Levi P. Neukirch

Geodynamo, Solar Wind, and Magnetopause 3.4 to 3.45 Billion Years Ago

Early Origin of Earths Magnetic Field Earths magnetic field protects us from stellar winds and radiation from the Sun. Understanding when, during the Earths formation, the large-scale magnetic field was established is important because it impacts understanding of the young Earths atmosphere and exosphere. By analyzing ancient silicate crystals, Tarduno et al. (p. 1238; see the Perspective by Jardine) demonstrate that the Earths magnetic field existed 3.4 to 3.45 billion years ago, pushing back the oldest record of geomagnetic field strength by 200 million years. This result combined with estimates of the conditions within the solar wind at that time implies that the size of the paleomagnetosphere was about half of that typical today, but with an auroral oval of about three times the area. The smaller magnetosphere and larger auroral oval would have promoted loss of volatiles and water from the early atmosphere. Analysis of ancient silicate crystals indicates that Earth’s magnetic field existed 3.40 to 3.45 billion years ago. Stellar wind standoff by a planetary magnetic field prevents atmospheric erosion and water loss. Although the early Earth retained its water and atmosphere, and thus evolved as a habitable planet, little is known about Earth’s magnetic field strength during that time. We report paleointensity results from single silicate crystals bearing magnetic inclusions that record a geodynamo 3.4 to 3.45 billion years ago. The measured field strength is ~50 to 70% that of the present-day field. When combined with a greater Paleoarchean solar wind pressure, the paleofield strength data suggest steady-state magnetopause standoff distances of ≤5 Earth radii, similar to values observed during recent coronal mass ejection events. The data also suggest lower-latitude aurora and increases in polar cap area, as well as heating, expansion, and volatile loss from the exosphere that would have affected long-term atmospheric composition.

WITHDRAWN: An Evaluation of Modern Pottery from Southern Africa as a Magnetic Recorder

Studies of the recent history of Earths magnetic field have revealed a rich spatial and temporal structure, but face limitations by a lack of Southern Hemisphere archeomagnetic data. Studies of Iron Age (200-1850 AD) peoples of southern Africa have revealed a potentially rich source of archeomagnetic information in the form of ceramics (specifically pottery). Additionally, contemporary pottery made with traditional techniques and materials can still be found. Reported here is the first step in addressing whether ancient pottery from southern Africa might faithfully record the geomagnetic field. We analyze contemporary pottery made with traditional techniques and methods. Rock magnetic measurements, including magnetic susceptibility as a function of temperature and magnetic hysteresis behavior, are discussed. Intensity results generated by three common paleointensity methods: Thellier- Coe double heating experiments, the multi-specimen method of Dekkers and Bohnel, and Shaws method (with and without the corrections of Kono) are compared to the known field at the time of firing. The Thellier-Coe method reproduces the field (with an accuracy of 1.3 μT), the Shaw technique with the correction approach of Kono overestimates the field by 3.7%. The multispecimen method overestimates the field by 20%, however improvement upon this could be expected given recent improvements to the technique. These values bound the accuracies we can expect when applying the methods to ideal samples, representing a best-case for dealing with archeological ceramics from southern Africa

Observation of nitrogen vacancy photoluminescence from an optically levitated nanodiamond

We present what we believe to be the first evidence of nitrogen vacancy (NV) photoluminescence (PL) from a nanodiamond suspended in a free-space optical dipole trap at atmospheric pressure. The PL rates are shown to decrease with increasing trap laser power, but are inconsistent with a thermal quenching process. For a continuous-wave trap, the neutral charge state (NV(0)) appears to be suppressed. Chopping the trap laser yields higher total count rates and results in a mixture of both NV(0) and the negative charge state (NV(-).

Nano-optomechanics with optically levitated nanoparticles

Nano-optomechanics is a vibrant area of research that continues to push the boundary of quantum science and measurement technology. Recently, it has been realised that the optical forces experienced by polarisable nanoparticles can provide a novel platform for nano-optomechanics with untethered mechanical oscillators. Remarkably, these oscillators are expected to exhibit quality factors approaching . The pronounced quality factors are a direct result of the mechanical oscillator being freed from a supporting substrate. This review provides an overview of the basic optical physics underpinning optical trapping and optical levitation experiments, it discusses a number of experimental approaches to optical trapping and finally outlines possible applications of this nano-optomechanics modality in hybrid quantum systems and nanoscale optical metrology.

Quantum model of cooling and force sensing with an optically trapped nanoparticle

Optically trapped nanoparticles have recently emerged as exciting candidates for tests of quantum mechanics at the macroscale and as versatile platforms for ultrasensitive metrology. Recent experiments have demonstrated parametric feedback cooling, nonequilibrium physics, and temperature detection, all in the classical regime. Here we provide the first quantum model for trapped nanoparticle cooling and force sensing. In contrast to existing theories, our work indicates that the nanomechanical ground state may be prepared without using an optical resonator; that the cooling mechanism corresponds to nonlinear friction; and that the energy loss during cooling is nonexponential in time. Our results show excellent agreement with experimental data in the classical limit, and constitute an underlying theoretical framework for experiments aiming at ground state preparation. Our theory also addresses the optimization of, and the fundamental quantum limit to, force sensing, thus providing theoretical direction to ongoing searches for ultra-weak forces using levitated nanoparticles.

Inverse-collimated proton radiography for imaging thin materials

Relativistic, magnetically focused proton radiography was invented at Los Alamos National Laboratory using the 800 MeV LANSCE beam and is inherently well-suited to imaging dense objects, at areal densities >20 g cm-2. However, if the unscattered portion of the transmitted beam is removed at the Fourier plane through inverse-collimation, this system becomes highly sensitive to very thin media, of areal densities <100 mg cm-2. Here, this inverse-collimation scheme is described in detail and demonstrated by imaging Xe gas with a shockwave generated by an aluminum plate compressing the gas at Mach 8.8. With a 5-mrad inverse collimator, an areal density change of just 49 mg cm-2 across the shock front is discernible with a contrast-to-noise ratio of 3. Geant4 modeling of idealized and realistic proton transports can guide the design of inverse-collimators optimized for specific experimental conditions and show that this technique performs better for thin targets with reduced incident proton beam emittance. This work increases the range of areal densities to which the system is sensitive to span from ∼25 mg cm-2 to 100 g cm-2, exceeding three orders of magnitude. This enables the simultaneous imaging of a dense system as well as thin jets and ejecta material that are otherwise difficult to characterize with high-energy proton radiography.

A Study of Optically Levitated NV Centers

We present nitrogen vacancy photoluminescence measurements from a nanodiamond levitated in a free-space optical-dipole trap. Photoluminescence decreases as trap laser power increases, and modulating the trap laser results in changes in the defect charge state.

Diamond nanocrystal levitated with a single laser

The idea that light can lead to observable mechanical effects on material objects dates back to the 1600s when Johannes Kepler suggested in De Cometis that deflection of comet tails was the result of radiant pressure from the sun. As descriptions of light, and more generally the electromagnetic field, were refined over time, first by Maxwell’s equations and later quantum theory, the notion of the mechanism by which light exhibits mechanical forces similarly evolved. It wasn’t until the late 1960s and early 1970s that the researchers Vladilen S. Letokhov1 and Arthur Ashkin2 suggested optical forces could be used to trap and manipulate neutral atoms and later dielectric crystals. The work of Ashkin and Letokhov laid the groundwork for numerous breakthroughs leveraging optical forces. In the biological sciences ‘optical tweezers’ have revolutionized how we can measure forces and interrogate biological matter.3, 4 In atomic physics, optical forces have enabled laser cooling of atomic beams5 and eventually single atoms and ions,6, 7 which has resulted in experiments that address foundational questions on the control and measurement of single microscopic quantum systems. The importance of optical forces in the optical sciences cannot be overstated and is evidenced by the Nobel Prizes awarded to this theme, in 1989 (ion trapping), 1997 (atomic trapping), 2001 (Bose-Einstein condensation), and 2012 (trapping of photons and ions). During the last decade there has been a renewed interest in the optical control of mechanical systems. Potential applications are the observation of quantum effects in ever-larger objects as well as the development of ultra-sensitive force sensors. The optomechanical coupling of a wide range of mechanical resonators— ranging from bridges and cantilevers to microtoroids—with lasers have been studied.8, 9 In contrast to all the previous work focusing on mechanical resonators clamped to a support substrate, our approach to nano-optomechanics exploits Figure 1. (a) An optically levitated diamond nanocrystal in a freespace dipole trap. The green is laser scatter off the diamond nanocrystal. Credit: J. Adam Fenster/University of Rochester. (b) Fluorescence from nitrogen vacancy centers embedded in the diamond nanocrystal as a function of the trapping laser power.