We show how resonant laser spectroscopy of the trion optical transitions in a self-assembled quantum dot can be used to determine the temperature of a nearby electron reservoir. At finite magnetic field, the spin-state occupation of the Zeeman-split quantum-dot electron ground states is governed by thermalization with the electron reservoir via cotunneling. With resonant spectroscopy of the corresponding excited trion states, we map out the spin occupation as a function of magnetic field to establish optical thermometry for the electron reservoir. We demonstrate the implementation of the technique in the subkelvin temperature range where it is most sensitive and where the electron temperature is not necessarily given by the cryostat base temperature.

Resonant laser spectroscopy of a negatively charged self-assembled quantum dot is utilized to measure the temperature of a three-dimensional fermionic reservoir down to 100 mK. With a magnetic field applied to the quantum dot, the single-charged ground state is split by the Zeeman energy. As the quantum dot is in tunnel contact with a thermal electron reservoir, a thermal occupation of the quantum-dot spin states is enforced by cotunneling processes. Resonant laser-induced fluorescence is used in order to measure the thermal quantum-dot spin-state population.

Metamaterial concepts have opened the door to high-optical anisotropy beyond levels of naturally occurring materials but usually with limited spectral bandwidth. Here, we report on the design, realization, and experimental and numerical characterization of broadband chiral metafoils exhibiting at the same time exceptionally high-contrast circular polarization in the THz range. We demonstrate that the observed chirality is achieved by a simple modification of the structure of well-established metafoils, namely, through a shift of interconnecting lines by half a unit cell length between each row. The bandwidth of the observed circular-polarization-selective response is demonstrated to be up to about one octave at a center frequency of 2.4 THz and the ratio of the transmission of oppositely circularly polarized radiation is shown to reach about 700%, with the maximum transmittance being approximately 70%. Although implemented here at THz frequencies, broadband chiral metafoils may be extended to higher infrared and optical frequencies by hot embossing or nanoimprinting. They may be used as circular polarizers and beam stops in THz optical and infrared systems.

The ability to manipulate microscale and nanoscale particles is highly desirable for various applications ranging from targeting drug delivery to additive manufacturing. Here we report an acoustic sieve that is capable of aligning, trapping, sorting, and transferring a large number of particles according to their size or mass density, all in a tunable manner. The concept is based on the highly localized periodic radiation force induced by the resonance transmission of an acoustic wave across a phononic crystal plate, a phenomenon analogous to the surface-phonon-enhanced optical force, yet the physical concept has not been explored in acoustics. The acoustic sieve demonstrates the effective manipulation of massive particles using an artificially engineered acoustic field by a phononic crystal, and it has potential application for a wide range of applications.

Metal whiskers often grow across leads of electric equipment and electronic package causing current leakage or short circuits and raising significant reliability issues. The nature of metal whiskers remains a mystery after several decades of research. Here, the existence of metal whiskers is attributed to the energy gain due to electrostatic polarization of metal filaments in the electric field. The field is induced by surface imperfections: contaminations, oxide states, grain boundaries, etc. A proposed theory provides closed form expressions and quantitative estimates for the whisker nucleation and growth rates, explains the range of whisker parameters and effects of external biasing, and predicts statistical distribution of their lengths.

Nanopore DNA sequencing holds great promise for producing long read lengths from small amounts of starting material, however, high error rates are a problem. We perform nonequilibrium electron transport calculations within an effective tight-binding model of the DNA molecule to study the intrinsic structural noise in DNA sequencing via transverse current in nanopores. The structural noise arises from the effect of neighboring bases on the tunneling current. We find that it could be comparable to the environmental noise, which is caused by changes of the position of the molecule with respect to the electrodes in the nanopore. Moreover, while the environmental noise can be reduced by continuous measurement and by improving the measurement setup, the structural noise is intrinsic. With the help of our methodology we optimize the dependence of the structural noise on the measurement parameters, such as the type of the electrodes and the applied bias. We also propose a statistical technique, utilizing not only the currents through the nucleotides but also the correlations in the currents, to improve the fidelity of the sequencing.

Mechanical resonators shaped like microcantilevers have been demonstrated as a platform for very sensitive detection of chemical and biological analytes. However, their use as an analytical tool requires fundamental understanding of the molecular absorption-induced effects in the static and dynamic sensor response. The effect of absorption-induced surface stress on the microcantilever response is here investigated using palladium hydride formation. It is shown that the dynamic and static responses of the cantilever monitored simultaneously exhibit excellent correlation with the crystalline phases of hydride formation. However, the resonance frequency shifts and quasistatic bending are observed to be independent during the solid solution phase. Importantly, absorption-induced changes in the elastic parameters of the palladium film are found to play a dominant role in the static and dynamic response. The presented results help in discerning between changes in swelling and elastic modulus that control the cantilever response as well as the relationships between these parameters.

Inkjet printing deposits droplets with a well-controlled narrow size distribution. This paper aims at improving experimental and numerical methods for the optimization of drop formation. We introduce a method to extract the one-dimensional velocity profile inside a single droplet during drop formation. We use a novel experimental approach to capture two detailed images of the very same droplet with a small time delay. The one-dimensional velocity within the droplet is resolved by accurately determining the volume distribution of the droplet. We compare the obtained velocity profiles to a numerical simulation based on the slender jet approximation of the Navier-Stokes equation and we find very good agreement.

Listening is a complex sound selection process thought to be located in the auditory cortex. A biophysically motivated Hopf model of the mammalian cochlea reveals that pitch, a main characteristic in the perception of sound, is already materialized at the level of the mammalian hearing sensor. Here, we provide evidence that major elements of listening may similarly be implemented at the auditory periphery by means of efferent connections to the cochlea that tune the hearing sensor towards an auditory object of interest. The cochlea model we use in our investigations is advocated by its performance quality, the simplicity by which efferent control can be implemented, and by the closeness of the control results compared to the biological data. We tune the Hopf parameters to target on a sound, using pitch as the guiding feature. How well we achieve our goal is tested on real-world sounds and measured by a specifically developed tuning-error measure. The results provide a first estimate of how much the peripheral hearing system can assist a listener in focusing on an auditory signal and, thus, what is contributed by the auditory cortex.

The refractive index of biological specimens is a source of intrinsic contrast that can be explored without any concerns of photobleaching or harmful effects caused by extra contrast agents. In addition, the refractive index contains rich information related to the metabolism of cells at the cellular and subcellular levels. Here, we report a no-moving-parts approach that provides three-dimensional refractive-index maps of biological samples continuously flowing in a microfluidic channel. Specifically, we use line illumination and off-axis digital holography to record the angular spectra of light scattered from flowing samples at high speed. Applying the scalar diffraction theory, we obtain accurate refractive-index maps of the samples from the measured spectra. Using this method, we demonstrate label-free three-dimensional imaging of live RKO human colon cancer cells and RPMI8226 multiple myeloma cells, and obtain the volume, dry mass, and density of these cells from the measured three-dimensional refractive-index maps. Our results show that the reported method, alone or in combination with the existing flow cytometry techniques, shows promise as a quantitative tool for stain-free characterization of a large number of cells.

We present a method by which first-principles calculations are linked quite naturally to experimental observables, which determine and characterize the state of an electrochemical system. The method is based on the formation energies of ions in solution and utilizes a grand canonical framework. This is particularly well suited to use in conjunction with ab initio calculations, since it allows charged defects to be treated individually, rather than requiring the consideration of full charge-neutral reactions. It allows the identification of a region of water stability, the $p\mathrm{H}$ scale, and the electrode potential. We discuss and demonstrate the possibilities and capabilities of the approach by the extraction of ion-hydration energies from the Nernst equation and the construction of a $\text{potential}/p\mathrm{H}$ diagram for zinc by an alternative route deviating from the standard approach used to obtain Pourbaix diagrams.