This PDF file contains the front matter associated with SPIE Proceedings Volume 12912, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

There is an ever-growing requirement for compact atomic devices, such as optical atomic clocks, taking them from a labscale technology to a more robust solution. Optical atomic clocks have made significant advances over the last few decades and represent the pinnacle of precision measurement technology. However, many systems make use of large, expensive lasers which are power hungry and often frequency doubled to hit key wavelengths or alternatively rely on vibration sensitive external cavity diode lasers (ECDL). New approaches and technologies are required such as working with ion-based optical clocks where small, robust ion traps can be realized with the ion cooling controlled using a distributed feedback (DFB) laser. A promising platform for an optical atomic clock is the strontium ion system due to its convenient wavelengths and simple level structure. Of the required lasers only the 422 nm cooling laser is not wellserved by existing technology. The National Physical Laboratory (NPL) are developing a compact ion trap physics package and vibrationally insensitive cubic cavity that will form the basis of the portable optical clock. DFB lasers have been realized at 422 nm with high output powers and narrow linewidths. Modelling of the device epitaxy and grating structure show how these devices can be improved further. Overall, this will significantly reduce the SWaP compared to current systems.

We optimize the strength of the Four-Wave Mixing (FWM) in warm ⁸⁵Rb atoms in a double-ladder scheme to identify the optimal conditions for generating the bi-chromatic intensity squeezing. By optimizing the experimental parameters, such as laser frequency and intensity, cell temperature, beam geometry, etc., we achieved FWM gain up to 1.92 with only modest resonant optical losses, and observed some preliminary evidence of the noise correlations between the amplified probe and generated stokes optical field.

Propagation of quantum field interacting with single two-level or three-level atoms has been studied. Using the Gaussian quantum mode functions, we calculate evolution of the quantum state that includes atomic and field variable. We demonstrated the phase acquired by the single photon propagation that can be of great importance for long quantum communications. The results can be used for controlling quantum field propagation, and for design of optical elements such as a quantum prism and a quantum lens. The vacuum fields have been used to generate the strongly correlated quantum fields.

The unique properties of Rydberg atom-based sensors allow for intriguing applications. For example, Rydberg atom receivers allow for the detection and receiving of time-varying fields and communication signals without an antenna and front-end electronics.

An antenna is a key component of E-field signal pickup. However, an antenna has major limitations due to the metal-based probes, the geometry it carries, and the use of metal transmission lines; this can lead to perturbations or disturbance of the fields which limits the precision for field sensing. Rydberg atoms such as Cesium (Cs) or Rubidium (Rb) are utilized for Rydberg sensing. This can be utilized over a large range of frequencies from DC MHz and THz upto (>100 GHz) to measure amplitude, polarization, power, phase, and Angle-of-Arrival of RF Efield. Rydberg sensor detection scheme provides a multitude of applications, including far field characterization using near field or subwavelength imaging, strong RF E-field measurements, weak field detections, mapping of microwave circuitry, Binary Phase Shift Keying (BPSK), Quadrature Amplitude Modulation (QAM) and Quadrature Phase Shift Keying (QPSK) signals, metrology, and radars. Recently, practical RF E-field probes such as the RFP and movable probe have been prototyped for application specific RF sensing and measurement needs, further, antenna and waveguide embedded Rydberg sensors have also been developed. Few limitations in the Rydberg sensing scheme are due to lasers, EIT line-width, earth magnetic effects, photodiode circuit noise, and vapor cell in-homogeneity. The purpose of the review is to brief about the thematic work done across the Rydberg atom domain and its applications as RF E-field sensors. The findings of this review indicate the advantages and applications of Rydberg atom sensing as well as the gaps and uncertainties the scheme carries.

We discuss our recent experiment demonstrating superradiantly-coupled trapped atomic ensemble in an optical microtrap above a nanophotonic microring resonator. Here, efficient trap loading is achieved via a degenerate Raman-sideband cooling (dRSC) scheme using built-in spin-motion coupling in the microtrap and a single optical pumping beam sent from freespace. We show that these dRSC-cooled atoms display large cooperative coupling and enhanced superradiant decay into a whispering-gallery mode in the microring resonator.

We present an assortment of experiments exploring loading, control, and probing of laser-cooled caesium atoms inside a hollow-core photonic-bandgap fiber.

A key challenge in realizing practical quantum networks for long-distance quantum communication involves robust entanglement between quantum memory nodes connected via fiber optical infrastructure. I will talk about our recent work on utilizing silicon vacancy (SiV) centers in nanophotonic diamond cavities integrated with a telecommunication (telecom) metropolitan quantum network. Specifically, remote entanglement generation is generated by the cavity-enhanced interactions, and long-lived auxiliary memory qubits are used to provide second-long entanglement storage with integrated error detection. By interfacing with efficient bi-directional frequency conversion to telecommunication frequencies, we demonstrate entanglement of two nuclear spin memories through a 35 km long fiber deployed in the Boston urban area, an enabling step towards practical quantum repeaters and large-scale quantum network. I will also talk about an in-progress work on exploring blind and distributed quantum computation through this two-node quantum network.

Integrated narrow-linewidth lasers in the visible and near-IR are a critical component of next-generation atomic systems for quantum sensing, time keeping, and navigation. Technologies such as low frequency noise lasers that are tunable and referenced to an absolute frequency set by atomic transitions are required for sensing applications such as cold atom interferometers. While bulk-optic reference cavities can be used for laser noise reduction and stabilization, longer-term frequency drifts are mitigated with a secondary lock to an atomic reference using power-consuming bulk optic technologies such as an acousto-optic frequency shifter. Photonic integrated cavities based on ultra-low-loss silicon nitride (SiN) waveguides enable laser stabilization in a wafer-scale integration platform. Incorporating a secondary lock of these integrated cavities to an atomic reference is an attractive solution for compact chip-scale long term stable references. In this paper we demonstrate the use of a thermo-optic tunable, 118 million Q, 0.44 dB/m loss reference cavity for simultaneous laser frequency noise reduction and absolute frequency referencing to 780 nm rubidium spectroscopy. By tuning the integrated cavity resonance by a range >200 MHz using a thermal tuner with 20 MHz/mW efficiency at over 1 kHz tuning rate, we demonstrate long-term locking of the stabilized laser to rubidium saturation absorption spectroscopy. We achieve up to 4 orders magnitude frequency noise reduction, integral linewidth (beta-separation) reduction from 5 MHz (free-running) to 326 kHz (dual lock) and simultaneously a fractional frequency drift of 8.5e-12 at 1 second, two orders of magnitude improvement compared to locking to the cavity only. These results represent a compact and robust laser for photonic integrated atomic systems that can be extended to probing and locking to narrower linewidth transitions such as the rubidium two-photon at 778 nm and for laser frequency control sequences in cold atom experiments.

We present our next-generation micro-integrated diode laser modules. Based on the ECDL-MOPA concept, the modules allow independent tuning of emission frequency and output power. They currently operate at 689, 767, 780 and 794 nm, but can also be adapted for other wavelengths. The modules achieve mode-hop-free tuning even beyond the free spectral range of the laser. Additionally, we realized a Bragg grating based frequency reference using the same technology. It demonstrates high stability and a wide tuning range. Currently, we expand the application of the technology towards distribution modules that efficiently split and shift laser signals for seamless transmission.

We present experimental advances in comparative studies of optical parametric amplification (OPA) in microstructured fused silica solid-core fibers and hollow-core fibers filled with acetylene (C2H2). Both media exhibit third-order nonlinearity, enabling the OPA process in collinear configurations with a high spatial concentration of light power. In the former, non-resonant case, we investigated the parametric amplification via four-wave mixing (FWM) with a degenerate pump by picosecond laser pulses centered at a wavelength of 737 nm. This process ensured the generation of the correlated signal/idler photon pairs that could be parametrically amplified in a similar nonlinear micro-structured fiber. For the resonant acetylene-filled fibers, we present an experimental evaluation of the OPA gain in a degenerate collinear FWM at 1530 nm near the P9 acetylene absorption line. We specifically studied the transformation of amplitude modulation in the quasi-continuous W-scale input pump wave to output phase modulation and vice versa. Our research compares OPA efficiencies and the potential to generate squeezed and entangled light states in resonant and non- resonant fiber-based media.

We apply intensity squeezed light to thermoreflectivity sensing in electronic devices. We develop a scanning-based quantum imaging technique to study hot spots and heat dissipation in electronic devices with sub-shot-noise sensitivity.

Dark matter is the name that we give to the 84% of matter in the universe that interacts via gravity but negligibly with any of the other known forces. One compelling model for dark matter is the axion, as it simultaneously solves the existence of dark matter and the strong CP problem in QCD. The traditional axion experiment is called a haloscope, which consists of a strong magnetic field, a microwave cavity to resonantly enhance the converted photon, and a low-noise amplifier to enhance the inevitably tiny signal. This proceedings discusses the development of RAY (Rydberg atoms for Axions at Yale), a single photon detector that can be integrated into a standard haloscope. A major challenge of axion searches at higher masses is that the time required becomes increasingly long because of lower signal and increased quantum noise when using a standard haloscope. Eliminating this quantum noise can be accomplished with single photon counting using Potassium-39 Rydberg atoms. Using a beam of Rydberg atoms to detect the photons generated through the Primakoff effect would render the axion search at higher masses (> 50 µeV) tractable. We have done initial work towards this goal using electromagnetically-induced transparency. Depending on the haloscope cavity this scheme is attached to, we may be able to measure masses in the range of 20-30 GHz at KSVZ sensitivity in 5 years in a standard tunable cavity, or 10-50 GHz at KSVZ sensitivity in 5 years in a resonator with volume independent of frequency.

This paper describes the progress made in developing a resonant optical gyroscope fabricated with a silicon-nitride (SiN) waveguide using CMOS-compatible processes. The ultra-low loss of SiN waveguides allows ring resonators to be fabricated with small footprints (~1 cm²) while achieving higher Q-factors (~10⁸) than similar resonators made from other materials. For this reason, SiN is a very promising platform for developing a miniaturized optical gyroscope with tactical-grade specifications, which require an angular random walk (ARW) of 0.05 deg/h/√Hz and a drift of 10 deg/h. Our first-generation SiN ring gyro, reported in 2022, had an affective diameter of 11.6 mm, a perimeter of 37 mm and a finesses of 1270. When interrogated with a 10-kHz linewidth laser, it had a measured ARW of 1.3 deg/h/√Hz and a drift of 4000 deg/h, and its dominant noise was backscattering noise. In this paper, we present a second-generation of SiN gyro with a longer ring waveguide and a lower finesse to reduce the backscattering noise. This multi-turn ring has the shape of a spiral with 33 turns and an average diameter of 12.2 mm, a waveguide length of 1.2 m, and a finesse of 30. The laser linewidth was also decreased to 100 Hz to reduce the dominant noise sources, including laser frequency noise and backscattering noise. The reported ARW of this new gyro is 0.28 deg/√h, which is a factor of 4.5 lower than that of the first-generation gyro. After splicing several of the components together to reduce instabilities due to mechanical connectors, the drift was reduced to 500 deg/h. This work provides an incentive to move towards integrating more components on the chip. With continued research, this technology could soon meet the performance requirements of a wide variety of navigation-related applications.

Quantum research at Montana State University is focused on implementing a hybrid optical network comprised of both fiber-optic and free-space point-to-point optical links for interconnecting quantum and classical digital hardware. This presentation summarizes the ongoing effort, which, over several phases, would expand to integrate distributed information processing platforms utilizing quantum systems of different physical types.

Distributed optical fiber sensing based on backward Brillouin scattering has been widely developed during the last decade. Making use of stimulated Brillouin scattering, Brillouin optical time-domain analysis (BOTDA) is considered one of the most performing distributed sensing techniques existing today for long range and quasi-static monitoring of variables like temperature and strain. This has enabled the monitoring of assets over tens of kilometers (even over more than 100 km with advanced configurations and techniques) with typical spatial resolutions of a few meters (typically below 5 m). This paper reviews the fundamentals of BOTDA sensing, its main limitations (essentially imposed by nonlinear effects in the sensing fiber), and advanced methods to enhance the sensing performance. While the performance is ultimately determined by the signal-to-noise ratio (SNR) of the measurements, some of the most relevant methods for SNR enhancement are here reviewed. In particular, and based on recent developments, optimized pulse coding and hybrid optical amplification approaches, specially designed for ultra-long-range BOTDA sensing, are discussed.

Submarine optical fiber communications are nowadays the most important infrastructure of international communications, carrying over 99% of the intercontinental data traffic. These critical infrastructures for communications also have a strong potential for geophysical monitoring in the bottom of the oceans. Here, we review our work on oceanographic monitoring using Distributed Acoustic Sensing (DAS) over submarine fiber cables. We show that these measurements can be used to obtain information of ocean dynamics, including accurate observations of surface waves, currents, and tides, and all the associated nonlinear phenomena driving water mixing, which have strong impact in climate change estimations. We show that internal waves, a large-scale phenomenon generated by the interaction of barotropic tides with bathymetric changes in the sea-bottom, can be very accurately observed using chirped-pulse DAS sensing technology over these cables.

We theoretically study a new approach to matter-wave interferometer that utilizes ultracold atoms confined in an optical lattice. Through patterned phase modulation of the lattice, the matter wave is split, mirrored, and recombined, resulting in sensitivity to an applied inertial signal as was recently demonstrated experimentally in [LeDesma et al., arXiv:2305.17603 (2023)]. Compared to free-space equivalents, this “shaken lattice” interferometer has the advantage that atoms remain always supported against external forces and perturbations and that by applying different shaking sequences the device could be in principle made sensitive to different signals (inertial, gravitational, etc...) on the fly. In this work, we give a brief overview of this sensing platform and its working principles.

Atom interferometers that operate in the spatial domain through continuous measurement of an atomic beam provide benefits in the elimination of sensor dead time and reduced sensitivity to certain noise sources. Further improving its operation, time-domain control of a spatial-domain interferometer can provide necessary methods of error suppression and dynamic range improvement. We model numerically and experimentally demonstrate methods of time-domain control in a 3D-cooled atomic beam interferometer. We demonstrate suppression of magnetic-field-induced phase noise through rapid reversal of the direction of inertial sensitivity at a rate faster than the inverse interrogation time of the interferometer.

Precision measurements of gravitational acceleration g have far reaching applications in navigation and sensing as well as for tests of general relativity. Grating-echo atom interferometers (AIs) utilize simple setups and distinctive excitation schemes that involve a single excitation laser, and do not require velocity selection. They have demonstrated measurements of gravity precise to 75 parts per billion (ppb) by dropping laser-cooled atomic samples through ~ 1 cm. Here we describe progress toward realizing a cold atom gravimeter using an echo AI designed for drop heights of ~30 cm. The experimental technique involves illuminating the falling sample of laser-cooled rubidium atoms with two standing wave (sw) pulses separated by time t = T. The sw pulses are composed of two traveling-wave components, each having a wave vector of magnitude k = 2π/λ. Momentum state interference produces one-dimensional density gratings with a period λ/2 immediately after each excitation pulse. These gratings dephase due to the velocity distribution of the sample along the sw axis. The AI uses an echo technique to cancel the effect of velocity dephasing and observe a rephased density grating in the vicinity of the echo time τ = 2Τ. The grating contrast and phase are measured by coherently backscattering a traveling wave readout pulse from the sample. The grating phase, measured with respect to a vibrationally stabilized inertial reference frame, scales as 2kgΤ². A drawback of echo AIs is the signal-to-noise ratio, which is limited by the contrast of the grating and systematic effects due the refractive index of the sample. Here, we review improvements to the experimental design and investigate methods of improving the signal-to-noise ratio by optimizing the atom-field coupling. We describe progress toward realizing our goals of increasing the grating contrast and the backscattered signal. The improved contrast is expected to allow the experiment to be carried out at a lower density to reduce corrections due to the refractive index. We discuss a variety of excitation schemes for achieving a target precision of a few ppb.

Quantum interferometers represent a powerful class of devices that exploit the principles of quantum mechanics to achieve highly sensitive measurements and precise detection capabilities. In classical interferometry, light waves or matter waves combine and interfere, resulting in constructive or destructive interference patterns that encode information about the system being studied. In the quantum realm, interferometers leverage the unique properties of quantum states, such as superposition and entanglement, to surpass the sensitivity limits imposed by classical physics. We developed a new class of quantum interferometers, namely, the temporal SU(1,1) interferometer. Here, we present the code for numerically comparing classical SU(2) interferometer, regular quantum SU(1,1) interferometer, and our temporal SU(1,1) interferometer.

Optical frequency combs based on quantum cascade lasers (QCLs) are promising broadband light sources in the mid-infrared and terahertz spectral regions. Their bandwidths are limited by two main parameters: dispersion, which originates from variation in the group velocity, and diffusion, which originates from variation in the gain. While dispersion has been extensively engineered, diffusion shaping has been elusive. We show that the addition of carefully engineered diffusive loss can enhance the bandwidth of QCL combs, demonstrating theoretically and experimentally that adding resonant loss to the cavity of a terahertz QCL can counteract the diffusive effect of the gain medium and allow broader bandwidth combs to form. Our results give a new degree of freedom for the creation of active chip-scale combs and can be applied to a wide array of cavity geometries and comb systems.

Single-photon avalanche detectors (SPADs) are used ubiquitously in optical and quantum science, but they are not photon-number-resolving detectors. Despite this, in this work we present preliminary results that show that a single SPAD can still be used to perform number-state reconstruction. Through detector characterization and use of maximum-likelihood analysis, we perform number-state reconstruction with a single SPAD and obtain good agreement with independently measured distributions for both Poissonian and anti-bunched light. Our method works well for photon rates up to roughly one input photon per dead time as well as pulse lengths and correlation times of at least a few dead times, fitting many of today’s quantum optics experiments.

Here, we demonstrate local writing and erasing of selected light-emitting defects using fs laser pulses in combination with hydrogen-based defect activation and passivation. By selecting forming gas (N2/H2) during thermal annealing of carbon-implanted silicon, we form Ci centers while passivating the more common G-centers. The Ci center is a telecom S-band emitter with very promising spin properties that consists of a single interstitial carbon atom in the silicon lattice. Density functional theory calculations show that the Ci center brightness is enhanced by several orders of magnitude in the presence of hydrogen. Fs-laser pulses locally affect the passivation or activation of quantum emitters with hydrogen and enable programmable quantum emitter formation in a qubit-by-design paradigm.

The SwissSPAD2/3 camera family is based on quarter megapixel single-photon avalanche diode (SPAD) time gated imagers. The 16.38-µm low-noise pixels feature a single-bit memory and built-in all-solid-state nanosecond time gating without the need for external image intensifiers. Microlenses have also been made available to increase the overall system sensitivity, including for high NA applications. SwissSPAD2/3 are coupled to FPGA platforms enabling a virtually noiseless streaming at up to 100 kpfs. A 1-bit accumulation of frames to reconfigurable number of bits was programmed on the FPGA for applications such as fluorescence lifetime imaging microscopy (FLIM). In other applications, a burst-mode read-out of 130,000 binary frames to a DDD3 memory of one sensor half was programmed on one FPGA for applications requiring full bitplanes. These initial configurations were extended to dual-FPGA systems capable of streaming data at near 100 kfps in continuous mode for long acquisition times. In such configuration one FPGA streams data from one sensor half to the other FPGA, which then sends the combined data stream to a host PC over PCIe at up to 3 GB/s. The eight PCIe lanes require careful design with differential routing and controlled impedance and the whole development presented significant hardware and firmware challenges. We also achieved full synchronization of two SwissSPAD2 camera systems over PCIe and characterized the pixel-to-pixel exposure timing alignment error to better than 150 ps with a time gate of 10 ns. The resulting platforms are unique enablers for quantum imaging applications, such as plenoptic maging, quantum LIDAR or quanta burst photography.

Backward Brillouin scattering in whispering-gallery-mode micro-resonators offers an exciting avenue to pursue both classical and quantum optomechanics applications. Our team—the Quantum Measurement Lab—together with our collaborators, are currently exploring and utilizing the favourable properties this platform affords for non-Gaussian motional state preparation of acoustic fields. In particular, the high acoustic frequencies, acoustic mode selectivity, and low optical absorption provide a promising route to overcome current hindrances within optomechanics. Some of our key recent results in this direction include: the observation of Brillouin optomechanical strong coupling, single-phonon addition and subtraction to a thermal state of the acoustic field, advancing the state-of-the-art of mechanical state tomography to observe the non-Gaussian states generated by single- and multi-phonon subtraction, studying the second-order coherence across the Brillouin lasing threshold, and enhancing sideband cooling via zero-photon detection. This talk will cover these results, what they enable, and the broader direction of our lab.

Quantum optomechanics has led to advances in quantum sensing, optical manipulation of mechanical systems, and macroscopic quantum physics. However, previous studies have typically focused on dispersive optomechanical coupling, which modifies the phase of the light field. Here, we discuss recent advances in “imaging-based” quantum optomechanics – where information about the mechanical resonator’s motion is imprinted onto the spatial mode of the optical field, akin to how information encoded in an image. Additionally, we find radiation pressure backaction, a phenomenon not usually discussed in imaging studies, comes from spatially uncorrelated fluctuations of the optical field. First, we examine a simple thought experiment in which the displacement of a membrane resonator can be measured by extracting the amplitude of specific spatial modes. Torsion modes are naturally measured with this coupling and are interesting for applications such as precision torque sensing, tests of gravity, and measurements of angular displacement at and beyond the standard quantum limit. As an experimental demonstration, we measure the angular displacement of the torsion mode of a Si₃N₄ nanoribbon near the quantum imprecision limit using both an optical lever and a spatial mode demultiplexer. Finally, we discuss the potential for future imaging-based quantum optomechanics experiments, including observing pondermotive squeezing of different spatial modes and quantum back-action evasion in angular displacement measurements.

Endoscopic imaging systems based upon bundles of optical fibers are commonplace across medical and industrial applications. However, in principle even just one of these optical fibers transports enough spatial modes to transmit an entire image, the problem being that modal dispersion scrambles the output such that any input image becomes unrecognizable. Many groups across the world are trying to tackle this problem with various approaches. Our approach uses the measure transmission-matrix of the fiber to calculate the required sequence of patterned input beams to create a raster scanned spot at the output, to illuminate the scene. The corresponding sequence of backscattered light is recorded, again through a fiber, and the resulting image reconstructed. This approach is limited by the large size of the transmission matrix which potentially needs to be updated whenever the fiber is moved, typically taking 10 minutes to hours. Here we report a measurement and computation approach that produce a scanning spot in the far field of a needle mounted optical fiber in less than one minute. This rapid approach allows us to recalibrate the system for different fiber configurations and switch between them to account for fiber movement, without interrupting the live image feed. We apply this approach to minimally invasive imaging in low photon-number configurations, showing video rate acquisition at ranges of a meter, or more, from the distal end of the fiber.

The secure transmission of an image can be accomplished by encoding the image information, securely communicating this information, and subsequently reconstructing the image. As an alternative, here we show how the image itself can be directly transmitted while ensuring that the presence of any eavesdropper is revealed in a way akin to quantum key distribution. We achieve this transmission using a photon-pair source with the deliberate addition of a thermal light source as background noise. One photon of the pair illuminates the object, which is masked from an eavesdropper by adding indistinguishable thermal photons, the other photon of the pair acts as a time reference from which the intended recipient can preferentially detect the image carrying photons. These reference photons are themselves made sensitive to the presence of an eavesdropper by traditional polarization-based QKD encoding. Interestingly, the security encoding is performed in the two-dimensional polarization-basis, but the image information is encoded in a much higher-dimensional, hence information-rich, pixel basis. In our example implementation, our images have more than 100 independent pixels. Beyond the secure transmission of images, our approach to the distribution of secure high-dimensional information may create new high-bandwidth approaches to traditional QKD.

After long-term operation and use of the dam, affected by various external and internal factors, the surface of the dam will produce deformation or even cracks, if not treated in time, it will greatly increase the safety risks of the dam operation. According to previous research, quantum infrared detection can obtain more clear weak information. We use quantum infrared detector to conduct imaging detection on the surface of the dam body. Compared with traditional detection methods, quantum infrared detection has the characteristics of high resolution, high signal-to-noise ratio and high sensitivity, which can improve the detection accuracy and obtain clearer image information. Through post-processing of imaging information, cracks or other deformation and failure information are marked, and risk warning is issued for subsequent engineering construction treatment.

Quantum Ghost Imaging (QGI) is a scheme using entangled pairs of photons (signal and idler) in order to perform imaging with both single photons and with only a single-element detector in the spectrum of interest. It utilises the temporal coincidence of the photons to identify associated pairs, while their spatial correlation allows to obtain image information from of the idler photon from the measurement of the signal photon. It is especially useful when using nondegenerate photon pairs, allowing to keep the signal photon in the silicon detection window, while the interacting wavelength can be freely chosen.However, current schemes are limited, as they rely on time-gating and heralding. Recent advances in single photon avalanche diodes (SPADs) allow the design of new single photon cameras, which can be outfitted with dedicated in-pixel timing circuitry. This allows to register single photons in both time and space. These detectors allowed us to design a new scheme for QGI, in which the coincidence is evaluated after the measurement. It also allows us to perform depth-resolved 3D imaging based on the time-of-flight of photons, first results of which are presented here.

Trapping and manipulating ultracold atoms through the use of atom chips offers the ability to engineer complex electromagnetic field geometries in a compact form factor. One of the primary limitations hindering their use is trap potential roughness which arises as a result of defects in the atom chip wires when atoms are brought close to the chip. This roughness can play a limiting role in atom interferometry and strong 1D confinement experiments. We present an initial experimental demonstration of atom chip potential roughness suppression using radio-frequency (RF) AC Zeeman (ACZ) potentials on an atom chip. Using ∼20 MHz RF magnetic near-fields from the chip to target intra-manifold transitions in the ⁸⁷Rb ground state, we trap atoms in a spindependent ACZ potential. We compare the axial trapping potential for atoms in comparable 2-wire DC and AC Zeeman traps and show evidence of roughness suppression in the AC trap.

In the realm of precision metrology, optical frequency combs, and lasers support the world’s most precise atomic clocks. Optical frequency combs, specialized lasers that serve as optical rulers for light, play an essential role across various applications. At TOPTICA Photonics Inc., a leading authority in laser technology for quantum applications, we integrate various laser sources into difference frequency combs (DFCs), enabling applications that span from high -precision spectroscopy to Rydberg sensing and atomic clocks. In this presentation, I will dive into our innovative work and demonstrate how this integration has opened new possibilities in the field of quantum technology and sensing.

Quantum technologies containing key GaN laser components will enable a new generation of precision sensors, optical atomic clocks and secure communication systems for many applications such as next generation navigation, gravity mapping and timing since the AlGaInN material system allows for laser diodes to be fabricated over a wide range of wavelengths from the U.V. to the visible. We report our latest results on a range of AlGaInN diode-lasers targeted to meet the linewidth, wavelength and power requirements suitable for quantum sensors such as optical clocks and cold-atom interferometry systems. This includes the [5s²S_1/2-5p²P_1/2] cooling transition in strontium⁺ ion optical clocks at 422 nm, the [5s₂¹S₀-5p¹P₁] cooling transition in neutral strontium clocks at 461 nm and the [5s² s_1/2 – 6p²P_3/2] transition in rubidium at 420 nm. Several approaches are taken to achieve the required linewidth, wavelength and power, including an extended cavity laser diode (ECLD) system and an on-chip grating, distributed feedback (DFB) GaN laser diode.

Zero-field optically pumped magnetometers (OPMs) have emerged as an important technology in the realm of biomagnetic research, providing extremely small magnetic field detection capabilities, femtotesla-level, contained in a non-cryogenic compact form factor. Often, compact zero-field OPMs extract single or two-axis magnetic information, typically with a sensing bandwidth of < 100 Hz. The resolution of multiple axes of magnetic field is particularly important for accurate representation of radial components of biomagnetic fields. However, the presence of multi-axis static magnetic fields across the OPM causes measurement errors that degrade signal resolution. Here, we utilise our compact caesium single beam zero-field OPM to address these limitations. We magnetically modulated along both transverse axes of the sensor, at unique frequencies, to extract all axes static-field information. Active feedback can be realised through a lock-in detection scheme at f_Mod,x/y for the x- and y-axes, and at 2f_Mod,x for the beam axis, z. Operation in this scheme allows for the extraction of three-axis magnetic field information from only a single beam and highlights the importance of active feedback in high-sensitivity biomagnetic applications. The portable sensor also demonstrates a bandwidth with a -3 dB point at ≃ 1600 Hz. The combination of high bandwidth and the capability to extract three-axis magnetic fields opens up exciting prospects for resolving high-frequency biomagnetic signals.

Exploiting the precession of a levitated magnetic particle in ultra-high vacuum, it is shown that ac magnetic fields smaller than a picotesla can be detected. It is also argued that this new AC magnetometer will have a large dynamic range of more than a millitesla and can be continuously tuned over several GHz. Such a magnetometer can be used as a receiver for electromagnetic waves.

It is almost exactly 100 years since De-Broglie made public his outrageous hypothesis regarding Wave-Particle Duality (WPD), where the latter plays a key role in interferometry. In parallel, the Stern-Gerlach (SG) effect, observed also a century ago, has become a paradigm of quantum mechanics. I will describe the realization of a half- and full-loop SG interferometer for single atoms, and show how WPD, or complementarity, manifests itself. I will then use the acquired understanding to show how this setup may be used to realize an interferometer for macroscopic objects doped with a single spin, namely, to show that even rocks may reveal themselves as waves. I emphasize decoherence channels which are unique to macroscopic objects such as those relating to phonons and rotation. These must be addressed in such a challenging experiment. The realization of such an experiment could open the door to a new era of fundamental probes, including the realization of previously inaccessible tests of the foundations of quantum theory and the interface of quantum mechanics and gravity, including the probing of exotic theories such as the Diosi-Penrose gravitationally induced collapse. Time permitting, and as an anecdote noting also De-Broglie's less popular assertion, namely, that the standard description of QM is lacking, I will also present our recent work on Bohmian mechanics, which is an extension of De-Broglie's ideas concerning the pilot wave.

With this talk, I will first illustrate the implementation of our machine-learning (ML) enhanced quantum state tomography (QST) for continuous variables, through the experimentally measured data generated from squeezed vacuum states, as an example of quantum machine learning. At the same time, as a collaborator for LIGO-VirgoKAGRA (LVK) gravitational wave network and Einstein Telescope, our plan to inject this squeezed vacuum field into the advanced gravitational wave detectors (GWD) will be introduced. Finally, I will report our recent progress in applying such a ML-QST as a crucial diagnostic toolbox for applications with squeezed states, from Wigner currents, optical cat state generation, and Bayesian estimation for GWD.

Quantum eraser is known as one of the mysterious quantum features, where the action of the delayed choice retrospectively determines the photon’s nature. Over the last decades, various photon characteristics have been used to demonstrate the quantum eraser, especially for violating the cause-effect relation. In this manuscript, recent observations of the quantum eraser based on a Mach-Zehnder interferometer (MZI) using an attenuated laser are speculated as the origin of the quantum mystery, where the delayed choice is conducted for the MZI output photons via polarization projection measurements. For this, the wave nature of a photon is taken for the present pure coherence optics-based analysis. By the definition of group velocity-based information, the violation of the cause-effect relation in the quantum eraser should be related to the ensemble coherence of measured photons, but not to individual photon’s coherence, where the ensemble coherence is dramatically decreased as the spectral bandwidth of the photon ensemble increases.

Mid-infrared liquid sensing on the chip-scale is a newly emerging field of research, especially with respect to fully monolithic integrated devices. They enable addressing applications scenarios in chemical reaction monitoring and real-time sensing, which were so far prevented by the existing much more bulky technology (e.g. FTIR-based systems). In this work we present a quantum cascade laser (QCL), QC detector (QCD) and novel type of midinfrared plasmonic waveguide that are integrated into one substrate and which we use in real-time protein sensing and residual water in solvent measurements. Furthermore, we present how this rather simple linear geometry can be further improved by implementing other (more spectrally broadband) materials such as Germanium and integrating surface-passivation and -functionalization for improving sensing capabilities. In the last part we will demonstrate two pathways for introducing plasmonic mode-guiding along the chip-surface, which is the key to realizing much more complex geometries including integrating more active and passive elements into one PIC.

We report on the work about photonic quantum sensing, in particular, the demonstration of quantum infrared spectroscopy using a nonlinear quantum interference of photon-pair generation processes with the ultra-broadband region.

Quantum sensing has now become one of the most advanced, rapidly growing areas of research, which permits precise scale of measurement. We have experimentally demonstrated a novel method of probing quantum phenomena of lightmatter interaction especially the fluorescence by utilizing matured fiber Bragg grating (FBG) technology. In response to the incident excitation, quantum electrodynamic response of fluorophores coated on the FBG causes a shift in the Bragg wavelength. The Bragg wavelength shift is dependent on excitation wavelength and intensity, where the increased lightmatter interaction leads to a higher shift in the Bragg wavelength. Our sensor could probe the fluorescence at microscopic scale showing Bragg wavelength shift of 10 pm per 400 μW of incident excitation power. Capturing fluorescence at this small scale with microwatt of excitation power can be potentially helpful for biosensing applications where the photodamage limit of excitation power is crucial for the dynamic measurement of biological specimens.