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Category: quantum physics – Page 7

Streamlined method to directly generate photons in optical fiber could secure future quantum internet

With the rise of quantum computers, the security of our existing communication systems is at risk. Quantum computers will be able to break many of the encryption methods used in current communication systems. To counter this, scientists are developing quantum communication systems, which utilize quantum mechanics to offer stronger security. A crucial building block of these systems is a single-photon source: a device that generates only one light particle at a time.

These photons, carrying quantum information, are then sent through optical fibers. For to work, it is essential that single photons are injected into optical fibers with extremely low loss.

In conventional systems, single-photon emitters, like and rare-earth (RE) element ions, are placed outside the fiber. These photons then must be guided to enter the fiber. However, not all photons make it into the fibers, causing high transmission loss. For practical quantum communication systems, it is necessary to achieve a high-coupling and channeling efficiency between the and the emitter.

Twice around to return home: A hidden reset button for spins and qubits

The world is filled with rotating objects—gyroscopes, magnetic spins, and more recently, qubits in quantum computers. For example, the atomic nuclei in our bodies precess at megahertz frequencies inside NMR machines. In practice, it is often desirable to return such a rotating system precisely to its starting point. At first glance, this seems impossible: after an elaborate sequence of twists and wobbles, how could one possibly retrace the path back to the origin?

The astonishing answer is that it is always possible. No matter how tangled the history of rotations, there exists a simple recipe: rescale the driving force and apply it twice. A single application is never sufficient, but applying this doubled, rescaled force guarantees an exact return. Under this operation, the spin—or the qubit, or any rotor—will unfailingly come home.

This discovery was made by Distinguished Professor Tsvi Tlusty from the Department of Physics at UNIST and Jean-Pierre Eckmann from the University of Geneva, Switzerland. Their study, published in Physical Review Letters on October 1, 2025, reveals that, despite their apparent complexity, rotations conceal a fundamental order.

Record spin waves thanks to flux quanta

Spin waves are considered to be promising candidates for a new form of electronics. Instead of electrons, the focus here is on magnons. These quantized units of spin waves describe how spin precession propagates. Similar to electrons, magnons can transmit information in a conductor. However, they do so with much lower resistance and thus a fraction of the energy consumption.

At TU Braunschweig, the Cryogenic Quantum Electronics working group, together with international partners, has now set a new record for the wavelength of excited propagating magnons. The researchers led by Professor Oleksandr Dobrovolskiy used another quasiparticle, fluxons, to excite the spin waves. The team collaborated with partners from Huazhong University of Science and Technology in China, Goethe University Frankfurt am Main, the University of Vienna and the University of Bordeaux.

“Fluxons move as magnetic flux quanta of a superconductor at speeds of up to 10 kilometers per second. We succeeded in using the ultra-fast fluxons to excite a spin wave in a neighboring magnet,” explains Dobrovolskiy. “This effect can be imagined as similar to the bow wave created by a speedboat in water. Except that our boat is so fast that it literally creates a kind of .”

Time crystals could power future quantum computers

A glittering hunk of crystal gets its iridescence from a highly regular atomic structure. Frank Wilczek, the 2012 Nobel Laureate in Physics, proposed quantum systems––like groups of particles––could construct themselves in the same way, but in time instead of space. He dubbed such systems time crystals, defining them by their lowest possible energy state, which perpetually repeats movements without external energy input. Time crystals were experimentally proved to exist in 2016.

Quantum mechanics trumps the second law of thermodynamics at the atomic scale

Two physicists at the University of Stuttgart have proven that the Carnot principle, a central law of thermodynamics, does not apply to objects on the atomic scale whose physical properties are linked (so-called correlated objects). This discovery could, for example, advance the development of tiny, energy-efficient quantum motors. The derivation has been published in the journal Science Advances.

Ultrasensitive sensor maps magnetization textures in rhombohedral graphene

Graphene, which is comprised of a single layer of carbon atoms arranged in a hexagonal lattice, is a widely used material known for its advantageous electrical and mechanical properties. When graphene is stacked in a so-called rhombohedral (i.e., ABC) pattern, new electronic features are known to emerge, including a tunable band structure and a non-trivial topology.

Due to these emerging properties, electrons in rhombohedral can behave as if they are being influenced by “hidden” magnetic fields, even if no is applied to them. While this interesting effect is well-documented, closely studying how electrons organize themselves in the material, with their spins and valley states pointing in different directions, has so far proved challenging.

Researchers at Weizmann Institute of Science recently set out to further examine the local magnetization textures in rhombohedral graphene, using a nanoscale superconducting quantum interference device (nano-SQUID). Their paper, published in Nature Physics, offers new insight into the physical processes governing the correlated states previously observed in the material.

Rigorous approach quantifies and verifies almost all quantum states

Quantum information systems, systems that process, store or transmit information leveraging quantum mechanical effects, could, in principle, outperform classical systems in some optimization, computational, sensing, and learning tasks. An important aspect of quantum information science is the reliable quantification of quantum states in a system, to verify that they match desired (i.e., target) states.

Why some quantum materials stall while others scale

People tend to think of quantum materials—whose properties arise from quantum mechanical effects—as exotic curiosities. But some quantum materials have become a ubiquitous part of our computer hard drives, TV screens, and medical devices. Still, the vast majority of quantum materials never accomplish much outside of the lab.

What makes certain commercial successes and others commercially irrelevant? If researchers knew, they could direct their efforts toward more promising materials—a big deal since they may spend years studying a single material.

Now, MIT researchers have developed a system for evaluating the scale-up potential of quantum materials. Their framework combines a material’s quantum behavior with its cost, supply chain resilience, environmental footprint, and other factors.

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