arXiv subjects

Nate Harvey

Publications and source records attributed to Nate Harvey.

5 recordsLinked to original sources

arXiv2023

NASA's Cold Atom Laboratory: Five Years of Quantum Science Operations in Space

NASA's Cold Atom Laboratory (CAL) is a multi-user science facility for studying quantum gases in the microgravity environment of the International Space Station. The persistent microgravity environment of the ISS enables research with ultracold atoms in a temperature regime and force-free environment inaccessible to terrestrial laboratories, unlocking the potential to observe novel quantum phenomena. CAL launched to the ISS in May 2018, and has operated continuously since then as the worlds first multi-user quantum science facility in space. CAL is the first experimental facility to produce the fifth state of matter known as a Bose-Einstein condensate with ultracold rubidium atoms on orbit and, more recently, with mixtures of rubidium and potassium. We present an overview of CAL's design and operation, review the scientific contributions to date, and discuss recent on-orbit upgrades to extend its useful mission lifetime and provide enhanced science. We also consider opportunities for follow-on missions informed by lessons learned from over five years of operation on orbit.

quant-ph↗

arXiv2020

Radio Detection of Ultra-high Energy Cosmic Rays with Low Lunar Orbiting SmallSats

Ultra-high energy cosmic rays (UHECRs) are the most energetic particles observed and serve as a probe of the extreme universe. A key question to understanding the violent processes responsible for their acceleration is identifying which classes of astrophysical objects (active galactic nuclei or starburst galaxies, for example) correlate to their arrival directions. While source clustering is limited by deflections in the Galactic magnetic field, at the highest energies the scattering angles are sufficiently low to retain correlation with source catalogues. While there have been several studies attempting to identify source catalogue correlations with data from the Pierre Auger Observatory and the Telescope Array, the significance above an isotropic background has not yet reached the threshold for discovery. It has been known for several decades that a full-sky UHECR observatory would provide a substantial increase in sensitivity to the anisotropic component of UHECRs. There have been several concepts developed in that time targeting the identification of UHECR sources such as OWL, JEM-EUSO, and POEMMA, using fluorescence detection in the Earth's atmosphere from orbit. In this white paper, we present a concept called the Zettavolt Askaryan Polarimeter (ZAP), designed to identify the source of UHECRs using radio detection of the Askaryan radio emissions produced by UHECRs interacting in the Moon's regolith from low lunar orbit.

astro-ph.HE↗

arXiv2020

GipsyX/RTGx, A New Tool Set for Space Geodetic Operations and Research

GipsyX/RTGx is the Jet Propulsion Laboratory's (JPL) next generation software package for positioning, navigation, timing, and Earth science using measurements from three geodetic techniques: Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS); with Very Long Baseline Interferometry (VLBI) under development. The software facilitates combined estimation of geodetic and geophysical parameters using a Kalman filter approach on real or simulated data in both post-processing and in real-time. The estimated parameters include station coordinates and velocities, satellite orbits and clocks, Earth orientation, ionospheric and tropospheric delays. The software is also capable of full realization of a dynamic terrestrial reference through analysis and combination of time series of ground station coordinates. We present some key aspects of its new architecture, and describe some of its major applications, including Real-time orbit determination and ephemeris predictions in the U.S. Air Force Next Generation GPS Operational Control Segment (OCX), as well as in JPL's Global Differential GPS (GDGPS) System, supporting User Range Error (URE) of $<$ 5 cm RMS; precision post-processing GNSS orbit determination, including JPL's contributions to the International GNSS Service (IGS) with URE in the 2 cm RMS range; Precise point positioning (PPP) with ambiguity resolution, both statically and kinematically, for geodetic applications with 2 mm horizontal, and 6.5 mm vertical repeatability for static positioning; Operational orbit and clock determination for Low Earth Orbiting (LEO) satellites, such as NASA's Gravity Recovery and Climate Experiment (GRACE) mission with GRACE relative clock alignment at the 20 ps level.

physics.geo-ph↗

arXiv2005

Universal finitary codes with exponential tails

In 1977, Keane and Smorodinsky showed that there exists a finitary homomorphism from any finite-alphabet Bernoulli process to any other finite-alphabet Bernoulli process of strictly lower entropy. In 1996, Serafin proved the existence of a finitary homomorphism with finite expected coding length. In this paper, we construct such a homomorphism in which the coding length has exponential tails. Our construction is source-universal, in the sense that it does not use any information on the source distribution other than the alphabet size and a bound on the entropy gap between the source and target distributions. We also indicate how our methods can be extended to prove a source-specific version of the result for Markov chains.

math.PR↗

arXiv2003

An invariant of finitary codes with finite expected square root coding length

Let $p$ and $q$ be probability vectors with the same entropy $h$. Denote by $B(p)$ the Bernoulli shift indexed by $\Z$ with marginal distribution $p$. Suppose that $ϕ$ is a measure preserving homomorphism from $B(p)$ to $B(q)$. We prove that if the coding length of $ϕ$ has a finite 1/2 moment, then $σ_p^2=σ_q^2$, where $σ_p^2=\sum_i p_i(-\log p_i-h)^2$ is the {\dof informational variance} of $p$. In this result, which sharpens a theorem of Parry (1979), the 1/2 moment cannot be replaced by a lower moment. On the other hand, for any $θ<1$, we exhibit probability vectors $p$ and $q$ that are not permutations of each other, such that there exists a finitary isomorphism $Φ$ from $B(p)$ to $B(q)$ where the coding lengths of $Φ$ and of its inverse have a finite $θ$ moment. We also present an extension to ergodic Markov chains.

math.PR↗