Quantum computing with an electron spin ensemble

We propose to encode a register of quantum bits in different collective electron spin wave excitations in a solid medium. Coupling to spins is enabled by locating them in the vicinity of a superconducting transmission line cavity, and making use of their strong collective coupling to the quantized radiation field. The transformation between different spin waves is achieved by applying gradient magnetic fields across the sample, while a Cooper Pair Box, resonant with the cavity field, may be used to carry out one- and two-qubit gate operations.Comment: Several small corrections and modifications. This version is identical to the version published in Phys. Rev. Let

Engineering DUB-deficient Viral Proteases from FIPV and PEDV Coronaviruses

Coronaviruses form a class of viral pathogens lethal to humans and livestock. This issue is compounded by a lack of commercially available treatments or vaccines. In 2014, porcine epidemic diarrhea virus (PEDV) emerged in the United States and accounted for an estimated 7 million porcine deaths. Deaths of humans, companion animals, and livestock caused by coronaviruses highlight the need for therapeutic strategies to combat this devastating disease. One strategy involves engineering papain-like protease 2 (PLP2), an enzyme conserved among coronavirus species that is critical for virus replication and pathogenesis. PLP2’s de-ubiquitinating (DUB) activity aids in the suppression of the host’s innate antiviral immune response. By targeting and disrupting ubiquitin binding in PLP2 and thus its DUB activity, the virus would no longer be able to antagonize the innate immune response. To this end, we introduced informed single-point mutations in PEDV and in feline infectious peritonitis virus (FIPV) PLP2s using structure-guided mutagenesis. We then characterized the kinetic activity of the resulting mutants in vitro using fluorescent peptide and ubiquitin substrates. Through these studies, we were able to evaluate the relationship between PLP2-ubiquitin binding and DUB activity. Preliminary data analysis suggests that residues outside the active site of PLP2 and within the ubiquitin-binding interface are necessary for DUB activity; these residues can be selectively disrupted to abolish DUB activity relative to the wild-type. These results describe a series of DUB-deficient PLP2 mutants that can be leveraged as tools for use in future coronavirus research. Such tools will allow creation of an attenuated virus strain that could aid in vaccine and drug design

Selection for Greater β-Glucan Content in Oat Grain

Oat (Avena sativa L.) β-glucan lowers serum cholesterol in humans. Development of oat cultivars with greater groat (caryopsis) β-glucan content would increase the nutritional and economic value of the crop. The objectives of this experiment were to evaluate the response to phenotypic selection among individual S0 plants for greater groat β-glucan content in two genetically broad-based populations; to compare selected experimental lines to standard check cultivars; and to estimate genetic variances and heritabilities and to test for nonadditive genetic variance for β-glucan content. We measured groat β-glucan contents of check cultivars and parental lines and random S0:1 lines from initial and selected generations of each population grown in field experiments in 1996 and 1997 at two Iowa locations. Mean β-glucan content increased from 53.9 to 59.9 g kg−1 in one population, and from 63.5 to 66.0 g kg−1 in the other, following selection. Genetic variance of β-glucan content decreased by 9 to 22% following selection, but heritability for β-glucan content did not change significantly. Heritability estimates ranged from 0.80 to 0.85 on a line mean basis. Additive variance was the only substantial component of genetic variance. Some experimental lines had significantly greater β-glucan content than the best check cultivars and lines. Phenotypic selection for greater groat β-glucan content will be effective for developing cultivars with elevated β-glucan contents

Fluorescence during Doppler cooling of a single trapped atom

We investigate the temporal dynamics of Doppler cooling of an initially hot single trapped atom in the weak binding regime using a semiclassical approach. We develop an analytical model for the simplest case of a single vibrational mode for a harmonic trap, and show how this model allows us to estimate the initial energy of the trapped particle by observing the fluorescence rate during the cooling process. The experimental implementation of this temperature measurement provides a way to measure atom heating rates by observing the temperature rise in the absence of cooling. This method is technically relatively simple compared to conventional sideband detection methods, and the two methods are in reasonable agreement. We also discuss the effects of RF micromotion, relevant for a trapped atomic ion, and the effect of coupling between the vibrational modes on the cooling dynamics.Comment: 12 pages, 11 figures, Submitted to Phys. Rev.

A microfabricated surface-electrode ion trap for scalable quantum information processing

We demonstrate confinement of individual atomic ions in a radio-frequency Paul trap with a novel geometry where the electrodes are located in a single plane and the ions confined above this plane. This device is realized with a relatively simple fabrication procedure and has important implications for quantum state manipulation and quantum information processing using large numbers of ions. We confine laser-cooled Mg-24 ions approximately 40 micrometer above planar gold electrodes. We measure the ions' motional frequencies and compare them to simulations. From measurements of the escape time of ions from the trap, we also determine a heating rate of approximately five motional quanta per millisecond for a trap frequency of 5.3 MHz.Comment: 4 pages, 4 figure