Program Overview



15 Feb, Wed Venue: Botanique Room, Level 7, Park Hotel Alexandra
9:00 Opening and Welcome address
9:20 Sven Sturm, MPIK Heidelberg
Testing strong field QED via the magnetic moment of highly charged ions
Arrow Abstract

The ultra-precise determination of the g-factor of highly charged ions is a unique possibility to test the validity of the Standard Model, particularly Quantum Electrodynamics (QED) in extreme electric fields up to 1016 V/cm. While the weak-field regime has been exquisitely tested, in the presence of strong fields higher-order contributions beyond the Standard Model might become significant. It is possible to sensitively search for such effects by measuring the Larmor- and cyclotron frequencies of single, highly charged ions in a cryogenic Penning trap with high precision. This way, by measuring the g-factor of medium heavy hydrogenilike ions with previously unprecedented precision, we have been able to perform the most stringent test of QED in strong fields. Particularly the effect of the nucleus on the g-factor of the electron is a novel and unique access to nuclear size and structure information. Currently, a new setup, ALPHATRAP, is being commissioned at the Max-PIanck-Institut für Kernphysik in Heidelberg, which will push these experiments towards the heaviest elements up to hydrogenlike 208Pb81+. This will not only enable the most sensitive tests of QED, but also open a unique access to fundamental constants as the atomic mass of the electron and the finestructure constant α.

10:00 Rima Schussler, MPIK Heidelberg
High-Precision Mass Measurements with PENTATRAP
Arrow Abstract

The high-precision Penning-trap mass spectrometer PENTATRAP [1] is in the commissioning phase at the Max-Planck-Institut für Kernphysik, Heidelberg. It aims at mass-ratio measurements of stable and long lived highly charged ions with a relative uncertainty of a few 10-12, which has so far only been achieved for a few relatively light nuclides [2].
Mass-ratio measurements at PENTATRAP are carried out by determining the cyclotron frequencies of the ion species of interest in the strong magnetic field inside a Penning trap. A unique feature of the experimental setup of PENTATRAP is the use of five cylindrical Penning traps [3], making simultaneous storage of several ion species possible. This allows for simultaneous in-situ calibration and reference measurements and reduces systematic errors in the determination of mass ratios. Long storage times in a cryogenic environment and dedicated image current detection systems [4] with single ion sensitivity will allow for high-precision determinations of cyclotron frequencies in all traps.
Mass data at this level of precision find, among others, application in neutrino physics research. The fact that neutrinos are massive particles, contrary to the prediction of the Standard Model, is known since the discovery of neutrino oscillations. Still unknown is the absolute neutrino mass scale. The analysis of electron capture spectra of suitable nuclides allows to gain information on the value of the electron neutrino mass. An important input parameter in the analysis is the energy available to the electron capture process, Q-value, which is the mass difference of mother and daughter nuclides. The ECHo experiment [5] is designed to reach sub-eV sensitivity on the electron neutrino mass using Ho-163. So far a measurement with SHIPTRAP [6] has determined the Q-value to an uncertainty of a few ten eV and PENTATRAP plans to decrease the uncertainty to a few eV. The precise measurement of Q-value will be of utmost importance to reduce systematic errors in the analysis of the Ho-163 spectrum.

[1] J. Repp et al., Appl. Phys. B 107, 983 (2012)
[2] S. Rainville et al., Nature 438, 1096 (2005)
[3] C. Roux et al., Appl. Phys B108, 997 (2012)
[4] S.R. Jefferts et al., Rev. Sci. Instrum. 64(3), 737 (1993)
[5] L. Gastaldo et al., J. Low. Temp. Phys., 176, 876 (2014)
[6] S. Eliseev et al., PRL 115, 062501 (2015)

10:40 Coffee/Tea Break
11:10 Dahyun Yum, CQT, NUS
Optical control of 6S1/2 to 5D5/2 transition of a Ba+ ion and its applications
Arrow Abstract

We have built 1762 nm diode based lasers and a stable cavity system for phase lock to control the 6S1/2 to 5D5/2 quadrupole transition of a Ba+ ion. The resonance wavelength of the 6S1/2 to 5D5/2 quadrupole transition is about 1762 nm, which suitably falls close to the U-band of the telecommunication wavelength. Thus, that transition is a naturally attractive choice for optical qubit towards implementation of quantum repeater or quantum networks using existing telecommunication networks. We demonstrate an optical single qubit based on 6S1/2 to 5D5/2 quadrupole transition of a single Ba+ ion. The relatively narrow linewidth of the quadrupole transition is an advantage to measure magnetic field strength, optical pumping rate and temperature of ion. The experimental results using the 6S1/2 to 5D5/2 quadrupole transition of a Ba+ ion will be presented in this talk.

11:50 Dzmitry Matsukevich, CQT, NUS
Quantum absorption refrigerator with trapped ions
Arrow Abstract

We report on an experimental realization of a quantum absorption refrigerator in a system of the three trapped Yb+ ions. The three normal modes of motion of the ions that represent "hot", "work" and "cold" bodies of the refrigerator are coupled by a trilinear Hamiltonian that arises from their mutual (anharmonic) Coulomb interaction, such that the energy transfer between work and hot modes can refrigerate the cold mode. We investigate the equilibrium properties of the refrigerator, and the coherent dynamics of such a system away from equilibrium. We compare the cooling capabilities of thermal versus squeezed thermal states prepared in the work mode and exploit the coherent dynamics of the system to demonstrate single-shot cooling in the refrigerator. By stopping the evolution in the right moment, we achieve cooling of the cold mode below both the steady-state energy and that predicted by a simple classical thermodynamic benchmark.

12:30 Lunch
14:00 Jose Crespo, MPIK Heidelberg
Highly charged ions as sensitive probes for the time variation of the fine-structure constant α
Arrow Abstract

Stability of fundamental constants is not an a priori tenet of physics. Our current as-sumption of its validity is merely based on experimental knowledge of Nature. A vari-ation of the dimensionless fine-structure constant α in space or time is an intriguing possibility in theory. Its existence has been claimed based on astrophysical observa-tions, yet its presumptive magnitude is too small for laboratory consistency checks. Nonetheless, the currently best benchmarks on the time stability of any fundamental constant have been carried out for α. They have been based on comparing the opti-cal transition frequencies of different atomic clocks with a relative accuracy of 10-17 per year. Sympathetically cooled highly charged ions (HCI) have been proposed for improving optical clocks in order to more stringently test possible variations: Forbid-den optical transitions in HCI [1] offer major advantages as frequency references. Compared with atoms or singly charged ions, the deeply bound optically active elec-tron in a HCI shows greatly reduced sensitivity to external perturbations, such as those due to laser interrogation or blackbody radiation. Additionally, relativistic effects enhance the sensitivity of HCI transitions to a variation of α by large factors. For these reasons, we have investigated in HCI certain near-degeneracies of electronic states that are very amenable to frequency metrology, and therefore particularly sensitive to the effect of interest [2]. In order to perform frequency metrology, we have developed a cryogenic radiofrequency trap, CryPTEx (Cryogenic Paul Trap Experiment) [3,4], in which sympathetically cooled Ar13+ ions [5] have been prepared at temperatures of currently less than 30 mK. Presently we are searching for the lasing transitions of interest. Furthermore, since HCI have high ionization potentials, they can be exposed to even x-ray photons without becoming photo-ionized and changing charge state by very fast Auger processes. This makes them suitable as future frequency standards beyond the vacuum ultraviolet, a regime where the only alternative would be the excitation of a few, still poorly known nuclear transitions. In contrast, HCI have a huge number of both forbidden and allowed transitions up to the keV range which would be appropriate for frequency metrology at such energies. We are currently developing a frequency comb for the vacuum ultraviolet region for exploiting these possibilities.
[1] V. Mäckel, et al., Phys. Rev. Lett. 107 (2011) 143002
[2] A. Windberger, et al., Phys. Rev. Lett. 114 (2015) 150801,
[3] M. Schwarz et al., Rev. Sci. Instrum. 83 (2012) 083115
[4] L. Schmöger et al., Rev. Sci. Instrum. 86, 103111 (2016)
[5] L. Schmöger, et al., Science 347 (2015) 1233

14:40 Holger Kreckel, MPIK Heidelberg
Laboratory Astrophysics with Stored Molecular Ions
Arrow Abstract

Almost 200 different molecular species have been discovered in interstellar space and the exploration of the molecular universe is the driver for major new astronomical observatories. This topic touches on active areas of research like the formation of extrasolar planets and the origin of water on Earth. The diverse chemistry of the interstellar medium is surprising at first glance, since the harsh physical conditions in interstellar environments – with temperatures down to 10 K and densities of only 10-1000 particles per cubic centimeter -- appear adverse to an active chemical network. The key reaction type for interstellar gas phase chemistry are ion-neutral reactions, because this class of processes can be efficient even at low temperatures and densities. To understand the role of ion-neutral reactions in space, detailed laboratory experiments are essential. The new Cryogenic Storage Ring (CSR) represents an almost ideal test bench for studies of formation and destruction processes of interstellar molecules. Measurements with atomic ions as well as complex molecules and clusters are foreseen. These studies are complemented by spectroscopic experiments in ion traps. We will present first results from the CSR commissioning phase and introduce some of the most relevant astrophysical processes we intend to study.

15:20 Coffee/Tea Break
16:00 Dario Poletti, SUTD
Geometry of system-bath coupling and gauge fields in bosonic ladders
Arrow Abstract

Quantum systems in contact with an environment display a rich physics emerging from the interplay between dissipative and Hamiltonian terms. Here we consider a dissipative boundary driven ladder in presence of a gauge field which can be implemented with ion microtraps arrays. In particular we focus on the interplay between the gauge field and the geometry of the coupling between the system and the baths. First we analyze the non-interacting case. We show that, depending on the geometry, the currents imposed by the baths can be strongly affected by the gauge field resulting in non-equilibrium phase transitions. In different phases both the magnitude of the current and its spatial distribution are significantly different. We then study the transport for hard-core bosons and show a much weaker dependence of the current on the gauge gield and the emergence of negative differential conductivity.

16:40 Thomas Gasenzer, Uni Heidelberg
Strongly anomalous non-thermal fixed point in a quenched two-dimensional Bose gas
Arrow Abstract

Non-equilibrated quantum many-body systems show much richer characteristics than those in equilibrium. There is the possibility for universal dynamics, showing up with the same properties in very different systems irrespective of their concrete building blocks. Prominent examples are the phenomenon of prethermalisation and the development of Generalised Gibbs Ensembles [1]. Superfluid turbulence in an ultracold atomic gas has the potential to show universal aspects shared by dynamics which occurred after the inflationary period of the early universe [2]. Non-thermal fixed points have been proposed in this context which lead beyond standard equilibrium universality. Turbulent dynamics in two-dimensional bosonic matter-wave systems will be discussed which are characterized by universal scaling behavior in space and time, with strong anomalous effects caused by conservation laws and non-dissipative dynamics [3]. This exhibits a close relation between quantum turbulence, the dynamics of topological defects, as well as magnetic and charge ordering phenomena.
[1] T. Langen, T. Gasenzer, and J. Schmiedmayer, JSTAT 064009, 2016. arXiv:1603.09385 [cond-mat.quant-gas].
[2] B. Nowak, S. Erne, M. Karl, J. Schole, D. Sexty, and T. Gasenzer, arXiv:1302.1448 [cond-mat.quant-gas], in Strongly Interacting Quantum Systems out of Equilibrium, edited by T. Giamarchi, et al. (Oxford University Press, 2016).
[3] M. Karl and T. Gasenzer, arXiv:1611.01163 (2016).

16:30 End of day

16 Feb, Thurs Venue: Botanique Room, Level 7, Park Hotel Alexandra
9:20 Murray Barrett, CQT, NUS
Progress towards an optical clock based on singly ionized lutetium
Arrow Abstract

We are investigating singly ionized lutetium as a potential optical clock candidate. By averaging over highly forbidden M1 transitions to multiple hyperfine levels, we can realize an effective frequency reference that is inherently insensitive to perturbations arising from external electromagnetic fields. In addition, lutetium offers intriguing possibilities for clock operation on large Coulomb crystals which would signicantly improve the stability of ion based clocks. We discuss these ideas and report our progress towards establishing a lutetium ion optical clock.

10:00 Selim Jochem, Uni Heidelberg
Deterministic quantum simulators with cold atoms
Arrow Abstract

Experiments with ultracold gases have been extremely successful in studying many body physics, such as Bose Einstein condensates or fermionic superfluids. In general, they are deep in the regime of statistical physics, where adding or removing an individual particle does not matter. An essential challenge for current experiments, in particular with fermions, is to reach low enough entropies to observe low-temperature phases such as magnetically ordered states. In our work we deterministically prepare generic model systems containing a precise number of few ultracold fermionic atoms with tunable interaction in a well-defined quantum state. We have started the exploration of such few-body systems with a two-particle system that can be described with analytic theory. As we increase the system size atom by atom, we have been working in a one-dimensional framework allowing us to describe the system as a Heisenberg spin chain at strong repulsion. This allowed us to deterministically prepare a finite antiferromagnetically ordered state. It is our vision to use our few-body systems as microscopic building blocks to assemble deterministic quantum systems that allow for the simulation of complex many-body models close to zero temperature.

10:40 Coffee/Tea Break
11:10 Berge Englert, CQT, NUS
Many-particle systems in single-particle terms
Arrow Abstract

The tools of density-functional theory allow the investigation of interacting many-particle systems by coupled equations for single-particle densities and effective single-particle potentials. The equations for "potential from density" and "density from potential" are to be solved self-consistently ― and these relations require reliable approximations. This talk reports recent developments on the potential-to-density link for two-dimensional systems of fermion.

11:50 Tarun Dutta
Precision measurement of branching fractions of 138Ba+ ion : a direct test of atomic many-body theories.
Arrow Abstract

A new protocol for measuring the branching fraction of hydrogenic atoms with only statistically limited uncertainty is proposed and demonstrated for the decay of the P3/2 level of the barium ion. This measurement has been performed with a precision of 0.2%. Previous measurements on the P1/2 state along with these latest results, for the first time allows cross-checking the atomic many body calculations in barium ion to below one percent level. Therefore setting the floor for possible measurements of the atomic parity violation in barium ion.

12:30 Shau-Yu Lan, NTU
A velocity sensor based on large Fizeau’s light dragging effect in a moving electromagnetically-induced transparent medium
Arrow Abstract

Atoms based velocimeter typically relies on measuring the first order Doppler shift of individual atoms. To determine the center-of-mass motion of an atomic ensemble, one usually needs to map out or truncate the velocity distribution of the ensemble. Here, I will describe the light dragging effect in a moving electromagnetically induced transparent (EIT) medium and use it to sense the center-of-mass motion of an atomic ensemble directly. The light dragging effect or the deviation of phase velocity from the speed of light c in a moving medium was first observed by Fizeau in a flowing water experiment for the study of ether in the pre Einstein’s special theory of relativity era. It was later explained by the Lorentz velocity addition to the first order. We enhance the dragging effect in a cold atomic medium under EIT condition and demonstrate a velocity sensor at a sensitivity two orders of magnitude higher than the velocity width of the atomic medium used. This new type of sensor depends on the collective motion of the atomic ensemble and could lead to a new design of motional sensor beyond the limitation of Doppler broadening of atoms.

13:05 Lunch
14:00 Rainer Dumke, CQT, NUS and NTU
High Precision Quantum Sensors for Biomagnetic Characterization
Arrow Abstract

Utilising highly sensitive quantum sensors gives us a tool to quantitatively determine the dynamics of magnetic materials in biological samples at room temperature. This leads to the possibility to do in vivo measurements. In fact we have observed strikingly different behaviour in alive and dead samples. The observed dynamics allows for determination of physical properties of the sub-micron size deposits and matter around them despite their small volumes. These properties will be discussed in light of other experiments and their possible relation to magneto-reception.

14:40 Jiangbin Gong, Dept of Physics, NUS
Aspects of work fluctuations: Why nonequilibrium statistics is a challenge
Arrow Abstract

One seminal topic in modern nonequilibrium statistical mechanics is fluctuation theorems, with the Jarzynski’s equality being one celebrated foundational result relevant to many research topics including chemical physics, biophysics, and nanoscale quantum thermodynamics. Via Jayzynski’s equality, an ensemble average of an exponential form of non-equilibrium work values can be directly connected with a free energy difference as equilibrium statistical properties, regardless of the details of the work protocol. The effectiveness or efficiency of such nonequilibrium statistics is implicitly based on a finite statistical variance of the exponential work. Through a principle of minimal exponential work fluctuations in ergodic systems, we uncover the general possibility of a diverging variance of the exponential work in nonequilibrium work protocols. That is, in many cases, the divergence of the variance of the exponential work is not isolated but systematic. As shown by specific examples, under such circumstances the free energy simulation can become impractical at all due to the extremely slow error scaling of such simulations. For example, to double the simulation precision by a factor of two might need an enormous increase in the simulation sample size. We hence discover a previously unforeseen limitation on the direct applicability of Jarzynski’s equality in free-energy simulation tasks.

15:20 Coffee/Tea Break
16:00 Visit to CQT Labs in NUS

17 Feb, Fri Venue: Botanique Room, Level 7, Park Hotel Alexandra
9:20 Benoît Grémaud, CQT, NUS
Haldane phase in the sawtooth lattice: edge states, entanglement spectrum and the flat band
Arrow Abstract

Using density matrix renormalization group numerical calculations, we study the phase diagram of the half filled Bose-Hubbard system in the sawtooth lattice with strong frustration in the kinetic energy term. We focus in particular on values of the hopping terms which produce a flat band and show that, in the presence of contact and near neighbor repulsion, three phases exist: Mott insulator (MI), charge density wave (CDW), and the topological Haldane insulating (HI) phase. After a short review of these phases for the regular Bose-Hubbard model in one dimension, I will discuss how their properties are modified by the flat band, especially the ones of the Haldane phase.

10:00 Jan-Michael Rost, MPI komplexe Systeme Dresden
Non-adiabatic photoionization: pump and probe by a single pulse
Arrow Abstract

In this contribution we will discuss properties of non-adiabatic photoionization which is realized when the length of the light pulse is comparable with the time scale of the bound electron-orbital to be ionized. Since dynamics becomes relevant to the derivative of the pulse envelope, a typical Gaussian pulse acts like a double pulse. The resulting two ionization bursts interfer. This opens the possibility of a precise determination of energy differences despite the large energy width of a short pulse.

Our theoretical description is based on the Envelope Hamiltonian, which we have developed in Toyota etal, New J. Phys. 17, 073005 (2015).

10:40 Coffee/Tea Break
11:10 Wenhui Li, CQT, NUS
Coherent microwave-to-optical conversion via six-wave mixing in Rydberg atoms
Arrow Abstract

Efficient and coherent interconversion of millimetre waves and optical fields is critical for classical and quantum technologies. To achieve this, the challenge resides in the design of a device that interacts strongly with both frequency bands, microwave and optical. In this poster, we report an experimental demonstration of a new scheme based on six-wave mixing in Rydberg atoms [1]. Our scheme utilizes the strong coupling of millimetre waves to Rydberg atoms as well as electromagnetically induced transparency that greatly enhances the nonlinearity for the conversion process. The microwave-to-optical conversion demonstrated here is free-space, broadband and has the potential to reach near-unity photon conversion efficiency upon modification of the geometry of our setup. Our results indicate the tremendous potential of Rydberg atoms for the efficient conversion between microwave and optical fields, and thus paves the way to many applications.

[1] J. Han, T. Vogt, Ch. Gross, D. Jaksch, M. Kiffner, and W. Li, arXiv:1701.07969.

11:50 Gerhard Zurn, Uni Heidelberg
Spin dynamics of dipolar interacting Rydberg atoms
Arrow Abstract

The relaxation dynamics of strongly coupled systems brought out of equilibrium is of particular interest in the presence of long range interactions which can be introduced by resonant dipolar exchange interactions between Rydberg atoms. We present an experimental realization of such a prototypical dipolar spin model by coupling two strongly interacting Rydberg states using a microwave field. At low Rydberg density where interactions are negligible, we show that our system can be mapped onto a spin-1/2 model. By driving the many-body system out-of-equilibrium for higher densities we report the observation of coherent spin oscillations with interaction-induced damping, which can be described in terms of a dipolar XX-model in effective magnetic fields. The comparison with theoretical calculations allows us to identify the initial quantum fluctuations as a source of relaxation.

12:30 Lunch
14:00 Discussion

15:20 Concluding Remarks
16:00 Visit to CQT Labs in NTU