways to detect and manipulate the rich internal structure of topological materials.
“We discovered a real material that can support the axion insulator state,” Xu said. “We confirmed that it had the predicted properties, a strong coupling between electricity and magnetism.”
Having provided evidence for a theorized particle, Xu plans to explore the spin properties of Weyl semimetals, a new state of matter that has an unusual electronic structure that has deep analogies with particle physics and leads to unique topological properties.
See the full article here .
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Harvard University is the oldest institution of higher education in the United States, established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. It was named after the College’s first benefactor, the young minister John Harvard of Charlestown, who upon his death in 1638 left his library and half his estate to the institution. A statue of John Harvard stands today in front of University Hall in Harvard Yard, and is perhaps the University’s bestknown landmark.
Harvard University has 12 degree-granting Schools in addition to the Radcliffe Institute for Advanced Study. The University has grown from nine students with a single master to an enrollment of more than 20,000 degree candidates including undergraduate, graduate, and professional students. There are more than 360,000 living alumni in the U.S. and over 190 other countries.
The Massachusetts colonial legislature, the General Court, authorized Harvard University (US)’s founding. In its early years, Harvard College primarily trained Congregational and Unitarian clergy, although it has never been formally affiliated with any denomination. Its curriculum and student body were gradually secularized during the 18th century, and by the 19th century, Harvard University (US) had emerged as the central cultural establishment among the Boston elite. Following the American Civil War, President Charles William Eliot’s long tenure (1869–1909) transformed the college and affiliated professional schools into a modern research university; Harvard became a founding member of the Association of American Universities in 1900. James B. Conant led the university through the Great Depression and World War II; he liberalized admissions after the war.
The university is composed of ten academic faculties plus the Radcliffe Institute for Advanced Study. Arts and Sciences offers study in a wide range of academic disciplines for undergraduates and for graduates, while the other faculties offer only graduate degrees, mostly professional. Harvard has three main campuses: the 209-acre (85 ha) Cambridge campus centered on Harvard Yard; an adjoining campus immediately across the Charles River in the Allston neighborhood of Boston; and the medical campus in Boston’s Longwood Medical Area. Harvard University’s endowment is valued at $41.9 billion, making it the largest of any academic institution. Endowment income helps enable the undergraduate college to admit students regardless of financial need and provide generous financial aid with no loans The Harvard Library is the world’s largest academic library system, comprising 79 individual libraries holding about 20.4 million items.
Harvard University has more alumni, faculty, and researchers who have won Nobel Prizes (161) and Fields Medals (18) than any other university in the world and more alumni who have been members of the U.S. Congress, MacArthur Fellows, Rhodes Scholars (375), and Marshall Scholars (255) than any other university in the United States. Its alumni also include eight U.S. presidents and 188 living billionaires, the most of any university. Fourteen Turing Award laureates have been Harvard affiliates. Students and alumni have also won 10 Academy Awards, 48 Pulitzer Prizes, and 108 Olympic medals (46 gold), and they have founded many notable companies.
Colonial
Harvard University was established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. In 1638, it acquired British North America’s first known printing press. In 1639, it was named Harvard College after deceased clergyman John Harvard, an alumnus of the University of Cambridge(UK) who had left the school £779 and his library of some 400 volumes. The charter creating the Harvard Corporation was granted in 1650.
A 1643 publication gave the school’s purpose as “to advance learning and perpetuate it to posterity, dreading to leave an illiterate ministry to the churches when our present ministers shall lie in the dust.” It trained many Puritan ministers in its early years and offered a classic curriculum based on the English university model—many leaders in the colony had attended the University of Cambridge—but conformed to the tenets of Puritanism. Harvard University has never affiliated with any particular denomination, though many of its earliest graduates went on to become clergymen in Congregational and Unitarian churches.
Increase Mather served as president from 1681 to 1701. In 1708, John Leverett became the first president who was not also a clergyman, marking a turning of the college away from Puritanism and toward intellectual independence.
19th century
In the 19th century, Enlightenment ideas of reason and free will were widespread among Congregational ministers, putting those ministers and their congregations in tension with more traditionalist, Calvinist parties. When Hollis Professor of Divinity David Tappan died in 1803 and President Joseph Willard died a year later, a struggle broke out over their replacements. Henry Ware was elected to the Hollis chair in 1805, and the liberal Samuel Webber was appointed to the presidency two years later, signaling the shift from the dominance of traditional ideas at Harvard to the dominance of liberal, Arminian ideas.
Charles William Eliot, president 1869–1909, eliminated the favored position of Christianity from the curriculum while opening it to student self-direction. Though Eliot was the crucial figure in the secularization of American higher education, he was motivated not by a desire to secularize education but by Transcendentalist Unitarian convictions influenced by William Ellery Channing and Ralph Waldo Emerson.
20th century
In the 20th century, Harvard University’s reputation grew as a burgeoning endowment and prominent professors expanded the university’s scope. Rapid enrollment growth continued as new graduate schools were begun and the undergraduate college expanded. Radcliffe College, established in 1879 as the female counterpart of Harvard College, became one of the most prominent schools for women in the United States. Harvard University became a founding member of the Association of American Universities in 1900.
The student body in the early decades of the century was predominantly “old-stock, high-status Protestants, especially Episcopalians, Congregationalists, and Presbyterians.” A 1923 proposal by President A. Lawrence Lowell that Jews be limited to 15% of undergraduates was rejected, but Lowell did ban blacks from freshman dormitories.
President James B. Conant reinvigorated creative scholarship to guarantee Harvard University’s preeminence among research institutions. He saw higher education as a vehicle of opportunity for the talented rather than an entitlement for the wealthy, so Conant devised programs to identify, recruit, and support talented youth. In 1943, he asked the faculty to make a definitive statement about what general education ought to be, at the secondary as well as at the college level. The resulting Report, published in 1945, was one of the most influential manifestos in 20th century American education.
Between 1945 and 1960, admissions were opened up to bring in a more diverse group of students. No longer drawing mostly from select New England prep schools, the undergraduate college became accessible to striving middle class students from public schools; many more Jews and Catholics were admitted, but few blacks, Hispanics, or Asians. Throughout the rest of the 20th century, Harvard became more diverse.
Harvard University’s graduate schools began admitting women in small numbers in the late 19th century. During World War II, students at Radcliffe College (which since 1879 had been paying Harvard University professors to repeat their lectures for women) began attending Harvard University classes alongside men. Women were first admitted to the medical school in 1945. Since 1971, Harvard University has controlled essentially all aspects of undergraduate admission, instruction, and housing for Radcliffe women. In 1999, Radcliffe was formally merged into Harvard University.
21st century
Drew Gilpin Faust, previously the dean of the Radcliffe Institute for Advanced Study, became Harvard University’s first woman president on July 1, 2007. She was succeeded by Lawrence Bacow on July 1, 2018.
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