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 $\pm$ 1.95 % and 93.4 $\pm$ 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 ($Q$) factors are essential to a wide range of integrated photonic devices. Steady efforts have been directed towards increasing microresonator $Q$ factors across a variety of platforms. With success in reducing microfabrication process-related optical loss as a limitation of $Q$, the ultimate attainable $Q$, as determined solely by the constituent microresonator material absorption, has come into focus. Here, we report measurements of the material-limited $Q$ factors in several photonic material platforms. High-$Q$ microresonators are fabricated from thin films of SiO$_2$, Si$_3$N$_4$, Al$_{0.2}$Ga$_{0.8}$As and Ta$_2$O$_5$. By using cavity-enhanced photothermal spectroscopy, the material-limited $Q$ is determined. The method simultaneously measures the Kerr nonlinearity in each material and reveals how material nonlinearity and ultimate $Q$ 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