Helmholtz Prize for high-precision measurements

From fundamental physics related to Einstein’s special theory of relativity to fundamentals of metrological applications in the range of thousandths of micrometers (i.e. nanometers) – the bandwidth of this year’s Helmholtz Prize is considerable. The Helmholtz Prize, which recognizes outstanding scientific and technological research in the field of precision measurement in physics, chemistry and medicine, is awarded every second year. Three scientists at the Physikalisch-Technische Bundesanstalt (PTB) have been awarded the prize in fundamental research for their work. By means of a long-term comparison between two highly accurate clocks (optical ytterbium clocks) of PTB, Christian Sanner, Nils Huntemann and Richard Lange have succeeded in considerably improving the procedure to test the fundamental symmetry of space (Lorentz symmetry) for electrons. The Helmholtz Prize in applied metrology has been awarded to a team consisting of nine researchers from the Humboldt-Universität zu Berlin and from the University of Freiburg working with the physicist Saskia F. Fischer from Berlin and the microsystems expert Peter Woias from Freiburg. This group has also broken new ground by laying down the scientific and technical prerequisites to standardize the measurement of individual nanostructures. In metrology, the science of precise measurement, the Helmholtz Prize is considered one of the world’s most prominent distinctions. The prize is awarded in two categories – fundamental research and applied metrology – and endowed with €20,000 in prize money.

Testing the symmetry of space-time by means of atomic clocks:

The team from PTB dealt with a fundamental question of physics. One of the basic assumptions of Einstein’s special theory of relativity is that the speed of light is always the same, independent of the direction in which the light spreads. Now one can ask: How universal is this symmetry of space (which was named after Hendrik Antoon Lorentz)? Does it also apply to the motion of material particles in the same way,? or are there any directions along which these particles move faster or more slowly although the energy remains the same? Especially for high energies of the particles, theoretical models of quantum gravitation predict a violation of the Lorentz symmetry. These models are designed to describe the universe of the infinitesimal, quanta, gravitation and the force of gravitation

Optical spectroscopy of atomic transitions, which consists in investigating the interaction of light with atoms, offers a unique level of accuracy. This accuracy means that such spectroscopy allows assumptions and predictions of the theory of relativity to be experimentally tested. In 2016, the physicists from PTB presented a clock based on this interaction of high-precision lasers with a defined atom (the ytterbium ion 171Yb+) and achieved a relative accuracy of 3 × 10E-18. If this clock had started ticking at the time of the Big Bang (13.7 billion years ago), its error would now amount to no more than one second. Two versions of this optical Yb+ clock in different spatial orientations are being used to measure the Lorentz symmetry and specifically the isotropy of space-time with unprecedented accuracy. To put it simply, the laws of physics have no directional dependence.

In a universe that obeys the laws of the Lorentz symmetry (as assumed in the theory of relativity), a physical experiment must always yield the same result, independent of its orientation in space or its uniform motion. But can we be sure that this symmetry is maintained up to the limits of what Yb+ clocks can measure? Building on the tradition of the Michelson-Morley experiment, which began more than 100 years ago, Christian Sanner, Nils Huntemann and Richard Lange succeeded in improving the best anisotropy limits up to that point by another two orders of magnitude. As a “side-effect” – but an important one – their long-term comparison has confirmed the extremely small systematic measurement uncertainty of the two optical ytterbium clocks, which amounts to less than 4 × 10E-18. The results were published in Nature.

A new path to standardized nanometrology:

The 2020 Helmholtz Prize in applied metrology was awarded to a team consisting of researchers from the Humboldt-Universität zu Berlin and from the University of Freiburg. Maximilian Kockert, Danny Kojda, Rüdiger Mitdank, Anna Mogilatenko and Saskia F. Fischer (Humboldt-Universität Berlin), and Zhi Wang, Johannes Ruhhammer, Michael Kröner and Peter Woias (University of Freiburg) have succeeded in developing the first standardizable procedure to measure structures in the nanometer range (thousandths of micrometers).

The problem with nanostructured materials is that they often have properties that are completely different from those of macroscopic materials. In the nanometer range, besides the type of material, the form of surfaces – i.e. the dimensions and the surface texture – plays a key role. The motto for industrial design and architecture coined a hundred years ago in connection with the Bauhaus school – “form follows function” – no longer applies in the nanometer range. Often, this motto must even be turned on its head for parameters of nanostructured materials – “form defines structure.” This allows these parameters to be customized by the shape given to the material. It is therefore even more important to be able to measure these materials parameters accurately and reliably, which presents metrology with a challenge.

In their work, the team of researchers has presented standardizable precision measurements of the Seebeck coefficient whose scope can be extended from their model system (namely silver wires with a diameter in the nanometer range and a crystalline structure (single crystals)) to cover other nanostructures and additional parameters. The researchers have thus demonstrated that standardized high-precision measurements over a wide temperature range are possible for the entire thermoelectric characterization (i.e. when measuring electrical conductivity, thermal conductivity and the Seebeck coefficient), even for metallic nanomaterials. Their results have now been published in Scientific Reports.

The prize:

The Helmholtz Prize is awarded by the Helmholtz Fund for outstanding scientific and technological research in the field of precision measurement in physics, chemistry and medicine in the categories of fundamental research and applied metrology. Due to the current situation surrounding the coronavirus, it has not yet been decided when and where the award will be presented to this year’s prizewinners. The Heraeus Seminar (“Hybrid Solid State Quantum Circuits, Sensors, and Metrology”), which was planned to take place from 11 to 14 May in Bad Honnef and which was to have included the award ceremony, has been cancelled.

The prizewinners:

2020 Helmholtz Prize for precision measurement in fundamental research:

Dr. Christian Sanner (PTB, currently working at JILA in Boulder, CO, USA), Dr. Nils Huntemann and Richard Lange (both from PTB)
for their work titled “Single-atom spectroscopy with eighteen-digit accuracy to measure the symmetry of space-time”

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Scientific publication:

Christian Sanner, Nils Huntemann, Richard Lange, Christian Tamm, Ekkehard Peik, Marianna S. Safronova, Sergey G. Porsev: Optical clock comparison for Lorentz symmetry testing. Nature 567, 204 (2019)

Contact:

Dr. Nils Huntemann, Working Group 4.43 “Optical Clocks with Trapped Ions”, Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany, phone: +49 531 592-4430, e-mail: [email protected]

2020 Helmholtz Prize for precision measurement in applied metrology:

Maximilian Kockert, Dr. Danny Kojda, Dr. Rüdiger Mitdank, Dr. Anna Mogilatenko and Prof. Dr. Saskia F. Fischer (contributed research from the Humboldt-Universität zu Berlin), and Dr. Zhi Wang, Dr. Johannes Ruhhammer, Dr. Michael Kröner and

Prof. Dr. Peter Woias (contributed research from the University of Freiburg) for their work titled “Nanometrology: Absolute Seebeck coefficient of individual silver nanowires.”

Scientific publication:

M. Kockert, D. Kojda, R. Mitdank, A. Mogilatenko, Z. Wang, J. Ruhhammer, M. Kroener, P. Woias, S. F. Fischer: Nanometrology: Absolute Seebeck coefficient of individual silver nanowires. Scientific Reports 9, 20265 (2019)

Contact:

Prof. Dr. Saskia F. Fischer, Humboldt-Universität zu Berlin, Department of Physics, WG Novel Materials, Newtonstraße 15, 12489 Berlin phone: +49 30 2093-8044, e-mail: [email protected]

Prof. Dr. Peter Woias, University of Freiburg, Department of Microsystems Engineering (IMTEK), Laboratory for the Design of Microsystems, Georges-Köhler-Allee 102, 79110 Freiburg, phone: +49 761 203-7490, e-mail: [email protected]