Program Overview
Program
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 Abstract The ultraprecise determination of the gfactor 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 weakfield regime has been exquisitely tested, in the presence of strong fields higherorder 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 gfactor 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 gfactor 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 MaxPIanckInstitut 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 HighPrecision Mass Measurements with PENTATRAP Abstract The highprecision Penningtrap mass spectrometer PENTATRAP [1] is in the commissioning phase at the MaxPlanckInstitut für Kernphysik, Heidelberg. It aims at massratio measurements of stable and long lived highly charged ions with a relative uncertainty of a few 1012, which has so far only been achieved for a few relatively light nuclides [2]. 
10:40  Coffee/Tea Break 
11:10 
Dahyun Yum, CQT, NUS Optical control of 6S_{1/2} to 5D_{5/2} transition of a Ba+ ion and its applications Abstract We have built 1762 nm diode based lasers and a stable cavity system for phase lock to control the 6S_{1/2} to 5D_{5/2} quadrupole transition of a Ba+ ion. The resonance wavelength of the 6S_{1/2} to 5D_{5/2} quadrupole transition is about 1762 nm, which suitably falls close to the Uband 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 6S_{1/2} to 5D_{5/2} 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 6S_{1/2} to 5D_{5/2} quadrupole transition of a Ba+ ion will be presented in this talk. 
11:50 
Dzmitry Matsukevich, CQT, NUS Quantum absorption refrigerator with trapped ions 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 singleshot cooling in the refrigerator. By stopping the evolution in the right moment, we achieve cooling of the cold mode below both the steadystate 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 finestructure constant α Abstract Stability of fundamental constants is not an a priori tenet of physics. Our current assumption of its validity is merely based on experimental knowledge of Nature. A variation of the dimensionless finestructure constant α in space or time is an intriguing possibility in theory. Its existence has been claimed based on astrophysical observations, 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 optical transition frequencies of different atomic clocks with a relative accuracy of 1017 per year. Sympathetically cooled highly charged ions (HCI) have been proposed for improving optical clocks in order to more stringently test possible variations: Forbidden optical transitions in HCI [1] offer major advantages as frequency references. Compared with atoms or singly charged ions, the deeply bound optically active electron 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 neardegeneracies 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 xray photons without becoming photoionized 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.

14:40 
Holger Kreckel, MPIK Heidelberg Laboratory Astrophysics with Stored Molecular Ions 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 101000 particles per cubic centimeter  appear adverse to an active chemical network. The key reaction type for interstellar gas phase chemistry are ionneutral reactions, because this class of processes can be efficient even at low temperatures and densities. To understand the role of ionneutral 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 systembath coupling and gauge fields in bosonic ladders 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 noninteracting case. We show that, depending on the geometry, the currents imposed by the baths can be strongly affected by the gauge field resulting in nonequilibrium phase transitions. In different phases both the magnitude of the current and its spatial distribution are significantly different. We then study the transport for hardcore 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 nonthermal fixed point in a quenched twodimensional Bose gas Abstract
Nonequilibrated quantum manybody 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]. Nonthermal fixed points have been proposed in this context which lead beyond standard equilibrium universality. Turbulent dynamics in twodimensional bosonic matterwave systems will be discussed which are characterized by universal scaling behavior in space and time, with strong anomalous effects caused by conservation laws and nondissipative dynamics [3]. This exhibits a close relation between quantum turbulence, the dynamics of topological defects, as well as magnetic and charge ordering phenomena.

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 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 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 lowtemperature 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 welldefined quantum state. We have started the exploration of such fewbody systems with a twoparticle system that can be described with analytic theory. As we increase the system size atom by atom, we have been working in a onedimensional 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 fewbody systems as microscopic building blocks to assemble deterministic quantum systems that allow for the simulation of complex manybody models close to zero temperature. 
10:40  Coffee/Tea Break 
11:10 
Berge Englert, CQT, NUS Manyparticle systems in singleparticle terms Abstract The tools of densityfunctional theory allow the investigation of interacting manyparticle systems by coupled equations for singleparticle densities and effective singleparticle potentials. The equations for "potential from density" and "density from potential" are to be solved selfconsistently ― and these relations require reliable approximations. This talk reports recent developments on the potentialtodensity link for twodimensional systems of fermion. 
11:50 
Tarun Dutta Precision measurement of branching fractions of 138Ba+ ion : a direct test of atomic manybody theories. 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 P_{3/2} level of the barium ion. This measurement has been performed with a precision of 0.2%. Previous measurements on the P_{1/2} state along with these latest results, for the first time allows crosschecking 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 
ShauYu Lan, NTU A velocity sensor based on large Fizeau’s light dragging effect in a moving electromagneticallyinduced transparent medium Abstract Atoms based velocimeter typically relies on measuring the first order Doppler shift of individual atoms. To determine the centerofmass 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 centerofmass 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 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 submicron 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 magnetoreception. 
14:40 
Jiangbin Gong, Dept of Physics, NUS Aspects of work fluctuations: Why nonequilibrium statistics is a challenge 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 nonequilibrium 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 freeenergy 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 Abstract Using density matrix renormalization group numerical calculations, we study the phase diagram of the half filled BoseHubbard 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 BoseHubbard 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 
JanMichael Rost, MPI komplexe Systeme Dresden Nonadiabatic photoionization: pump and probe by a single pulse Abstract In this contribution we will discuss properties of nonadiabatic
photoionization which is realized when the length of the light pulse is
comparable with the time scale of the bound electronorbital 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.

10:40  Coffee/Tea Break 
11:10 
Wenhui Li, CQT, NUS Coherent microwavetooptical conversion via sixwave mixing in Rydberg atoms 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 sixwave 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 microwavetooptical conversion demonstrated here is freespace, broadband and has the potential to reach nearunity 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.

11:50 
Gerhard Zurn, Uni Heidelberg Spin dynamics of dipolar interacting Rydberg atoms 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 spin1/2 model. By driving the manybody system outofequilibrium for higher densities we report the observation of coherent spin oscillations with interactioninduced damping, which can be described in terms of a dipolar XXmodel 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 