177 research outputs found
Quantum control via a genetic algorithm of the field ionization pathway of a Rydberg electron
Quantum control of the pathway along which a Rydberg electron field ionizes
is experimentally and computationally demonstrated. Selective field ionization
is typically done with a slowly rising electric field pulse. The
scaling of the classical ionization threshold leads to a rough mapping between
arrival time of the electron signal and principal quantum number of the Rydberg
electron. This is complicated by the many avoided level crossings that the
electron must traverse on the way to ionization, which in general leads to
broadening of the time-resolved field ionization signal. In order to control
the ionization pathway, thus directing the signal to the desired arrival time,
a perturbing electric field produced by an arbitrary waveform generator is
added to a slowly rising electric field. A genetic algorithm evolves the
perturbing field in an effort to achieve the target time-resolved field
ionization signal.Comment: Corrected minor typographic errors and changed the titl
Time Dependence of Few-Body Forster Interactions Among Ultracold Rydberg Atoms
Rubidium Rydberg atoms in either |mj| sublevel of the 36p3/2 state can exchange energy via Stark-tuned Förster resonances, including two-, three-, and four-body dipole-dipole interactions. Three-body interactions of this type were first reported and categorized by Faoro et al. [Nat. Commun. 6, 8173 (2015)] and their Borromean nature was confirmed by Tretyakov et al. [Phys. Rev. Lett. 119, 173402 (2017)]. We report the time dependence of the N-body Förster resonance N×36p3/2,|mj|=1/2→36s1/2+37s1/2+(N−2)×36p3/2,|mj|=3/2, for N=2, 3, and 4, by measuring the fraction of initially excited atoms that end up in the 37s1/2 state as a function of time. The essential features of these interactions are captured in an analytical model that includes only the many-body matrix elements and neighboring atom distribution. A more sophisticated simulation reveals the importance of beyond-nearest-neighbor interactions and of always-resonant interactions
Genome-Wide Gene Expression Profiling of Nucleus Accumbens Neurons Projecting to Ventral Pallidum Using both Microarray and Transcriptome Sequencing
The cellular heterogeneity of brain poses a particularly thorny issue in genome-wide gene expression studies. Because laser capture microdissection (LCM) enables the precise extraction of a small area of tissue, we combined LCM with neuronal track tracing to collect nucleus accumbens shell neurons that project to ventral pallidum, which are of particular interest in the study of reward and addiction. Four independent biological samples of accumbens projection neurons were obtained. Approximately 500 pg of total RNA from each sample was then amplified linearly and subjected to Affymetrix microarray and Applied Biosystems sequencing by oligonucleotide ligation and detection (SOLiD) transcriptome sequencing (RNA-seq). A total of 375 million 50-bp reads were obtained from RNA-seq. Approximately 57% of these reads were mapped to the rat reference genome (Baylor 3.4/rn4). Approximately 11,000 unique RefSeq genes and 100,000 unique exons were identified from each sample. Of the unmapped reads, the quality scores were 4.74 ± 0.42 lower than the mapped reads. When RNA-seq and microarray data from the same samples were compared, Pearson correlations were between 0.764 and 0.798. The variances in data obtained for the four samples by microarray and RNA-seq were similar for medium to high abundance genes, but less among low abundance genes detected by microarray. Analysis of 34 genes by real-time polymerase chain reaction showed higher correlation with RNA-seq (0.66) than with microarray (0.46). Further analysis showed 20–30 million 50-bp reads are sufficient to provide estimates of gene expression levels comparable to those produced by microarray. In summary, this study showed that picogram quantities of total RNA obtained by LCM of ∼700 individual neurons is sufficient to take advantage of the benefits provided by the transcriptome sequencing technology, such as low background noise, high dynamic range, and high precision
Improving the state selectivity of field ionization with quantum control
The electron signals from the field ionization of two closely-spaced Rydberg
states of \mbox{rubidium-85} are separated using quantum control. In selective
field ionization, the state distribution of a collection of Rydberg atoms is
measured by ionizing the atoms with a ramped electric field. Generally, atoms
in higher energy states ionize at lower fields, so ionized electrons which are
detected earlier in time can be correlated with higher energy Rydberg states.
However, the resolution of this technique is limited by the Stark effect. As
the electric field is increased, the electron encounters numerous avoided Stark
level crossings which split the amplitude among many states, thus broadening
the time-resolved ionization signal. Previously, a genetic algorithm has been
used to control the signal shape of a single Rydberg state. The present work
extends this technique to separate the signals from the and states
of rubidium-85, which are overlapped when using a simple field ramp as in
selective field ionization
Improving the State Selectivity of Field Ionization With Quantum Control
The electron signals from the field ionization of two closely spaced Rydberg states of rubidium-85 are separated using quantum control. In selective field ionization, the state distribution of a collection of Rydberg atoms is measured by ionizing the atoms with a ramped electric field. Generally, atoms in higher energy states ionize at lower fields, so ionized electrons which are detected earlier in time can be correlated with higher energy Rydberg states. However, the resolution of this technique is limited by the Stark effect. As the electric field is increased, the electron encounters numerous avoided Stark level crossings which split the amplitude among many states, thus broadening the time-resolved ionization signal. Previously, a genetic algorithm has been used to control the signal shape of a single Rydberg state. The present work extends this technique to separate the signals from the 34s and 33p states of rubidium-85, which are overlapped when using a simple field ramp as in selective field ionization
Extraction of Electron Self-Energy and Gap Function in the Superconducting State of Bi_2Sr_2CaCu_2O_8 Superconductor via Laser-Based Angle-Resolved Photoemission
Super-high resolution laser-based angle-resolved photoemission measurements
have been performed on a high temperature superconductor Bi_2Sr_2CaCu_2O_8. The
band back-bending characteristic of the Bogoliubov-like quasiparticle
dispersion is clearly revealed at low temperature in the superconducting state.
This makes it possible for the first time to experimentally extract the complex
electron self-energy and the complex gap function in the superconducting state.
The resultant electron self-energy and gap function exhibit features at ~54 meV
and ~40 meV, in addition to the superconducting gap-induced structure at lower
binding energy and a broad featureless structure at higher binding energy.
These information will provide key insight and constraints on the origin of
electron pairing in high temperature superconductors.Comment: 4 pages, 4 figure
Perturbed Field Ionization for Improved State Selectivity
Selective field ionization (SFI) is used to determine the state or distribution of states to which a Rydberg atom is excited. By evolving a small perturbation to the ramped electric field using a genetic algorithm, the shape of the time-resolved ionization signal can be controlled. This allows for the separation of signals from pairs of states that would be indistinguishable with unperturbed SFI. Measurements and calculations are presented that demonstrate this technique and shed light on how the perturbation directs the pathway of the electron to ionization. Pseudocode for the genetic algorithm is provided. Using the improved resolution afforded by this technique, quantitative measurements of the 36p3/2 + 36p3/2 --\u3e 36s1/2 + 37s1/2 dipole–dipole interaction are made
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