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Category: quantum physics

The Philosophy of Entropy: Order, Decay, and the Meaning of Equilibrium

Entropy is one of the most profound and misunderstood concepts in modern science — at once a physical quantity, a measure of uncertainty, and a metaphor for the passage of time itself. Entropy: The Order of Disorder explores this concept in its full philosophical and scientific depth, tracing its evolution from the thermodynamics of Clausius and Boltzmann to the cosmology of the expanding universe, the information theory of Shannon, and the paradoxes of quantum mechanics.

At the heart of this study lies a critical insight: entropy in its ideal form can exist only in a perfectly closed and isolated system — a condition that is impossible to realize, even for the universe itself. From this impossibility arises the central tension of modern thought: the laws that describe equilibrium govern a world that never rests.

Bridging physics, philosophy, and cosmology, this book examines entropy as a universal principle of transformation rather than decay. It situates the second law of thermodynamics within a broader intellectual landscape, connecting it to the philosophies of Heraclitus, Kant, Hegel, and Whitehead, and to contemporary discussions of information, complexity, and emergence.

Encapsulated PbS quantum dots boost solar water splitting without sacrificial agents

A research team affiliated with UNIST has developed stable and efficient chalcogenide-based photoelectrodes, addressing a longstanding challenge of corrosion. This advancement paves the way for the commercial viability of solar-driven water splitting technology—producing hydrogen directly from sunlight without electrical input.

Jointly led by Professors Ji-Wook Jang and Sung-Yeon Jang from the School of Energy and Chemical Engineering, the team reported a highly durable, corrosion-resistant metal-encapsulated PbS quantum dot (PbS-QD) solar cell-based photoelectrode that delivers both high photocurrent and long-term operational stability for photoelectrochemical (PEC) water splitting without the need for sacrificial agents. The research is published in the journal Nature Communications.

PEC water splitting is a promising route for sustainable hydrogen production, where sunlight is used to drive the decomposition of water into hydrogen and oxygen within an electrolyte solution. The efficiency of this process depends heavily on the stability of the semiconductor material in the photoelectrode, which absorbs sunlight and facilitates the electrochemical reactions. Although chalcogenide-based sulfides, like PbS are highly valued for their excellent light absorption and charge transport properties, they are prone to oxidation and degradation when submerged in water, limiting their operational stability.

Quantum defects in carbon nanotubes as single-photon sources

This Review surveys progress in the development of carbon nanotubes as single-photon sources for emerging quantum technologies, with a focus on chemical synthesis and quantum defect engineering, computational studies of structure-property relationships, and experimental investigations of quantum optical properties.

Quantum Twins simulator unveils 15,000 controllable quantum dots for materials research

Researchers in Australia have unveiled the largest quantum simulation platform built to date, opening a new route to exploring the complex behavior of quantum materials at unprecedented scales.

Reporting in Nature, a team led by Michelle Simmons at the University of New South Wales (UNSW) Sydney has demonstrated a platform they call “Quantum Twins”: a two-dimensional array of around 15,000 individually controllable quantum dots. The researchers say the system could soon be used to simulate a wide range of exotic quantum effects that emerge in large, strongly correlated materials.

As quantum technologies advance, it is becoming increasingly important to understand how advanced quantum materials behave under different conditions.

Quantum encryption method demonstrated at city-sized distances for the first time

Concerns that quantum computers may start easily hacking into previously secure communications has motivated researchers to work on innovative new ways to encrypt information. One such method is quantum key distribution (QKD), a secure, quantum-based method in which eavesdropping attempts disrupt the quantum state, making unauthorized interception immediately detectable.

Previous attempts at this solution were limited by short distances and reliance on special devices, but a research team in China recently demonstrated the ability to maintain quantum encryption over longer distances. The research, published in Science, describes device-independent QKD (DI-QKD) between two single-atom nodes over up to 100 km of optical fiber.

Broken inversion symmetry lets 3D crystals mimic 2D Ising superconductivity

Two-dimensional (2D) materials, in general, allow the realization of unique quantum phenomena unattainable in the common three-dimensional (3D) world. A prime example is graphene. Transition metal dichalcogenides (TMDs) have a similar structure. Both can be stacked to form van der Waals heterostructures or can be exfoliated into single layers. But TMDs have an extra variety of excellent properties, including strong spin-orbit coupling and superconductivity.

In 2D (single atomic layer film) NbSe2, a prominent example of TMD, the combination of these two effects with the crystal symmetries leads to the so-called Ising superconductivity (IS), which can withstand extremely high magnetic fields oriented parallel to the crystal plane. Perhaps more exciting than this resilience against magnetic fields is the potential application of IS in realizing various exotic phenomena such as equal spin Andreev reflections, topological superconductivity, and Majorana fermions.

However, 2D structures are prone to degradation and impractical for applications. 3D materials are robust, easily scalable and accessible to a larger range of scientific analytical techniques. Therefore, it is desirable to find ways of protecting unique features of 2D materials in their 3D counterparts.

Three-way quantum correlations fade exponentially with distance at any temperature, study shows

The properties of a quantum material are driven by links between its electrons known as quantum correlations. A RIKEN researcher has shown mathematically that, at non-zero temperatures, these connections can only exist over very short distances when more than two particles are involved. This finding, now published in Physical Review X, sets a fundamental limit on just how “exotic” a quantum material can be under realistic, finite-temperature conditions.

A fascinating aspect of quantum physics is the concept that two particles that are spatially separated can communicate with each other. This so-called “spooky action at a distance,” as Einstein referred to it, is crucial for understanding the origin of the exotic properties that arise in some materials, particularly at low temperatures.

These unusual material properties are determined by the exact nature of the quantum correlation, and the material is said to be in a specific quantum phase. This is analogous to the traditional phases of matter—solid, liquid, and gas—being defined by the chemical interactions between the atoms.

Study reveals microscopic origins of surface noise limiting diamond quantum sensors

A new theoretical study led by researchers at the University of Chicago and Argonne National Laboratory has identified the microscopic mechanisms by which diamond surfaces affect the quantum coherence of nitrogen-vacancy (NV) centers—defects in diamond that underpin some of today’s most sensitive quantum sensors. The study has appeared in Physical Review Materials and was selected to be an Editors’ Suggestion paper.

“One long-standing challenge has been understanding why shallow NV centers lose coherence so quickly,” said Giulia Galli, professor at the University of Chicago Pritzker School of Molecular Engineering (UChicago PME) and senior scientist at Argonne National Laboratory. “By combining first-principles surface models with quantum dynamics simulations, we understood that the culprit of decoherence is not just which spins live on the diamond surface, but how they move: surface noise is dynamical.”

The findings of the study provide clear, physics-based guidelines for engineering diamond surfaces that help preserve quantum coherence, a key requirement for quantum sensing and emerging quantum information technologies.

Measuring time at the quantum level depends on material symmetry

EPFL physicists have found a way to measure the time involved in quantum events and found it depends on the symmetry of the material. “The concept of time has troubled philosophers and physicists for thousands of years, and the advent of quantum mechanics has not simplified the problem,” says Professor Hugo Dil, a physicist at EPFL. “The central problem is the general role of time in quantum mechanics, and especially the timescale associated with a quantum transition.”

Quantum events, like tunneling, or an electron changing its state by absorbing a photon, happen at mind-bending speeds. Some take only a few tenths of attoseconds (10-18 seconds), which is so short that light would not even cross the width of a small virus. But measuring time intervals this small is notoriously difficult, also because any external timing tool can distort the very thing we want to observe.

“Although the 2023 Nobel prize in physics shows we can access such short times, the use of such an external time scale risks inducing artifacts,” says Dil. “This challenge can be resolved by using quantum interference methods, based on the link between accumulated phase and time.”

Scientists discover ‘levitating’ time crystals that you can hold in your hand

Time crystals, a collection of particles that “tick”—or move back and forth in repeating cycles—were first theorized and then discovered about a decade ago. While scientists have yet to create commercial or industrial applications for this intriguing form of matter, these crystals hold great promise for advancing quantum computing and data storage, among other uses.

Over the years, different types of time crystals have been observed or created, with their varying properties offering a range of potential uses.

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