32 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
Dissipative Quantum Feedback in Measurements Using a Parametrically Coupled Microcavity
Micro- and nanoscale optical or microwave cavities are used in a wide range
of classical applications and quantum science experiments, ranging from
precision measurements, laser technologies to quantum control of mechanical
motion. The dissipative photon loss via absorption, present to some extent in
any optical cavity, is known to introduce thermo-optical effects and thereby
impose fundamental limits on precision measurements. Here, we theoretically and
experimentally reveal that such dissipative photon absorption can result in
quantum feedback via in-loop field detection of the absorbed optical field,
leading to the intracavity field fluctuations to be squashed or antisquashed.
Strikingly, this modifies the optical cavity susceptibility in coherent
response measurements and causes excess noise and correlations in incoherent
interferometric optomechanical measurements using a cavity. We experimentally
observe such unanticipated dissipative dynamics in optomechanical spectroscopy
of sideband-cooled optomechanical crystal cavitiess at both cryogenic
temperature (approximately 8 K) and ambient conditions. The dissipative
feedback introduces effective modifications to the optical cavity linewidth and
the optomechanical scattering rate and gives rise to excess imprecision noise
in the interferometric quantum measurement of mechanical motion. Such
dissipative feedback differs fundamentally from a quantum nondemolition
feedback, e.g., optical Kerr squeezing. The dissipative feedback itself always
results in an antisqueezed out-of-loop optical field, while it can enhance the
coexisting Kerr squeezing under certain conditions. Our result has wide-ranging
implications for future dissipation engineering, such as dissipation enhanced
sideband cooling and Kerr squeezing, quantum frequency conversion, and
nonreciprocity in photonic systems
Efficiently Measuring the Cognitive Ability of LLMs: An Adaptive Testing Perspective
Large language models (LLMs), like ChatGPT, have shown some human-like
cognitive abilities. For comparing these abilities of different models, several
benchmarks (i.e. sets of standard test questions) from different fields (e.g.,
Literature, Biology and Psychology) are often adopted and the test results
under traditional metrics such as accuracy, recall and F1, are reported.
However, such way for evaluating LLMs can be inefficient and inaccurate from
the cognitive science perspective. Inspired by Computerized Adaptive Testing
(CAT) used in psychometrics, we propose an adaptive testing framework for LLM
evaluation. Rather than using a standard test set and simply reporting
accuracy, this approach dynamically adjusts the characteristics of the test
questions, such as difficulty, based on the model's performance. This allows
for a more accurate estimation of the model's abilities, using fewer questions.
More importantly, it allows LLMs to be compared with humans easily, which is
essential for NLP models that aim for human-level ability. Our diagnostic
reports have found that ChatGPT often behaves like a ``careless student'',
prone to slip and occasionally guessing the questions. We conduct a
fine-grained diagnosis and rank the latest 6 instruction-tuned LLMs from three
aspects of Subject Knowledge, Mathematical Reasoning, and Programming, where
GPT4 can outperform other models significantly and reach the cognitive ability
of middle-level students. Different tests for different models using efficient
adaptive testing -- we believe this has the potential to become a new norm in
evaluating large language models
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
Scalable and Programmable Phononic Network with Trapped Ions
Controllable bosonic systems can provide post-classical computational power
with sub-universal quantum computational capability. A network that consists of
a number of bosons evolving through beam-splitters and phase-shifters between
different modes, has been proposed and applied to demonstrate quantum
advantages. While the network has been implemented mostly in optical systems
with photons, recently alternative realizations have been explored, where major
limitations in photonic systems such as photon loss, and probabilistic
manipulation can be addressed. Phonons, the quantized excitations of
vibrational modes, of trapped ions can be a promising candidate to realize the
bosonic network. Here, we experimentally demonstrate a minimal-loss phononic
network that can be programmed and in which any phononic states are
deterministically prepared and detected. We realize the network with up to four
collective-vibrational modes, which can be straightforwardly extended to reveal
quantum advantage. We benchmark the performance of the network with an
exemplary algorithm of tomography for arbitrary multi-mode states with a fixed
total phonon number. We obtain reconstruction fidelities of 94.5 1.95 %
and 93.4 3.15 % for single-phonon and two-phonon states, respectively.
Our experiment demonstrates a clear and novel pathway to scale up a phononic
network for various quantum information processing beyond the limitations of
classical and other quantum systems
Free-electron interaction with nonlinear optical states in microresonators
The short de Broglie wavelength and strong interaction empower free electrons
to probe scattering and excitations in materials and resolve the structure of
biomolecules. Recent advances in using nanophotonic structures to mediate
bilinear electron-photon interaction have brought novel optical manipulation
schemes to electron beams, enabling high space-time-energy resolution electron
microscopy, quantum-coherent optical modulation, attosecond metrology and pulse
generation, transverse electron wavefront shaping, dielectric laser
acceleration, and electron-photon pair generation. However, photonic
nanostructures also exhibit nonlinearities, which have to date not been
exploited for electron-photon interactions. Here, we report the interaction of
electrons with spontaneously generated Kerr nonlinear optical states inside a
continuous-wave driven photonic chip-based microresonator. Optical parametric
processes give rise to spatiotemporal pattern formation, or dissipative
structures, corresponding to coherent or incoherent optical frequency combs. By
coupling such microcombs in situ to electron beams, we demonstrate that
different dissipative structures induce distinct fingerprints in the electron
spectra and Ramsey-type interference patterns. In particular, using
spontaneously formed femtosecond temporal solitons, we achieve ultrafast
temporal gating of the electron beam without the necessity of a pulsed laser
source or a pulsed electron source. Our work elucidates the interaction of free
electrons with a variety of nonlinear dissipative states, demonstrates the
ability to access solitons inside an electron microscope, and extends the use
of microcombs to unexplored territories, with ramifications in novel ultrafast
electron microscopy, light-matter interactions driven by on-chip temporal
solitons, and ultra-high spatiotemporal resolution sampling of nonlinear
optical dynamics and devices
Probing material absorption and optical nonlinearity of integrated photonic materials
Optical microresonators with high quality () factors are essential to a
wide range of integrated photonic devices. Steady efforts have been directed
towards increasing microresonator factors across a variety of platforms.
With success in reducing microfabrication process-related optical loss as a
limitation of , the ultimate attainable , as determined solely by the
constituent microresonator material absorption, has come into focus. Here, we
report measurements of the material-limited factors in several photonic
material platforms. High- microresonators are fabricated from thin films of
SiO, SiN, AlGaAs and TaO. By using
cavity-enhanced photothermal spectroscopy, the material-limited is
determined. The method simultaneously measures the Kerr nonlinearity in each
material and reveals how material nonlinearity and ultimate vary in a
complementary fashion across photonic materials. Besides guiding microresonator
design and material development in four material platforms, the results help
establish performance limits in future photonic integrated systems.Comment: Maodong Gao, Qi-Fan Yang and Qing-Xin Ji contributed equally to this
work. 9 pages, 4 figures, 1 tabl