Invited speakers
“Magnetometers and their
applications including fundamental physics”
In this accessible talk (that will cover a
wide range of topics), I will start by briefly reviewing optical magnetometry
with atoms and color centers, and then move on to describe two new projects
that are presently being setup to attempt detection of dark-matter and
dark-energy constituents: the Cosmic Axion Spin Precession experiment and the
Global Network of Optical Magnetometers for Exotic-physics searches. These are
table-top-style experiments based on nuclear magnetic resonance and modern
atomic sensors.
"Microwave Electrometry and Coherent Control of Strongly Interacting
Rydberg Gases in Thermal Vapor Cells"
Rydberg atoms have unique properties like their
large polarizability and their longrange interactions. Their sensitivity to
AC/DC electric fields makes them very promising for sensing applications,
whereas the excitation blockade can be employed as an optical non-linearity on
the single photon level. Quantum based standards of length and time as well as
measurements of other useful physical quantities, ex. magnetic fields, are
important because quantum systems, like atoms, show clear advantages for
providing stable and uniform measurements.
We demonstrate a new method for measuring
microwave electric fields based on quantum interference in a Rubidium atom. Using a bright
resonance prepared within an electromagnetically induced transparency window we are able to achieve a sensitivity
of 30 μVcm-1Hz-1/2
with a modest setup [1]. This method can be used for vector electrometry
with a precision below 1∘ [2] and microwave field imaging with a
sub-wavelength resolution [3]. The excitation of Rydberg atoms within
Hollow-Core Photonic Crystal Fiber paves the way towards integrated sensors
based on Rydberg atoms [4].
Furthermore we present our progress on the
coherent control and investigation of Rydberg atoms in small vapor cells. We
show that we are able to drive Rabi oscillations on the nanosecond timescale to
a Rydberg state by using a pulsed laser excitation and are therefore faster
than the coherence time limitation given by the Doppler width [5].
A systematic investigation reveals a clear
signature for van der Waals interaction between Rydberg atoms which is the basis for quantum devices based
on the Rydberg blockade. The strength of the interaction exceeds the energy
scale of thermal motion (i.e. the Doppler broadening) and therefore enables
strong quantum correlations above room temperature [6]. Due to this strong
interaction we observe evidence for aggregate formation of Rydberg atoms [7].
So in short, miniaturization and integration of
Rydberg based devices and sensors is within reach.
[1] J. Sedlacek, et al. Nature Physics 8,
819 (2012)
2] J. Sedlacek, et al. Phys. Rev. Lett. 111, 063001 (2013)
[3] H.Q. Fan, et al. Opt. Lett. 39,
3030 (2014)
[4] G. Epple, et al, Nature comm. 5,
4132 (2014)
[5] B. Huber et al., Phys. Rev. Lett. 107,
243001 (2011)
[6] T. Baluktsian et al., Phys. Rev. Lett.
110, 123001 (2013)
[7] A. Urvoy et al., Phys. rev. Lett. 114,
203002 (2015)
Time and frequency are the most accurately measurable quantities today.
In particular, optical clocks, that nowadays can reach a relative frequency
inaccuracy as low as 10-18, will open up a new field of search for
deviations in the predictions of Einstein’s general relativity, tests of modern
unifying theories and the development of new sensors for gravity and
navigation.
In my
talk, I will introduce the concepts of optical ion clocks and the application
of portable devices for relativistic geodesy. The international
state-of-the-art in ion clock development and challenges in clock laser
stabilization and ion control to go beyond resolutions of 10-19 will
be discussed.
In order to exploit
their full potential and to resolve frequencies with a fractional frequency
instability of 10-18and below, optical ion clocks need to integrate
over many days to weeks. For the characterisation of the clock, as well as for
applications, such as relativistic geodesy, the long averaging times pose
severe limits. Scaling up the number of ions for optical clock spectroscopy is
a natural way to significantly reduce the integration time, but was hindered so
far by the poor control of the dynamics of coupled many body systems. In our
experiment, we implement linear Coulomb crystals of Yb+and In+
ions for a first evaluation for optical clock operation. For optimal
control of the ion motion segmented chip-based ion traps are engineered in the
clean room facilities of PTB.
"Optical clocks: towards a redefinition of the second?"
Optical clocks have reached a level of accuracy and stability that has now considerably surpassed the traditional microwave clocks realizing the SI second. A stunning illustration: the level of performance is such that knowing the altitude difference between two clocks with a resolution of 1 cm over continental distances will soon be necessary.
This field of research has led to a growing architecture of optical clocks in the world, based either on ions or on neutral atoms. In order to provide means to compare them, new methods are being developed and implemented. An optical fiber links network is presently spreading throughout Europe, with the objective to ascertain that independent technological developments lead to an agreement between the different groups.
Are we ready for a new definition of the second? In this presentation I will describe the challenges connected to the quest of a “reference” frequency, which would be free of any systematic perturbing effect and reproducible in the long run. I will present how a frequency chain works in practice and what would the advent of an “optical second” imply.