The Tapanui region of New Zealand: Site of a Tunguska around 800 years ago?

Evidence is discussed that the wide-spread fires ca. 800 years ago which denuded the southern provinces of the South Island of New Zealand of the extensive forests present at that time were due to the entry of a large bolide into the atmosphere, the conflagration being ignited by the intense heat generated as this extraterrestrial projectile ablated/detonated in a similar manner to that of the Tunguska object of 1908. These fires led to the extinction of the giant terrestrial bird known as the Moa, and the end of the archaic epoch of Maori history known as the Moa Hunter period. This interpretation is well attested to in Maori myth and legend

1991 DA: An asteroid in a bizarre orbit

Asteroidal object 1991 DA has an orbit of high inclination, crossing the planets from Mars to Uranus. This is unique for an asteroid, but not unusual for a comet of the Halley-type: it therefore seems likely that 1991 DA is an extinct or dormant comet. Previous CCD imaging has shown no indication of a coma; spectroscopic observations of 1991 DA which lack any evidence of strong comet-like emissions are reported. Numerical integrations of the orbit of this object were performed which show that is has been remarkably stable for the past approximately 20,000 yr, but chaotic before that. This may allow a new estimate to be made of the physical lifetimes of comets

A Southern Hemisphere radar meteor orbit survey

A meteor radar system has been operated on a routine basis near Christchurch, New Zealand, to determine the orbits of Earth-impacting interplanetary dust and meteoroids. The system sensitivity is +13 visual magnitude, corresponding to approximately 100 micron sized meteoroids. With an orbital precision of 2 degrees in angular elements and 10 percent in orbital energy (1/a), the operation yields an average of 1500 orbits daily with a total to date in excess of 10(exp 5). The use of pc's and automated data reduction permit the large orbital data sets we collect to be routinely reduced. Some illustrative examples are presented of the signal formats/processing and the results of data reduction, giving the individual orbital elements and hence the overall distributions. Current studies include the distribution of dust in the inner solar system; the influx of meteoroids associated with near-Earth asteroids; and the orbital structure existing in comet-produced streams

Nonlinear optical absorption and dynamics in quantum wells

We present measurements of differential transmission and four‐wave mixing in GaAs quantum well structures at 1.8 K near the inhomogeneously broadened lowest heavy‐hole (hh1) exciton resonance using narrow band cw excitation. The data show an increase in absorption and an excitation lifetime of order 1–10 μs outside the spectral hole produced by the pump. The long lifetime and the experimentally determined absence of excitation spatial diffusion in this region suggests that optical absorption produces electron‐hole pairs that are correlated but separately localized due to disorder. A phenomenological model is proposed to explain the nonlinear response based on two‐photon absorption.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69941/2/APPLAB-61-11-1301-1.pd

Generation of frequency sidebands on single photons with indistinguishability from quantum dots

Generation and manipulation of the quantum state of a single photon is at the heart of many quantum information protocols. There has been growing interest in using phase modulators as quantum optics devices that preserve coherence. In this Letter, we have used an electro-optic phase modulator to shape the state vector of single photons emitted by a quantum dot to generate new frequency components (modes) and explicitly demonstrate that the phase modulation process agrees with the theoretical prediction at a single photon level. Through two-photon interference measurements we show that for an output consisting of three modes (the original mode and two sidebands), the indistinguishability of the mode engineered photon, measured through the secondorder intensity correlation (g2(0)) is preserved. This work demonstrates a robust means to generate a photonic qubit or more complex state (e.g., a qutrit) for quantum communication applications by encoding information in the sidebands without the loss of coherence

Non-local nuclear spin quieting in quantum dot molecules: Optically-induced extended two-electron spin coherence time

We demonstrate the extension of coherence between all four two-electron spin ground states of an InAs quantum dot molecule (QDM) via non-local suppression of nuclear spin fluctuations in both constituent quantum dots (QDs), while optically addressing only the upper QD transitions. Long coherence times are revealed through dark-state spectroscopy as resulting from nuclear spin locking mediated by the exchange interaction between the QDs. Lineshape analysis provides the first measurement of the quieting of the Overhauser field distribution correlating with reduced nuclear spin fluctuations.Comment: Supplementary materials can be found on the publication page of our website. http://research.physics.lsa.umich.edu/dst/Publications.htm