7,937 research outputs found
Investigating Water Ice in Persistently Shadowed Craters in Mercury\u27s North Polar Region
Through a combination of Earth-based radar observations, available spacecraft neutron spectrometer and laser altimeter data, and thermal modeling, it has previously been suggested that the planet Mercury hosts extensive water ice deposits in its polar regions. This study concentrates on observations of the permanently shadowed craters of Mercury’s north polar region, where water ice is expected. To examine the interior of craters that host radar-bright material, images from the Wide Angle Camera (WAC) aboard the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft were processed using Integrated Software for Imagers and Spectrometers (ISIS) and stretched on a grayscale to expose reflectivity differences and surface features. This process revealed intriguing dark material within 53.2% of the individual craters studied in the region 75º N and northward, which is interpreted to be sublimation lags. The relationships between visible reflectivity material, radar-bright deposits, and regions of persistent shadow were mapped for these craters. Reflectivity-light material was revealed in the Prokofiev and Kandinsky craters (4.2%), indicating exposed water ice deposits. The remaining craters either did not reveal dark or light material (29.8%) or did not return images of high enough quality for analysis (12.8%). Additionally, the area of 84º N and northward was analyzed on a regional scale. Areas of persistent shadow were mapped and then compared to radar data to both qualify and quantify the relationship between shadowed areas and radar-bright features. In the study area, ~82% of the Harmon et al. (2011) radar-bright features aligned with the mapped areas of persistent shadow. The results of this study indicate that water ice stably resides in the persistently shadowed craters on Mercury’s north polar region and is typically insulated by a reflectivity-dark lag deposit
The Roughness Properties of Small Ice-Bearing Craters at the South Pole of the Moon: Implications for Accessing Fresh Water Ice in Future Surface Operations
The lunar poles provide a fascinating thermal environment capable of cold-trapping water ice on geologic timescales [1]. While there have been many observations indicating the presence of water ice at the lunar surface [e.g., 24], it is still not clear when this ice was delivered to the Moon. The timing of volatile dep-osition provides important constraints on the origin of lunar ice because different delivery mechanisms have been active at different times throughout lunar history. We previously found that some small (<10 km) cra-ters at the south pole of the Moon have morphologies suggestive of relatively young ages, on the basis of crisp crater rims [5]. These craters are too small to date with robust cratering statistics [5], but the possibility of ice in young craters is intriguing because it suggests that there is some recent and perhaps ongoing mechanism that is delivering or redistributing water to polar cold traps. Therefore, understanding if these small, ice-bear-ing craters are indeed young is essential in understand-ing the age and source of volatiles on the Moon. Here we take a new approach to understand the ages of these small polar cold traps: analyzing the roughness properties of small ice-bearing craters. It is well under-stood that impact crater properties (e.g., morphology, rock abundance, and roughness) evolve with time due to a variety of geologic and space-weathering processes [611]. Topographic roughness is a measurement of the local deviation from the mean topography, providing a measurement of surface texture, and is a powerful tool for evaluating surface evolution over geologic time [e.g., 1114]. In this study we analyze the roughness of southern lunar craters (40S90S) from all geologic eras, and determine how the roughness of small (<10 km) ice-bearing craters compare. We discuss the implications of the ages of ice-bearing south polar craters, and potential strategies for accessing fresh ice on the Moon
Conditional Quantum Dynamics and Logic Gates
Quantum logic gates provide fundamental examples of conditional quantum
dynamics. They could form the building blocks of general quantum information
processing systems which have recently been shown to have many interesting
non--classical properties. We describe a simple quantum logic gate, the quantum
controlled--NOT, and analyse some of its applications. We discuss two possible
physical realisations of the gate; one based on Ramsey atomic interferometry
and the other on the selective driving of optical resonances of two subsystems
undergoing a dipole--dipole interaction.Comment: 5 pages, RevTeX, two figures in a uuencoded, compressed fil
Nonlinear quantum state transformation of spin-1/2
A non-linear quantum state transformation is presented. The transformation,
which operates on pairs of spin-1/2, can be used to distinguish optimally
between two non-orthogonal states. Similar transformations applied locally on
each component of an entangled pair of spin-1/2 can be used to transform a
mixed nonlocal state into a quasi-pure maximally entangled singlet state. In
both cases the transformation makes use of the basic building block of the
quantum computer, namely the quantum-XOR gate.Comment: 12 pages, LaTeX, amssym, epsfig (2 figures included
Rapid solution of problems by nuclear-magnetic-resonance quantum computation
We offer an improved method for using a nuclear-magnetic-resonance quantum
computer (NMRQC) to solve the Deutsch-Jozsa problem. Two known obstacles to the
application of the NMRQC are exponential diminishment of density-matrix
elements with the number of bits, threatening weak signal levels, and the high
cost of preparing a suitable starting state. A third obstacle is a heretofore
unnoticed restriction on measurement operators available for use by an NMRQC.
Variations on the function classes of the Deutsch-Jozsa problem are introduced,
both to extend the range of problems advantageous for quantum computation and
to escape all three obstacles to use of an NMRQC. By adapting it to one such
function class, the Deutsch-Jozsa problem is made solvable without exponential
loss of signal. The method involves an extra work bit and a polynomially more
involved Oracle; it uses the thermal-equilibrium density matrix systematically
for an arbitrary number of spins, thereby avoiding both the preparation of a
pseudopure state and temporal averaging.Comment: 19 page
Experimental study of optimal measurements for quantum state tomography
Quantum tomography is a critically important tool to evaluate quantum
hardware, making it essential to develop optimized measurement strategies that
are both accurate and efficient. We compare a variety of strategies using
nearly pure test states. Those that are informationally complete for all states
are found to be accurate and reliable even in the presence of errors in the
measurements themselves, while those designed to be complete only for pure
states are far more efficient but highly sensitive to such errors. Our results
highlight the unavoidable tradeoffs inherent to quantum tomography.Comment: 5 pages, 3 figure
Information Flow in Entangled Quantum Systems
All information in quantum systems is, notwithstanding Bell's theorem,
localised. Measuring or otherwise interacting with a quantum system S has no
effect on distant systems from which S is dynamically isolated, even if they
are entangled with S. Using the Heisenberg picture to analyse quantum
information processing makes this locality explicit, and reveals that under
some circumstances (in particular, in Einstein-Podolski-Rosen experiments and
in quantum teleportation) quantum information is transmitted through
'classical' (i.e. decoherent) information channels.Comment: PostScript version now available:
http://www.qubit.org/people/patrickh/Papers/InformationFlow.p
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