Global Assimilation of Loon Stratospheric Balloon Observations and Their Trajectories Relative to Tropical Waves

Project Loon has an overall goal of providing worldwide internet coverage using a network of long-duration super-pressure balloons. Beginning in 2013, Loon has launched over 1600 balloons from multiple tropical and middle latitude locations. These GPS tracked balloon trajectories provide lower stratospheric wind information over the oceans and remote land areas where traditional radiosonde soundings are sparse, thus providing unique coverage of lower stratospheric winds. To fully investigate these Loon winds we: 1) compare the Loon winds to winds produced by a global data assimilation system (DAS: NASA GEOS) and 2) assimilate the Loon winds into the same comprehensive DAS. During May through December 2016 Loon balloons were often able to remain near the equator by selectively adjusting the Loon altitude. Our results based on global wind analyses show that the expected mean poleward motion from the Brewer-Dobson circulation can be circumvented by vertically adjusting the Loon altitudes with the phasing with the meridional wind of equatorial Rossby waves, allowing the Loon balloons to remain in the tropics

Suppression of the optical linewidth and spin decoherence of a quantum spin center in a pp−-nn diode

We present a quantitative theory of the suppression of the optical linewidth due to charge fluctuation noise in a ${p}$$-$${n}$ diode, recently observed in Anderson et al., Science 366, 1225 (2019). We connect the local electric field with the voltage across the diode, allowing for the identification of the defect depth from the experimental threshold voltage. Furthermore, we show that an accurate description of the decoherence of such spin centers requires a complete spin$-$1 formalism that yields a bi-exponential decoherence process, and predict how reduced charge fluctuation noise suppresses the spin center's decoherence rate.Comment: 17 pages, 9 figure

Opportunities for long-range magnon-mediated entanglement of spin qubits via on- and off-resonant coupling

The ability to manipulate entanglement between multiple spatially-separated qubits is essential for quantum information processing. Although nitrogen-vacancy (NV) centers in diamond provide a promising qubit platform, developing scalable two-qubit gates remains a well-known challenge. To this end, magnon-mediated entanglement proposals have attracted attention due to their long-range spin-coherent propagation. Optimal device geometries and gate protocols of such schemes, however, have yet to be determined. Here we predict strong long-distance ($>\mu$m) NV-NV coupling via magnon modes with cooperativities exceeding unity in ferromagnetic bar and waveguide structures. Moreover, we explore and compare on-resonant transduction and off-resonant virtual-magnon exchange protocols, and discuss their suitability for generating or manipulating entangled states at low temperatures ($T\lesssim 150$ mK) under realistic experimental conditions. This work will guide future experiments that aim to entangle spin qubits in solids with magnon excitations.Comment: PRX Quantum in press, 10 pages, 5 figure