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The switching and control of optical fields based on nonlinear optical effects are often limited to relatively weak nonlinear susceptibility and strong optical pump fields. Here, an optical medium with programmable susceptibility tensor based on polarizable atoms is proposed. Under a structured optical pump, the ground state population of atoms could be efficiently controlled by tuning the chirality and intensity of optical fields, and thus the optical response of the medium is programmable in both space and time. We demonstrate the potential of this approach by engineering the spatial distribution of the complex susceptibility tensor of the medium in photonic structures to realize nonreciprocal optical effects. Specifically, we investigate the advantages of chiral interaction between atoms and photons in an atom-cladded waveguide, theoretically showing that reconfigurable, strong, and fastly switchable isolation of optical signals in a selected optical mode is possible. The susceptibility-programmable medium provides a promising way to efficiently control the optical field, opening up a wide range of applications for integrated photonic devices and structured optics., Comment: 7 pages, 4 figures

On-chip micro-ring resonators (MRRs) have been proposed for constructing delay reservoir computing (RC) systems, offering a highly scalable, high-density computational architecture that is easy to manufacture. However, most proposed RC schemes have utilized passive integrated optical components based on silicon-on-insulator (SOI), and RC systems based on lithium niobate on insulator (LNOI) have not yet been reported. The nonlinear optical effects exhibited by lithium niobate microphotonic devices introduce new possibilities for RC design. In this work, we design an RC scheme based on a series-coupled MRR array, leveraging the unique interplay between thermo-optic nonlinearity and photorefractive effects in lithium niobate. We first demonstrate the existence of three regions defined by wavelength detuning between the primary LNOI micro-ring resonator and the coupled micro-ring array, where one region achieves an optimal balance between nonlinearity and high memory capacity at extremely low input energy, leading to superior computational performance. We then discuss in detail the impact of each ring's nonlinearity and the system's symbol duration on performance. Finally, we design a wavelength-division multiplexing (WDM) based multi-task parallel computing scheme, showing that the computational performance for multiple tasks matches that of single-task computations., Comment: 17 pages, 6 figures

Optical frequency combs (OFCs), composed of equally spaced frequency tones, have spurred advancements in communications, spectroscopy, precision measurement and fundamental physics research. A prevalent method for generating OFCs involves the electro-optic (EO) effect, i.e., EO comb, renowned for its rapid tunability via precise microwave field control. Recent advances in integrated lithium niobate (LN) photonics have greatly enhanced the efficiency of EO effect, enabling the generation of broadband combs with reduced microwave power. However, parasitic nonlinear effects, such as Raman scattering and four-wave mixing, often emerge in high quality nonlinear devices, impeding the expansion of comb bandwidth and the minimization of frequency noise. Here, we tame these nonlinear effects and present a novel type of OFC, i.e., the self-locked Raman-electro-optic (REO) microcomb by leveraging the collaboration of EO, Kerr and Raman scattering processes. The spectral width of the REO microcomb benefits from the Raman gain and Kerr effect, encompassing nearly 1400 comb lines spanning over 300 nm with a fine repetition rate of 26.03 GHz, much larger than the pure EO combs. Remarkably, the system can maintain a self-locked low-noise state in the presence of multiple nonlinearities without the need for external active feedback. Our approach points to a direction for improving the performance of microcombs and paves the way for exploring new nonlinear physics, such as new laser locking techniques, through the collaboration of inevitable multiple nonlinear effects in integrated photonics.

Single atoms trapped in tightly focused optical dipole traps provide an excellent experimental platform for quantum computing, precision measurement, and fundamental physics research. In this work, we propose and demonstrate a novel approach to enhancing the loading of single atoms by introducing a weak ancillary dipole beam. The loading rate of single atoms in a dipole trap can be significantly improved by only a few tens of microwatts of counter-propagating beam. It was also demonstrated that multiple atoms could be loaded with the assistance of a counter-propagating beam. By reducing the power requirements for trapping single atoms and enabling the trapping of multiple atoms, our method facilitates the extension of single-atom arrays and the investigation of collective light-atom interactions., Comment: 10 pages, 7 figures

On-chip microring resonators (MRRs) have been proposed to construct the time-delayed reservoir computing (RC), which offers promising configurations available for computation with high scalability, high-density computing, and easy fabrication. A single MRR, however, is inadequate to supply enough memory for the computational task with diverse memory requirements. Large memory needs are met by the MRR with optical feedback waveguide, but at the expense of its large footprint. In the structure, the ultra-long optical feedback waveguide substantially limits the scalable photonic RC integrated designs. In this paper, a time-delayed RC is proposed by utilizing a silicon-based nonlinear MRR in conjunction with an array of linear MRRs. These linear MRRs possess a high quality factor, providing sufficient memory capacity for the entire system. We quantitatively analyze and assess the proposed RC structure's performance on three classical tasks with diverse memory requirements, i.e., the Narma 10, Mackey-Glass, and Santa Fe chaotic timeseries prediction tasks. The proposed system exhibits comparable performance to the MRR with an ultra-long optical feedback waveguide-based system when it comes to handling the Narma 10 task, which requires a significant memory capacity. Nevertheless, the overall length of these linear MRRs is significantly smaller, by three orders of magnitude, compared to the ultra-long feedback waveguide in the MRR with optical feedback waveguide-based system. The compactness of this structure has significant implications for the scalability and seamless integration of photonic RC.

An optical frequency comb is a spectrum of optical radiation which consists of evenly spaced and phase-coherent narrow spectral lines and is initially invented in laser for frequency metrology purposes. A direct analogue of frequency combs in the magnonic systems has not been demonstrated to date. In our experiment, we generate a new magnonic frequency comb in the resonator with giant mechanical oscillation through the magnomechanical interaction. We observe the magnonic frequency comb contains up to 20 comb lines, which are separated to the mechanical frequency of the 10.08 MHz. The thermal effect based on the strong pump power induces the cyclic oscillation of the magnon frequency shift, which leads to a periodic oscillation of the magnonic frequency comb. Moreover, we demonstrate the stabilization and control of the frequency spacing of the magnonic frequency comb via injection locking. Our work lays the groundwork of magnonic frequency combs for sensing and metrology., Comment: 6 Pages, 4 figures

Generated in high-Q optical microresonators, dissipative Kerr soliton microcombs constitute broadband optical frequency combs with chip sizes and repetition rates in the microwave to millimeter-wave range. For frequency metrology applications such as spectroscopy, optical atomic clocks and frequency synthesizers, octave-spanning soliton microcombs generated in dispersion optimized microresonator are required, which allow self-referencing for full frequency stabilization. In addition, field-deployable applications require the generation of such soliton microcombs simple, deterministic, and reproducible. Here, we demonstrate a novel scheme to generate self-emerging solitons in integrated lithium niobate microresonators. The single soliton features a broadband spectral bandwidth with dual dispersive waves, allowing 2f-3f self-referencing. Via harnessing the photorefractive effect of lithium niobate to significantly extend the soliton existence range, we observe a spontaneous yet deterministic single-soliton formation. The soliton is immune to external perturbation and can operate continuously over 13 hours without active feedback control. Finally, via integration with a pre-programed DFB laser, we demonstrate turnkey soliton generation. With further improvement of microresonator Q and hybrid integration with chip-scale laser chips, compact soliton microcomb devices with electronic actuation can be created, which can become central elements for future LiDAR, microwave photonics and optical telecommunications., Comment: 9 pages, 4 figures

For the applications of the frequency comb in microresonators, it is essential to obtain a fully frequency-stabilized microcomb laser source. Here, we demonstrate an atom-referenced stabilized soliton microcomb generation system based on the integrated microring resonator. The pump light around $1560.48\,\mathrm{nm}$ locked to an ultra-low-expansion (ULE) cavity, is frequency-doubled and referenced to the atomic transition of $^{87}\mathrm{Rb}$. The repetition rate of the soliton microcomb is injection-locked to an atomic-clock-stabilized radio frequency (RF) source, leading to mHz stabilization at $1$ seconds. As a result, all comb lines have been frequency-stabilized based on the atomic reference and could be determined with very high precision reaching $\sim18\,\mathrm{Hz}$ at 1 second, corresponding to the frequency stability of $9.5\times10^{-14}$. Our approach provides an integrated and fully stabilized microcomb experiment scheme with no requirement of $f-2f$ technique, which could be easily implemented and generalized to various photonic platforms, thus paving the way towards the portable and ultraprecise optical sources for high precision spectroscopy., Comment: 7 pages, 8 figures

Single atoms are interesting candidates for studying quantum optics and quantum information processing. Recently, trapping and manipulation of single atoms using tight optical dipole traps have generated considerable interest. Here we report an experimental investigation of the dynamics of atoms in a modified optical dipole trap with a backward propagating dipole trap beam, where a change in the two-atom collision rate by six times has been achieved. The theoretical model presented gives a prediction of high probabilities of few-atom loading rates under proper experimental conditions. This work provides an alternative approach to the control of the few-atom dynamics in a dipole trap and the study of the collective quantum optical effects of a few atoms., Comment: 5 pages, 3 figures

Non-reciprocal optical components are indispensable in optical applications, and their realization without any magnetic field arose increasing research interests in photonics. Exciting experimental progress has been achieved by either introducing spatial-temporal modulation of the optical medium or combining Kerr-type optical nonlinearity with spatial asymmetry in photonic structures. However, extra driving fields are required for the first approach, while the isolation of noise and the transmission of the signal cannot be simultaneously achieved for the other approach. Here, we experimentally demonstrate a new concept of nonlinear non-reciprocal susceptibility for optical media and realize the completely passive isolation of optical signals without any external bias field. The self-induced isolation by the input signal is demonstrated with an extremely high isolation ratio of 63.4 dB, a bandwidth of 2.1 GHz for 60 dB isolation, and a low insertion loss of around 1 dB. Furthermore, novel functional optical devices are realized, including polarization purification and non-reciprocal leverage. The demonstrated nonlinear non-reciprocity provides a versatile tool to control light and deepen our understanding of light-matter interactions, and enables applications ranging from topological photonics to unidirectional quantum information transfer in a network., Comment: 9 pages, 6 figures

The nonlinear optical radiation of an integrated lithium niobate microcavity is demonstrated, which has been neglected in previous studies of nonlinear photonic devices. We find that the nonlinear coupling between confined optical modes on the chip and continuum modes in free space can be greatly enhanced on the platform of integrated microcavity, with feasible relaxation of the phase-matching condition. With an infrared pump laser, we observe the vertical radiation of second-harmonic wave at the visible band, which indicates a robust phase-matching-free chip-to-free-space frequency converter and also unveils an extra energy dissipation channel for integrated devices. Such an unexpected coherent nonlinear interaction between the free-space beam and the confined mode is also validated by the different frequency generation. Furthermore, based on the phase-matching-free nature of the nonlinear radiation, we build an integrated atomic gas sensor to characterize Rb isotopes with a single telecom laser. The unveiled mechanism of nonlinear optical radiation is universal for all dielectric photonic integrated devices, and provides a simple and robust chip-to-free-space as well as visible-to-telecom interface., Comment: 7 Pages, 4 figures

Nonlinear optics processes lie at the heart of photonics and quantum optics for their indispensable role in light sources and information processing. During the past decades, the three- and four-wave mixing ($\chi^{(2)}$ and $\chi^{(3)}$) effects have been extensively studied, especially in the micro-/nano-structures by which the photon-photon interaction strength is greatly enhanced. So far, the high-order nonlinearity beyond the $\chi^{(3)}$ has rarely been studied in dielectric materials due to their weak intrinsic nonlinear susceptibility, even in high-quality microcavities. Here, an effective five-wave mixing process ($\chi^{(4)}$) is synthesized for the first time, by incorporating $\chi^{(2)}$ and $\chi^{(3)}$ processes in a single microcavity. The coherence of the synthetic $\chi^{(4)}$ is verified by generating time-energy entangled visible-telecom photon-pairs, which requires only one drive laser at the telecom waveband. The photon pair generation rate from the synthetic process shows an enhancement factor over $500$ times upon intrinsic five-wave mixing. Our work demonstrates a universal approach of nonlinear synthesis via photonic structure engineering at the mesoscopic scale rather than material engineering, and thus opens a new avenue for realizing high-order optical nonlinearities and exploring novel functional photonic devices., Comment: 4 figures

Dissipative Kerr soliton (DKS) offers a compact solution of coherent comb sources and holds huge potential for applications, but has long been suffering from poor power conversion efficiency when driving by a continuous-wave laser. Here, a general approach to resolving this challenge is provided. By deriving the critical coupling condition of a multimode nonlinear optics system in a generalized theoretical framework, two efficiency limitations of the conventional pump method of DKS are revealed: the effective coupling rate is too small and is also power-dependent. Nonlinear couplers are proposed to sustain the DKS indirectly through nonlinear energy conversion processes, realizing a power-adaptive effective coupling rate to the DKS and matching the total dissipation rate of the system, which promises near-unity power conversion efficiencies. For instance, a conversion efficiency exceeding $90\:\%$ is predicted for aluminum nitride microrings with a nonlinear coupler utilizing second-harmonic generation. The nonlinear coupler approach for high-efficiency generation of DKS is experimentally feasible as its mechanism applies to various nonlinear processes, including Raman and Brillouin scattering, and thus paves the way of micro-solitons towards practical applications., Comment: 8 pages, 3 figures

Thin-film gallium nitride (GaN) as a proven piezoelectric material is a promising platform for the phononic integrated circuits, which hold great potential for scalable information processing processors. Here, an unsuspended traveling phononic resonator based on high-acoustic-index-contrast mechanism is realized in GaN-on-Sapphire with a frequency up to 5 GHz, which matches the typical superconducting qubit frequency. A sixfold increment in quality factor was found when temperature decreases from room temperature ($Q=5000$) to $7\,\mathrm{K}$ ($Q=30000$) and thus a frequency-quality factor product of $1.5\times10^{14}$ is obtained. Higher quality factors are available when the fabrication process is further optimized. Our system shows great potential in hybrid quantum devices via circuit quantum acoustodynamics.

Coherent conversion of microwave and optical photons can significantly expand the ability to control the information processing and communication systems. Here, we experimentally demonstrate the microwave-to-optical frequency conversion in a magneto-optical whispering gallery mode microcavity. By applying a magnetic field parallel to the microsphere equator, the intra-cavity optical field will be modulated when the magnon is excited by the microwave drive, leading to microwave-to-optical conversion via the magnetic Stokes and anti-Stokes scattering processes. The observed single sideband conversion phenomenon indicates a non-trivial optical photon-magnon interaction mechanism, which is derived from the magnon induced both the frequency shift and modulated coupling rate of optical modes. In addition, we demonstrate the single-sideband frequency conversion with an ultrawide tuning range up to 2.5GHz, showing its great potential in microwave-to-optical conversion., Comment: 6 pages, 4 figures

The transportation of photons and phonons typically obeys the principle of reciprocity. Breaking reciprocity of these bosonic excitations will enable the corresponding non-reciprocal devices, such as isolators and circulators. Here, we use two optical modes and two mechanical modes in a microresonator to form a four-mode plaquette via radiation pressure force. The phase-controlled non-reciprocal routing between any two modes with completely different frequencies is demonstrated, including the routing of phonon to phonon (MHz to MHz), photon to phonon (THz to MHz), and especially photon to photon with frequency difference of around 80 THz for the first time. In addition, one more mechanical mode is introduced to this plaquette to realize a phononic circulator in such single microresonator. The non-reciprocity is derived from interference between multi-mode transfer processes involving optomechanical interactions in an optomechanical resonator. It not only demonstrates the non-reciprocal routing of photons and phonons in a single resonator but also realizes the non-reciprocal frequency conversion for photons and circulation for phonons, laying a foundation for studying directional routing and thermal management in an optomechanical hybrid network., Comment: 6 pages,4 figures

On-chip bright quantum sources with multiplexing ability are extremely high in demand for the integrated quantum networks with unprecedented scalability and complexity. Here, we demonstrate an ultrabright and broadband biphoton quantum source generated in a lithium niobate microresonator system.Without introducing the conventional domain poling, the on-chip microdisk produces entangled photon pairs covering a broad bandwidth promised by natural phase matching in spontaneous parametric down conversion.Experimentally, the multiplexed photon pairs are characterized by $30\ \rm nm$ bandwidth limited by the filtering system, which can be furthered enlarged.Meanwhile, the generation rate reaches $5.13\ {\rm MHz}/\upmu \rm W$ with a coincidence-to-accidental ratio up to $804$.Besides, the quantum source manifests the prominent purity with heralded single photon correlation $g_H^{(2)}(0)=0.0098\pm0.0021$ and energy-time entanglement with excellent interference visibility of $96.5\%\pm1.9\%$. Such quantum sources at the telecommunication band pave the way for high-dimensional entanglement and future integrated quantum information systems., Comment: 8 pages,4 figures

The modern information networks are built on hybrid systems working at disparate optical wavelengths. Coherent interconnects for converting photons between different wavelengths are highly desired. Although coherent interconnects have conventionally been realized with nonlinear optical effects, those systems require demanding experimental conditions such as phase matching and/or cavity enhancement, which not only bring difficulties in experimental implementation but also set a narrow operating bandwidth (typically in MHz to GHz range as determined by the cavity linewidth). Here, we propose and experimentally demonstrate coherent information transfer between two orthogonally propagating light beams of disparate wavelengths in a fiber-based optomechanical system, which does not require any sort of phase matching or cavity enhancement of the pump beam. The coherent process is demonstrated by phenomena of optomechanically induced transparency and absorption. Our scheme not only significantly simplifies the experimental implementation of coherent wavelength conversion, but also extends the operating bandwidth to that of an optical fiber (tens of THz), which will enable a broad range of coherent-optics-based applications such as optical sensing, spectroscopy, and communication.

Abstract The magneto-optical trap (MOT) is an essential tool for collecting and preparing cold atoms with a wide range of applications. We demonstrate a planar-integrated MOT by combining an optical grating chip with a magnetic coil chip. The flat grating chip simplifies the conventional six-beam configuration down to a single laser beam; the flat coil chip replaces the conventional anti-Helmholtz coils of a cylindrical geometry. We trap 10^{4} cold ^{87}\text{Rb} atoms in the planar-integrated MOT, at a point 3-9 mm above the chip surface. This novel configuration effectively reduces the volume, weight, and complexity of the MOT, bringing benefits to applications including gravimeter, clock and quantum memory devices.

In a traveling wave microresonator, the cascaded four-wave mixing (FWM) between optical modes allows the generation of frequency combs, including intriguing dissipative Kerr solitons (DKS). In this study, we explore the quantum fluctuations of frequency combs and unveil the quantum features of solitons. The entanglement of DKS exhibits two distinct characteristics. For modes located at the spectral edge with a small number of excitations, different comb modes with multiple colors become entangled due to photon-pair generation and coherent photon conversion stimulated by the FWM. Notably, we observe a sudden disappearance of quantum entanglement in the center of the DKS spectrum, which is attributed to the self-locking phenomena in the FWM network. Our findings demonstrate the prominent quantum nature of DKS, which is of fundamental significance in quantum optics and has the potential to be utilized in quantum networking and distributed quantum sensing applications., Comment: 7 pages,3 figures

Microresonators on a photonic chip could enhance nonlinear optics effects, thus are promising for realizing scalable high-efficiency frequency conversion devices. However, fulfilling phase matching conditions among multiple wavelengths remains a significant challenge. Here, we present a feasible scheme for degenerate sum-frequency conversion that only requires the two-mode phase matching condition. When the drive and the signal are both near resonance to the same telecom mode, an efficient on-chip photon-number conversion efficiency upto 42% was achieved, showing a broad tuning bandwidth over 250GHz. Furthermore, cascaded Pockels and Kerr nonlinear optical effects are observed, enabling the parametric amplification of the optical signal to a distinct wavelength in a single device. The scheme demonstrated in this work provides an alternative approach to realizing high-efficiency frequency conversion and is promising for future studies on communications, atom clocks, sensing, and imaging., Comment: 6 pages, 4 figures

A multimode microcavity sensor based on a self-interference microring resonator is demonstrated experimentally. The proposed multimode sensing method is implemented by recording wideband transmission spectra that consist of multiple resonant modes. It is different from the previous dissipative sensing scheme, which aims at measuring the transmission depth changes of a single resonant mode in a microcavity. Here, by combining the dissipative sensing mechanism and the machine learning algorithm, the multimode sensing information extracted from a broadband spectrum can be efficiently fused to estimate the target parameter. The multimode sensing method is immune to laser frequency noises and robust against system imperfection, thus our work presents a great step towards practical applications of microcavity sensors outside the research laboratory. The voltage applied across the microheater on the chip was adjusted to bring its influence on transmittance through the thermo-optic effects. As a proof-of-principle experiment, the voltage was detected by the multimode sensing approach. The experimental results demonstrate that the limit of detection of the multimode sensing by the general regression neural network is reduced to 6.7% of that of single-mode sensing within a large measuring range., Comment: 9 pages, 7 figures

The realization of optical non-reciprocity is crucial for many device applications, and also of fundamental importance for manipulating and protecting the photons with desired time-reversal symmetry. Recently, various new mechanisms of magnetic-free non-reciprocity have been proposed and implemented, avoiding the limitation of the strong magnetic field imposed by the Faraday effect. However, due to the difficulties in suppressing the drive and its induced noises, these devices exhibit limited isolation performances and leave the quantum noise properties rarely studied. Here, we demonstrate a new approach of magnetic-free non-reciprocity by optically induced magnetization in an atom ensemble. Excellent isolation of signal (highest isolation ratio is 51.4 dB) is observed over a power dynamic range of 7 orders of magnitude, with the noiseless property verified by quantum statistics measurement. The approach is applicable to other atoms and atom-like emitters in solids, paving the way for future studies of integrated photonic non-reciprocal devices, unidirectional quantum storage and state transfer, as well as topological photonics technologies., Comment: 6 pages, 5 figures

A narrow linewidth laser operating at the telecommunications band combined with both fast and wide-band tuning features will have promising applications. Here, we demonstrate a single-mode (both transverse and longitude mode) continuous microlaser around 1535 nm based on a fiber Fabry-P\'erot microcavity, which achieves wide-band tuning without mode hopping to 1.3 THz range and fast tuning rate to 60 kHz, yields a frequency scan rate of $1.6\times10^{17}$ Hz/s. Moreover, the linewidth of the laser is measured as narrow as 3.1 MHz. As the microlaser combines all these features into one fiber component, it can serve as the seed laser for versatile applications in optical communication, sensing, frequency-modulated continuous-wave radar and high resolution imaging.

The textbook-accepted formulation of electromagnetic force was proposed by Lorentz in the 19th century, but its validity has been challenged due to incompatibility with the special relativity and momentum conservation. The Einstein-Laub formulation, which can reconcile those conflicts, was suggested as an alternative to the Lorentz formulation. However, intense debates on the exact force are still going on due to lack of experimental evidence. Here, we report the first experimental investigation of angular symmetry of optical force inside a solid dielectric, aiming to distinguish the two formulations. The experiments surprisingly show that the optical force exerted by a Gaussian beam has components with the angular mode number of both 2 and 0, which cannot be explained solely by the Lorentz or the Einstein-Laub formulation. Instead, we found a modified Helmholtz theory by combining the Lorentz force with additional electrostrictive force could explain our experimental results. Our results represent a fundamental leap forward in determining the correct force formulation, and will update the working principles of many applications involving electromagnetic forces.

Dissipative Kerr soliton offers broadband coherent and low-noise frequency comb and stable temporal pulse train, having shown great potential applications in spectroscopy, communications, and metrology. Breathing soliton is a particular dissipative Kerr soliton that the pulse duration and peak intensity show periodic oscillation. However, the noise and stability of the breathing soliton is still remaining unexplored, which would be the main obstacle for future applications. Here, we have investigated the breathing dissipative Kerr solitons in the silicon nitride (SiN) microrings, while the breather period shows uncertainties around MHz in both simulation and experiments. By applying a modulated pump, the breathing frequency can be injectively locked to the modulation and tuned over tens of MHz with frequency noise significantly suppressed. Our demonstration offers an alternative knob for the controlling of soliton dynamics in microresonator and paves a new avenue towards practical applications of breathing soliton.

We propose an optomechanical dissipation engineering scheme by introducing an ancillary mechanical mode with a large decay rate to control the density of states of the optical mode. The effective linewidth of the optical mode can be reduced or broadened, manifesting the dissipation engineering. To prove the ability of our scheme in improving the performances of the optomechanical system, we studied optomechanical entanglement and phonon cooling. It is demonstrated that the optomechanical entanglement overwhelmed by thermal phonon excitations could be restored via dissipation engineering. For the phonon cooling, an order of magnitude improvement could be achieved. Our scheme can be generalized to other systems with multiple bosonic modes, which is experimentally feasible with advances in materials and nanofabrication, including optical Fabry-Perot cavities, superconducting circuits, and nanobeam photonic crystals., Comment: 8 pages, 6 figures

The construction of photon-photon quantum phase gate based on photonic nonlinearity has long been a fundamental issue, which is vital for deterministic and scalable photonic quantum information processing. It requires not only strong nonlinear interaction at the single-photon level, but also suppressed phase noise and spectral entanglement for high gate fidelity. In this paper, we propose that high-quality factor microcavity with strong $\chi^{(2)}$ nonlinearity can be quantized to anharmonic energy levels and be effectively treated as an artificial atom. Such artificial atom has a size much larger than the photon wavelength, which enables passive and active ultra-strong coupling to traveling photons. High-fidelity quantum control-phase gate is realized by mediating the phase between photons with an intermediate artificial atom in a photonic molecule structure. The scheme avoids the two-photon emission and thus eliminates the spectral entanglement and quantum phase noises. Experimental realization of the artificial atom can be envisioned on the integrated photonic chip and holds great potential for single-emitter-free, room-temperature quantum information processing., Comment: 16 Pages,3 figures

Synthetic gauge fields have recently emerged, arising in the context of quantum simulations, topological matter, and the protected transportation of excitations against defects. For example, an ultracold atom experiences a light-induced effective magnetic field when tunnelling in an optical lattice, and offering a platform to simulate the quantum Hall effect and topological insulators. Similarly, the magnetic field associated with photon transport between sites has been demonstrated in a coupled resonator array. Here, we report the first experimental demonstration of a synthetic gauge field in the virtual dimension of bosonic modes in a single optomechanical resonator. By employing degenerate clockwise (CW) and counter-clockwise (CCW) optical modes and a mechanical mode, a controllable synthetic gauge field is realized by tuning the phase of the driving lasers. The non-reciprocal conversion between the three modes is realized for different synthetic magnetic fluxes. As a proof-of-principle demonstration, we also show the dynamics of the system under a fast-varying synthetic gauge field. Our demonstration not only provides a versatile and controllable platform for studying synthetic gauge fields in high dimensions but also enables an exploration of ultra-fast gauge field tuning with a large dynamic range, which is restricted for a magnetic field., Comment: 6 pages, 3 figures

Photonic integrated resonators stand out as reliable frequency converters due to their compactness and stability, with second-harmonic generation (SHG) efficiencies of up to 17000%/W reported recently in aluminum nitride microrings. In this work, a sufficiently strong second-harmonic (SH) signal up to microwatts was generated by a photonic integrated frequency doubler using a milliwatt infrared (IR) laser source. Furthermore, increased SHG bandwidth covering $^{85}$Rb and $^{87}$Rb D$_2$ transition lines as well as saturated absorption spectroscopy (SAS) were demonstrated by tuning the pump power and chip temperature. Here, we present, to the best of our knowledge, the first successful locking of an IR laser to Rb saturated absorption lines via a photonic chip frequency doubler., Comment: 4 pages, 4 figures

Quantum key distribution (QKD) can distribute symmetric key bits between remote legitimate users with the guarantee of quantum mechanics principles. For practical applications, the compact and robust photonic components for QKD are essential, and there are increasing attention to integrate the source, detector and modulators on a photonic chip. However, the massive and parallel QKD based on wavelength multiplexing are still challenge, due to the limited coherent light sources on the chip. Here, we introduce the Kerr dissipative soliton in a microresonator, which provides the locked coherent frequency comb with 49GHz frequency spacing, for QKD. We demonstrate the parallel QKD by demulplexing the coherent comb lines form the soliton, and showing the potential of Gbps secret key rate if the hundreds of channels covering C and L bands are fully exploited. The demonstrated soliton based QKD architecture are compatible with the efforts of quantum photonic integrated circuits, which are compact, robust and low-cost, and provides a competitive platform of practical QKD chip.

Dissipative Kerr solitons (DKSs) in the high-Q micro-resonator corresponds to self-organized short pulse in time domain via double balance between dispersion and Kerr nonlinearity, as well as cavity loss and parametric gain. In this paper, we first experimentally demonstrate deterministic generation and switching of DKSs in a thermally controlled micro-ring resonator based on high-index doped silica glass platform. In our scheme, an auxiliary laser is introduced to timely balance the intra-cavity heat fluctuation. By decreasing the operating temperature through a thermo-electric cooler, soliton crystal is firstly generated, then increasing the temperature, DKSs switching and single soliton are robustly accessed, which is independent of the tuning speed. During the switching process, varieties of DKSs are identified by tens of featured discrete soliton-steps, which is favorable for study of on-chip soliton interactions and nonlinear applications., Comment: 4 pages, 5 figures

The coherent temporal soliton in optical microresonators has attracted great attention recently. Here, we demonstrate the dissipative Kerr soliton generation in a microrod resonator, by utilizing an auxiliary-laser-assisted thermal response control. By external stress tuning, the repetition rate of the soliton has been controlled over a large range of 30 MHz. Our platform promises precise tuning and locking of the repetition frequency of coherent mode-locked comb in the microresonator, and holds great potential for applications in spectroscopy and precision measurements., Comment: 5 Pages, 4 figures

A new category of optical microring resonator, which is analogous to the M\"obius strip, is proposed. The "M\"obius" microring resonator allows the conversion between modes with different polarizations in the ring and light must circulate two cycles to be converted back to the original polarization status, which is similar to a M\"obius strip. This topology structure of polarization leads to the free spectral range be half of that corresponds to the cavity round trip. The eigenmodes of this microring are hybridizations of different polarizations and the breaking of the rotation invariance of the ring makes the transmission be related with the polarization of input light. Our work opens the door towards the photonic devices with nontrivial mode topology and provides a novel way to engineering photonic structures for fundamental studies., Comment: 6 pages, 3 figures

We present an experimental study on the cavity-atom ensemble system, and realize the doubly-resonant cavity enhanced electromagnetically induced transparency, where both the probe and control lasers are resonant with a Fabry-Perot cavity. We demonstrate the precise frequency manipulating of the hybrid optical-atomic resonances, through either temperature or cavity length tuning. In such a system, the control power can be greatly enhanced due to the cavity, and all-optical switching is achieved with a much lower control laser power compared to previous studies. A new theoretical model is developed to describe the effective three-wave mixing process between spin-wave and optical modes. Interesting non-Hermitian physics are predicted theoretically and demonstrated experimentally. Such a doubly-resonant cavity-atom ensemble system without a specially designed cavity can be used for future applications, such as optical signal storage and microwave-to-optical frequency conversion., Comment: 8 pages, 5 figures

Third-harmonic generation can be realized via both $\chi^{(3)}$ and cascaded $\chi^{(2)}$ nonlinear processes in a triply-resonant microcavity. It is still unknown how these processes interfere with each other and the optimization of the conversion efficiency still remains as a question. In this work, the interplay between the direct third-harmonic generation and the cascaded process combining of the second-harmonic generation and the sum-frequency generation are investigated. It is found that the interference effect between these two processes can be used to improve the conversion efficiency. By optimizing the cavity resonance and the external coupling conditions, the saturation of the nonlinear conversion is mitigated and the third-harmonic conversion efficiency is increased. A design rule is provided for achieving efficient third-harmonic generation in an optical microcavity, which can be generalized further to the high-order harmonic generations., Comment: 7 pages, 4 figures

Optical microcavities are often used to realize enhanced nonlinear optical interactions for highly efficient second-harmonic generation. With increased pump power, the efficiency of nonlinear frequency conversion can be increased further, while some other unwanted nonlinear effects will also emerge, leading to complicated dynamics or instability. Here, we study the interplay between cascaded second- and third-order nonlinear processes and investigate their impact on the second-harmonic generation in microcavities. It is found that the non-degenerate optical parametric oscillation (OPO) appears and the presence of $\chi^{(3)}$ process can modify the OPO threshold significantly when the multimode cavity is strongly pumped at the fundamental optical mode. One can even break the efficiency limitation of the second-harmonic mode restricted by the OPO by utilizing the interference between the OPO and the four-wave mixing. The present coherent interplay between nonlinear optical processes in microcavities is conducive to exploring new physics in the cavity nonlinear photonics., Comment: 8 pages, 4 figures