Multi-parameter Quantum Metrology

The simultaneous quantum estimation of multiple parameters can provide a better precision than estimating them individually. This is an effect that is impossible classically. We review the rich background of multi-parameter quantum metrology, some of the main results in the field and its recent advances. We close by highlighting future challenges and open questions

Reaching for the quantum limits in the simultaneous estimation of phase and phase diffusion

Phase diffusion invariably accompanies all phase estimation strategies – quantum or classical. A precise esti- mation of the former can often provide valuable understanding of the physics of the phase generating phenom- ena itself. We theoretically examine the performance of fixed-particle number probe states in the simultaneous estimation of phase and collective phase diffusion. We derive analytical quantum limits associated with the si- multaneous local estimation of phase and phase diffusion within the quantum Crame ́r-Rao bound framework in the regimes of large and small phase diffusive noise. The former is for a general fixed-particle number state and the latter for Holland Burnett states, for which we show quantum-enhanced estimation of phase as well as phase diffusion. We next investigate the simultaneous attainability of these quantum limits using projective measure- ments acting on a single copy of the state in terms of a trade-off relation. In particular, we are interested how this trade-off varies as a function of the dimension of the state. We derive an analytical bound for this trade-off in the large phase diffusion regime for a particular form of the measurement, and show that the maximum of 2, set by the quantum Crame ́r-Rao bound, is attainable. Further, we show numerical evidence that as diffusion approaches zero, the optimal trade-off relation approaches 1 for Holland-Burnett states. These numerical results are valid in the small particle number regime and suggest that the trade-off for estimating one parameter with quantum-limited precision leads to a complete lack of precision for the other parameter as the diffusion strength approaches zero. Finally, we provide numerical results showing behaviour of the trade-off for a general value of phase diffusion when using Holland-Burnett probe states

COSMOS-UK: the UK national soil moisture measurement network – surface observations for EO Cal/Val applications

The COSMOS-UK network delivers high quality continuous near real-time monitoring of soil moisture and meteorological variables across the whole of the UK, at 48 long-term field-monitoring locations, from 2013 ongoing. UKCEH operate the network on behalf of the Natural Environment Research Council (NERC), as part of their National Capability programme, for the benefit of the national academic research community and the private sector. Research grade datasets are publically available for comparison with EO products as a ground based calibration and validation (Cal/Val) network. A range of in situ data are available, focusing on large area (0.1 km2) soil moisture measurements using Cosmic Ray Neutron Sensors (CRNS), as well as point soil moisture measurements at various soil depths; and when applicable the CRNS is used to derive snow water equivalent. Phenology camera imagery is processed to provide greenness products, cropping patterns, and other vegetation and land use changes; upwelling longwave radiation measurements can be related to land surface temperatures in addition to soil temperature profiles from near surface to 50 cm soil depth. Shortwave radiometers give albedo and cloudiness. Sonic anemometers not only provide wind speed and direction, but are also processed to give sensible heat fluxes, and evapotranspiration is estimated as the residual of the land surface energy balance using net radiation and soil heat flux measurements. The suite of data is an invaluable resource in testing EO products, primarily for SAR and other combined EO soil moisture products, and with great potential for further Cal/Val applications

P4_9 Stealing Our Atmosphere

This paper investigates two scenarios; the first is the solar wind velocity required to compress Earth’s magnetopause to an altitude of 1500km and an unrealistic value of 1.6x108ms-1 is found. The second scenario is the time it would take the solar wind to erode all of the oxygen in the atmosphere if the Earth did not have a magnetic field and an approximate value of 1.97x109 years is calculated

P4_7 Greatest Gravity

Earth is not of uniform density, but consists of many layers, causing acceleration due to free fall to be a non-linear function of radius. A model is constructed to evaluate at which radius the greatest gravitational acceleration is felt. This point was found to be at the meeting point of the lower mantle and the outer core, where the acceleration peaks at a = 10.8 ms-2

P4_1 Dead Sea Walking

The paper investigates the possibility of walking on the water of the Dead Sea under the assumption that salt can be added to the lake. The current salinity is not sufficient to enable a person to walk on the water. Theoretically, this feat would be achievable if the lake contained 9.71 × 1015 kg of salt. Practically, this amount of salt would not dissolve in the volume of water present in the Dead Sea

P4_4 The Solar Cell Efficiency of Superman

The paper investigates how efficiently Superman must absorb energy from the Sun's emission spectrum to be able to perform flight for 8 hours at a constant altitude. A solar cell efficiency of 656000% is calculated, which seemingly disobeys the law of conservation of energy assuming the model of Superman as a solar cell is reasonable

P4_5 The Relativistic Ionisation Speed Limit

The paper explores a possible speed limit to be enforced on relativistic vehicles so as to not expose pedestrians to ionising electromagnetic radiation; a result of Doppler shifted light from the vehicle’s headlights. A maximum speed limit of 2.89 × 108 ms-1, 0.96 times the speed of light, was established.Â

P4_2 Using the Forks: The Energy Yield of a Lightning Bolt

Lightning may be considered as a potential energy source if the yield is comparable to other renewable energy sources. The energy yield of one strike was evaluated to be 7.5×107 J, where approximately 50 strikes produce a yield equivalent to that of an average wind turbine in a year