Observation of directly interacting coherent two-level systems in a solid

Parasitic two-level tunneling systems originating from structural material defects affect the functionality of various microfabricated devices by acting as a source of noise. In particular, superconducting quantum bits may be sensitive to even single defects when these reside in the tunnel barrier of the qubit's Josephson junctions, and this can be exploited to observe and manipulate the quantum states of individual tunneling systems. Here, we detect and fully characterize a system of two strongly interacting defects using a novel technique for high-resolution spectroscopy. Mutual defect coupling has been conjectured to explain various anomalies of glasses, and was recently suggested as the origin of low frequency noise in superconducting devices. Our study provides conclusive evidence of defect interactions with full access to the individual constituents, demonstrating the potential of superconducting qubits for studying material defects. All our observations are consistent with the assumption that defects are generated by atomic tunneling.Comment: 13 pages, 7 figures. Includes supplementary materia

On the use of ancient DNA from plants and microbes for evolutionary inference

Our ability to cost-effectively sequence entire genomes has revolutionized many areas of science, from applied fields like medicine and breeding, to evolutionary biology and archaeology. Although the sequencing of extant genomes has led to significant breakthroughs, our understanding of many fields can be further enhanced by sequencing the genomes of historical and ancient specimens such as mammalian skeletal remains, archaeobotanical remains or museum specimens. Studying this ancient DNA has greatly improved our understanding of human history, allowed the reconstruction of genomes of extinct species, and has enabled us to track genetic changes during processes such as the domestication of plants and animals. To make meaningful inferences from ancient DNA sequencing data, however, requires understanding the unique characteristics of ancient DNA molecules extracted from different types of specimens. Particularly the post-mortem degradation of DNA molecules poses challenges for data generation and analysis that need to be addressed. This work contributes to overcoming several of these challenges. To improve our understanding of the kinetics of DNA degradation and to aid experimental design, we studied degradation processes in a time-series dataset of herbarium specimens. This allowed us to identify patterns of age-associated DNA damage which accumulate over time, most notably those caused by random fragmentation of the DNA backbone and by the deamination of cytosines. Next, we focused on the implications of these damage patterns for ancient DNA data analysis. One consequence of DNA degradation is an increased risk of contamination with modern DNA, which is often at a much higher concentration than the highly fragmented endogenous DNA of an ancient or historical specimen. This necessitates the authentication of DNA sequences by providing proof of their ancient origin. Motivated by the constant danger of exogenous contamination in ancient DNA research, we investigated several approaches to aid authentication, from the application of novel laboratory procedures to the development of a statistical method for data analysis. These methods primarily rely on the presence of age-associated damage patterns, which we and others have shown to be present ubiquitously in authentic ancient DNA sequences. Once positive evidence of authenticity has been provided, the aim is often to study the genetic variation within a collected sample set, or between newly acquired samples and reference panels of genetic variation. To facilitate this, we present methods which are designed to allow the assessment of nucleotide variation from low-coverage sequencing data typical for ancient DNA. In addition, we developed a method to investigate intra-specific ploidy variation from sequencing data directly. All of these methods are designed with a focus on ancient DNA applications but can also be applied more broadly. Finally, we applied what we learned about the characteristics of ancient DNA, and the methods we developed, to study ancient DNA sequences from archaeological sediments. We show how specialized experimental procedures and analytical methods permit meaningful evolutionary inference from such sequences, which allowed us to illuminate the domestication history of cultivated grape, an important fruit crop. Altogether, the work we present contributes to our understanding of many aspects of working with DNA from ancient and historical specimens and opens up opportunities to apply the experimental and analytical procedures presented here to a larger variety of sample types. This will allow the use of ancient DNA sequencing for an increasing diversity of organisms, especially plants and microbes, to enhance evolutionary inference. In addition, we anticipate that our contributions add to the continuous improvement of the standards applied when working with ancient DNA, especially regarding the authenticity of sequences on which subsequent inferences are based

Universal dephasing in a chiral 1D interacting fermion system

We consider dephasing by interactions in a one-dimensional chiral fermion system (e.g. a Quantum Hall edge state). For finite-range interactions, we calculate the spatial decay of the Green's function at fixed energy, which sets the contrast in a Mach-Zehnder interferometer. Using a physically transparent semiclassical ansatz, we find a power-law decay of the coherence at high energies and zero temperature (T=0), with a universal asymptotic exponent of 1, independent of the interaction strength. We obtain the dephasing rate at T>0 and the fluctuation spectrum acting on an electron.Comment: 5 pages, 3 figures; minor changes, version as published

Influence of the hyperfine structure on plutonium in resonant laser-SNMS

Resonance ionization mass spectrometry is an ultra-sensitive and highly element selective tool for spectroscopy, ionization and detection of atoms and thus enables rare isotope determination. In combination with spatially resolved sputtering of neutrals by an initial ion beam, e.g. within a commercial secondary ion mass spectrometer, an isotope and isobar selective analysis technique with resolution on the micrometer scale for particles and surfaces is realized. Detection of minuscule amounts of specific actinides, e.g. of plutonium, in environmental and technical samples by this ultra-trace analysis technique requires detailed knowledge about the atomic physics of the element. Identification and characterization of the specific resonance ionization scheme applied within the particular geometry of the apparatus in use is needed. An analysis of the dependence of the specifications, specifically regarding the influence of the relative laser beam polarizations is presented here as an aspect, that could have a severe impact on isotope ratio precision and overall efficiency in the resulting ion signal

Relaxation of Josephson qubits due to strong coupling to two-level systems

We investigate the energy relaxation (T1) process of a qubit coupled to a bath of dissipative two-level fluctuators (TLF). We consider the fluctuators strongly coupled to the qubit both in the limit of spectrally separated single TLF's as well as in the limit of spectrally dense TLF's. We conclude that the avoided level crossings, usually attributed to very strongly coupled single TLF's, could also be caused by many weakly coupled spectrally dense fluctuators.Comment: 11+ pages, 10 figures, citations added, discussion extende

Increased mesiotemporal delta activity characterizes virtual navigation in humans

Hippocampal theta or rhythmic slow activity (RSA) occurring during exploratory behaviors and rapid-eye-movement (REM) sleep is a characteristic and well-identifiable oscillatory rhythm in animals. In contrast, controversy surrounds the existence and electrophysiological correlates of this activity in humans. Some argue that the human hippocampal theta occurs in short and phasic bursts. On the contrary, our earlier studies provide evidence that REM-dependent mesiotemporal RSA is continuous like in animals but instead of the theta it falls in the delta frequency range. Here we used a virtual navigation task in 24 epilepsy patients implanted with foramen ovale electrodes. EEG was analyzed for 1-Hz wide frequency bins up to 10 Hz according to four conditions: resting, non-learning route-following, acquisition and recall. We found progressively increasing spectral power in frequency bins up the 4 Hz across these conditions. No spectral power increase relative to resting was revealed within the traditional theta band and above in any of the navigation conditions. Thus the affected frequency bins were below the theta band and were similar to those characterizing REM sleep in our previous studies providing further indication that it is delta rather than theta that should be regarded as a human analogue of the animal RSA

New horizons in microparticle forensics: Actinide imaging and detection of 238 Pu and 242m Am in hot particles

Micrometer-sized pollutant particles are of highest concern in environmental and life sciences, cosmochemistry, and forensics. From their composition, detailed information on origin and potential risks to human health or environment is obtained. We combine secondary ion mass spectrometry with resonant laser ionization to selectively examine elemental and isotopic composition of individual particles at submicrometer spatial resolution. Avoiding any chemical sample preparation, isobaric interferences are suppressed by five orders of magnitude. In contrast to most mass spectrometric techniques, only negligible mass is consumed, leaving the particle intact for further studies. Identification of actinide elements and their isotopes on a Chernobyl hot particle, including 242mAm at ultratrace levels, proved the performance. Beyond that, the technique is applicable to almost all elements and opens up previously unexplored scientific applications

The chemical journey of Europium(III) through winter rye (Secale cereale L.) – Understanding through mass spectrometry and chemical microscopy

A combination of biochemical preparation methods with microscopic, spectroscopic, and mass spectrometric analysis techniques as contemplating state of the art application, was used for direct visualization, localization, and chemical identification of europium in plants. This works illustrates the chemical journey of europium (Eu(III)) through winter rye (Secale cereale L.), providing insight into the possibilities of speciation for Rare Earth Elements (REE) and trivalent f-elements. Kinetic experiments of contaminated plants show a maximum europium concentration in Secale cereale L. after four days. Transport of the element through the vascular bundle was confirmed with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDS). For chemical speciation, plants were grown in a liquid nutrition medium, whereby Eu(III) species distribution could be measured by mass spectrometry and luminescence measurements. Both techniques confirm the occurrence of Eu malate species in the nutrition medium, and further analysis of the plant was performed. Luminescence results indicate a change in Eu(III) species distribution from root tip to plant leaves. Microscopic analysis show at least three different Eu(III) species with potential binding to organic and inorganic phosphate groups and a Eu(III) protein complex. With plant root extraction, further europium species could be identified by using Electrospray Ionization Mass Spectrometry (ESI MS). Complexation with malate, citrate, a combined malate-citrate ligand, and aspartate was confirmed mostly in a 1:1 stoichiometry (Eu:ligand). The combination of the used analytical techniques opens new possibilities in direct species analysis, especially regarding to the understanding of rare earth elements (REE) uptake in plants. This work provides a contribution in better understanding of plant mechanisms of the f-elements and their species uptake

The Impact and Design of the MDGs: Some Reflections

The MDGs appear to have been more influential than most other attempts at international target?setting in the field of development, at least at the level of international discourse. But has this translated into impact on either development policy or resource allocation, and if so has the impact been constructive or not? And what lessons does this suggest for any future target?setting proposals