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.

  • 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).

  • 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.

  • 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).

  • 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.

  • 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.

  • Entanglement Becomes Easier to Measure

    Physicists have developed a new protocol to detect entanglement of many-particle quantum states using a much easier approach. The protocol is particularly interesting for characterizing entanglement in systems involving many particles. These systems could help us not only to improve our understanding of matter but to develop measurement techniques beyond current existing technologies.

  • Exotischer Materiezustand: "Flüssige" Quantenspins bei tiefsten Temperaturen beobachtet

    Exotischer Materiezustand Flüssige Quantenspins bei tiefsten Temperaturen beobachtet | Im Kristallgitter von Kalzium-Chrom-Oxid gibt es sowohl ferromagnetische Wechselwirkungen (grüne und rote Balken) als auch antiferromagnetische (blaue Balken). Abbildung: HZB

    Ein Team am HZB hat experimentell eine sogenannte Quanten-Spinflüssigkeit in einem Einkristall aus Kalzium-Chrom-Oxid nachgewiesen. Dabei handelt es sich um einen neuartigen Materiezustand. Das Besondere an dieser Entdeckung: Nach gängigen Vorstellungen war das Quantenphänomen in diesem Material gar nicht möglich. Nun liegt eine Erklärung vor. Die Arbeit erweitert das Verständnis von kondensierter Materie und könnte auch für die zukünftige Entwicklung von Quantencomputern von Bedeutung sein. Die Ergebnisse sind nun in Nature Physics veröffentlicht.

  • First experimental quantum simulation of particle physics phenomena

    First experimental quantum simulation of particle physics phenomena | Physicists have simulated the creation of elementary particle pairs out of the vacuum by using a quantum computer. IQOQI/Harald Ritsch

    Physicists in Innsbruck have realized the first quantum simulation of lattice gauge theories, building a bridge between high-energy theory and atomic physics. In the journal Nature, Rainer Blatt‘s and Peter Zoller’s research teams describe how they simulated the creation of elementary particle pairs out of the vacuum by using a quantum computer.

  • Fundamental properties of spin Seebeck effect unveiled

    Fundamental properties of spin Seebeck effect unveiled | Thermally excited spin waves carry a spin current from the ferromagnet (YIG in this case) into the metal layer. Depending on the YIG thickness and the interface condition the amplitude of the spin current as well as transmission properties change. illustraton: Joel Cramer, JGU

    Direct correlation between temperature dependent generation of spin currents and atomic composition of interfaces found

    Thermoelectric effects are a fundamental building block for the conception and development of new processes for information processing. They enable to re-use waste heat obtained in different processes for the operation of respective devices and thus contribute to the establishment of more energy-efficient, ecofriendly processes. A promising representative of this effect category is the so-called spin Seebeck effect, which became prominent within recent years. This effect allows to convert waste heat into spin currents and thereby to transport energy as well as information in magnetic, electrically insulating materials.

  • Making magnets flip like cats at room temperature

    Making magnets flip like cats at room temperature | Flipping NiMnSb magnet Illustration: Inspire Group, JGU

    Heusler alloy NiMnSb could prove valuable as a new material for digital information processing and storage. The direction of its magnetic field can be switched by changing the direction of an electric current running through it.

  • Manipulating superconducting plasma waves with terahertz light

    Manipulating superconducting plasma waves with terahertz light | Josephson plasma wave in a layered superconductor, parametrically amplified through a strong terahertz light pulse. Image: J.M. Harms/MPI for the Structure and Dynamics of Matter

    Terahertz illumination amplifies Josephson plasma waves in high temperature superconductors, potentially paving the way for stabilizing fluctuating superconductivity

    Most systems in nature are inherently nonlinear, meaning that their response to any external excitation is not proportional to the strength of the applied stimulus. Nonlinearities are observed, for example, in macroscopic phenomena such as the flow of fluids like water and air or of currents in electronic circuits. Manipulating the nonlinear behavior is therefore inherently interesting for achieving control over several processes. An international team of researchers led by Andrea Cavalleri from the Max Planck Institute for the Structure and Dynamics of Matter at CFEL in Hamburg utilized the nonlinear interaction between a terahertz light field and a superconducting plasma wave in a high temperature cuprate superconductor to amplify the latter. This resulted in a more coherent superconductor, which is less susceptible to thermal fluctuations. Due to the non-dissipative superconducting nature of the plasma wave, the study opens up new avenues for “plasmonics”, a field of science utilizing plasma waves for transmitting information. These findings are reported in the journal Nature Physics.

  • Observing the birth of a spectral line

    Absorption in a helium as it depends on the photon energy of the exciting extreme-ultraviolet flash of light and the time delay to the ionizing near-infrared laser pulse acting as a cut-off gate. graphics: MPIK

    Ultrashort intense laser pulses cut into a fundamental quantum phenomenon.
    For the first time, physicists managed to observe in real time how an atomic spectral line emerges within the incredibly short time span of a few femtoseconds, verifying a theoretical prediction. This has been possible by applying a very fast temporal switch: An intense laser pulse cuts off the natural decay shortly after excitation by a preceding laser pulse. The build-up of the asymmetric Fano line shape of two quantum-mechanically interfering electrons in the Helium atom is measured by varying the time delay between the two laser pulses.

  • One impurity to bind them all

    One impurity to bind them all | Illustration of the trapping process: a two-level atomic impurity is localized in a periodic structure. Because the atomic frequency lies in the bandgap of the material the photons that are released after excitation of the atom are trapped inside the structure Graphic: MPQ, Theory Division

    MPQ researchers show that a single atomic impurity is able to trap infinitely many bosons around it.

    Nobody is perfect, but sometimes it is the defect that makes the difference. For example, the electric properties of semiconductors undergo significant changes by the slightest variation in the dopant concentration, and though a perfect diamond is without any colour, atomic impurities make them shine in pale blue, violet or pink which even enhances their value. All these effects go back to processes that are triggered by the interaction of the impurity with the quantum many-body system it is embedded in. A team of physicists in the Theory Division of Prof. Ignacio Cirac at the Max Planck Institute of Quantum Optics (MPQ) has now investigated the more general case where an impurity atom is coupled to a structured bath of bosons (for example, photons in a periodically engineered dielectric) showing how a single atom can bind many bosons around it. Bound states of bosons are of particular interest because they give rise to long and strong interactions enabling new regimes for quantum simulations. (Phys. Rev. X 6, 021027 (2016), 25 May 2016).

  • One-dimensional light on graphene

    Nanostructured graphene illuminated with light holds potential for a wide range of applications in photonics and optoelectronics, including infrared and terahertz photodetectors, sensors, reflect arrays or modulators. Development of graphene nanopatterning technology has in recent years enabled the construction of such devices that hold promise for a quick transfer from scientific labs to the marketplace. Now scientists have carefully mapped, with nanoresolution, the structure of light on graphene nanoresonators, observing light that is confined to extremely small volumes at the edges of the nanostructures. The nearly 1D form of this light is expected to lead to novel device applications, for example to efficient control of quantum emitters, a sort of “bit” in future quantum computers.

  • Physicists Couple Distant Nuclear Spins Using a Single Electron

    For the first time, researchers at the University of Basel have coupled the nuclear spins of distant atoms using just a single electron. Three research groups from the Department of Physics took part in this complex experiment, the results of which have recently been published in the journal Nature Nanotechnology.