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Category: quantum physics – Page 262

Harvard’s breakthrough in quantum computing features a new logical quantum processor with 48 logical qubits, enabling large-scale algorithm execution on an error-corrected system. This development, led by Mikhail Lukin, represents a major advance towards practical, fault-tolerant quantum computers.

In quantum computing, a quantum bit or “qubit” is one unit of information, just like a binary bit in classical computing. For more than two decades, physicists and engineers have shown the world that quantum computing is, in principle, possible by manipulating quantum particles ­– be they atoms, ions or photons – to create physical qubits.

But successfully exploiting the weirdness of quantum mechanics for computation is more complicated than simply amassing a large-enough number of physical qubits, which are inherently unstable and prone to collapse out of their quantum states.

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Quantum computing is often hailed as the next frontier of technology, promising to solve some of the most complex and challenging problems in science, engineering, and business. But how close are we to achieving this quantum dream, and what are the limitations of this emerging field?

As IEEE Spectrum shares in its detailed report, some of the leading voices in quantum computing have recently expressed doubts and concerns about the technology’s current state and prospects. They argue that quantum computers are far from being ready for practical use and that their applications are more restricted than commonly assumed.

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Purdue quantum researchers twist double bilayers of an antiferromagnet to demonstrate tunable moiré magnetism.

Twistronics isn’t a new dance move, exercise equipment, or new music fad. No, it’s much cooler than any of that. It is an exciting new development in quantum physics and material science where van der Waals materials are stacked on top of each other in layers, like sheets of paper in a ream that can easily twist and rotate while remaining flat, and quantum physicists have used these stacks to discover intriguing quantum phenomena.

Adding the concept of quantum spin with twisted double bilayers of an antiferromagnet, it is possible to have tunable moiré magnetism. This suggests a new class of material platform for the next step in twistronics: spintronics. This new science could lead to promising memory and spin-logic devices, opening the world of physics up to a whole new avenue with spintronic applications.

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In a typical battery, charged ions zip one way through a sea of other particles as the battery recharges, before racing back in the other direction to release the stored energy on cue.

Back and forth the ions go, some getting diverted along the way, until the capacity of the battery is drained, and it loses energy too quickly to be of any use.

But physicists, good on them, are imagining new ways of storing energy in handy portable devices by drawing on a strange quantum phenomenon that twists time, amongst other unusual happenings.

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Major technical improvements to a quantum computer based on trapped ions could bring a large-scale version closer to reality.

Scientists are exploring various platforms for future large-scale quantum computation. Among the leading contenders, those in which the quantum bits (qubits) are trapped ions stand out for their low-error operation. However, scaling up such platforms to the millions of qubits needed for utility-scale quantum computing is a daunting task. Now Steven Moses at Quantinuum in Colorado and colleagues describe an impressive new trapped-ion quantum computer, the Quantinuum System Model H2, in which they have been able to increase the number of qubits (from 20 to 32) without increasing the error rate [1]. The researchers have put this system through its paces with full component-level testing, a suite of industry-standard benchmark tests, and a set of diverse applications.

In a typical trapped-ion quantum computer, a linear chain of ions is confined by an electric potential using direct-current (dc) and radio-frequency (rf) fields. Whereas the ion-trap apparatus can be at any temperature, the ions themselves need to be laser cooled to near their ground state. Their motion can then be quantized, and the resulting motional modes can be used to entangle any pair of ions in the chain—a requirement for performing quantum operations. However, controlling individual ions in a long chain comes with its own technical difficulties, and it is unlikely that a million qubits—as needed to build a universal, fault-tolerant quantum computer [2]—could be trapped in a single potential.

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Attempts to turn string theory into a workable theory of nature have led to the potential conclusion that our universe is a hologram—that what we perceive as three spatial dimensions is actually composed of only two. The greatest realization of this hologram-led program is a proposal that goes by the awkward and clunky name of the AdS/CFT correspondence, first proposed by string theorist Juan Maldacena in the late 1990s.

The AdS/CFT correspondence is not a solution to the problems posed by per se, but a statement motivated by advances in the theory when one takes the holographic principle seriously. It is also not a by itself, but it does tell us that we are not entirely misguided when we make the bold claim that we live in a , and begin to dream about what that revelation might entail.

We need to, briefly I assure you, unpack these acronyms to see how powerful this connection is, and what it might teach us about the wider . The “AdS” stands for anti-de Sitter, which is a particular kind of solution to Einstein’s general theory of relativity. The name comes from Dutch physicist Willem de Sitter, who constructed a mock universe that was empty of all matter and energy with the exception of a strong outwards curvature.

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String theory found its origins in an attempt to understand the nascent experiments revealing the strong nuclear force. Eventually another theory, one based on particles called quarks and force carriers called gluons, would supplant it, but in the deep mathematical bones of the young string theory physicists would find curious structures, half-glimpsed ghosts, that would point to something more. Something deeper.

String claims that what we call —the point-like entities that wander freely, interact, and bind together to make up the bulk of material existence—are nothing but. Instead, there is but a single kind of fundamental object: the string. These strings, each one existing at the smallest possible limit of existence itself, vibrate. And the way those strings vibrate dictates how they manifest themselves in the larger universe. Like notes on a strummed guitar, a string vibrating with one mode will appear to us as an electron, while another vibrating at a different frequency will appear as a photon, and so on.

String theory is an audacious attempt at a theory of everything. A single mathematical framework that explains the particles that make us who and what we are along with the forces that act as the fundamental messengers among those particles. They are all, every quark in the cosmos and every photon in the field, bits of vibrating strings.

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Even though the guts of General Relativity are obtusely mathematical, and for decades was relegated to math departments rather than proper physics, you get to experience the technological gift of relativity every time you navigate to your favorite restaurant. GPS, the global positioning system, consists of a network of orbiting satellites constantly beaming out precise timing data. Your phone compares those signals to figure out where you are on the Earth. But there is a difference in spacetime between the surface of the Earth and the orbit of the satellites. Without taking general relativity into account, your navigation would simply be incorrect, and you’d be late for dinner.

As revolutions go, general relativity is a big one. And as unifications go, it’s a warning. To make this union happen Einstein had to radically, permanently alter not just our conceptions of gravity as a force acting through space and time, but our conceptions of space and time itself. It took no less than a complete overhaul of our entire philosophical understanding of the relation between space and time to bridge the gap.

And as Einstein would find in the ensuing decades, all the way to the time of his death, that bringing other forces like electromagnetism into the same unified fold would be all but impossible. Electromagnetism, and the other forces, cannot be conceptualized in the same way. Instead we have to use quantum probabilities to make predictions, and when we apply the same technique to gravity we just get infinities.

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Quantum technology is now at a point where practical work can begin on creating the quantum internet. However, numerous challenges must be overcome before this vision becomes a reality. A global-scale quantum internet requires the development of the quantum repeater, a device that stores and manipulates qubits while interacting with or emitting entangled photons. This review examines different approaches to quantum repeaters and networks, covering their conceptual frameworks, architectures, and current progress in experimental implementation.

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