This PDF file contains the front matter associated with SPIE Proceedings Volume 11296, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists

"Sensing protocols for the NV-NMR spectrometer" was recorded at Photonics West 2020 in San Francisco, California.

"Attosecond-resolution optical path evaluation and sensing using quantum optical interferometry with dispersion cancellation" was recorded at Photonics West 2020 in San Francisco, California.

Raman scattering is a powerful instrument for spectroscopic sensing, which offers superb selectivity but typically at the expense of low signal and long collection times. In this paper we discuss mechanisms for signal enhancement that dramatically improve the performance of Raman spectroscopic systems. Several approaches, as well as their combinations are considered. One approach is to produce Raman coherence; other approaches exploit the advantages of nanosized antenna-like structures, or employ wavefront shaping of the applied laser beams. Combining these techniques in one system leads to multiplicative signal enhancement and results in an unprecedented sensitivity. In a sequence of steps toward this goal, we show that the automated feedback-based wavefront shaping algorithm is capable of improving coherent cascaded Raman scattering in crystals. In addition, we utilize the fact that specially designed nanoantennas, placed in the vicinity of the target molecule, can significantly increase the probability of exciting dipole-forbidden electronic transitions. Nanostructure-enhanced spectroscopy with shaped beams will allow for an increase in spectroscopic sensitivity and efficient detection of magnetic dipole and electric quadrupole transitions induced in molecules. The ultimate goal for developing these techniques is to achieve single-molecule sensitivity in spectroscopy, combined with atomic spatial resolution, study the layout and chemical bonds of the molecular structure and extract information relevant to chirality.

We study decoherence in continuously cooled atom interferometers by performing Raman-Ramsey fringe measurements in a continuous beam of 3D-sub-Doppler-cooled rubidium atoms. The atom beam is produced by a two-stage cold atom source that is designed to mitigate the decoherence of atomic interference caused by cooling induced fluorescence. The atom beam source produces a collimated beam of over 10⁹ atoms/s that is cooled by polarization gradient cooling to temperatures as low as 14 µK. We infer the potential performance of this atom beam source in a cold-atom gyroscope and use numerical models of motion in 6 degrees of freedom to study the expected performance on dynamic platforms.

The ultralong-range Cs₂ Rydberg molecules consisting of a Rydberg, nD_5/2 ( principal quantum number n =35-38), and a ground state atom, 6S_1/2 (F=4) are prepared by a two-photon photoassociation spectroscopy in an ultracold Cs gas. This kind of molecule is bound with the low energy scattering and has a permanent dipole moment. We observe two Rydberg-ground state molecular spectra, one is deep-bound molecule, ^TΣ state, bound by triplet s-wave scattering length and the other one is shallow-bound molecule, ^S,TΣ state, bound by mixed singlet-triplet s-wave scattering length. The binding energy of Rydberg-ground molecules are attained by analyzing the two photon photoassociation spectrum, corresponding permanent dipole moment is measured by applying an external electric field, which is compared to the calculation.

An atomic clock based on a compact source of cold atoms and coherent population trapping (CPT) is an encouraging goal for future low-volume atomic frequency references. Our experiment seeks to investigate the performance of such a system by applying CPT in a high-contrast lin⊥lin polarisation scheme to our ⁸⁷Rb grating magneto optical trap (GMOT) apparatus. In this paper, we report on our progress of improving short- term stability of our cold-atom CPT apparatus. Our recent measurements have shown a short-term stability of 5 x 10^-11/√_τ, with the ability to average down for times τ>100s.

Atomic clocks based on Coherent Population Trapping (CPT) in cesium [1] or other sensors based on CPT require the development of specific low noise laser sources at resonant wavelengths. For instance, the double lambda scheme for CPT probed by lin ⊥ lin laser beams, which has been shown to create Raman–Ramsey fringes with a larger contrast than the usual simple lambda scheme in [2], requires the availability of two cross-linearly polarized frequencies at 852 nm with a low beat note phase noise and a low intensity noise. One way to generate these two frequencies with low amplitude and phase noises is to build a dual-frequency VECSEL (Vertical External Cavity Surface Emitting Laser) [3]. In this talk we will present our efforts to understand the physical origin of the laser amplitude and phase noises [4], and the developments that we have made to reduce these noises to the levels necessary to achieve a relative clock stability of 10-13 at 1 s integration time.

Achieving quantum-enhanced sensing in high-level applications in the real-world has proven to be challenging. High-level applications typically involve the simultaneous quantum sensing of multiple parameters. We highlight some recent advances and open problems in this area. Quantum-enhanced sensing in the real world is incumbent on tackling decoherence. We discuss how fault-tolerant quantum metrology can pave the path for quantumenhanced sensing in the real world.

State of the art atomic sensors operate near the standard quantum limit (SQL) of projection noise, and overcoming this limit by using atom-atom entanglement such as spin squeezing is a major goal in quantum metrology. By coupling an ensemble of approximately 1000 Yb-171 atoms to a high-finesse asymmetric micromirror cavity with single-atom cooperativity of 1.8., we produce a near-unitary spin squeezed state. The observed spin noise suppression and metrological gain are limited by the state readout to 9.4(4) dB and 6.5(4) dB, respectively, while the generated states offer a spin noise suppression of 15.9(6) dB and a metrological gain of 12.9(6) dB over the standard quantum limit, limited by the curvature of the Bloch sphere. When requiring the squeezing process to be within 30% of unitarity, we demonstrate an interferometer that improves the averaging time over the SQL by a factor of 3.7(2).

The question of how long a tunneling particle spends in the forbidden region of a barrier has been a perplexing puzzle in foundational quantum mechanics for many decades. The Larmor time, one definition of tunneling time, uses an auxiliary degree of freedom of the tunneling particles to clock the time spent inside the barrier. Recently, we made our first measurement of the Larmor time for Bose-condensed ⁸⁷Rb atoms tunneling through an optical barrier.¹ Here, we report on follow up measurements with improved precision in the measured times and also study the time for the reflected atomic cloud. We observe significant discrepancies between our results and a simple theory based on weak measurement. We discuss our findings, hypothesize explanations for our results, and suggest future studies.

In this manuscript, we discuss the performance of a recently demonstrated polarization-based truncated SU(1,1) interferometer¹ which can potentially generate polarization-entangled twin beams for applications in quantum communications or in quantum metrology as an interferometer with enhanced phase sensitivity. Using the intensity-squeezed twin beams generated via four-wave mixing (FWM) in hot Rubidium vapor, we report the detection of nearly -2 dB of noise reduction below the shot-noise in the joint-quadrature measurements in such interferometer. We also used this setup to confirms the non-classical nature of quantum correlations between the twin beams with an inseparability parameter I = 1:32±0:04 that falls below the classical limit of 2. One of the important advantages of the proposed interferometer is its better rejection of common-mode, technical, and environmental noises due to its intrinsic symmetry, which allows for squeezing and entanglement measurements at wide spectrum of detection frequencies from as low as 200 Hz (limited by 1=f electronic noise) to up to a few MHz (limited by the photodetector gain bandwidth).

"Two-photon sensing and microscopy with quantum light" was recorded at Photonics West 2020 in San Francisco, California.

We explore Fabry-Perot cavities formed by a pair of photonic-crystal slabs acting as mirrors as a platform for quantum optics at low light levels. We present our recent experimental demonstrations of polarization dichroic mirrors for both linearly and circularly polarized light and propose schemes in which cavities formed by such mirrors can be used to create single-photon optical nonlinearities in atomic ensembles.

A time-lens can image signals in time and map ultrafast signals from frequency to time. The concept of time-lens is based on the duality between the diffraction of light in space and the dispersion of pulses in time, which arises from the similarity between the equations describing these two phenomena. In this paper we explain how to use time-lenses in order to perform high-resolution temporal imaging on non-classical ultrafast signals. Such a scheme can be used e.g. for diagnosing quantum cryptography schemes on optical fiber networks or assessing the performance of photonic quantum computers and simulators.

This Conference Presentation, “Molecular lattice clock with long vibrational coherence” was recorded at Photonics West 2020 held in San Francisco, California, United States.

"Atom-based electromagnetic field sensing" was recorded at Photonics West 2020 in San Francisco, California.

"Large momentum transfer point source atom interferometry" was recorded at Photonics West 2020 in San Francisco, California.

The design and performance of a compact laser system for autonomous cooling of rubidium atoms in a small Cube-Sat satellite is described. The laser system is suitable for use in cold atom interferometers that are deployed in space for accurate observation of earth’s gravity and magnetic fields and detection of tectonic changes. The laser system features a frequency doubled DFB laser and erbium doped amplifier, which is mainly fabricated from telecommunications qualified components with proven high reliability. The laser has an output power of greater than 75mW with a sub-MHz linewidth and a tuning range of greater than 300GHz. The laser and drive electronics fit into a 200mm x 100mm x 30mm package and have a mass of less than 1kg. On-board the CubeSat the laser has been used to demonstrate atom cooling and to autonomously acquire and lock to the magneto-optical trap using feedback from the cold Rb-atom fluorescence to control the dfb laser frequency. The complete cube-sat has passed vibration tests for rocket launched conditions.

"Optical atomic clock comparisons using correlation spectroscopy" was recorded at Photonics West 2020 in San Francisco, California.

This Conference Presentation, One-axis twisting in a Rydberg-dressed atomic clock was recorded at Photonics West 2020 held in San Francisco, California, United States.

"Applications in optical quantum metrology" was recorded at Photonics West 2020 in San Francisco, California.

"Recent progress towards the development of a spin-squeezed atomic interferometer" was recorded at Photonics West 2020 in San Francisco, California.

"Quantum sensing with neutral atoms" was recorded at Photonics West 2020 in San Francisco, California.

I discuss new ways to grow diamond that promise near-deterministic design of fluorescent color-centers, optimized for quantum sensing and metrology applications. The key is to grow diamond from organic molecules at a low enough temperature such that only some of the molecules decompose. This approach gives unprecedented control over the properties of diamond color centers by decoupling diamond-growth from color-center creation. In addition, low growth temperature produces high quality diamonds and allows a wider choice of growth pressures than is currently believed possible.

The study of many-body quantum systems, and specifically spin systems, is a main pillar of quantum physics. As part of this research direction, various experimental platforms have emerged which allow for controlled experiments in this context, with nitrogen vacancy (NV) ensembles in diamond being one of them. In order to realize relevant experiments in the NV system, advanced controlled schemes are required in order to generate the required interacting spin Hamiltonians, as well as to robustly control such dense spin ensembles. Here we tackle both issues: we develop a framework for Hamiltonian engineering based on the icosahedral symmetry group, demonstrating its advantages over existing schemes in terms of obtainable interacting Hamiltonians; we develop and demonstrate robust control pulses based on rapid adiabatic passage (RAP), which result in improved coherence times and sensing.

"Heisenberg limited atomic sensing using Schrödinger cat states with extreme insensitivity to excess noise" was recorded at Photonics West 2020 in San Francisco, California.

"Quantum sensing of rapidly varying magnetic fields" was recorded at Photonics West 2020 in San Francisco, California.

Since the demonstration of the first quantum cascade laser (QCL) in 1997, QCLs have undergone considerable developments in output power, wall plug efficiency (WPE), beam quality, wavelength coverage and tunability. Among them, many world-class breakthroughs were achieved at the Center for Quantum Device at Northwestern University. In this paper, we will discuss the recent progress of our research and present the main contributions of the Center for Quantum Devices to the QCL family on high power, high wall-plug efficiency (WPE), continuous-wave (CW) and room temperature operation lasers.

"Narrowing the linewidth of a distributed Bragg reflector laser with an intracavity electro-optic modulator" was recorded at Photonics West 2020 in San Francisco, California.

"Laser wavefront perturbations in extreme momentum transfer atom interferometers: effects and mitigation strategies" was recorded at Photonics West 2020 in San Francisco, California.

Two strontium optical lattice clocks (Sr1 and Sr2) are being built at National Institute of Metrology(NIM) of China. Sr1 was firstly evaluated in 2015, and later equipped with a new clock laser based on a 30 cm reference cavity, which helped to improve its stability. Sr2 is built on a new campus of NIM, which has some different designs compared to Sr1, for example, a permanent magnets based Zeeman slower, a differential pumping stage, and a robust laser system. A time interleaved self-comparison campaign of Sr2 of more than 7 days shows an up-time of ~90% and a measurement stability of 3.7×10^-15/√𝜏 with a 10 cm ULE cavity based clock laser. The link between these two optical clocks, that consists of two fiber optical frequency combs and a 54 km fiber connection, are being constructed. The comparison of these two clocks is planned in the near future.

This Conference Presentation, Large-scale atom interferometers: towards tests of general relativity was recorded at Photonics West 2020 held in San Francisco, California, United States.

"Searching for new physics with differential optical lattice clock comparisons" was recorded at Photonics West 2020 in San Francisco, California.

Atomic clock research at The Aerospace Corporation focuses on basic atomic physics in support of critical space technologies such as timekeeping for GNSS and communications. GPS and other GNSS play pivotal roles throughout modern society’s infrastructure, and clock stability in space can significantly impact the signals necessary for safe and reliable navigation and positioning. For secure communications, technology such as spread spectrum telecom is dependent on accurate and relatively unchanging timekeeping signals and frequency references. Many of our fundamental research investigations directly impact these technologies as they evolve in commercial space systems. In this presentation, we offer an introduction to The Aerospace Corporation with an overview of our laboratory’s basic physics research capabilities and their impact. Several clock physics investigations will be addressed and described in context with satellite-based timekeeping, which supports present and future space missions.

A vector curvature sensor based on a single fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The sensor is easily fabricated by encapsulating an FBG on a thin steel plate with ultraviolet glue. When the FBG deviates from the neutral plane, its effective refractive index and grating constant are changed by bending, therefore, the sensor can realize curvature measurement. Due to the opposite stress direction on the two sides of the neutral plane during bending, the sensor can realize vector measurement of curvature. The curvature sensitivity of the sensor in convex and concave bending is 558.42 pm/m^-1 and -818.09 pm/m^-1, respectively. This sensor has the advantage of simple structure, low cost, and easy industrial production. It has potential applications in engineering health monitoring and deformation measurement.

Atomic vapors are a crucial platform for precision metrology but in their simplest implementation, a thermal vapor, the intrinsic optical resonances are broadened due to the random and isotropic thermal motion of the atoms. By structuring the container of a thermal vapor with narrow emission apertures, the velocity distribution can be modified to create a directed beam of atoms.¹ These atomic beams can then interact sequentially with a series of optical fields, or interaction zones, and ultimately allow precision control over the internal state of the atom. This is useful for optical frequency standards and precision spectroscopy^{2, 3} and may also provide the means to build a simple flying qubit platform.⁴ Furthermore, atomic beams on a chip can be used as a compact, directed source to load magneto-optical traps (MOTs) while minimally increasing the ambient pressure.⁵ We apply microfabrication techniques to microscopically structure silicon to deterministically control the ow of Rb between connected cavities. We describe a methodology to measure the experimental parameters that govern the flux of atomic vapors in these microfabricated structures with a goal of creating an equivalent electrical circuit model. This toolkit will provide a simple platform for the creation of atomic beams on a chip with controllable pressure profiles and a thorough understanding of the influence of adsorptive effects and pseudo- ballistic trajectories on the resultant atomic beam.

"Precision measurements with Rydberg atoms" was recorded at Photonics West 2020 in San Francisco, California.

Atom interferometry has proven both a powerful means for probing fundamental physics, and a promising technology for high-precision inertial sensing. However, their performance has been limited by the available interrogation time of atoms falling freely in Earth's gravitational field. Trapped geometries have thus been explored as a means to improve the sensitivity of atom interferometers, but attempts to date have suffered from decoherence caused by trap inhomogeneities. We have demonstrated a trapped atom interferometer with an unprecedented interrogation time of 20 seconds,1 achieved by trapping the interferometer in the resonant mode of an optical cavity. The cavity is instrumental to this advance, as it provides spatial mode filtering for the trapping potential. Because the interferometer is held with the arms vertically separated along the gravitational axis, a phase shift accumulates due to the gravitational potential energy difference between the arms. Moreover, this phase accumulates continuously during the hold time, providing an orders-of-magnitude greater immunity to vibrations than previous atom-interferometric gravimeters at the same sensitivity.

"Search for non-Newtonian gravity with optically-levitated microspheres" was recorded at Photonics West 2020 in San Francisco, California.

Nowadays, optical fiber links are key elements in optical metrology, spectroscopy, quantum communication and geodesy. In geodetic Very Long Baseline Interferometry, a local maser is responsible for providing time and frequency reference at radiotelescope. Here, we present our recent results on frequency dissemination using a coherent fiber link 1800 km long from Turin to Medicina and Matera, Italy. Metrological reference disseminated via fiber link improve the stability of about two order with respect to the local H-maser clocks. This kind of dissemination paves the way to VLBI observation using a remote clock reference on the Italian and European radio observatories.

New applications of dynamic population Bragg gratings recorded in saturable ytterbium doped fibers (YDF) by 10mW-scale cw Nd:YAG laser power at 1064nm are considered. In particular, adaptive interferometric Sagnac configuration for detection of optical phase modulation with resolution close to that determined by photon noise is reported. Spectral and nonlinear properties of all-fiber resonance cavity filled with an artificial dispersive media – dynamic Bragg grating in YDF - are also investigated.

The development of laser-machined, ultralow roughness micromirrors on optical fiber tips has enabled a new type of high-finesse Fiber Fabry-Perot cavities (FFPs). These microcavities are used very successfully in an increasing number of quantum technology applications, reaching from single-photon sources with various solid-state emitters to entanglement generation in ultracold atomic ensembles. They are also attractive for general photonics applications where high cavity finesse is desired, combinin narrow resonance width and large stopband with high transmission, excellent passive stability and built-in fiber coupling. I will give a short overview of this cavity technology and describe an experiment where we are using a next-generation FFP cavity to generate long-lived spin squeezed states in an atomic clock on a chip.

Analysis of influence of the Maxwell distribution of the transverse thermal velocities and of the flight-time-determined characteristic relaxation rates (i.e. the inverse relaxation times T_1,2) of the acetylene (C₂H₂) molecules in the hollow-core photonic crystal fiber on nonlinear optical effects are presented. The theoretical predictions are compared with the experimental data obtained in the ~0.4Torr acetylene-filled fiber cell at the wavelength 1530.37nm of the most effective P9 vibrational-rotational transition of ¹²C₂H₂. At room temperature and the fiber mode field diameter of 7.5 μm, the average transverse thermal velocity of ~390m/s ensured relaxation times T_1,2 ~8-10ns. These are in good agreement with the corresponding values experimentally measured using delayed optical nutation and two-photon echo techniques. The experimentally observed nonlinear effect of the polarization ellipse self-rotation proves to be at least two orders of magnitude less efficient comparing with that reported earlier for the alkali metals vapors.

"Nonlinear pulse measurement with a multimode fiber" was recorded at Photonics West 2020 in San Francisco, California.

"Gravimetry through nonlinear optomechanics" was recorded at Photonics West 2020 in San Francisco, California.

"New optomechanical probing methods for high-precision sensing" was recorded at Photonics West 2020, in San Francisco, California.

"Laser-driven GHz rotation and ultrasensitive torque detection" was recorded at Photonics West 2020, in San Francisco, California.

"Ultra-high-resolution comb spectroscopy" was recorded at Photonics West 2020, in San Francisco, California.

"Ultrasensitive sensing with combs: when squeezing is not only for hugs" was recorded at Photonics West 2020, in San Francisco, California.

Optical frequency combs have in the recent past revolutionized the field of high-resolution spectroscopy by being applied both as frequency references and light sources for direct comb spectroscopy. With respect to the latter application, we have demonstrated the use of an optical frequency comb to coherently drive stimulated Raman transitions between terahertz-spaced atomic energy levels. Specifically, we have measured the 3d 2D3/2 - 3d 2D5/2 fine structure splitting of a single trapped 40Ca+ ion to be 1,819,599,021,534±8Hz, which is five times more accurate than previous measurements, and currently only limited by the stability of our atomic clock reference. Furthermore, Rabi oscillations with a contrast of 99.3(6)% and millisecond coherence time have been realized experimentally, indicating great potentials for future qubit applications. Importantly, the technique should generally be applicable to drive Raman transitions spanning the level spacings ranging from sub-kHz to tens of THz range, including hyperfine transitions in highly charged ions and spin-resolved rovibrational transitions in molecular ions. High-resolution spectroscopy of such systems may find applications in the search for new physics beyond the Standard Model.

This Conference Presentation, Recent results on gravitational decoherence and collapse, was recorded at Photonics West 2020 held in San Francisco, United States.

"Testing collapse models for macroscopic quantum superpositions using an atomic interferometer without entanglement" was recorded at Photonics West 2020, in San Francisco, California.

"A quantum-enhanced search for ultra-light axion-like dark matter" was recorded at Photonics West 2020, in San Francisco, California.

"Precision tests of charge quantization and searches for millicharged particles using levitated optomechanics" was recorded at Photonics West 2020, in San Francisco, California.

We present the design and the status of an optical lattice clock at Jet Propulsion Laboratory (JPL) based on bosonic ⁸⁸Sr atoms with an emphasis on the laser system. The design of the clock aims for future implementation and science applications in space. The atomic source employs a two-dimensional magneto-optical trap realized with permanent magnets and a simple dispenser-based atomic oven. This design results in a low system size, weight and power, suppresses thermal atoms in the clock interrogation zone, and eliminates hot blackbody radiation in the science cell. The laser system utilizes exclusively direct diode lasers without second harmonic generation to minimize the complexity and power consumption of the overall system. The clock interrogation laser at 698nm and the laser for the second cooling stage at 689nm are both locked to the same high finesse optical cavity to further reduce the size of the system. Future paths to system miniaturization are also discussed.

The 2015 seminal discovery of gravitational waves (GW) from the collision of the binary black holes has boosted interest to development of a more sensitive next generation gravitational-wave interferometers. As the current Advanced LIGO and Virgo detectors are limited by fundamental quantum fluctuations of light in the most of their detection band, the next generation of interferometers must use advanced quantum noise-mitigation methods and quantum non-demolition (QND) techniques to achieve the planned design sensitivity of 10 times better than the current detectors have. In this paper, we attempt to give an overview of some advanced quantum metrology techniques being considered as potential sensitivity boosters for the next generation GW detectors.

Time delay interferometer (TDI) is the baseline technique to mitigate laser phase noises in laser interferometer space antenna (LISA) for gravitational wave detection. Just as important in the TDI scheme is the ability to suppress the local oscillator radio-frequency (rf) noises in the optical heterodyne measurements. This is accomplished currently by sending additional clock tones in the ranging laser and recovering the clock signals with additional heterodyne measurements. We show that the laser and local oscillator noises can be simultaneously cancelled by employing optical frequency combs in which the rf signal phases are coherent with the optical phases. We describe an effort for the experimental demonstration of the optical frequency comb based TDI. The deployment of optical combs eliminates the need for separate ultra-stable oscillators. This approach can be a simpler and more reliable approach than the current modulation scheme. It is applicable to the most generalized TDI combinations.

Advances in material science and fabrication techniques enabled the fabrication of samples with nanometric dimensions where it is possible to confine photons and phonons (GHz-THz frequencies) in a single nanostructure. In this presentation, I will describe the behavior of a few devices able to control the interactions between light, sound and charge at the nanoscale based on semiconductor micropillars. I will introduce strategies to generate, manipulate and detect ultra-high frequency acoustic phonons both in the time and spectral domains.

Moving refractive index fronts in waveguides with dispersion is a special type of spatio-temporal modulation. The interaction of light with that front allows frequency conversion, light stopping, optical delays, and bandwidth and pulse duration manipulation. Here, we present examples of signal transmission, reflection, trapping and stopping. We will geometrically consider indirect transitions in the dispersion relation using the phase continuity relation at the front and present numerical solutions of the linear Schrödinger equation which follows from the slowly varying envelope approximation of the wave equation.

Fiber Bragg gratings (FBGs) with strong apodized index modulations behave like an in-line Fabry-Perot interferometer and exhibit a series of narrow resonances in the short-wavelength portion of their transmission spectrum. These resonances have proven invaluable for detecting extremely small strains (30-femtostrain/√Hz level) or temperature changes (millidegreeC/√Hz level). The sensitivity of these fiber sensors is limited by the linewidth and peak transmission of the resonance used to interrogate the sensor, which are themselves limited by the intrinsic loss of the grating. In this work, significantly narrower and stronger resonances are demonstrated by introducing a small amount of optical gain in the FBG to offset the intrinsic loss and create a resonator with a much smaller net internal loss. The fiber Bragg grating is written in an Er-doped single-mode fiber and optically pumped to provide the required gain. The device reported here is a 6.5-mm grating with an AC index modulation of 1.59×10^-3. With only 30 μW of pump power absorbed by the grating (32.6 mW launched), the fundamental resonance of the FBG was observed to narrow from 737 fm in the absence of pump to a record linewidth of 8.5 fm. The measured peak transmission of the resonance improved from ~-37 dB to -0.2 dB. A new model that predicts the slow-light resonance spectrum of a slow-light grating in the presence of optical gain is presented. This model is in good quantitative agreement with the measured evolution of the resonance linewidth as the pump power and the power of the laser that probes the resonance lineshape are varied.

"Slow light in SNAP structures: new classical and quantum applications" was recorded at Photonics West 2020 in San Francisco, California.

With the lowest threshold, stimulated Brillouin scattering (SBS) is one of the most common nonlinear effects in optical fibers. Due to the Kramers-Kronig relation, every SBS interaction is inevitably accompanied by a phase response, providing an excellent chance for dispersion manipulation. By engineering the Brillouin gain spectrum, numerous demanding requirements on dispersion engineering can be fufilled via SBS interactions in various applications. In this paper, examples of gain spectrum engineering and dispersion engineering for Brillouin static and dynamic sensing will be presented. With a well engineered gain spectrum, a static Brillouin sensor is more robust to noise and offers a 3-dB measurement accuracy enhancement. In simulations, more than one magnitude of sensitivity enhancement has been demonstrated for dynamic sensors.

Multipartite entanglement is a key resource for various quantum information tasks. Here, we present multiple schemes for multimode entanglement and squeezing via nonlinear optical processes. We define a new "coupled three-mode squeezed vacuum" state. Non-intuitive behaviors arise in intensity squeezing between two of the three output modes due to the coupling. We also show that this state can be genuinely tripartite entangled, and extend the work to a four-mode output system.

Exabytes of data are sent through the internet monthly, and the demand grows exponentially. Quantum measurement enables sensitivity beyond the shot noise, with a potential to minimize the energy and bandwidth required to transmit a bit. We developed a fully quantum-mechanical treatment of this measurement problem. We introduce new protocols of data exchange that are designed to take full advantage of quantum measurement, unlike legacy communication methods that seek to optimize classical measurements. We discuss the theoretical bounds of the new protocols and demonstrate proof of principle experiments.

This Conference Presenatation, Non-Hermitian ring laser gyroscope with an enhanced Sagnac sensitivity, was recorded at Photonics West 2020 held in San Francisco, California, United States.

We describe our progress in the development of an atom based rotation sensor, which employs state-dependent trapping potentials to transport ultracold atoms along a closed path and perform Sagnac interferometry. Whilst guided atom interferometers are sought after to build miniaturized devices that overcome size restrictions from free-falling atoms, fully trapped interferometers also remove free-propagation along an atomic waveguide. This provides additional control of motion, e.g. removing wave-packet dispersion and enabling operation that remains independent of external acceleration. Our experimental scheme relies on radio-frequency and microwave-fields, which are partly generated via atom-chip technology, providing a step towards implementing a small, robust, and eventually portable atomic-gyroscope.

"A dual cold atom beam accelerometer/gyroscope" was recorded at Photonics West 2020 in San Francisco, California.

A time-orbiting potential trap can provide stable confinement for ultracold atoms. To lowest order the potential is harmonic, but it intrinsically includes anharominic contributions. These contributions are analyzed in terms of both the time-averaging mechanism and the inhomogeneity of the constituent fields. Methods to empirically characterize anharmonicity are developed and demonstrated.

Sensors based on optically-pumped magnetometers allow the development of room-temperature, wearable imaging systems for biomagnetism detection due to their excellent sensitivity, with applications such as Magnetoencephalography and Brain-Computer Interfaces. The small size of sensors based on microfabricated vapor cell technology promises high spatial resolution. The high sensitivity also opens up the possibility to use OPM sensors in other applications such as Very Low Frequency communications and ultrasensitive microwave detection.

Optical microresonators, in particular whispering-gallery microresonators, have proven to be especially useful as chemical sensors. In most applications, the sensing modality has been dispersive; an example is the frequency shift of resonator modes in response to a change in the ambient index of refraction. However, it has been shown that the response to dissipative interaction can be even more sensitive than the dispersive response. Dissipative sensing is most often carried out via a change in the mode linewidth owing to absorption in the analyte, but it has been demonstrated that the change in the throughput dip depth of a mode can provide better sensitivity than linewidth change. Dispersive sensing can be enhanced when the input to the microresonator consists of multiple fiber or waveguide modes. Here we show that multimode input can enhance dissipative sensing by an even greater factor. Having multimode input does not affect the linewidth response, but the enhancement factor for the dip-depth response can be quite large. We demonstrate that the multimode-input response relative to single-mode-input response using the same fiber or waveguide can be enhanced by more than three orders of magnitude. Furthermore, this enhancement is independent of the mode linewidth, or quality factor Q of the mode. The enhancement factor can be predicted by making only two measurements of dip depth in the absence of analyte: one with the two input modes in phase with each other, and one with them out of phase.

Wavelength references in the telecom spectrum have applications in communications and dimensional metrology. However, they typically consist of bulk optics and vapor cells. Photonic integration of these components may lead to low cost, portable devices. Here we demonstrate the incorporation of a photonic Rb spectrometer with an AlN microresonator frequency doubler. Light at 1560 nm is coupled onto a chip containing the AlN microresonator frequency doubler. The resulting 780 nm light is sent to the photonic Rb spectrometer, which consists of an apodized grating beam expander and microfabricated MEMS vapor cell. We perform Doppler broadened spectroscopy of the D2 line and demonstrate preliminary laser stabilization to these features.

We demonstrate dynamic beam steering by mechanically tuning a flexible 20° beam deflector metasurface made of PDMS. The deflective device is a 2D array consist of resonant sub-wavelength meta atoms operating at 1550 𝑛𝑚. The tuning is obtained by a designated stretching device able to strongly clamp and stretch a flexible metasurface allowing the monitoring and controlling of the applied external strain. Stretching a deflector changes the array geometry which consequently changes the aperture phase function. This results in a continuous change of the deflection angle thus creating a beam scanner. We show the steering range can reach 9.9° with a corresponding stretch ratio of 1.73. These results validates the potential of reconfigurable metasurfaces to yield dynamic beam steering which is an essential building block for both existing and future optical systems.

"Integrating atomic ensembles with photonics: new devices and instruments " was recorded at Photonics West 2020 in San Francisco, California.

Quantum photonics benefits from the scientific advances in the development of quantum light sources. To gain inside into the underlying physical processes of light generation, we use photon-number-resolving (PNR) transition edge sensors (TESs), which are able to directly access the photon-number distribution of nanophotonic devices. We present results on the transition from thermal to coherent emission of two different classes of microlasers: electrically driven bimodal quantum dot micropillar lasers and exciton polariton lasers. Furthermore, the photon number distribution of deterministically fabricated quantum dot based single-photon sources is investigated to explore the single-photon purity and indistinguishability of photons emitted by these sources.

Spatial-spectral holographic materials enable the development of microwave photonic devices that can perform a variety of demanding microwave signal processing functions, including spectrum analysis, signal correlation, time-difference of arrival measurements, and first pulse signal capture. This paper summarizes the recently published advances in the technology, which include demonstration systems with over 20 GHz of instantaneous bandwidth with sub-MHz resolution, over 60 dB of spur free dynamic range, and time-difference-of-arrival geolocation of emitters down to the sub-foot level.

Optical whispering-gallery mode (WGM) microresonators have proven their ability to enhance light-matter interaction and hence are widely used for sensing. In contrast to the traditional approach of using symmetric adiabatic tapers to couple light into the resonators, we use an asymmetric non-adiabatically tapered fiber to couple light from two fiber modes into a microresonator. Previously it was shown that dissipative sensing of an absorbing analyte can be more sensitive than dispersive sensing, and that dissipative sensing based on dip depth change can be more sensitive than dissipative sensing based on linewidth change. In this report, we demonstrate an enhancement in sensitivity by three orders of magnitude for dissipative sensing based on dip depth change. The enhancement factor is independent of the quality factor Q of the WGM and is determined solely by the values of the throughput power in the absence of analyte when the two fiber modes are in and out of phase at the point where they couple into the WGM.

"Self-homodyne detection of a narrow EIT signal using the superflash effect" was recorded at Photonics West 2020 in San Francisco, California.

Nonlocal light-mediated interactions between cold atoms coupled to the mode of an optical cavity present unique prospects for simulating the quantum dynamics of strongly-interacting many-body systems. In a recent publication, we introduced a tunable, nonlocal sparse spin network that can be engineered in near-term single-mode cavity QED platforms.¹ In this companion paper, we study this spin network in detail and pedagogically review its basic dynamical properties, providing theoretical details and calculations that expand on the statements made in our original publication. We show that the network exhibits two distinct notions of emergent geometry - linear and treelike - that can be accessed using a single tunable parameter. In either of these two extreme limits, we find a succinct description of the resulting dynamics in terms of two distinct metrics on the network, encoding a notion of either linear or treelike distance between spins. We also show that the network can be mapped in these two extreme limits onto exactly solvable models: a linear Heisenberg spin chain in one limit, and a Dyson hierarchical model in the other. These observations highlight the essential role played by the geometry of the interaction structure in determining a system's dynamics, and raise prospects for novel studies of nonlocal and highly chaotic quantum dynamics in near-term experiments.

Two seemingly different questions arise on the interface between quantum mechanics and gravity: How is a spin affected by a gravitational field? How is spacetime affected by a spin? With regards to the first, we propose opto-atomic interference experiments for testing the predictions of Dirac equation in curved spacetime. We then present a thought experiment [arXiv:1812.11450], which enables a quantum informational analysis of the second question. Within this framework, several known models are shown to contradict relativistic causality and hence they have to be modified or replaced. Our results suggest a general spin-spacetime censorship principle in nature.

Quantum non-demolition measurements play an important role in quantum theory and many of its applications. In theory they are the most fundamental quantum measurements, but in practice their realization can be chal- lenging due to realistic constraints. In optics for example, most measurements are destructive since photons get absorbed by the detector. While some simple single particle non-demolition measurements are routinely done in optical setups by using a second degree of freedom to encode the results at an intermediate stage, measurements of degenerate non-local observables involving multiple photons remain challenging, especially when these are done at intermediate measurement strengths. Here we present an optical setup for performing variable strength non-demolition measurements of non-local observables in a pre and postselected setting. At the heart of the setup is an apparatus that can be used to turn a strong (projective) measurement into an arbitrary strength measurement by using a quantum eraser. We present our initial calibration results for this apparatus.

"Quantum-enhanced x-ray detection" was recorded at Photonics West 2020 in San Francisco, California.

Despite being very influential on both foundations and applications of quantum mechanics, weak values are still somewhat controversial. Although there are some indications that weak values are physical properties of a single quantum system, the common way weak values are presented is statistical: it is commonly believed that for measuring weak values one has to perform many weak measurements over a large ensemble of pre- and postselected particles. Other debates surround the anomalous nature of weak value and even their quantumness. To address these issues, we present some preliminary data showing that anomalous weak values can be measured using just a single detection, i.e. with no statistics. In our experiment, a single click of a detector indicates the weak value as a single photon property, which moreover lies well beyond the range of eigenvelues of the measured operator. Importantly, the uncertainty with which the weak values is measured is smaller than the difference between the weak value and the closet eigenvalue. This is the first experimental realization of robust weak measurements.