Enhancement of laser cooling by the use of magnetic gradients

We present a laser cooling scheme for trapped ions and atoms using a combination of laser couplings and a magnetic gradient field. In a Schrieffer-Wolff transformed picture, this setup cancels the carrier and blue sideband terms completely resulting in an improved cooling behaviour compared to standard cooling schemes (e.g. sideband cooling) and allowing cooling to the vibrational ground state. A condition for optimal cooling rates is presented and the cooling behaviour for different Lamb-Dicke parameters and spontaneous decay rates is discussed. Cooling rates of one order of magnitude less than the trapping frequency are achieved using the new cooling method. Furthermore the scheme turns out to be robust under deviations from the optimal parameters and moreover provides good cooling rates also in the multi particle case.Comment: 14 pages, 8 figure

Trapped ion chain as a neural network

We demonstrate the possibility of realizing a neural network in a chain of trapped ions with induced long range interactions. Such models permit to store information distributed over the whole system. The storage capacity of such network, which depends on the phonon spectrum of the system, can be controlled by changing the external trapping potential and/or by applying longitudinal local magnetic fields. The system properties suggest the possibility of implementing robust distributed realizations of quantum logic.Comment: 4 pages, 3 figure

ALS-associated mutations in the FUS nuclear localization signal in mice alter the cytosolic protein and RNA interactome of FUS

Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) are neurodegenerative diseases affecting motor neurons and neurons in the frontal/temporal lobes of the cortex, respectively. A pathological hallmark of both ALS and FTD patients are neuronal and glial proteinaceous inclusions in the affected brain regions. In a subset of patients, these inclusions contain the RNA-binding protein (RBP) Fused in Sarcoma (FUS). Although most cases are sporadic, there are familial cases in which several causal genes have been identified for both diseases. In a subset of ALS patients, several ALS-causing mutations in the FUS gene have been identified. Disease-associated FUS mutations are found primarily in the nuclear localization signal (NLS) of FUS. NLS mutations impair nuclear import of FUS and hence result in increased cytosolic accumulation of FUS. As FUS is primarily localized in the nucleus and plays important roles in transcription, alternative splicing, DNA damage repair and miRNA biogenesis, most studies have focused on the nuclear role of FUS. In recent years, a cytoplasmic role for FUS has become more evident, e.g. in the regulation of mRNA stability or mRNA transport. In ALS and FTD patients, FUS is partially lost from the nucleus and found in cytoplasmic aggregates, resulting in loss of the nuclear function of FUS as well as toxic gain-of-function by cytosolic FUS aggregates. This leads to the question as to the effect of the cytosolic mislocalization of FUS. In order to determine if this mislocalization results in an altered FUS interactome, I aimed to isolate FUS mRNP complexes from a FUS mutant mouse model and identify both RNA and protein interactors. The Fus ΔNLS/+mouse model was created by removing the FUS NLS, causing FUS cytoplasmic mislocalization and resulting in an early cortical and a late motor phenotype. Using the cytosolic fraction from the cortices of 50 day old Fus ΔNLS/+ mice, I performed immunoprecipitation (IP) of FUS followed by mass spectrometry (MS) and RNA sequencing (RNASeq). I identified an altered FUS interactome, both on an RNA and protein level. Differentially bound RNAs included those whose proteins are involved in transcription, proteasomal activity, nicotinic signaling and RNA binding. I found changes in alternatively spliced mRNAs present in the cytoplasm of these mice, including Ddhd1 and Ptprf1. This could indicate a nuclear loss-of-function of FUS and hence missplicing of FUS target genes. Differential protein interactors included those important to synapse function and RNA regulation. The altered FUS interactome caused by FUS cytosolic mislocalization may not only result in expression of alternative isoforms, but also perhaps affect RNA stability and localization resulting in impaired neuronal function. This study provides new insights into the pathomechanisms of FUS-associated neurodegeneration

Systematics of the odd-even effect in the resonance ionization of Os and Ti

Measurements of the odd-even effect in the mass spectrometric analysis of Ti and Os isotopes by resonance ionization mass spectrometry have been performed for ΔJ = + 1, 0 and -1 transitions. Under saturating conditions of the ionization and for ΔJ = + 1 transitions odd-even effects are reduced below the 0.5% level. Depending on the polarization state of the laser large odd isotope enrichments are observed for ΔJ = 0 and -1 transitions which can be reduced below the 0.5% level by depolarization of the laser field

Laser-induced isotopic selectivity in the resonance ionization of Os

Isotope selective effects in resonance ionization mass spectrometry (RIMS) pose a potentially serious limitation to the application of this technique to the precise and reproducible measurement of isotope ratios. In order to identify some of the underlying causes of isotope selectivity in RIMS and to establish procedures for minimizing these effects, we investigated laser-induced isotope selectivity in the resonance ionization of Os. A single-color, one-photon resonant ionization scheme was used for several different transitions to produce Os photoions from a thermal atomization source. Variations in Os isotope ratios were studied as a function of laser parameters such as wavelength, bandwidth, power and polarization state. Isotope selectivity is strongly dependent on laser power and wavelength, even when the bandwidth of the laser radiation is much larger than the optical isotope shift. Variations in the ^(190)Os/^(188)Os ratio of ≈20% for a detuning of 0.8 cm^(−1) were observed on a transition with a small oscillator strength. Large even—odd isotope selectivity with a 13% depletion of ^(189)Os was observed on a ΔJ = +1 transition at low laser intensity; the odd mass Os isotopes are systematically depleted. For ΔJ = −1 and 0 transitions the isotope selectivity was reduced by polarization scrambling and for strongly saturating conditions. A technique employing the wavelength dependence of even—even isotope selectivity as an internal wavelength standard was developed to permit accurate and reproducible wavelength adjustment of the laser radiation. This technique provides control over laser-induced isotope selectivity for single-color ionization and enabled us to obtain reproducible measurements of ^(192)Os/^(188)Os and ^(189)Os/^(190)Os ratios in the saturation regime for a ΔJ = +1 transition with a precision of better than 0.5%. The application of this wavelength-tuning procedure should significantly improve the quality of RIMS isotope ratio data for many elements

Spin and Orbital Splitting in Ferromagnetic Contacted Single Wall Carbon Nanotube Devices

We observed the coulomb blockade phenomena in ferromagnetic contacting single wall semiconducting carbon nanotube devices. No obvious Coulomb peaks shift was observed with existing only the Zeeman splitting at 4K. Combining with other effects, the ferromagnetic leads prevent the orbital spin states splitting with magnetic field up to 2 Tesla at 4K. With increasing magnetic field further, both positive or negative coulomb peaks shift slopes are observed associating with clockwise and anticlockwise orbital state splitting. The strongly suppressed/enhanced of the conductance has been observed associating with the magnetic field induced orbital states splitting/converging