Impact of Electric Fields on Highly Excited Rovibrational States of Polar Dimers

We study the effect of a strong static homogeneous electric field on the highly excited rovibrational levels of the LiCs dimer in its electronic ground state. Our full rovibrational investigation of the system includes the interaction with the field due to the permanent electric dipole moment and the polarizability of the molecule. We explore the evolution of the states next to the dissociation threshold as the field strength is increased. The rotational and vibrational dynamics are influenced by the field; effects such as orientation, angular motion hybridization and squeezing of the vibrational motion are demonstrated and analyzed. The field also induces avoided crossings causing a strong mixing of the electrically dressed rovibrational states. Importantly, we show how some of these highly excited levels can be shifted to the continuum as the field strength is increased, and reversely how two atoms in the continuum can be brought into a bound state by lowering the electric field strength.Comment: 10 pages, 4 figure

Giant enhancement of photodissociation of polar dimers in electric fields

We explore the photodissociation of polar dimers in static electric fields in the cold regime using the example of the LiCs molecule. A giant enhancement of the differential cross section is found for laboratory electric field strengths, and analyzed with varying rovibrational bound states, continuum energies as well as field strengths.Comment: 6 pages, 6 figure

Mixed-field orientation of a thermal ensemble of linear polar molecules

We present a theoretical study of the impact of an electrostatic field combined with nonresonant linearly polarized laser pulses on the rotational dynamics of a thermal ensemble of linear molecules. We solve the time-dependent Schr\"odinger equation within the rigid rotor approximation for several rotational states. Using the carbonyl sulfide (OCS) molecule as a prototype, the mixed-field orientation of a thermal sample is analyzed in detail for experimentally accessible static field strengths and laser pulses. We demonstrate that for the characteristic field configuration used in current mixed-field orientation experiments, a significant orientation is obtained for rotational temperatures below 0.7K or using stronger dc fields.Comment: 9 pages, 10 figure

Improving I/O performance through an in-kernel disk simulator

This paper presents two mechanisms that can significantly improve the I/O performance of both hard and solid-state drives for read operations: KDSim and REDCAP. KDSim is an in-kernel disk simulator that provides a framework for simultaneously simulating the performance obtained by different I/O system mechanisms and algorithms, and for dynamically turning them on and off, or selecting between different options or policies, to improve the overall system performance. REDCAP is a RAM-based disk cache that effectively enlarges the built-in cache present in disk drives. By using KDSim, this cache is dynamically activated/deactivated according to the throughput achieved. Results show that, by using KDSim and REDCAP together, a system can improve its I/O performance up to 88% for workloads with some spatial locality on both hard and solid-state drives, while it achieves the same performance as a ‘regular system’ for workloads with random or sequential access patterns.Peer ReviewedPostprint (author's final draft

NUMA impact on network storage protocolsover high-speed raw Ethernet

Proceedings of: Second International Workshop on Sustainable Ultrascale Computing Systems (NESUS 2015). Krakow (Poland), September 10-11, 2015.Current storage trends dictate placing fast storage devices in all servers and using them as a single distributed storage system. In this converged model where storage and compute resources co-exist in the same server, the role of the network is becoming more important: network overhead is becoming a main imitation to improving storage performance. In our previous work we have designed Tyche, a network protocol for converged storage that bundles multiple 10GigE links transparently and reduces protocol overheads over raw Ethernet without hardware support. However, current technology trends and server consolidation dictates building servers with large amounts of resources (CPU, memory, network, storage). Such servers need to employ Non-Uniform Memory Architectures (NUMA) to scale memory performance. NUMA introduces significant problems with the placement of data and buffers at all software levels. In this paper, we first use Tyche to examine the performance implications of NUMA servers on end-to-end network storage performance. Our results show that NUMA effects have significant negative impact and can reduce throughput by almost 2x on servers with as few as 8 cores (16 hyper-threads). Then, we propose extensions to network protocols that can mitigate this impact. We use information about the location of data, cores, and NICs to properly align data transfers and minimize the impact of NUMA servers. Our design almost entirely eliminates NUMA effects by encapsulating all protocol structures to a “channel” concept and then carefully mapping channels and their resources to NICs and NUMA nodes.We thankfully acknowledge the support of the European Commission under the 7th Framework Programs through the NanoStreams (FP7-ICT-610509) project, the HiPEAC3 (FP7-ICT-287759) Network of Excellence, and the COST programme Action IC1305, ’Network for Sustainable Ultrascale Computing (NESUS)’

Fermionic collective excitations in a lattice gas of Rydberg atoms

We investigate the many-body quantum states of a laser-driven gas of Rydberg atoms confined to a large spacing ring lattice. If the laser driving is much stronger than the van-der-Waals interaction among the Rydberg sates, these many-body states are collective fermionic excitations. The first excited state is a spin-wave that extends over the entire lattice. We demonstrate that our system permits to study fermions in the presence of disorder although no external atomic motion takes place. We analyze how this disorder influences the excitation properties of the fermionic states. Our work shows a route towards the creation of complex many-particle states with atoms in lattices

Creating collective many-body states with highly excited atoms

We study the collective excitation of a gas of highly excited atoms confined to a large spacing ring lattice, where the ground and the excited states are coupled resonantly via a laser field. Our attention is focused on the regime where the interaction between the highly excited atoms is very weak in comparison to the Rabi frequency of the laser. We demonstrate that in this case the many-body excitations of the system can be expressed in terms of free spinless fermions. The complex many-particle states arising in this regime are characterized and their properties, e.g. their correlation functions, are studied. In addition we investigate how one can actually experimentally access some of these many-particle states by a temporal variation of the laser parameters.Comment: 10 pages, 7 figure