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The Quantum Quest for Dark Matter’s Elusive Axion Particle

Aalto University researchers will probe the secrets of dark matter using a quantum detector of unprecedented sensitivity.

In the vast darkness of the cosmos lurks an invisible kind of matter. Its presence is seen in the rippling ebb and flow of galaxies, but it’s never been directly observed. What secrets lie beneath the surface, brewing in the deep?

Physicists have long theorized about the composition of dark matter, which is thought to be five times more abundant than regular matter. Among competing hypotheses, one particle has emerged as a promising candidate: the axion.

Quieting Noise in Gravitational-Wave Detectors

To tackle the problem, the LIGO Scientific Collaboration followed an approach, proposed in 2001, that involves squeezing the noise ellipse differently at different frequencies. This frequency-dependent squeezing is realized by coupling the interferometer to a 300-m-long “filter” cavity. Through the cavity, the team could tailor the spectrum of the squeezed state, injecting amplitude squeezing in the low-frequency region and phase squeezing in the high-frequency region, says Victoria Xu, also of MIT LIGO Lab. “This [approach] allows us to reduce the limiting forms of quantum noise in each frequency band,” she says.

The frequency-dependent approach had previously been demonstrated in tabletop systems but implementing it to mitigate radiation-pressure noise in a full-scale gravitational-wave detector was a massive engineering challenge, Xu says. An important aspect was the minimization of optical losses due to imperfect optical components or to a mismatch of the light modes propagating in the various parts of the setup—the filter cavity, the squeezer, and the interferometer. “Any loss can be seen as a ‘port’ through which regular, nonsqueezed vacuum can enter,” Barsotti says.

The LIGO Scientific Collaboration tested frequency-dependent squeezing during the commissioning of the instrument upgrades for the fourth run, comparing detector noise spectra for no squeezing, frequency-independent squeezing, and frequency-dependent squeezing. Frequency-dependent squeezing yielded similar enhancements to frequency-independent squeezing at high frequencies while eliminating the degradation below 300 Hz due to radiation-pressure noise. The team estimated that the improved noise performance would increase the distance over which mergers can be detected by 15%–18%, corresponding to up to a 65% increase in the volume of the Universe that the LIGO interferometer will be able to probe. Quantum optics specialist Haixing Miao of Tsinghua University in China says this result demonstrates an exceptional ability to manipulate quantum states of light with optical cavities but also offers an impressive demonstration that quantum measurement theory applies to the kilometer scales of a gravitational-wave detector.

Dependence of measurement outcomes on the dynamics of quantum coherent interactions between the system and the meter

Information about the internal properties of a system can only be obtained through interactions of the system with an external meter. However, such interactions generally result in entanglement between the system and the meter, making it difficult to trace the measurement result back to a specific value of the physical property in the system. It is therefore possible that the outcomes of quantum measurements depend in a nontrivial manner on the dynamics of the measurement interaction, possibly providing a physical explanation for the role of measurement contexts in quantum mechanics. Here we show that the effects of the measurement interaction on the meter can be described entirely in terms of the quantum coherent system dynamics associated with the back-action on the system.

Quantum Breakthrough: Scientists Rethink the Nature of Reality

Whenever measurement precision nears the uncertainty limit set by quantum mechanics, the results become dependent on the interaction dynamics between the measuring device and the system. This finding may explain why quantum experiments often produce conflicting results and may contradict basic assumptions regarding physical reality.

Two quantum physicists from Hiroshima University recently analyzed the dynamics of a measurement interaction, where the value of a physical property is identified with a quantitative change in the meter state. This is a difficult problem, because quantum theory does not identify the value of a physical property unless the system is in a so-called “eigenstate” of that physical property, a very small set of special quantum states for which the physical property has a fixed value.

The researchers solved this fundamental problem by combining information about the past of the system with information about its future in a description of the dynamics of the system during the measurement interaction, demonstrating that the observable values of a physical system depend on the dynamics of the measurement interaction by which they are observed.

1,000+ Qubit Quantum Computer Announced

California-based startup Atom Computing has announced a 1,225-qubit quantum computer, the first to break the 1,000+ barrier, which it plans to release in 2024.

Quantum bits, or qubits, are the basic units of information in quantum computing – equivalent to bits in classical computing. Unlike bits, however, qubits can exist in multiple states simultaneously, allowing them to perform calculations that would take millions of years for an ordinary computer.

Breaking the Quantum Limit: From Einstein-Bohr Debates to Achieving “Unattainable” Efficiency

Researchers at the University of Stuttgart have demonstrated that a key ingredient for many quantum computation and communication schemes can be performed with an efficiency that exceeds the commonly assumed upper theoretical limit — thereby opening up new perspectives for a wide range of photonic quantum technologies.

Quantum science not only has revolutionized our understanding of nature, but is also inspiring groundbreaking new computing, communication, and sensor devices. Exploiting quantum effects in such ‘quantum technologies’ typically requires a combination of deep insight into the underlying quantum-physical principles, systematic methodological advances, and clever engineering. And it is precisely this combination that researchers in the group of Prof. Stefanie Barz at the University of Stuttgart and the Center for Integrated Quantum Science and Technology (IQST) have delivered in recent study, in which they have improved the efficiency of an essential building block of many quantum devices beyond a seemingly inherent limit.

Historical foundations: from philosophy to technology.

Scientists demonstrate the existence of a universal lower bound on topological entanglement entropy

In a new study, scientists from the US and Taiwan have theoretically demonstrated the existence of a universal lower bound on topological entanglement entropy, which is always non-negative. The findings are published in the journal Physical Review Letters.

Quantum systems are bizarre and follow their own rules, with quantum states telling us everything we know about that system. Topological entanglement entropy (TEE) is a measure that provides insights into emergent non-local phenomena and entanglement in with topological properties.

Given the fundamental role of quantum entanglement in and various information applications, understanding TEE becomes essential for gaining insights into the behavior of quantum systems.

Physicists Say Time Travel Can Be Simulated Using Quantum Entanglement

A simulation offers a means of probing time travel without worrying about whether it’s actually permitted by the rules of the universe.

“Whether closed timelike curves exist in reality, we don’t know. The laws of physics that we know of allow for the existence of CTCs, but those laws are incomplete; most glaringly, we don’t have a theory of quantum gravity,” said Yunger Halpern. “Regardless of whether true CTCs exist, though, one can use entanglement to simulate CTCs, as others showed before we wrote our paper.”

Cybernetic Theory: Information Physics, Quantum Cosmology, Simulation Metaphysics

Building upon the foundational paradigms outlined in The Syntellect Hypothesis: Five Paradigms of the Mind’s Evolution (2020), my latest work titled The Cybernetic Theory of Mind (2022), a Kindle eBook series published last year, serves as an extension and refinement, operating at the intersection of information physics, quantum cosmology, and simulation metaphysics. The objective is not merely to inform but to elucidate through an “explanatory” theory of everything, providing an integrative framework for a deeper understanding of reality.

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The Cybernetic Theory of Mind is an explanatory TOE at the intersection of information physics, quantum cosmology and simulation metaphysics.