4-year Postdoc position at LMU Munich for nuclear clock laser development

ThoriumNuclearClock is an ERC Synergy Grant project that started on February 1st 2020, for
a duration of 6 years. 4 international research teams (3 experimental: LMU Munich/Germany,
PI: P.G. Thirolf, TU Vienna/Austria, PI: T. Schumm, PTB Braunschweig/Germany, PI: E.
Peik; 1 theoretical: U Delaware/USA, PI: M. Safronova) join forces to build world’s first op-
tical nuclear clock and apply it to fundamental physics studies.

Project background:
Today’s most precise time and frequency measurements are performed with optical atomic
clocks. However, it has been proposed that they could potentially be outperformed by a nuclear
clock, which employs a nuclear transition instead of an atomic shell transition. There is only
one known nuclear state that could serve as a nuclear clock using currently available technol-
ogy, namely, the isomeric first excited state of 229 Th. Since more than 40 years nuclear physi-
cists have targeted the identification and characterization of the elusive isomeric ground state
transition of 229m Th. Evidence for its existence until recently could only be inferred from indi-
rect measurements, suggesting since 2009 an excitation energy of 7.8(5) eV. Thus the first
excited state in 229 Th represents the lowest nuclear excitation so far reported in the whole land-
scape of known isotopes. In 2016, the first direct detection of this nuclear state could be realized
via its internal conversion decay branch, laying the foundation for precise studies of its decay
parameters [1]. Subsequently, a measurement of the half-life of the neutral isomer was
achieved, confirming the expected reduction of 9 orders of magnitude compared to the one of
charged 229m Th [2]. Recently, collinear laser spectroscopy was applied to resolve the hyperfine
structure of the electronic states of the thorium ion with the nucleus in the isomeric first excited
state, providing information on nuclear moments and the charge radius [3]. Most recently, also
the cornerstone on the road towards the nuclear clock, which is a more precise and direct de-
termination of the excitation energy of the isomer, could be achieved [4, 5]. Thus major pro-
gress on the properties of this elusive nuclear state could be achieved in the last three years,
opening the door towards an all-optical control and thus the development of an ultra-precise
nuclear clock. Such a nuclear clock promises intriguing applications in applied as well as fun-
damental physics, ranging from geodesy and seismology to the investigation of possible time
variations of fundamental constants.
[1] L. v.d. Wense et al., Nature 533, 47-51 (2016).
[2] B. Seiferle, L. v.d. Wense, P.G. Thirolf, Phys. Rev. Lett. 118, 042501 (2017).
[3] J. Thielking et al., Nature 556, 321 (2018).
[4] B. Seiferle, L. v.d. Wense, P.G. Thirolf, Eur. Phys. Jour. A 53, 108, (2017).
[5] B. Seiferle et al., Nature 573, 243 (2019).

Project description:
Supporting the development, setup and commissioning of a VUV frequency
comb laser source as driver for the nuclear clock transition in 229m Th
Target of the project is (i) the development, setup and commissioning of a coherent VUV
source suitable for the optical excitation of the
229 Th nuclear clock transition at Fraunhofer
Institute for Laser Technology (ILT) Aachen/Germany and (ii) the transfer of the source to
LMU Munich, followed by on-site commissioning and first application in nuclear-clock-re-
lated studies.
In order to pursue the research on the 229 Th nuclear-clock transition a coherent VUV source is
required in a wavelength range covering the expected nuclear transition (around 150 nm, 8.3
eV), in order to determine this energy with high precision by scanning the VUV frequency,
and in order to drive the transition for a nuclear clock. For this purpose, a VUV frequency
comb is suited, which at the same time covers a large search range with its bandwidth and
offers a small linewidth of the comb modes. The excitation requires a large power per comb
mode and therefore a large average power in the VUV. This can be reached with a laser system
of an IR frequency comb, a high-power femtosecond amplifier, an enhancement resonator and
generation of the seventh harmonic in a gas target.
The laser system will be developed and set up at the Fraunhofer ILT in Aachen. The successful
candidate will be fully integrated in the development process for about 2.5 years in Aachen,
then he/she will organize the transfer of the laser system to LMU Munich (to the research
campus in Garching). Here the candidate will transfer his/her operational know-how to the
local team and start up the experimental program with the laser for another ca. 1.5 years.
We seek an experienced laser physicist with a background in the following
- Frequency combs
- High-harmonic generation
- Laser spectroscopy
- Atomic clocks
- Phase noise
If you are highly motivated to work at the forefront of physics and technology in
a dynamic and internationally highly visible project and in close collaboration
with other leading experimentalists and theorists, then you are encouraged to ap-
ply to join our team for the described Postdoctoral Fellow position.
Applications including a list of professional experience and educational history,
transcripts of grades, publication list and 2 letters of recommendation should be
sent - latest by December 14 - to:
Priv. Doz. Dr. Peter G. Thirolf
Ludwig-Maximilians-University Munich
Am Coulombwall 1
85748 Garching, Germany