# Quantum mechanics/physics/theory

## Quantum mechanics (QM – also known as quantum physics, or quantum theory) is a branch of physics which deals with physical phenomena at nanoscopic scales where the action is on the order of the Planck constant.

It departs from classical mechanics primarily at the quantum realm of atomic and subatomic length scales. Quantum mechanics provides a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. Quantum mechanics provides a substantially useful framework for many features of the modern periodic table of elements including the behavior of atoms during chemical bonding and has played a significant role in the development of many modern technologies.

In advanced topics of quantum mechanics, some of these behaviors are macroscopic (see macroscopic quantum phenomena) and emerge at only extreme (i.e., very low or very high) energies or temperatures (such as in the use of superconducting magnets). For example, the angular momentum of an electron bound to an atom or molecule is quantized. In contrast, the angular momentum of an unbound electron is not quantized. In the context of quantum mechanics, the wave–particle duality of energy and matter and the uncertainty principle provide a unified view of the behavior of photons, electrons, and other atomic-scale objects.

The mathematical formulations of quantum mechanics are abstract. A mathematical function, the wavefunction, provides information about the probability amplitude of position, momentum, and other physical properties of a particle. Mathematical manipulations of the wavefunction usually involve bra–ket notation which requires an understanding of complex numbers and linear functionals. The wavefunction formulation treats the particle as a quantum harmonic oscillator, and the mathematics is akin to that describing acoustic resonance. Many of the results of quantum mechanics are not easily visualized in terms of classical mechanics. For instance, in a quantum mechanical model the lowest energy state of a system, the ground state, is non-zero as opposed to a more "traditional" ground state with zero kinetic energy (all particles at rest). Instead of a traditional static, unchanging zero energy state, quantum mechanics allows for far more dynamic, chaotic possibilities, according to John Wheeler.

The earliest versions of quantum mechanics were formulated in the first decade of the 20th century. About this time, the atomic theory and the corpuscular theory of light (as updated by Einstein)[1] first came to be widely accepted as scientific fact; these latter theories can be viewed as quantum theories of matter and electromagnetic radiation, respectively. Early quantum theory was significantly reformulated in the mid-1920s by Werner Heisenberg, Max Born and Pascual Jordan, (matrix mechanics); Louis de Broglie and Erwin Schrödinger (wave mechanics); and Wolfgang Pauli and Satyendra Nath Bose (statistics of subatomic particles).

Moreover, the Copenhagen interpretation of Niels Bohr became widely accepted. By 1930, quantum mechanics had been further unified and formalized by the work of David Hilbert, Paul Dirac and John von Neumann[2] with a greater emphasis placed on measurement in quantum mechanics, the statistical nature of our knowledge of reality, and philosophical speculation about the role of the observer. Quantum mechanics has since permeated throughout many aspects of 20th-century physics and other disciplines including quantum chemistry, quantum electronics, quantum optics, and quantum information science. Much 19th-century physics has been re-evaluated as the "classical limit" of quantum mechanics and its more advanced developments in terms of quantum field theory, string theory, and speculative quantum gravity theories.

The name quantum mechanics derives from the observation that some physical quantities can change only in discrete amounts (Latin quanta), and not in a continuous (cf. analog) way.

Quantum Mechanics Revisited: Physicists Propose New Structure of Time. The Nature of Time Does time flow continuously, gliding without interruption from one happening to another? Or is it choppy and pixelated, an illusory phenomenon formed of innumerable discrete elements? The world of our sensory experience would seem to support the former notion—that time moves ever, ever on; however, new research, which was recently published in The European Physical Journal C, suggests time may be much grainier than we suppose, and the idea has important implications for quantum mechanics.

The research centers on what is called the “Planck time,” approximately 10-43 seconds, which is widely believed to be the smallest meaningful unit of time. Defined as the time interval required for light to traverse the Planck length (about 1.6 x 10-35 meter), the Planck time resides at that incomprehensible scale where spacetime, reality, and everything that is begins to break down and lose all meaning. Time After Time Read a little further into the paper, and things get really weird. Scientists Have Figured Out What We Need to Achieve Secure Quantum Teleportation.

Quantum Teleportation An international collaboration of researcher from China, Europe, and Australia have demonstrated the precise requirements needed to secure quantum teleportation, a concept that is essential to the future of a quantum internet that lets information to be transmitted securely. Of course, quantum teleportation doesn’t mean that it’s possible for a person to instantly pop from New York to London, but they can instantly transport information through a bizarre quantum mechanics property called entanglement.

Learn more about the physics behind quantum entanglement in this video from Vertasium. In the press release, Professor Margaret Reid, from the Swinburne Institute of Technology, explains that the problem with quantum teleportation goes back to how the information is sent along: “Let’s say ‘Alice’ begins the process by performing operations on the quantum state–something that encodes the state of a system–at her station. Quantum Steering. Quantum Surreality: Scientists Observe the Motion of Entangled Photons. Physicists May Have Discovered a New "Tetraquark" Particle. Evidence for a never-before-seen particle containing four types of quark has shown up in data from the Tevatron collider at the Fermi National Accelerator Laboratory (Fermilab) in Illinois.

The new particle, a class of “tetraquark,” is made of a bottom quark, a strange quark, an up quark and a down quark. The discovery could help elucidate the complex rules that govern quarks—the tiny fundamental particles that make up the protons and neutrons inside all the atoms in the universe. Protons and neutrons each contain three quarks, which is by far the most stable grouping. Pairs of quarks, called mesons, also commonly appear, but larger conglomerations of quarks are extremely rare. Scientists at the Large Hadron Collider (LHC) in Switzerland last year saw the first signs of a pentaquark—a grouping of five quarks—which had long been predicted but never seen.

One open question is: How many quarks can stick together to form a particle? Quantum physics for the terminally confused. Credit: BSIP/Getty Images Does quantum physics melt your brain? First, don’t panic. You’re not alone in your confuddlement. As legendary physicist Richard Feynman said: “I think I can safely say that nobody understands quantum mechanics.” Nevertheless, quantum theory is vital for describing how our world is screwed together.

So we’ve broken down the ideas of quantum theory to the level where even a five-(or 55) year-old can get the gist. What is quantum theory? After a few thousand years of argument we finally know what “stuff” is made of – tiny particles called electrons and quarks. Atoms and molecules are the Lego blocks of our world. To describe the way this tiny world operates, scientists use a collection of ideas called quantum theory. The theory makes weird predictions (for example, that particles can be in two places at once), yet it is also the most precisely validated theory in physics. It’s weird, it’s right, it’s important. But what does 'quantum' actually mean? Particle/wave duality. Researchers discover new fundamental quantum mechanical property. Image (c): NASA/Sonoma State University/Aurore Simonnet A newly-discovered fundamental property of electrical currents in extremely small metal circuits demonstrates how negatively-charged particles can wash over said circuit like waves, generating interference in parts of the circuit where no current is delivered.

This characteristic, discovered by researchers at the University of Twente’s MESA+ institute and detailed in a recent Scientific Reports paper, is due largely to the circuit’s geometry as well as the quantum mechanical wave character of electrons, according to the study authors. As part of their research, the MESA+ team demonstrated electron interference—a phenomenon in which propagating waves interact coherently—in a gold ring with a 500 nanometer diameter. One side of the ring was connected to a tiny wire through which an electrical current could be driven, while the other side was connected to a different wire attached to a voltmeter. Physicists discover easy way to measure entanglement—on a sphere.

Quantum entanglement—which occurs when two or more particles are correlated in such a way that they can influence each other even across large distances—is not an all-or-nothing phenomenon, but occurs in various degrees. The more a quantum state is entangled with its partner, the better the states will perform in quantum information applications. Unfortunately, quantifying entanglement is a difficult process involving complex optimization problems that give even physicists headaches. Now in a new paper to be published in Physical Review Letters, mathematical physicists Bartosz Regula and Gerardo Adesso at The University of Nottingham have greatly simplified the problem of measuring entanglement. To do this, the scientists turned the difficult analytical problem into an easy geometrical one. As the scientists explain, the traditionally difficult part of the math problem is that it requires finding the optimal decomposition of mixed states into pure states.

Theory of Everything: Unifying Gravity and Quantum Mechanics. Earth: The Blue Marble Credit: NASA/Goddard Space Flight Center/Reto Stöckli Quantum mechanics may seem like it is beyond our realm of experience; however, it is an integral part of the physics that governs our lives. Although it feels like we are only interacting with things that are rather large–things that we can see and feel–every second, our bodies are dancing through a sea of tiny particles. In fact, we are a part of this sea of microscopic particles. In short, we cannot separate ourselves and our experiences from quantum mechanics. Yet, there is an issue with this fact, as there is one very important aspect of our everyday experience that is not described within a quantum framework: Gravity.

This is rather problematic. Because it keeps planets and stars and over very bodies together, gravity is one of the most important forces of the cosmos. Some physicists hypothesize that gravity itself is the ultimate decoherence, or the weakest form of background noise. The Central Mystery of Quantum Mechanics, Animated. New Discovery in Particle Physics Raises Hope for a "Theory of Everything" The standard model of particle physics, which describes every particle we know of and how they interact, was given much credence when the Higgs boson was discovered in 2012.

Now, measurements of a rare particle-physics decay at the Large Hadron Collider offer further support for the model – but also hints at ways to find out what lies beyond it. The standard model is cherished by physicists because it can explain most of the fundamental phenomena in nature by referencing just a handful of elementary particles. The elementary particles that according to the standard model makes up matter. By HolgerFiedler nach Benutzer:Murphee via Wikimedia Commons, CC BY-SA These particles include quarks (one of the components of an atom) and electron-like particles called leptons – along with their so-called antiparticles which are identical but have opposite charge.

The model also includes the particles that carry forces between them (photons, gluons, W and Z bosons) and the Higgs. Scientists Report Teleportation of Physical Objects From One Location To Another. The concept of teleportation comes primarily from science fiction literature throughout human history, but things are changing. It’s 2015 and developments in quantum theory and general relativity physics have been successful in exploring the concept of teleportation for quite some time now.

Today, numerous teleportation breakthroughs have been made. One example is the work of Professor Rainer Blatt, at the University of Innsbruck. They were successfully able to perform teleportation on atoms for the first time, their work was published in the journal Nature.(1) They were able to transfer key properties of one particle to another without using any physical link. In this case, teleportation occurred in the form of transferring quantum states between two atoms, these include the atom’s energy, motion, magnetic field and other physical properties.

This is possible due to the strange behavior that exists at the atomic scale, known as entanglement. The experiments showed that: Sources: Quantum mechanics. Wavefunctions of the electron in a hydrogen atom at different energy levels. Quantum mechanics cannot predict the exact location of a particle in space, only the probability of finding it at different locations.[1] The brighter areas represent a higher probability of finding the electron. Quantum mechanics (QM; also known as quantum physics, quantum theory, the wave mechanical model, or matrix mechanics), including quantum field theory, is a fundamental theory in physics which describes nature at the smallest scales of atoms and subatomic particles.[2] Quantum mechanics gradually arose from theories to explain observations which could not be reconciled with classical physics, such as Max Planck's solution in 1900 to the black-body radiation problem, and from the correspondence between energy and frequency in Albert Einstein's 1905 paper which explained the photoelectric effect.

History In 1838, Michael Faraday discovered cathode rays. Where h is Planck's constant. Coulomb potential. QUANTUM PHYSICS.

## Attempts at simple explanations

History of Quantum mechanics. Fundamental components. Quantum field theory. Quantum mechanics equations. Interactions with other scientific theories. Philosophical implications. Examples. Articles. Ideas related to Quantum mechanics. Experiments.