Finite time St\"uckelberg interferometry with nanomechanical modes

St\"uckelberg interferometry describes the interference of two strongly coupled modes during a double passage through an avoided energy level crossing. In this work, we experimentally investigate finite time effects in St\"uckelberg interference and provide an exact analytical solution of the St\"uckelberg problem. Approximating this solution in distinct limits reveals uncharted parameter regimes of St\"uckelberg interferometry. Experimentally, we study these regimes using a purely classical, strongly coupled nanomechanical two-mode system of high quality factor. The classical two-mode system consists of the in-plane and out-of-plane fundamental flexural mode of a high stress silicon nitride string resonator, coupled via electric gradient fields. The dielectric control and microwave cavity enhanced universal transduction of the nanoelectromechanical system allows for the experimental access to all theoretically predicted St\"uckelberg parameter regimes. We exploit our experimental and theoretical findings by studying the onset of St\"uckelberg interference in dependence of the characteristic system control parameters and obtain characteristic excitation oscillations between the two modes even without the explicit need of traversing the avoided crossing. The presented theory is not limited to classical mechanical two-mode systems but can be applied to every strongly coupled (quantum) two-level system, for example a spin-1/2 system or superconducting qubit

Microwave cavity-enhanced transduction for plug and play nanomechanics at room temperature

Nanomechanical resonators with increasingly high quality factors are enabled following recent insights into energy storage and loss mechanisms in nanoelectromechanical systems (NEMS). Consequently, efficient, non-dissipative transduction schemes are required to avoid the dominating influence of coupling losses. We present an integrated NEMS transducer based on a microwave cavity dielectrically coupled to an array of doubly-clamped pre-stressed silicon nitride beam resonators. This cavity-enhanced detection scheme allows resolving the resonators' Brownian motion at room temperature while preserving their high mechanical quality factor of 290,000 at 6.6 MHz. Furthermore, our approach constitutes an "opto"mechanical system in which backaction effects of the microwave field are employed to alter the effective damping of the resonators. In particular, cavity-pumped self-oscillation yields a linewidth of only 5 Hz. Thereby, an adjustement-free, all-integrated and self-driven nanoelectromechanical resonator array interfaced by just two microwave connectors is realised, potentially useful for applications in sensing and signal processing

Coherent control of a nanomechanical two-level system

The Bloch sphere is a generic picture describing a coupled two-level system and the coherent dynamics of its superposition states under control of electromagnetic fields. It is commonly employed to visualise a broad variety of phenomena ranging from spin ensembles and atoms to quantum dots and superconducting circuits. The underlying Bloch equations describe the state evolution of the two-level system and allow characterising both energy and phase relaxation processes in a simple yet powerful manner. Here we demonstrate the realisation of a nanomechanical two-level system which is driven by radio frequency signals. It allows to extend the above Bloch sphere formalism to nanoelectromechanical systems. Our realisation is based on the two orthogonal fundamental flexural modes of a high quality factor nanostring resonator which are strongly coupled by a dielectric gradient field. Full Bloch sphere control is demonstrated via Rabi, Ramsey and Hahn echo experiments. This allows manipulating the classical superposition state of the coupled modes in amplitude and phase and enables deep insight into the decoherence mechanisms of nanomechanical systems. We have determined the energy relaxation time T1 and phase relaxation times T2 and T2*, and find them all to be equal. This not only indicates that energy relaxation is the dominating source of decoherence, but also demonstrates that reversible dephasing processes are negligible in such collective mechanical modes. We thus conclude that not only T1 but also T2 can be increased by engineering larger mechanical quality factors. After a series of ground-breaking experiments on ground state cooling and non-classical signatures of nanomechanical resonators in recent years, this is of particular interest in the context of quantum information processing

Signatures of two-level defects in the temperature-dependent damping of nanomechanical silicon nitride resonators

The damping rates of high quality factor nanomechanical resonators are well beyond intrinsic limits. Here, we explore the underlying microscopic loss mechanisms by investigating the temperature-dependent damping of the fundamental and third harmonic transverse flexural mode of a doubly clamped silicon nitride string. It exhibits characteristic maxima reminiscent of two-level defects typical for amorphous materials. Coupling to those defects relaxes the momentum selection rules, allowing energy transfer from discrete long wavelength resonator modes to the high frequency phonon environment

Severe cardiogenic shock due to acute onset of an aorto-to-right atrial shunt in a patient with aortic valve endocarditis

AbstractINTRODUCTIONHeart failure is the most common cause of death due to infective endocarditis. We report a case of a patient presenting with severe shock due to an infection-associated left-to-right cardiac shunt.PRESENTATION OF CASEA 62-year-old man, who underwent aortic valve replacement five years previously, was admitted to ICU due to acute hemodynamic deterioration. A few days earlier, he had a septic episode with blood cultures positive for Staphylococcus aureus and clinical features of infective endocarditis. In ICU, transthoracic echocardiography revealed shunting from the aortic root to the right atrium resulting in severe cardiogenic shock.DISCUSSIONThis case report describes a near fatal complication of infective endocarditis, detected by routine use of transthoracic echocardiography.CONCLUSIONOur case outlines the relevance of early cardiac surgery strategies in patients with infective endocarditis and we briefly discuss the current literature

Bewegungseinschränkung nach vorderer Kreuzbandrekonstruktion

5. Zusammenfassung: 223 Patienten , die sich einer Revision bei Bewegungseinschränkung nach Vorderer Kreuzbandrekonstruktion unterzogen hatten , wurden nachuntersucht. Es wurde eine Arthrofibrosegruppe (n=156; 70%) und eine Cyclops-Gruppe (n=67; 30%) gebildet. Es bestand ein durchschnittlicher Zeitraum zwischen Arthrolyse und Nachuntersuchung von 4,29 Jahren. Der Zeitabstand zwischen Unfall und vorderer Kreuzbandplastik, die Begleitverletzungen, der Reizzustand, die Schmerzhaftigkeit, der Verlauf der Beweglichkeit, die Art und Dauer der Physiotherapie, die Ausprägung und Art der Bewegungseinschränkung und der Zeitabstand zwischen Vorderer Kreuzbandplastik und Arthrolyse wurden festgehalten. Außerdem wurde der Istzustand dokumentiert. Bei 20 zufällig ausgewählten Arthrofibrosepatienten wurde eine HLA-Typisierung durchgeführt. Es besteht ein signifikanter Zusammenhang zwischen dem präoperativen Reizzustand bei vorderer Kreuzbandrekonstruktion (p<0,001), der präoperativen Bewegungseinschränkung (p=0,001), dem perioperativen Schmerz (p=0,046) und tendenziell mit dem frühzeitigen Muskelaufbautraining (p=0,064) und der Arthrofibroseentwicklung gefunden. Ähnliche Korrelationen wurden bei der Cyclopsentwicklung nicht gefunden. Es besteht eine signifikante Korrelation zwischen persistierendem Streckdefizit und der Entwicklung einer Arthrose (p=0,001). Das Endergebnis ermittelt mit dem IKDC Evaluationsbogen liegt deutlich hinter den Resultaten nach VKB-Rekonstruktion mit komplikationslosem postoperativem Verlauf. Die erreichte sportliche Aktivität ist gegenüber dem Level vor Unfall hochsignifikant vermindert (p<0,001). Es konnte eine signifikante Häufung des HLA-Motivs Cw*03 bei den untersuchten Arthrofibrosepatienten festgestellt werden (p=0,034)

Circuit Electromechanics with a Non-Metallized Nanobeam

We have realized a nano-electromechanical hybrid system consisting of a silicon nitride beam dielectrically coupled to a superconducting microwave resonator. We characterize the sample by making use of the Duffing nonlinearity of the strongly driven beam. In particular, we calibrate the amplitude spectrum of the mechanical motion and determine the electromechanical vacuum coupling. A high quality factor of 480,000 at a resonance frequency of 14 MHz is achieved at 0.5 K. The experimentally determined electromechanical vacuum coupling of 11.5 mHz is quantitatively compared with finite element based model calculations.Comment: Typos and one reference have been correcte

Non-adiabatic dynamics of two strongly coupled nanomechanical resonator modes

The Landau-Zener transition is a fundamental concept for dynamical quantum systems and has been studied in numerous fields of physics. Here we present a classical mechanical model system exhibiting analogous behaviour using two inversely tuneable, strongly coupled modes of the same nanomechanical beam resonator. In the adiabatic limit, the anticrossing between the two modes is observed and the coupling strength extracted. Sweeping an initialized mode across the coupling region allows mapping of the progression from diabatic to adiabatic transitions as a function of the sweep rate

Frequency and Q-factor control of nanomechanical resonators

We present an integrated scheme for dielectric drive and read-out of high-Q nanomechanical resonators which enables tuning of both the resonance frequency and quality factor with an applied DC voltage. A simple model for altering these quantities is derived, incorporating the resonator's complex electric polarizability and position in an inhomogeneous electric field, which agrees very well with the experimental findings as well as FEM simulations. By comparing two sample geometries we are able to show that careful electrode design can determine the direction of frequency tuning of flexural in- and out-of-plane modes of a string resonator. Furthermore we demonstrate that the mechanical quality factor can be voltage reduced more than fivefold