Boson Pairs in a One-dimensional Split Trap

We describe the properties of a pair of ultracold bosonic atoms in a one-dimensional harmonic trapping potential with a tunable zero-ranged barrier at the trap centre. The full characterisation of the ground state is done by calculating the reduced single-particle density, the momentum distribution and the two-particle entanglement. We derive several analytical expressions in the limit of infinite repulsion (Tonks-Girardeau limit) and extend the treatment to finite interparticle interactions by numerical solution. As pair interactions in double wells form a fundamental building block for many-body systems in periodic potentials, our results have implications for a wide range of problems.Comment: 9 pages, 8 figure

Assessing the critical material constraints on low carbon infrastructure transitions

We present an assessment method to analyze whether the disruption in supply of a group of materials endangers the transition to low-carbon infrastructure. We define criticality as the combination of the potential for supply disruption and the exposure of the system of interest to that disruption. Low-carbon energy depends on multiple technologies comprised of a multitude of materials of varying criticality. Our methodology allows us to assess the simultaneous potential for supply disruption of a range of materials. Generating a specific target level of low-carbon energy implies a dynamic roll-out of technology at a specific scale. Our approach is correspondingly dynamic, and monitors the change in criticality during the transition towards a low-carbon energy goal. It is thus not limited to the quantification of criticality of a particular material at a particular point in time. We apply our method to criticality in the proposed UK energy transition as a demonstration, with a focus on neodymium use in electric vehicles. Although we anticipate that the supply disruption of neodymium will decrease, our results show the criticality of low carbon energy generation increases, as a result of increasing exposure to neodymium-reliant technologies. We present a number of potential responses to reduce the criticality through a reduction in supply disruption potential of the exposure of the UK to that disruption

A formal definition and a new security mechanism of physical unclonable functions

The characteristic novelty of what is generally meant by a "physical unclonable function" (PUF) is precisely defined, in order to supply a firm basis for security evaluations and the proposal of new security mechanisms. A PUF is defined as a hardware device which implements a physical function with an output value that changes with its argument. A PUF can be clonable, but a secure PUF must be unclonable. This proposed meaning of a PUF is cleanly delineated from the closely related concepts of "conventional unclonable function", "physically obfuscated key", "random-number generator", "controlled PUF" and "strong PUF". The structure of a systematic security evaluation of a PUF enabled by the proposed formal definition is outlined. Practically all current and novel physical (but not conventional) unclonable physical functions are PUFs by our definition. Thereby the proposed definition captures the existing intuition about what is a PUF and remains flexible enough to encompass further research. In a second part we quantitatively characterize two classes of PUF security mechanisms, the standard one, based on a minimum secret read-out time, and a novel one, based on challenge-dependent erasure of stored information. The new mechanism is shown to allow in principle the construction of a "quantum-PUF", that is absolutely secure while not requiring the storage of an exponentially large secret. The construction of a PUF that is mathematically and physically unclonable in principle does not contradict the laws of physics.Comment: 13 pages, 1 figure, Conference Proceedings MMB & DFT 2012, Kaiserslautern, German

Fabrication of thick structures by sputtering

Deposit, 5500-gram of Cu-0.15 wt % Zr alloy, sputtered onto copper cylinder to average thickness of 12.29 mm. Structure was achieved with high-rate sputter deposition for about 100 hours total sputtering time. Material had twice the strength of unsputtered material at temperatures to 723 K and equivalent strength at nearly 873 K

Local simulation of singlet statistics for restricted set of measurement

The essence of Bell's theorem is that, in general, quantum statistics cannot be reproduced by local hidden variable (LHV) model. This impossibility is strongly manifested while analyzing the singlet state statistics for Bell-CHSH violations. In this work, we provide various subsets of two outcome POVMs for which a local hidden variable model can be constructed for singlet state.Comment: 2 column, 5 pages, 4 figures, new references, abstract modified, accepted in JP

Hemispherical total emissivity and specific heat capacity of deeply undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 melts

High-temperature high-vacuum electrostatic levitation (HTHVESL) and differential scanning calorimetry (DSC) were combined to determine the hemispherical total emissivity epsilon T, and the specific heat capacity cp, of the undercooled liquid and throughout the glass transition of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass forming alloy. The ratio of cp/epsilon T as a function of undercooling was determining from radiative cooling curves measured in the HTHVESL. Using specific heat capacity data obtained by DSC investigations close to the glass transition and above the melting point, epsilon T and cp were separated and the specific heat capacity of the whole undercooled liquid region was determined. Furthermore, the hemispherical total emissivity of the liquid was found to be about 0.22 at 980 K. On undercooling the liquid, the emissivity decreases to approximately 0.18 at about 670 K, where the undercooled liquid starts to freeze to a glass. No significant changes of the emissivity are observed as the alloy undergoes the glass transition

Closing the low-carbon material loop using a dynamic whole system approach

The transition to low carbon energy and transport systems requires an unprecedented roll-out of new infrastructure technologies, containing significant quantities of critical raw materials. Many of these technologies are based on general purpose technologies, such as permanent magnets and electric motors, that are common across different infrastructure systems. Circular economy initiatives that aim to institute better resource management practices could exploit these technological commonalities through the reuse and remanufacturing of technology components across infrastructure systems. In this paper, we analyze the implementation of such processes in the transition to low carbon electricity generation and transport on the Isle of Wight, UK. We model two scenarios relying on different renewable energy technologies, with the reuse of Lithium-ion batteries from electric vehicles for grid-attached storage. A whole-system analysis that considers both electricity and transport infrastructure demonstrates that the optimal choice of renewable technology can be dependent on opportunities for component reuse and material recycling between the different infrastructure systems. Hydrogen fuel cell based transport makes use of platinum from obsolete catalytic converters whereas lithium-ion batteries can be reused for grid-attached storage when they are no longer useful in vehicles. Trade-offs exist between the efficiency of technology reuse, which eliminates the need for new technologies for grid attached storage completely by 2033, and the higher flexibility afforded by recycling at the material level; reducing primary material demand for Lithium by 51% in 2033 compared to 30% achieved by battery reuse. This analysis demonstrates the value of a methodology that combines detailed representations of technologies and components with a systemic approach that includes multiple, interconnected infrastructure systems

Time-of-arrival probabilities and quantum measurements: II Application to tunneling times

We formulate quantum tunneling as a time-of-arrival problem: we determine the detection probability for particles passing through a barrier at a detector located a distance L from the tunneling region. For this purpose, we use a Positive-Operator-Valued-Measure (POVM) for the time-of-arrival determined in quant-ph/0509020 [JMP 47, 122106 (2006)]. This only depends on the initial state, the Hamiltonian and the location of the detector. The POVM above provides a well-defined probability density and an unambiguous interpretation of all quantities involved. We demonstrate that for a class of localized initial states, the detection probability allows for an identification of tunneling time with the classic phase time. We also establish limits to the definability of tunneling time. We then generalize these results to a sequential measurement set-up: the phase space properties of the particles are determined by an unsharp sampling before their attempt to cross the barrier. For such measurements the tunneling time is defined as a genuine observable. This allows us to construct a probability distribution for its values that is definable for all initial states and potentials. We also identify a regime, in which these probabilities correspond to a tunneling-time operator.Comment: 26 pages--revised version, small changes, to appear in J. Math. Phy