Mechanically probing coherent tunnelling in a double quantum dot

We study theoretically the interaction between the charge dynamics of a few-electron double quantum dot and a capacitively-coupled AFM cantilever, a setup realized in several recent experiments. We demonstrate that the dot-induced frequency shift and damping of the cantilever can be used as a sensitive probe of coherent inter-dot tunnelling, and that these effects can be used to quantitatively extract both the magnitude of the coherent interdot tunneling and (in some cases) the value of the double-dot T_1 time. We also show how the adiabatic modulation of the double-dot eigenstates by the cantilever motion leads to new effects compared to the single-dot case.Comment: 6 pages, 2 figure

Tablet computers in assessing performance in a high stakes exam : opinion matters

The authors would like to thank Dr Craig brown, University of Aberdeen for assistance with data analysis.Peer reviewedPublisher PD

Mixing with the radiofrequency single-electron transistor

By configuring a radio-frequency single-electron transistor as a mixer, we demonstrate a unique implementation of this device, that achieves good charge sensitivity with large bandwidth about a tunable center frequency. In our implementation we achieve a measurement bandwidth of 16 MHz, with a tunable center frequency from 0 to 1.2 GHz, demonstrated with the transistor operating at 300 mK. Ultimately this device is limited in center frequency by the RC time of the transistor's center island, which for our device is ~ 1.6 GHz, close to the measured value. The measurement bandwidth is determined by the quality factor of the readout tank circuit.Comment: Submitted to APL september 200

Nonlinear modal interactions in clamped-clamped mechanical resonators

A theoretical and experimental investigation is presented on the intermodal coupling between the flexural vibration modes of a single clamped-clamped beam. Nonlinear coupling allows an arbitrary flexural mode to be used as a self-detector for the amplitude of another mode, presenting a method to measure the energy stored in a specific resonance mode. Experimentally observed complex nonlinear dynamics of the coupled modes are quantitatively captured by a model which couples the modes via the beam extension; the same mechanism is responsible for the well-known Duffing nonlinearity in clamped-clamped beams.Comment: 5 pages, 3 figure

"It's going to be hard you know…" Teachers' perceived role in widening access to medicine.

Medical schools worldwide undertake widening access (WA) initiatives (e.g. pipeline, outreach and academic enrichment programmes) to support pupils from high schools which do not traditionally send high numbers of applicants to medicine. UK literature indicates that pupils in these schools feel that their teachers are ill-equipped, cautious or even discouraging towards their aspiration and/or application to medicine. This study aimed to explore teachers' perspectives and practices to include their voice in discussions and consider how medical schools might best engage with them to facilitate WA. Interviews were conducted with high school teachers in three UK regions, working in schools targeted by WA initiatives. Data were analysed thematically using template analysis, using a largely data-driven approach. Findings showed that although medicine was largely seen as a prestigious and worthwhile career, teachers held reservations about advocating this above other choices. Teachers saw it as their role to encourage pupils to educate themselves about medicine, but to ultimately allow pupils to make their own decisions. Their attitudes were influenced by material constraints in their schools, and the perception of daunting, long and emotionally difficult admissions requirements, with low chances of success. Medical schools may wish to work with teachers to understand their hesitations and help them develop the mindset required to advocate a challenging and unfamiliar career, emphasising that this encouragement can further the shared goal of empowering and preparing pupils to feel capable of choosing medicine. Reciprocally, medical schools should ensure pupils have fair opportunities for access, should they choose to apply

A macro-realism inequality for opto-electro-mechanical systems

We show how to apply the Leggett-Garg inequality to opto-electro-mechanical systems near their quantum ground state. We find that by using a dichotomic quantum non-demolition measurement (via, e.g., an additional circuit-QED measurement device) either on the cavity or on the nanomechanical system itself, the Leggett-Garg inequality is violated. We argue that only measurements on the mechanical system itself give a truly unambigous violation of the Leggett-Garg inequality for the mechanical system. In this case, a violation of the Leggett-Garg inequality indicates physics beyond that of "macroscopic realism" is occurring in the mechanical system. Finally, we discuss the difficulties in using unbound non-dichotomic observables with the Leggett-Garg inequality.Comment: 9 pages, 2 figures. Added additional figure (2b), and associated conten

Correlation of Solid Dosage Porosity and Tensile Strength with Acoustically Extracted Mechanical Properties

Currently, the compressed tablet and its oral administration is the most popular drug delivery modality in medicine. The accurate porosity and tensile strength characterization of a tablet design is vital for predicting its performance such as disintegration, dissolution, and drug-release efficiency upon administration as well as ensuring its mechanical integrity. In current work, a non-destructive contact ultrasonic approach and an associated testing procedure are presented and employed to quantify and relate the acoustically extracted mechanical properties of pharmaceutical compacts to direct porosity and tensile strength measurements. Based on a comprehensive set of experimental data, it is demonstrated how strongly the acoustic wave propagation is modulated and correlated to the tablet porosity and tensile strength of a compact made using spray-dried lactose and microcrystalline cellulose with varying mixture ratios. The effect of mixing ratio on the porosity and tensile strength on the resulting compacts is quantified and, with the acoustic experimental data, mixing ratio is related to the compact ultrasonic characteristics. The ultrasonic techniques provide a rapid, non-destructive means for evaluating compacts in formulation development and manufacturing. The presented approach and data could find critical applications in continuous tablet manufacturing, its real-time quality monitoring, as well as minimizing batch-to-batch quality variations

Hot electrons in low-dimensional phonon systems

A simple bulk model of electron-phonon coupling in metals has been surprisingly successful in explaining experiments on metal films that actually involve surface- or other low-dimensional phonons. However, by an exact application of this standard model to a semi-infinite substrate with a free surface, making use of the actual vibrational modes of the substrate, we show that such agreement is fortuitous, and that the model actually predicts a low-temperature crossover from the familiar T^5 temperature dependence to a stronger T^6 log T scaling. Comparison with existing experiments suggests a widespread breakdown of the standard model of electron-phonon thermalization in metals

Noise-enabled precision measurements of a Duffing nanomechanical resonator

We report quantitative experimental measurements of the nonlinear response of a radiofrequency mechanical resonator, with very high quality factor, driven by a large swept-frequency force. We directly measure the noise-free transition dynamics between the two basins of attraction that appear in the nonlinear regime, and find good agreement with those predicted by the one-dimensional Duffing equation of motion. We then measure the response of the transition rates to controlled levels of white noise, and extract the activation energy from each basin. The measurements of the noise-induced transitions allow us to obtain precise values for the critical frequencies, the natural resonance frequency, and the cubic nonlinear parameter in the Duffing oscillator, with direct applications to high sensitivity parametric sensors based on these resonators.Comment: 5 pages, 5 figure