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Under hood of quantum computer + Different cause for Type 1a supernova + New QM TD ex

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What’s under the hood of a quantum computer?
https://physicstoday.scitation.org/do/10...305a/full/

INTRO: When most people sit down at their computers to work, they’re thinking about all the things they need to get done; far from mind is any consideration of how their keystrokes and mouse clicks are translated into logic operations and electrical signals. That separation between hardware and user interface is the product of decades of development. Now quantum computer developers are navigating similar terrain.

The quantum computing stack is everything that lies between a user and the physical qubits. The stack needs to perform essential functions; for instance, it must facilitate user interaction, turn inputs into hardware manipulation, and correct for numerous error sources. (For more about quantum architectures, see the article by Anne Matsuura, Sonika Johri, and Justin Hogaboam, Physics Today, March 2019, page 40.) There’s no one right way to divide those tasks into discrete levels, though, and researchers and technology companies are still pursuing different visions for future quantum architectures.

On page 28 of Physics Today’s March 2021 issue, Harrison Ball, Michael Biercuk, and Michael Hush present the quantum computing stack proposed by Q-CTRL, the quantum technology company founded by Biercuk. The authors explain in detail how the functionality of a quantum firmware layer—one component of a quantum computer—is critical for managing qubit errors. Here we explain what happens in the rest of the layers of a quantum computer... (MORE)


Physicists Propose That the Universe Is Filled With Tiny, Natural Atomic Bombs
https://www.vice.com/en/article/m7ayq3/p...omic-bombs

INTRO: Stars across the universe run on nuclear fusion, but nuclear fission—the mechanism at the core of an atomic bomb—is an exceedingly rare process in nature. Now, two scientists think they may have identified an exotic natural environment where fission not only occurs, but could actually trigger one of the most important types of explosion in the universe: a supernova.

When stars die, they leave behind all kinds of strange remnants, from black holes to neutron stars to white dwarfs, all of which have their own trippy properties. White dwarfs, the necrotic remains of stars like our Sun, can weirdly die for a second time in blowups called Type 1a supernovae, which have such a consistent brightness that scientists use them as “standard candles” to measure the expansion of the universe.

These explosions are thought to occur when white dwarfs become overwhelmed by material tugged from a companion star, but a forthcoming study in Physical Review Letters suggests that an ultra-rare fission reaction may trigger some of these brilliant blasts. A copy of the study is available on the preprint server arXiv.

“People think [white dwarfs] have a companion star because they didn't know how to get the star to explode without a companion,” said Charles Horowitz, a professor of physics at Indiana University who led the study, in a call. The new research suggests that “we may be wrong about companions, for at least some of the Type 1as,” he added... (MORE)


New quantum theory heats up thermodynamic research
https://www.nottingham.ac.uk/news/new-qu...c-research

RELEASE: Researchers have developed a new quantum version of a 150-year-old thermodynamical thought experiment that could pave the way for the development of quantum heat engines. Mathematicians from the University of Nottingham have applied new quantum theory to the Gibbs paradox and demonstrated a fundamental difference in the roles of information and control between classical and quantum thermodynamics. Their research has been published today in Nature Communications.

The classical Gibbs paradox led to crucial insights for the development of early thermodynamics and emphasises the need to consider an experimenter's degree of control over a system. The research team developed a theory based on mixing two quantum gases -- for example, one red and one blue, otherwise identical -- which start separated and then mix in a box. Overall, the system has become more uniform, which is quantified by an increase in entropy. If the observer then puts on purple-tinted glasses and repeats the process; the gases look the same, so it appears as if nothing changes. In this case, the entropy change is zero.

The lead authors on the paper, Benjamin Yadin and Benjamin Morris, explain: "Our findings seem odd because we expect physical quantities such as entropy to have meaning independent of who calculates them. In order to resolve the paradox, we must realise that thermodynamics tells us what useful things can be done by an experimenter who has devices with specific capabilities. For example, a heated expanding gas can be used to drive an engine. In order to extract work (useful energy) from the mixing process, you need a device that can "see" the difference between red and blue gases."

Classically, an "ignorant" experimenter, who sees the gases as indistinguishable, cannot extract work from the mixing process. The research shows that in the quantum case, despite being unable to tell the difference between the gases, the ignorant experimenter can still extract work through mixing them.

Considering the situation when the system becomes large, where quantum behaviour would normally disappear, the researchers found that the quantum ignorant observer can extract as much work as if they had been able to distinguish the gases. Controlling these gases with a large quantum device would behave entirely differently from a classical macroscopic heat engine. This phenomenon results from the existence of special superposition states that encode more information than is available classically.

Professor Gerardo Adesso said: "Despite a century of research, there are so many aspects we don't know or we don't understand yet at the heart of quantum mechanics. Such a fundamental ignorance, however, doesn't prevent us from putting quantum features to good use, as our work reveals. We hope our theoretical study can inspire exciting developments in the burgeoning field of quantum thermodynamics and catalyse further progress in the ongoing race for quantum-enhanced technologies.

"Quantum heat engines are microscopic versions of our everyday heaters and refrigerators, which may be realised with just one or a few atoms (as already experimentally verified) and whose performance can be boosted by genuine quantum effects such as superposition and entanglement. Presently, to see our quantum Gibbs paradox played out in a laboratory would require exquisite control over the system parameters, something which may be possible in fine-tuned "optical lattice" systems or Bose-Einstein condensates -- we are currently at work to design such proposals in collaboration with experimental groups."
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