Research
Task Groups

The Workbenches of QUEST - Task Groups

The mission of our Task Groups is to specify research projects important to QUEST by an interdisciplinary collaboration of scientists from different research groups.

Our nine Task Groups are the “work benches” in QUEST, where “cross-linking” of the research areas results either in visions which are turned into reality or new research activities that are initiated and executed by a number of research groups working together.

INFORMATION ABOUT THE INDIVIDUAL TASK GROUPS

  • Physics of Spinor Systems

    This Task Group constitutes a joint effort between theorists and experimentalists in the fields of condensed-matter physics and quantum optics towards achieving a better common understanding of the physics of so-called spinor systems. These systems, which are formed by particles with various internal (spin)states, exhibit some very interesting physical phenomena due to the interplay between internal and external degrees of freedom.

    This group focuses its activities on four different scenarios where spinor physics plays a crucial role:

    • Spinor gases as a fascinating novel source for highly-accurate measurements.
    • Spinor gases in so-called optical lattices and their fascinating links to solid- state physics.
    • Quasi-relativistic physics in cold spinor gases, which display a striking resem- blance to high-energy physics.
    • Spin-noise spectroscopy, which constitutes an invaluable tool for solid-state and cold gas analysis.
    Spinor Bose-Einstein condensates may be used as a source for non-classical matter waves. Spinor Bose-Einstein condensates may be used as a source for non-classical matter waves. Spinor Bose-Einstein condensates may be used as a source for non-classical matter waves. © Source: C.Klempt/IQO
    Spinor Bose-Einstein condensates may be used as a source for non-classical matter waves. (Source: C.Klempt/IQO)

    Involved Research Projects

    • Non-Classical States of Matter
    • Condensed Matter Physics with Cold Atoms
    • Artificial Electromagnetism
    • Spin-Noise Spectroscopy
  • Quantum Test of the Equivalence Principle

    A better understanding of gravity is today one of the most important issues in fundamental physics. We lack a joint theory for gravity and quantum mechanics. Promising candidates for resolving this issue predict new forces, which might lead to a modification of the equivalence principle. The principle of equivalence states that the gravitational mass equals the inertial mass and that bodies of different mass and composition should display an equal rate of free fall.

    One of the most puzzling features of matter is its wave nature. The propagation of matter waves in gravity is at the heart of both gravity and quantum mechanics. The Task Group “Quantum Test of the Equivalence Principle” develops tools for tailoring matter waves for precision experiments. The tools enable testing of the universal propagation of matter waves. Matter waves are very efficiently formed from different isotopes of potassium and rubidium. The resultant wave propagation is compared using precision interferometry to an accuracy of a few billionths of the acceleration due to gravity.

    This will be the first dedicated experiment to compare the propagation of matter waves using state-of-the-art techniques. The sensitivity of these experiments is greatly enhanced by the extended time of free fall of these quantum objects. The scientists are therefore aiming at an even more challenging approach to do such an experiment to be carried out in a in drop tower or even in space. A first step is the demonstration of Bose-Einstein condensation in microgravity at the 146 meter high drop tower in Bremen.

    View from inside the droptower in Bremen with a typical experimental capsule. Photo: ZARM Universität Bremen View from inside the droptower in Bremen with a typical experimental capsule. Photo: ZARM Universität Bremen View from inside the droptower in Bremen with a typical experimental capsule. Photo: ZARM Universität Bremen
    View from inside the droptower in Bremen with a typical experimental capsule. Photo: ZARM Universität Bremen
  • Transportable Ultra-stable Clocks

    The Task Group “Transportable Ultra-stable Clocks” is focussed on the development and application of transportable highly accurate clocks. The best present optical clocks are so accurate that only clocks at the same location can be compared. However, the most interesting applications of these clocks occur outside the laboratory, for example in space, for navigation, geodesy and tracking spacecrafts in deep space missions.

    The Task Group investigates various methods to make such clocks available for these applications. Ultra-stable optical resonators are developed that can be transported without any loss of performance. For applications requiring high absolute accuracy, a complete optical lattice clock is miniaturized, making it suitable for field measurements such as relativistic geodesy. Further investigations quantify the improvements that are possible in satellite-based geodesy, when highly stable clocks are used in the receivers. To investigate this, a transportable hydrogen maser of the Physikalisch-Technische Bundesanstalt (PTB) was employed.

    Instead of transporting clocks, optical frequencies can also be transmitted through optical fibers that are widely used for telecommunication. In a first successfully test, a stabilized link between the PTB in Braunschweig and the Institute for Quantum Optics in Hannover was established. Over a distance of 73 kilometres an optical frequency could be transmitted with a residual uncertainty well below that of the participating optical clocks.

    Vibration-insensitive optical reference resonator. Photo: PTB Braunschweig Vibration-insensitive optical reference resonator. Photo: PTB Braunschweig Vibration-insensitive optical reference resonator. Photo: PTB Braunschweig
    Vibration-insensitive optical reference resonator. Photo: PTB Braunschweig

    Involved Research Areas and Projects

    • Research Field Quantum Engineering
    • Research Field Quantum Sensors
    • Research Field Enabling Technologies
    • Variations of Fundamental Constants
      (Dr. Ekkehard Peik)
    • High Precision Modelling
      (Prof. Dr. Claus Lämmerzahl)
  • Variations of Fundamental Constants

    This Task Group questions one of the fundamental postulates of physics by asking whether the so-called fundamental constants are really constant. Some theoretical models that strive for a unified description of quantum physics and gravity predict, for example, a temporal and spatial dependence of the strength of the electromagnetic forces within atoms. This would result, among other effects, in a time dependence of the frequencies of atomic transitions and hence in a drift between different kinds of atomic clocks. Astrophysical observations of spectral lines from interstellar gas clouds are used to look for such changes over a wide range of the cosmological past.

    Within our planetary system, a test is performed by precisely monitoring the relative motion of the earth and the moon, based on laser ranging to the reflectors positioned on the moon since 1969. The experimental search for minute changes at the limits of the available measurement accuracy is of great relevance because the detection of variability in one of the fundamental constants would provide a valuable guide for the development of theory. The task group establishes a discussion forum on this interdisciplinary topic within QUEST that allows an exchange between experimental, observational and theoretical work in order to stimulate the development of new approaches and methods.

    Setup of the optical clock with a trapped Yb+ ion. This system allows a sensitive search for a temporal variation of the fine structure constant. Photo: Aginmar/PTB Setup of the optical clock with a trapped Yb+ ion. This system allows a sensitive search for a temporal variation of the fine structure constant. Photo: Aginmar/PTB Setup of the optical clock with a trapped Yb+ ion. This system allows a sensitive search for a temporal variation of the fine structure constant. Photo: Aginmar/PTB
    Setup of the optical clock with a trapped Yb+ ion. This system allows a sensitive search for a temporal variation of the fine structure constant. Photo: Aginmar/PTB

    Involved Research Areas

    • Research Field Quantum Engineering
    • Research Field Space-Time Research
  • Third Generation Gravitational Wave Observatories

    Gravitational waves allow astrophysical observations of regions of the universe that are hidden from observation by electromagnetic waves, such as, for example, the inner processes of super novae, neutron stars, or the early phase of the universe. Although the existence of gravitational waves is proven by the change of the orbital period of pulsars in binary systems, the direct detection of the change of lengths by gravitational waves is still pending.

    Gravitational wave detectors of the first generation, installed at various locations around the world, have finished collecting data and are close to being upgraded to the second generation of advanced detectors, with which the detection of gravi- tational waves can be expected. However, astronomical observations and subsequent detailed analysis of the observed signals on a regular basis require an even more sensitive third generation of detectors, two orders of magnitude greater in sensitivity than the first generation.

    European researchers, united in their efforts to build such an observatory, are currently carrying out a conceptual design study funded as part of the European Union’s 7th Framework Programme. This task group is participating in this design study by researching various innovative optical read-out schemes and detector topologies, and investigating high-power lasers, the properties of alternative optical materials, the usability of alternatives to dielectric optical coatings, the potential and optimization in the utilization of squeezed light, and the requirements in computational resources for data analysis.

    Artist’s impression of a possible underground layout for the Einstein Telescope with an arm length of ten kilometres at a depth of about 100 metres. Image: Kees Huyser Artist’s impression of a possible underground layout for the Einstein Telescope with an arm length of ten kilometres at a depth of about 100 metres. Image: Kees Huyser Artist’s impression of a possible underground layout for the Einstein Telescope with an arm length of ten kilometres at a depth of about 100 metres. Image: Kees Huyser
    Artist’s impression of a possible underground layout for the Einstein Telescope with an arm length of ten kilometres at a depth of about 100 metres. Image: Kees Huyser
  • 10 m Prototype Interferometer

    The 10 m Prototype Interferometer is a test bed to develop techniques for upgrades of the gravitational wave detector GEO 600. These include, for example, new high-power lasers, advanced seismic isolation, and the reduction of quantum noise. Furthermore, the prototype facility, with its large ultra-high vacuum system, excellent seismic isolation, well stabilized high-power laser, and fully digitally control infrastructure, allows experiments to be conducted that would not be possible otherwise. These experiments aim at obtaining a better understanding of how quantum mechanical effects can govern the macroscopic world. A 10 m Michelson interferometer is set up which is solely limited by quantum noise— photon shot noise at high frequencies and quantum back-action noise at low frequencies. 

    This sensitivity, until recently thought to be the ultimate limit in interferometry, is referred to as Standard Quantum Limit (SQL). However, even this remarkable sensitivity can be overcome by the application of innovative techniques such as the injection of squeezed vacuum states.

    To reach the SQL, several innovative approaches and techniques must be employed: To reduce thermal noise, the optical components will be individually suspended from silica fibres as the last stage of a multiple cascaded pendulum system. These are mounted on passive isolation tables, which are interferometrically interconnected. To minimise thermal noise from the mirror coatings, we use anti-resonant Fabry-Perot cavities as compound mirrors.

    © AEI
    AEI 10 meter prototype interferometer (Source:H.Lück/AEI)
  • Next Generation Gravity Field Missions

    [Translate to Englisch:] Das Schwerefeld der Erde ist weder räumlich noch zeitlich konstant, wenn man genau genug hinsieht. Die kleinen Abweichungen enthalten eine Vielzahl von Informationen, zum Beispiel über die Struktur des Erdmantels, über Änderungen im globalen Wasserkreislauf oder über die Dicke der polaren Eismassen.

    Die gezielte Vermessung des Erdschwerefeldes mithilfe von Satelliten begann im Jahr 2000 und umfasst heute die Missionen CHAMP (Challenging Minisatellite Payload for Geoscience and Application), GRACE (Gravity Recovery And Climate Experiment) und GOCE (Gravity Field and Steady-State Ocean Circulation Explorer). Die Missionen erfassen neue und einzigartige Daten, beispielsweise über das Abschmelzen des Grönlandeises oder die Absenkung des Grundwasserspiegels in Nordindien, aber auch in ganz anderen Bereichen. Vor allem die US/deutsche Mission GRACE hat das enorme Potenzial eines solchen Konzeptes aufgezeigt. Gleichzeitig hat GRACE aber auch klargemacht, wie viel mehr man mit genaueren Daten und höherer räumlicher Auflösung erreichen könnte. Für Fragen zu Änderun- gen im Erdsystem sind dabei Datenreihen über viele Jahre entscheidend.

    Diese Task Group spielt eine zentrale Rolle bei der Planung für eine Mission mit verbesserter Auflösung zur Fortsetzung und Verbesserung der Beobachtungszeitreihen. Dies ist nur in einer, in QUEST mittlerweile etablierten, multi-disziplinären Zusammenarbeit möglich. In QUEST befassen wir uns insbesondere mit der detaillierten Analyse aktueller GRACE-Daten, mit dem Design eines Laserinterferometers basierend auf LISA-Technologie, um das Mikrowellengerät von GRACE zu ersetzen und die Abstandsmessung um einen Faktor von mindestens 10 zu verbessern, und mit Designstudien der Satelliten.

    Prototype optical bench for an inter-satellite laser interferometer in the cleanroom. Photo: Marina Dehne Prototype optical bench for an inter-satellite laser interferometer in the cleanroom. Photo: Marina Dehne Prototype optical bench for an inter-satellite laser interferometer in the cleanroom. Photo: Marina Dehne
    Prototype optical bench for an inter-satellite laser interferometer in the cleanroom. Photo: Marina Dehne

    Involved Research Areas and Institutes

    • Precision Geodesy on Earth and in Space
      (Prof. Dr. Jakob Flury)
    • Next Generation Geodesy Missions
      (Dr. Benjamin Sheard)
    • Global Geodetic Observing System (GGOS)
      (Prof. Dr. Jürgen Müller)
    • Atomic and Photonic Quantum Sensors
      (Prof. Dr. Ernst Rasel)
    • ZARM
    • PTB
  • Advanced Light Sources and Optical Materials

    In most of the research projects within QUEST, special laser sources and optical materials are needed. In some of the research groups, mainly within the research area “Enabling Technologies”, it is exactly these sources and materials which are being investigated, improved, developed, and tailored to overcome current limits and to explore new frontiers in QUEST research.

    The Task Group “Advanced Light Sources and Optical Materials” has been established for mainly two different purposes. On the one hand in order to optimize the cross-linking between the laser and optical materials research groups. For this reason, a monthly laser seminar takes place at the Laser Zentrum Hannover in which the different groups present their latest results and discuss the challenges they face. This seminar provides an efficient, quick, and informal means for exchanging information between these research groups. On the other hand, it also serves as an interface to the other “laser-using” groups in QUEST, who are given an opportunity to benefit from the latest laser and optics developments in their own research.

    Manufacture of optical components in the laboratory at the Laser Zentrum Hannover. Photo: LZH Manufacture of optical components in the laboratory at the Laser Zentrum Hannover. Photo: LZH Manufacture of optical components in the laboratory at the Laser Zentrum Hannover. Photo: LZH
    Manufacture of optical components in the laboratory at the Laser Zentrum Hannover. Photo: LZH
  • High Precision Modelling

    In many cases, the experimental accuracy which can be achieved requires precise knowledge of the apparatus used and the effects influencing the measurements. Sometimes influences on the measurement cannot be shielded out and, thus, have to be modelled very precisely. In experiments with lasers, for example, lenses and mirrors will be heated leading to distortions of the material, which obviously will influence the experimental result.

    Optimization of the experimental design as well as determination of the dominant influences on the experimental outcome can be achieved only through thorough precise modelling of the whole apparatus. A required modelling accuracy of 10-20 is derived based on the accuracy of existing clocks and resonators. The modelling takes into account mechanically and thermally induced stresses and deformations, thermal conduction, the influence of external radiation and mechanical forces as well as the calculation of electromagnetic fields. The results are of importance for the development of optical clocks, or for laser and atomic interferometry, which will be applied, for example, in the space mission LISA (Laser Interferometer Space Antenna) or in satellite based geodesy missions.

    A further area of activity which is very near to the idea of Quantum Engineering is high precision quantum modelling. One task is the precise numerical calculation of ground states and the dynamics of quantum fields, e.g. Bose-Einstein condensates, under various boundary conditions and time dependent external influences. Such numerical modelling is important for the design of future quantum experiments as well as for estimating the expected effects. One future task is modelling of the coupling of quantum systems to classical systems.