7 March 2018

The winners of this year's Helmholtz Prize have been chosen: they are scientists whose precise physical measurements take place in the quantum world. Some of the prizewinners are doctoral candidates at the Max Planck Institute of Quantum Optics who have re-determined the radius of a hydrogen nucleus, thus providing important information for solving the much-discussed “proton size puzzle” in quantum electrodynamics. The remaining prizewinners are a research group from the Physikalisch-Technische Bundesanstalt (PTB). The PTB scientists used electrical quantum effects to develop devices and measurement techniques by means of which extremely small currents can be measured with previously unattained accuracy. 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. The award ceremony will take place on 17 May at the DPG Physikzentrum in Bad Honnef.

The “proton size puzzle”

Dr. Axel Beyer and Lothar Maisenbacher from the Max Planck Institute of Quantum Optics have provided extremely exact measurements of a transition frequency in the hydrogen atom, which constitute important information for solving the “proton size puzzle” of quantum electrodynamics; for this work, they received the 2018 Helmholtz Prize in the category of “fundamental research”. They repeated previous experiments with markedly higher accuracy. These measurements were preceded by several years of laboratory work in which the two future prizewinners developed new models, researched systematic effects which had not previously been considered and improved their test setup. The result was that their measurements, which were taken using conventional hydrogen, confirmed measurements taken using muonic hydrogen, thus harmonizing quantum electrodynamics with the experimental observations.

The background of their research is as follows: quantum electrodynamics, or QED for short, describes how material particles (such as atoms) interact with light; furthermore, QED is considered to be exceptionally well established. Many findings are based on the exact investigation of the hydrogen atom. Since this atom consists of only one proton and one electron, it is the atom that can be best described mathematically. However, a few years ago, measurements taken using muonic hydrogen shattered previous theories about the makeup of the atom. Muonic hydrogen is generated by replacing the electron circling the nucleus with a muon. The muon is also negatively charged, but is much heavier than an electron. In this experiment, the radius of the proton (i.e., the radius of the atomic nucleus) was suddenly noticeably smaller than in previous measurements with conventional hydrogen. This set off a lively debate among researchers concerning this “proton size puzzle”: had a measurement error taken place? Or did the findings indicate that fundamental gaps existed in the understanding of the theory of quantum electrodynamics, which until then had been considered well understood? Via the new findings of the Helmholtz prizewinners, which were published in Science magazine, the information which became available in this debate indicated that errors had taken place in previous measurements.

Measuring and generating extremely small electric currents in a way suitable for industry

The 2018 Helmholtz Prize in the category of Applied Metrology was awarded to a team of researchers from the Physikalisch-Technische Bundesanstalt (PTB): Dr. Dietmar Drung, Dr. Martin Götz, Eckart Pesel and Dr. Hansjörg Scherer. Working at the interface between research and practical applications, these four scientists successfully developed both methods and instruments that bring about groundbreaking improvements in the field of traceable high-precision measurement and the generation of small electrical currents.

Specifically, their project concerns the development of a novel current amplifier, the Ultrastable Low-Noise Current Amplifier (ULCA), and its associated current comparator, which enables the traceable and highly accurate calibration of the ULCA. The characteristics of the ULCA are nothing short of revolutionary: although it is small and portable, it can be used to measure currents with outstanding accuracy (relative uncertainty of 10-7 for a 100 pA current). It can also be used as a reference current source for small electric currents at national metrology institutes – in other words, at the highest metrological level.

These new procedures and devices have improved and expanded calibration and measurement capabilities – for example, those in the semiconductor industry, in environmental measurement technology, in DNA sequencing and in quantum communication. In current research, they are being used in single-electron circuits for the future quantum-based realization of the unit of electric current, the ampere. The ULCA is licenced by PTB and is already being used by a small German enterprise. Clients who have used the ULCA to date include national metrology institutes in the United States, Asia and Europe as well as German calibration laboratories.

The Helmholtz Prize

The Helmholtz Prize is awarded 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”. The awarding ceremony will take place within the framework of the Heraeus Seminar titled “Fundamental constants: Basic physics and units” (13-18 May 2018, Bad Honnef).

The 2018 Helmholtz Prize for Precision Measurements in Fundamental Research is awarded to:

Dr. Axel Beyer, Lothar Maisenbacher (both of the Max Planck Institute of Quantum Optics): The most precise measurement of the Rydberg constant in hydrogen and important hints for solving the “proton size puzzle”


Prof. Dr. Thomas Udem, Laser Spectroscopy Department, Max Planck Institute of Quantum Optics, phone: +49-89-32905-282, e-mail:

Scientific publication

Axel Beyer, Lothar Maisenbacher, Arthur Matveev, Randolf Pohl, Ksenia Khabarova, Alexey Grinin, Tobias Lamour, Dylan C. Yost, Theodor W. Hänsch, Nikolai Kolachevsky, Thomas Udem: The Rydberg constant and proton size from atomic hydrogen. Science, 6 October 2017, DOI:10.1126/science.aah6677

The 2018 Helmholtz Prize for Precision Measurements in Applied Metrology is awarded to:

Dr. Dietmar Drung, Dr. Martin Götz, Eckart Pesel and Dr. Hansjörg Scherer (all of the Physikalisch-Technische Bundesanstalt): Improvements in the traceable high-precision measurement and generation of extremely small electrical currents


Dr. Hansjörg Scherer, Working Group 2.61 Current and Quantum Resistance, Physikalisch-Technische Bundesanstalt, phone: +49-531-592-2610

Scientific publication

Dietmar Drung, Martin Götz, Eckart Pesel, Hansjörg Scherer: Improving the Traceable Measurement and Generation of Small Direct Currents. IEEE Transactions on Instrumentation and Measurement, 64 (2015), 3021; DOI:10.1109/TIM.2015.2440564

 Author: Imke Frischmuth