Mechanical properties of Pt monatomic chains

The mechanical properties of platinum monatomic chains were investigated by simultaneous measurement of an effective stiffness and the conductance using our newly developed mechanically controllable break junction (MCBJ) technique with a tuning fork as a force sensor. When stretching a monatomic contact (two-atom chain), the stiffness and conductance increases at the early stage of stretching and then decreases just before breaking, which is attributed to a transition of the chain configuration and bond weakening. A statistical analysis was made to investigate the mechanical properties of monatomic chains. The average stiffness shows minima at the peak positions of the length-histogram. From this result we conclude that the peaks in the length-histogram are a measure of the number of atoms in the chains, and that the chains break from a strained state. Additionally, we find that the smaller the initial stiffness of the chain is, the longer the chain becomes. This shows that softer chains can be stretched longer.Comment: 6 pages, 5 figure

Modelling of Natural Gas Pipe Flow with Rapid Transients-case Study of Effect of Ambient Model

AbstractThe paper presents a study of gas pipeline to soil heat transfer. The effect of simplifications of the heat transfer model is investigated. Studied are steady, one dimensional unsteady and two dimensional unsteady models of the pipe wall and soil. Flow conditions at the pipeline inlet are varied. The effects of rapid changes in gas mass flow rate and temperature at the pipeline inlet are studied. The case presented is representative for export natural gas pipelines, containing offshore and buried sections along the route. Results are compared to experimental data from an existing export natural gas pipeline

An experimental proposal to study collapse of the wave function in travelling-wave parametric amplifiers

The read-out of a microwave qubit state occurs using an amplification chain that enlarges the quantum state to a signal detectable with a classical measurement apparatus. However, at what point in this process did we really `measure' the quantum state? In order to investigate whether the `measurement' takes place in the amplification chain, we propose to construct a microwave interferometer that has a parametric amplifier added to each of its arms. Feeding the interferometer with single photons, the visibility depends on the gain of the amplifiers and whether a measurement collapse has taken place during the amplification process. We calculate the interference visibility as given by standard quantum mechanics as a function of gain, insertion loss and temperature and find a magnitude of $1/3$ in the limit of large gain without taking into account losses. This number reduces to $0.26$ in case the insertion loss of the amplifiers is $2.2$ dB at a temperature of $50$ mK. We show that if the wave function collapses within the interferometer, we will measure a reduced visibility compared to the prediction from standard quantum mechanics once this collapse process sets in.Comment: 21 pages and 23 figures (including appendices and subfigures). v4: Abstract and introduction rewritten and note on stochasticity of quantum state collapse added to section 6. v5: no content changes w.r.t. v

Spin-mediated dissipation and frequency shifts of a cantilever at milliKelvin temperatures

We measure the dissipation and frequency shift of a magnetically coupled cantilever in the vicinity of a silicon chip, down to $25$ mK. The dissipation and frequency shift originates from the interaction with the unpaired electrons, associated with the dangling bonds in the native oxide layer of the silicon, which form a two dimensional system of electron spins. We approach the sample with a $3.43$ $\mu$m-diameter magnetic particle attached to an ultrasoft cantilever, and measure the frequency shift and quality factor as a function of temperature and the distance. Using a recent theoretical analysis [J. M. de Voogd et al., arXiv:1508.07972 (2015)] of the dynamics of a system consisting of a spin and a magnetic resonator, we are able to fit the data and extract the relaxation time $T_1=0.39\pm0.08$ ms and spin density $\sigma=0.14\pm0.01$ spins per nm$^2$. Our analysis shows that at temperatures $\leq500$ mK magnetic dissipation is an important source of non-contact friction.Comment: 5 pages, 3 figure

Upper Bounds on Spontaneous Wave-Function Collapse Models Using Millikelvin-Cooled Nanocantilevers

6siCollapse models predict a tiny violation of energy conservation, as a consequence of the spontaneous collapse of the wave function. This property allows us to set experimental bounds on their parameters. We consider an ultrasoft magnetically tipped nanocantilever cooled to millikelvin temperature. The thermal noise of the cantilever fundamental mode has been accurately estimated in the range 0.03 – 1 K, and any other excess noise is found to be negligible within the experimental uncertainty. From the measured data and the cantilever geometry, we estimate the upper bound on the continuous spontaneous localization collapse rate in a wide range of the correlation length rC. Our upper bound improves significantly previous constraints for r_C > 10^−6  m, and partially excludes the enhanced collapse rate suggested by Adler. We discuss future improvements.openopenVinante, A.; Bahrami, M.; Bassi, A.; Usenko, O.; Wijts, G.; Oosterkamp, T.H.Vinante, A.; Bahrami, Mohammad; Bassi, Angelo; Usenko, O.; Wijts, G.; Oosterkamp, T. H

Wigner crystallization in the two electron quantum dot

Wigner crystallization can be induced in a quantum dot by increasing the effective electron-electron interaction through a decrease of the electron density or by the application of a strong magnetic field. We show that the ground state in both cases is very similar but the energy scales are very different and therefore also the dynamics.Comment: 4 pages, 4 figure

A method for mechanical generation of radio frequency fields in nuclear magnetic resonance force microscopy

We present an innovative method for magnetic resonance force microscopy (MRFM) with ultra-low dissipation, by using the higher modes of the mechanical detector as radio frequency (rf) source. This method allows MRFM on samples without the need to be close to an rf source. Furthermore, since rf sources require currents that give dissipation, our method enables nuclear magnetic resonance experiments at ultra-low temperatures. Removing the need for an on-chip rf source is an important step towards a MRFM which can be widely used in condensed matter physics.Comment: 7 pages, 5 figures, to be submitted to Physical Review Applie

Probing the magnetic moment of FePt micromagnets prepared by Focused Ion Beam milling

We investigate the degradation of the magnetic moment of a 300 nm thick FePt film induced by Focused Ion Beam (FIB) milling. A $1~\mu \mathrm{m} \times 8~\mu \mathrm{m}$ rod is milled out of a film by a FIB process and is attached to a cantilever by electron beam induced deposition. Its magnetic moment is determined by frequency-shift cantilever magnetometry. We find that the magnetic moment of the rod is $\mu = 1.1 \pm 0.1 \times 10 ^{-12} \mathrm{Am}^2$, which implies that 70% of the magnetic moment is preserved during the FIB milling process. This result has important implications for atom trapping and magnetic resonance force microscopy (MRFM), that are addressed in this paper.Comment: 4 pages, 4 figure