Quantum Mechanics

Quantum mechanics is the branch of mechanics that deals with the mathematical description of the motion and interaction of subatomic particles, incorporating the concepts of quantization of energy, wave–particle duality, the uncertainty principle, and the correspondence principle.

  • “Bethe Strings” Experimentally Demonstrated as Many-Body Quantum States for the First Time

    In SrCo₂V₂O₈ the cobalt ions (CO²⁺) form in the interior of a chain of edges-linked oxygen octahedra a quasi-one-dimensional electron spin chain with spin S = ½. © Universität Augsburg/IfP/EP V

    The synthesis of quasi one-dimensional magnets and their investigation by means of optical spectroscopy in extremely high magnetic fields led to success. Augsburg /AL/KPP - “Bethe strings” are excitations of strongly bound electron spins in one-dimensional quantum spin systems. These quantum spin states are named after the physicist Hans Bethe, who first described them theoretically in 1931.

  • A glimpse inside the atom: energy-filtered TEM at a subatomic level

    A glimpse inside the atom energy filtered TEM at a subatomic level | Atomic orbitals of carbon atoms in graphene Image: TU Wien

    Using electron microscopes, it is possible to image individual atoms. Scientists at TU Wien have calculated how it is possible to look even further inside the atom to image individual electron orbitals, using EFTEM (energy-filtered transmission electron microoscopy).

  • A Quantum Low Pass for Photons

    Illustration of the two-photon blockade. Top: Irradiated by a laser pulse a single atom in free space can absorb and emit only one photon at a time, without constraints on the direction of the photons. Middle: A system consisting of a cavity can absorb and emit an unlimited number of photons. Below: In case of the strongly coupled atom-cavity system the frequency of the laser light can be chosen such that the system can store and emit two photons at maximum. MPQ, Quantum Dynamics Division

    Physicists in Garching observe novel quantum effect that limits the number of emitted photons. The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called Poisson-distribution. There are, however, light sources with non-classical photon number distributions that can only be described by the laws of quantum mechanics. A well-known example is the single-photon source that may find application in quantum cryptography for secret key distribution or in quantum networks for connecting quantum memories and processors. However, for many applications in nonlinear quantum optics light pulses with a certain fixed number of photons, e.g. two, three or four, are highly desirable.

  • An Atomic Quantum Bit Made Switchable

    Depending on the orientation of an applied magnetic field, quantum tunneling of the magnetisation allows to either freeze or to flip magnetic moments. © University of Augsburg/IfP/EKM

    One bit per atom: Augsburg-based physicists and US colleagues are reaching the ultimate limit for nanoscale data storage

  • An Experiment Seeks to Make Quantum Physics Visible to the Naked Eye

    Predictions from quantum physics have been confirmed by countless experiments, but no one has yet detected the quantum physical effect of entanglement directly with the naked eye. This should now be possible thanks to an experiment proposed by a team around a theoretical physicist at the University of Basel. The experiment might pave the way for new applications in quantum physics.

  • Artificial Agent Designs Quantum Experiments

    The artificial agent uses optical elements such as this beam splitter to construct new and optimized experiments. Harald Ritsch

    On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

  • Aus zwei mach eins: Wie aus grünem Licht blaues wird

    Aus zwei mach eins Wie aus grünem Licht blaues wird | Photonen-Hochkonversion: Die Energieübertragung zwischen den Molekülen basiert auf einem Austausch von Elektronen (Dexter-Transfer) Abbildung: Michael Oldenburg

    Die Hochkonversion von Photonen ermöglicht, Licht effizienter zu nutzen: Zwei Lichtteilchen werden in ein Lichtteilchen mit höherer Energie umgewandelt. Forscher am KIT haben nun erstmals gezeigt, dass innere Grenzflächen zwischen oberflächengebundenen metallorganischen Gerüstverbindungen (SURMOFs) sich optimal dafür eignen – sie haben aus grünem Licht blaues Licht gemacht. Dieses Ergebnis wurde nun in der Fachzeitschrift Advanced Materials vorgestellt und eröffnet neue Möglichkeiten für optoelektronische Anwendungen wie Solarzellen oder Leuchtdioden. (DOI: 10.1002/adma.201601718)

  • Better tests for Schrödinger cats

    MPQ scientists develop new methods to test the world view of macroscopic realism

    In a classical world, objects have pre-existing properties, physical influences are local and cannot travel faster than the speed of light, and it is in principle possible to measure the properties of macroscopic systems without altering them. This is referred to as local realism and macroscopic realism, and quantum mechanics is in strong contradiction with both of them. While Bell inequalities have been proven to be an optimal tool for ruling out local realism in quantum experiments, Lucas Clemente and Johannes Kofler from the Theory Division of the Max Planck Institute of Quantum Optics (MPQ) in Garching, Germany, have now shown that inequalities can never be optimal for tests of macroscopic realism. Their results reveal a hitherto unknown radical difference in the mathematical structures of spatial and temporal correlations in quantum physics, and also provide a better tool for the search of Schrödinger cat-like states (PRL.116.150401, 15. April 2016).

  • Breakthrough with a chain of gold atoms

    Arists’ view of the quantized thermal conductance of an atomically thin gold contact. Created by Enrique Sahagun

    In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport. The precise control of electron transport in microelectronics makes complex logic circuits possible that are in daily use in smartphones and laptops. Heat transport is of similar fundamental importance and its control is for instance necessary to efficiently cool the ever smaller chips. An international team including theoretical physicists from Konstanz, Junior Professor Fabian Pauly and Professor Peter Nielaba and their staff, has achieved a real breakthrough in better understanding heat transport at the nanoscale.

  • Brightest Source of Entangled Photon

    Optical setup for experiments with entangled photons at IFW Dresden. Photo: Jürgen Loesel

    Scientists at Leibniz Institute for Solid State and Materials Research Dresden (IFW) and at Leibniz University Hannover (LUH) have developed a broadband optical antenna for highly efficient extraction of entangled photons. With a yield of 37% per pulse, it is the brightest source of entangled photons reported so far.

  • Classical mechanics helps control quantum computers: Into the quantum world with a tennis racket

    While the racket rotates 360 degrees about its lateral axis, the tennis racket effect leads to an unintentional 180-degree flip about its longitudinal axis. Credit: Steffen Glaser / TUM

    Quantum technology is seen as an important future-oriented technology: smaller, faster and with higher performance than conventional electronics. However, exploiting quantum effects is difficult because nature’s smallest building blocks have properties quite distinct from those we know from our everyday world. An international team of researchers has now succeeded in extracting a fault tolerant manipulation of quanta from an effect of classical mechanics.

  • Controlling Quantum States Atom by Atom

    Controlling Quantum States Atom by Atom | Using the tip of a scanning tunnel microscope, a single xenon atom (yellow) is being moved from a quantum box (blue), thus specifically altering its electronic quantum state. (Image: University of Basel, Department of Physics)

    An international consortium led by researchers at the University of Basel has developed a method to precisely alter the quantum mechanical states of electrons within an array of quantum boxes. The method can be used to investigate the interactions between various types of atoms and electrons, which is essential for future quantum technologies, as the group reports in the journal Small.

  • Controlling Thermal and Particle Currents by Quantum Observation

    Artistic illustration of the role of a quantum observer in a nanodevice. © K. Aranburu

    Researchers from the Theory Department of the MPSD have realized the control of thermal and electrical currents in nanoscale devices by means of quantum local observations. Measurement plays a fundamental role in quantum mechanics. At the same time, it also constitutes one of the main problems regarding the interpretation of this whole field. The best-known illustration of the principles of superposition and entanglement is Schrödinger’s cat. Not being visible from the outside, the cat resides in a coherent superposition of two states: it is alive and dead at the same time.

  • Describing the Behaviour of Electrons Under Extreme Conditions for the First Time

    In nature, the hot, dense matter of electron gas occurs inside planets, such as here in Jupiter. Photo: NASA/JPL-Caltech/SwRI/MSSS/Gabriel Fiset

    Electrons are an elementary component of our world: they surround the core of all atoms, are essential to the formation of molecules, and primarily determine the properties of solids and liquids. They are also the charge carriers of electrical current, without which our high-tech environment with smartphones, computers and even the traditional light bulb would not be conceivable. In spite of their omnipresence in everyday life, we have not yet been able to accurately describe the behaviour of interacting electrons - only approximate it in models - especially at extreme temperatures and densities, such as inside planets or in stars.

  • Developing Reliable Quantum Computers

    Illustration: Quantum Optics and Statistics, University of Freiburg

    International research team makes important step on the path to solving certification problems. Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to ensure it is working reliably? Depending on the algorithmic task, this could be an easy or a very difficult certification problem.

  • Die Quantenschaukel - ein Pendel das gleichzeitig vor und zurück schwingt

    Ultrakurze Terahertz-Impulse regen Zwei-Quanten-Oszillationen von Atomen in einem Halbleiterkristall an. Die von den bewegten Atomen abgestrahlten Terahertz-Wellen werden mittels einer neuen zeitaufgelösten Technik analysiert und zeigen den nicht-klassischen Charakter der Atombewegungen von großer Amplitude.

  • Die Vermessung der Chemie: Wasserstoffbrücken-Bindungen experimentell erfasst

    Ein Team aus dem Helmholtz-Zentrum Berlin konnte nun erstmals messen, wie neue Verbindungen zwischen Molekülen diese beeinflussen: Sie haben aus Messdaten an der Swiss Lightsource des Paul-Scherrer-Instituts die „Energielandschaft“ von Azeton-Molekülen rekonstruiert und so experimentell den Aufbau von Wasserstoffbrücken zwischen Azeton- und Chloroform-Molekülen nachgewiesen. Die Ergebnisse sind in Nature Scientific Reports veröffentlicht und helfen, grundlegende Phänomene der Chemie zu verstehen.

  • Eine Mini-Antenne für die Erzeugung von hochfrequenten Spinwellen

    Eine Mini Antenne für die Erzeugung von hochfrequenten Spinwellen | Das Zentrum eines magnetischen Wirbels sendet unter hochfrequenten magnetischen Wechselfeldern Spinwellen mit sehr kurzen Wellenlängen aus. Abbildung: HZDR

    Im Zuge der rasant fortschreitenden Miniaturisierung steht die Datenverarbeitung mit Hilfe elektrischer Ströme vor zum Teil unlösbaren Herausforderungen. Eine vielversprechende Alternative für den Informationstransport in noch kompakteren Chips sind magnetische Spinwellen. Wissenschaftlern des Helmholtz-Zentrums Dresden-Rossendorf (HZDR) ist es nun bei einer internationalen Zusammenarbeit gelungen, Spinwellen mit extrem kurzen Wellenlängen im Nanometer-Bereich – eine entscheidende Eigenschaft für die spätere Anwendung – gezielt zu erzeugen.

  • Eine neue Art von Quanten-Bits: Elektronenlöcher

    Eine neue Art von Quanten Bits Elektronenlöcher picture 1 | Das Team vom Lehrstuhl für Festkörperphysik arbeitet mit winzigen Strukturen. Die Quantenpunkte, die die Forscher um Andreas Wieck erzeugen, sind gerade einmal 30 Nanometer breit. Photo: RUB, Marquard

    Ein Forscherteam aus Deutschland, Frankreich und der Schweiz hat Quanten-Bits, kurz Qubits, in einer neuen Form umgesetzt. Eines Tages könnten diese die Informationseinheiten eines Quantencomputers sein. Bislang hatten die Wissenschaftler Qubits in Form von einzelnen Elektronen realisiert. Das führte jedoch zu Störeffekten und machte die Informationsträger schwer zu programmieren und auszulesen. Dieses Problem beseitigte die Gruppe nun, indem sie Elektronenlöcher statt Elektronen als Qubits nutzte. Das Team berichtet in der Zeitschrift „Nature Materials“.

  • Electron Rivers

    Usually, the movement of electrons in a real material is rather different from the flow of water in a river. However, in extraordinary materials like the metal oxide PdCoO2, “electron rivers” can exist, as predicted theoretically over fifty years ago and now demonstrated by scientists from the MPI CPfS.