107 research outputs found
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
Nonlinear Switching Dynamics in a Nanomechanical Resonator
The oscillatory response of nonlinear systems exhibits characteristic
phenomena such as multistability, discontinuous jumps and hysteresis. These can
be utilized in applications leading, e.g., to precise frequency measurement,
mixing, memory elements, reduced noise characteristics in an oscillator or
signal amplification. Approaching the quantum regime, concepts have been
proposed that enable low backaction measurement techniques or facilitate the
visualisation of quantum mechanical effects. Here we study the dynamic response
of nanoelectromechanical resonators in the nonlinear regime aiming at a more
detailed understanding and an exploitation for switching applications. Whereas
most previous investigations concentrated on dynamic phenomena arising at the
onset of bistability, we present experiments that yield insight into the
non-adiabatic evolution of the system while subjected to strong driving pulses
and the subsequent relaxation. Modeling the behaviour quantitatively with a
Duffing oscillator, we can control switching between its two stable states at
high speeds, exceeding recently demonstrated results by 10,000
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
Resonant coupling of a Bose-Einstein condensate to a micromechanical oscillator
We report experiments in which the vibrations of a micromechanical oscillator
are coupled to the motion of Bose-condensed atoms in a trap. The interaction
relies on surface forces experienced by the atoms at about one micrometer
distance from the mechanical structure. We observe resonant coupling to several
well-resolved mechanical modes of the condensate. Coupling via surface forces
does not require magnets, electrodes, or mirrors on the oscillator and could
thus be employed to couple atoms to molecular-scale oscillators such as carbon
nanotubes.Comment: 9 pages, 4 figure
Dynamics of Long-Living Excitons in Tunable Potential Landscapes
A novel method to experimentally study the dynamics of long-living excitons
in coupled quantum well semiconductor heterostructures is presented.
Lithographically defined top gate electrodes imprint in-plane artificial
potential landscapes for excitons via the quantum confined Stark effect.
Excitons are shuttled laterally in a time-dependent potential landscape defined
by an interdigitated gate structure. Long-range drift exceeding a distance of
150 um at an exciton drift velocity > 1000 m/s is observed in a gradient
potential formed by a resistive gate stripe.Comment: 4 pages, 4 figures. To appear in Phys. E (MSS-12-Proceedings
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
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