19 research outputs found
Room-temperature quantum optomechanics using an ultra-low noise cavity
Ponderomotive squeezing of light, where a mechanical oscillator creates
quantum correlations between the phase and amplitude of the interacting light
field, is a canonical signature of the quantum regime of optomechanics. At room
temperature, this has only been reached in pioneering experiments where an
optical restoring force controls the oscillator stiffness, akin to the
vibrational motion of atoms in an optical lattice. These include both levitated
nanoparticles and optically-trapped cantilevers. Recent advances in engineered
mechanical resonators, where the restoring force is provided by material
rigidity rather than an external optical potential, have realized ultra-high
quality factors (Q) by exploiting `soft clamping'. However entering the quantum
regime with such resonators, has so far been prevented by optical cavity
frequency fluctuations and thermal intermodulation noise. Here, we overcome
this challenge and demonstrate optomechanical squeezing at room temperature in
a phononic-engineered membrane-in-the-middle system. By using a high finesse
cavity whose mirrors are patterned with phononic crystal structures, we reduce
cavity frequency noise by more than 700-fold. In this ultra-low noise cavity,
we introduce a silicon nitride membrane oscillator whose density is modulated
by silicon nano-pillars, yielding both high thermal conductance and a localized
mechanical mode with Q of 1.8e8. These advances enable operation within a
factor of 2.5 of the Heisenberg limit, leading to squeezing of the probing
field by 1.09 dB below the vacuum fluctuations. Moreover, the long thermal
decoherence time of the membrane oscillator (more than 30 vibrational periods)
allows us to obtain conditional displaced thermal states of motion with an
occupation of 0.97 phonon, using a multimode Kalman filter. Our work extends
quantum control of engineered macroscopic oscillators to room temperature
Clamp-tapering increases the quality factor of stressed nanobeams
Stressed nanomechanical resonators are known to have exceptionally high
quality factors () due to the dilution of intrinsic dissipation by stress.
Typically, the amount of dissipation dilution and thus the resonator is
limited by the high mode curvature region near the clamps. Here we study the
effect of clamp geometry on the of nanobeams made of high-stress
. We find that tapering the beam near the clamp - and locally
increasing the stress - leads to increased of MHz-frequency low order modes
due to enhanced dissipation dilution. Contrary to recent studies of
tethered-membrane resonators, we find that widening the clamps leads to
decreased despite increased stress in the beam bulk. The tapered-clamping
approach has practical advantages compared to the recently developed
"soft-clamping" technique. Tapered-clamping enhances the of the fundamental
mode and can be implemented without increasing the device size
Thermal intermodulation noise in cavity-based measurements
Thermal frequency fluctuations in optical cavities limit the sensitivity of
precision experiments ranging from gravitational wave observatories to optical
atomic clocks. Conventional modeling of these noises assumes a linear response
of the optical field to the fluctuations of cavity frequency. Fundamentally,
however, this response is nonlinear. Here we show that nonlinearly transduced
thermal fluctuations of cavity frequency can dominate the broadband noise in
photodetection, even when the magnitude of fluctuations is much smaller than
the cavity linewidth. We term this noise "thermal intermodulation noise" and
show that for a resonant laser probe it manifests as intensity fluctuations. We
report and characterize thermal intermodulation noise in an optomechanical
cavity, where the frequency fluctuations are caused by mechanical Brownian
motion, and find excellent agreement with our developed theoretical model. We
demonstrate that the effect is particularly relevant to quantum optomechanics:
using a phononic crystal membrane with a low mass, soft-clamped
mechanical mode we are able to operate in the regime where measurement quantum
backaction contributes as much force noise as the thermal environment does.
However, in the presence of intermodulation noise, quantum signatures of
measurement are not revealed in direct photodetectors. The reported noise
mechanism, while studied for an optomechanical system, can exist in any optical
cavity
Hierarchical tensile structures with ultralow mechanical dissipation
Structural hierarchy is found in myriad biological systems and has improved
man-made structures ranging from the Eiffel tower to optical cavities.
Hierarchical metamaterials utilize structure at multiple size scales to realize
new and highly desirable properties which can be strikingly different from
those of the constituent materials. In mechanical resonators whose rigidity is
provided by static tension, structural hierarchy can reduce the dissipation of
the fundamental mode to ultralow levels due to an unconventional form of soft
clamping. Here, we apply hierarchical design to silicon nitride nanomechanical
resonators and realize binary tree-shaped resonators with quality factors as
high as at 107 kHz frequency, reaching the parameter regime of levitated
particles. The resonators' thermal-noise-limited force sensitivities reach
at room temperature and $\mathrm{90\
zN/\sqrt{Hz}}$ at 6 K, surpassing state-of-the-art cantilevers currently used
for force microscopy. We also find that the self-similar structure of binary
tree resonators results in fractional spectral dimensions, which is
characteristic of fractal geometries. Moreover, we show that the hierarchical
design principles can be extended to 2D trampoline membranes, and we fabricate
ultralow dissipation membranes suitable for interferometric position
measurements in Fabry-P\'erot cavities. Hierarchical nanomechanical resonators
open new avenues in force sensing, signal transduction and quantum
optomechanics, where low dissipation is paramount and operation with the
fundamental mode is often advantageous.Comment: 19 pages, 11 figures. Fixed link to Zenodo repositor
Generalized dissipation dilution in strained mechanical resonators
Mechanical resonators with high quality factors are of relevance in precision
experiments, ranging from gravitational wave detection and force sensing to
quantum optomechanics. Beams and membranes are well known to exhibit flexural
modes with enhanced quality factors when subjected to tensile stress. The
mechanism for this enhancement has been a subject of debate, but is typically
attributed to elastic energy being "diluted" by a lossless potential. Here we
clarify the origin of the lossless potential to be the combination of tension
and geometric nonlinearity of strain. We present a general theory of
dissipation dilution that is applicable to arbitrary resonator geometries and
discuss why this effect is particularly strong for flexural modes of
nanomechanical structures with high aspect ratios. Applying the theory to a
non-uniform doubly clamped beam, we show analytically how dissipation dilution
can be enhanced by modifying the beam shape to implement "soft clamping", thin
clamping and geometric strain engineering, and derive the ultimate limit for
dissipation dilution
High-yield wafer-scale fabrication of ultralow-loss, dispersion-engineered silicon nitride photonic circuits
Low-loss photonic integrated circuits (PIC) and microresonators have enabled
novel applications ranging from narrow-linewidth lasers, microwave photonics,
to chip-scale optical frequency combs and quantum frequency conversion. To
translate these results into a widespread technology, attaining ultralow
optical losses with established foundry manufacturing is critical. Recent
advances in fabrication of integrated Si3N4 photonics have shown that
ultralow-loss, dispersion-engineered microresonators can be attained at
die-level throughput. For emerging nonlinear applications such as integrated
travelling-wave parametric amplifiers and mode-locked lasers, PICs of length
scales of up to a meter are required, placing stringent demands on yield and
performance that have not been met with current fabrication techniques. Here we
overcome these challenges and demonstrate a fabrication technology which meets
all these requirements on wafer-level yield, performance and length scale.
Photonic microresonators with a mean Q factor exceeding 30 million,
corresponding to a linear propagation loss of 1.0 dB/m, are obtained over full
4-inch wafers, as determined from a statistical analysis of tens of thousands
of optical resonances and cavity ringdown with 19 ns photon storage time. The
process operates over large areas with high yield, enabling 1-meter-long spiral
waveguides with 2.4 dB/m loss in dies of only 5x5 mm size. Using a modulation
response measurement self-calibrated via the Kerr nonlinearity, we reveal that,
strikingly, the intrinsic absorption-limited Q factor of our Si3N4
microresonators exceeds a billion. Transferring the present Si3N4 photonics
technology to standard commercial foundries, and merging it with silicon
photonics using heterogeneous integration technology, will significantly expand
the scope of today's integrated photonics and seed new applications
Electron-Photon Quantum State Heralding Using Photonic Integrated Circuits
Recently, integrated photonic circuits have brought new capabilities to electron microscopy and been used to demonstrate efficient electron phase modulation and electron-photon correlations. Here, we quantitatively analyze the feasibility of high-fidelity and high-purity quantum state heralding using a free electron and a photonic integrated circuit with parametric coupling, and propose schemes to shape useful electron and photonic states in different application scenarios. Adopting a dissipative quantum electrodynamics treatment, we formulate a framework for the coupling of free electrons to waveguide spatial-temporal modes. To avoid multimode-coupling-induced state decoherence, we show that with proper waveguide design, the interaction can be reduced to a single-mode coupling to a quasi-TM_{00} mode. In the single-mode coupling limit, we go beyond the conventional state ladder treatment, and show that the electron-photon energy correlations within the ladder subspace can still lead to a fundamental purity and fidelity limit on complex optical and electron state preparations through heralding schemes. We propose applications that use this underlying correlation to their advantage, but also show that the imposed limitations for general applications can be overcome by using photonic integrated circuits with an experimentally feasible interaction length, showing its promise as a platform for free-electron quantum optics