In thermodynamics, an “adiabatic process” is a system change that transfers no heat in or out of the system. Any and all energy change in that system are therefore accomplished by doing work on the system, work being action that moves matter over a distance. (An example is a bicycle tire pump or lifting a box from the floor.)
The “adiabatic theorem” says that if you change a system slowly enough, it will remain in the same energy state. For example, if you walk slowly enough holding a full cup of coffee, the coffee will not spill—the coffee system has time to relax back to its steady state—but if you make a quick and sudden change while holding the coffee cup, some coffee will spill over the cup’s edge.
There is a similar theorem in quantum mechanics—a quantum system that is changed (perturbed) slowly enough will remain in its existing quantum state (often its ground state), while a sudden change, such as a photon impinging upon an atom, changes its energy state.
An international research team has achieved an important milestone for astrophysics at GSI/FAIR in Darmstadt: In the CRYRING@ESR storage ring, scientists were able to measure nuclear reactions at extremely low energies for the first time, mirroring the conditions inside stars. This novel experimental approach lays the foundation for decoding the formation of elements in the universe with even greater precision in the future.
In the extreme environments of stars, nuclear processes often occur at very low energies. These so-called “sub-MeV energies” (below 1 megaelectron volt) are difficult to replicate in the laboratory because the probability of atomic nuclei interacting at such low speeds is exceptionally small.
In the FAIR storage ring CRYRING@ESR, researchers were able to lower the energy available for the nuclear reaction in the center-of-mass frame of the two particles down to 403 kiloelectron volts. This marks a new record: It is the lowest energy at which a nuclear reaction has ever been measured in a heavy-ion storage ring. The new findings were recently published in the journal European Physical Journal A.
Particle accelerators such as those at the European Organization for Nuclear Research (CERN) in Geneva are typically highly complex large-scale devices. In these ring-shaped facilities, which are often several kilometers in length, magnets and radio-frequency cavities are used to accelerate elementary particles. An alternative approach is now emerging: compact laser–plasma accelerators that can be built and operated at a fraction of the cost. These accelerators can achieve acceleration gradients up to around 1,000 times higher than those of conventional accelerators. Researchers at HHU contributed significantly to this development.
A research team led by Prof. Dr. Markus Büscher, a professor of physics at HHU and group leader at the Peter Grünberg Institute in Jülich, presented the current state of research in a review article in Reports on Progress in Physics. In a separate study published in High Power Laser Science and Engineering, they report on one specific aspect of laser–plasma acceleration, namely whether the polarization—that is to say, the collective spin alignment—of accelerated particles is preserved in laser–plasma accelerators.
Why is this relevant? “Spin alignment is crucial to a range of fundamental scientific questions as it influences the interaction between particles,” explains Professor Büscher. “In controlled nuclear fusion, the reaction probability—and thus ultimately the energy produced in the reactor—increases significantly when the spins of the fusing nuclei, the ‘fusion fuel’ so to speak, are aligned in parallel.”
Researchers at the Niels Bohr Institute have broken a longstanding barrier by managing to send single photons—that can’t be copied or split and thus are secure—in the network of optical fibers we already have. This opens up a broad range of applications relying on secure quantum information. The research is published in the journal Nature Nanotechnology.
Quantum dots are unsurpassed in their ability to generate coherent single photons—single particles of light which cannot be split or copied and therefore are secure for quantum communication. So far, the problem was that the best quantum dots only worked around 930 nm wavelengths, which is far short of the telecommunication-compatible wavelengths starting at 1,260 nm. Only these longer wavelengths can be used to distribute the information-carrying photons and it has so far been restricted to sub-optimal platforms.
Now, scientists have managed to create a new type of quantum dot, which exploits the best of both worlds.
Most physicists are materialists who believe the world consists of physical particles at the fundamental level. Others have argued reality is a simulation or a hallucination of the brain. But Andrew T. Jaffe challenges all of these views, proposing an alternative consciousness-first theory where space and time arise as within a dream.
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The gauge bosons of the standard model of particle physics are responsible for 3 of the 4 known forces in the universe. A force is conferred is through the exchange of virtual bosons. So for example in electromagnetism, an exchange of virtual photons results in an exchange of momentum which results in two like charges repelling each other.
Gravity is missing from this picture because in General relativity, gravity is not a force, but is a curvature of space-time. The problem is that stars and planets are made of molecules, atoms and radiation. And the forces that hold the atoms together are due to discrete units of virtual particles. It is the exchange or swapping of these virtual bosons that holds or breaks up atoms and molecules.
Quantum mechanics conflicts with general relativity, because QM treats every thing as being discrete, and GR treats everything as being continuous. We need a theory that combines the two because we live in one reality, not two different realities.
This is why most physicists believe General relativity is incomplete. Why can’t quantum mechanics be the one that is incomplete? Of the 4 fundamental forces, 3 have very robust quantum mechanical theories. Only gravity lacks a quantum description. Quantum mechanics also has almost all of classical physics within in its limits. Classical physics like general relativity, does not have quantum effects. We have learned is that Quantum physics is the fundamental language of reality.
One way to quantize gravity is to quantize space-time itself. This is what loop quantum gravity or LQG does. It shows that the fabric of space-time is not continuous, but is made up of discrete quanta, like the pixels on a TV screen. This is different than string theory, because in string theory, space is the background or the canvas, on which strings vibrate.
The transitions of hydrogen molecules embedded in a crystal depend on the surroundings—a behavior that could be used to tailor molecular quantum dynamics.
In quantum physics, we often learn that the rules governing a system are set by its symmetry. These rules—known as selection rules—determine which transitions between quantum states are allowed and which are forbidden. For example, rotational symmetry constrains how an atom’s angular momentum can change. But what if those rules are not fixed? A recent study of hydrogen (H2)—one of the simplest molecules in nature—showed that the allowed pathways between quantum states are determined not solely by the molecule’s internal symmetry but also by its surroundings. By embedding hydrogen molecules in different crystalline environments, Nathan McLane and colleagues from the University of Maryland, College Park, have demonstrated that the symmetry of the host material can selectively enable or suppress nuclear-spin transitions [1]. In doing so, the team revealed that quantum dynamics is not just an intrinsic property—it can be shaped by the environment.
H2 is one of the simplest systems for exploring quantum behavior. Its two identical protons can align their spins in two different ways: In so-called orthohydrogen the nuclear spins are parallel, whereas in parahydrogen they are antiparallel. Although this difference is subtle, it leads to markedly different physical properties for the two forms. Crucially, transitions between them are highly constrained: In an isolated hydrogen molecule, the overall wave function is symmetric under exchange of the two protons, and this exchange symmetry forbids direct conversion between ortho and para states [2]. This restriction makes H2 a textbook example of how symmetry governs quantum dynamics.
Simulations show that knot-like magnetic structures called hopfions can be pulled apart—a capability that could be harnessed for spintronic memory devices.
With a carefully designed experiment and a handful of tin atoms, University of Tennessee, Knoxville’s physicists have found a long-sought form of superconductivity, taking one more step toward creating custom quantum materials.
Scientists have known about superconductivity for more than a century. At low temperatures, resistance in certain materials vanishes and they carry electrical current without losing any energy. Superconductors are part of particle accelerators and magnetic resonance imaging machines. While they need extremely cool environments to work, the mechanism that drives them is quite well understood: electrons, which normally repel each other, form pairs and carry the current.
Spintronic devices enable data processing with significantly lower energy consumption. They are based on the interaction between ferromagnetic and antiferromagnetic layers. Now, a team from Freie Universität Berlin, HZB and Uppsala University has succeeded in tracking—separately for each layer—how the magnetic order changes after a short laser pulse has excited the system. The researchers were also able to identify the main cause of the loss of antiferromagnetic order in the oxide layer: The excitation is transported from the hot electrons in the ferromagnetic metal to the spins in the antiferromagnet. The findings are published in the journal Physical Review Letters.
While conventional microelectronics involves the movement of electric charges, spintronics is based on electron spins. Manipulating spins requires less energy than transporting charged particles. Consequently, spintronic components offer the potential for significant energy savings and high processing speeds.
However, future applications will require clock speeds in the terahertz range, which are not yet achievable today. The clock speeds of current spin-based applications are up to a hundred times lower. In order to advance spintronics, a large team at the Transregio Collaborative Research Center CRC/TRR 227 is investigating spin dynamics in solids at atomic resolution and on ultrafast timescales.
