This PDF file contains the front matter associated with SPIE Proceedings Volume 11844, including the Title Page, Copyright information, and Table of Contents.

We report on the realization of a three-node entanglement-based quantum network. We combine remote quantum nodes based on diamond communication qubits into a scalable phase-stabilized architecture, supplemented with a robust memory qubit and local quantum logic. Also, we achieve real-time communication and feed-forward gate operations across the network. We demonstrate two key quantum network protocols without post-selection: the distribution of genuine multipartite entangled states across the three nodes and entanglement swapping through an intermediary node. Finally, we will discuss the most recent experiments using the network as a platform for exploring, testing, and developing multi-node quantum network protocols and a quantum network control stack.

Distributing entanglement over long distances is a core challenge of Quantum Communications. Quantum repeaters, hosting entanglement swapping protocols, have been proposed as a viable solution, though they have yet to be realized commercially. Basic research groups have demonstrated memory-assisted entanglement swapping using NV diamond centers or cold atomic vapor memories. Qunnect is building a product suite to support entanglement swapping based on warm atomic vapor. While the engineering of these systems is challenging, the elimination of extreme cooling and vacuum support provides numerous advantages for network scalability. I will discuss our progress to date and upcoming fiber testbed demonstrations.

Quantum technologies have the potential to improve in an unprecedented way the security and efficiency of communications in network infrastructures. We discuss the current landscape in quantum communication and cryptography, and focus in particular on recent photonic implementations, using encoding in discrete or continuous properties of light, of central quantum network protocols, enabling secret key distribution, verification of multiparty entanglement and transactions of quantum money, with security guarantees impossible to achieve with only classical resources. We also describe current challenges in this field and our efforts towards the miniaturization of the developed photonic systems, their integration into telecommunication network infrastructures, including with satellite links, as well as the practical demonstration of novel protocols featuring a quantum advantage for a wide range of tasks. These advances enrich the resources and applications of the emerging quantum networks that will play a central role in the context of future global-scale quantum-safe communications.

Semiconductor quantum dots have emerged as an excellent platform for quantum light generation, providing quantum pure single photon wavepackets with unparalleled efficiency. These devices have started to accelerate the development of optical quantum technologies – notably in the field of optical quantum computing. In this talk, I will discuss our progresses toward the deterministic source, the use of these sources for the generation of linear cluster states and the generation of quantum light state using spontaneous emission as a resource for entanglement in the photon number basis.

Photonic quantum technologies are a promising platform for applications ranging from long-distance secure communications to the simulation of complex phenomena. Among the different material platforms direct bandgap semiconductors offer a wide range of functionalities opening promising perspectives for the implementation of future quantum technologies. In this talk, I review our progress on the generation and manipulation of quantum states of light in nonlinear AlGaAs chips and their use in quantum networks.

Quantum networks scale the advantages of quantum communication protocols to more than just two distant users. Here we present a fully connected quantum network architecture in which a single entangled photon source distributes quantum states to a multitude of users [1] and our work scaling the network to a complete end to end metropolitan quantum network with 8 users [2]. Our network architecture optimises the resources required by each user without sacrificing security or functionality. We established several long-distance loopback connections and demonstrated extended stable operation with high secure key rates. Unlike previous attempts at multi-user networks, which have been based on active components, and thus limited to some duty cycle, our implementation is fully passive. Further, we present our efforts towards coexistence of 100 Gbps classical communication and all quantum channels used in the network over the same deployed optical fibres. Most importantly, we have used our network to implement a wide variety of protocols. These protocols overcome major limitations of quantum networks and each of them represent the first implementation of that class of protocols on a large scale network.

PsiQuantum’s goal is to build the first useful quantum computer. Our approach is based on a scalable fault tolerant architecture that can be implemented using integrated photonics circuits connected by low loss optical fiber. We are developing the technology required for the photonics circuits in a commercial silicon foundry. We will discuss the fusion-based quantum computing architecture and highlight some of the technologies that have been developed by the company.

Honeywell has commercialized multiple high performance quantum computing systems and continues to accelerate the path to value with rapid system scaling. This talk presents an overview of integrated photonics for scaling beam delivery to trapped ion quantum computing systems, reviewing main benefits, challenges, work to date, and future directions.

Loss-induced errors are inevitable in long-distance information transfer and lead to quantum state degradation in quantum communication. It is possible to reduce the effect of loss on a quantum state using probabilistic quantum amplification which, however, destroys the input state in cases when it fails. Instead, what we present here is a realization of an error-corrected quantum channel, where we prepare a purified copy of entanglement. Upon success over this operation, it can be used to teleport the state over the so-improved channel. We test our channel by using it to transmit entanglement through a large amount of loss and demonstrate improved performance over direct transmission, without relying on post-selection.

Ultracold neutral atoms have emerged as a promising platform for scalable quantum computation. Universal single-qubit control requires high quality state preparation, spatially resolved manipulation, and projective readout of each qubit. For state preparation and readout, neutral atom platforms can apply techniques commonly used in quantum gas microscopes and single atom trapping machines. Furthermore, the ability to isolate the internal spin states of individual neutral atoms from both external fields and neighboring atoms allows for seconds-scale coherence times. Here, we will present progress on the coherent, site-resolved control of an array of atomic qubits comprised of neutral strontium atoms.

The promise of quantum computers is that certain computational tasks might be executed exponentially faster on a quantum processor than on a classical processor. We have used a programmable superconducting processor to create quantum states on 53 qubits, corresponding to a "parallel computation" of 10 million trillion states. For a simple algorithm, our Sycamore processor takes about 200 seconds to run a quantum circuit a million times - the equivalent task for a state-of-the-art classical supercomputer would take approximately 10,000 years. This dramatic increase in speed compared to all known classical algorithms is an experimental realization of quantum supremacy, heralding a much-anticipated computing paradigm.

Achieving scalability is one of the most pressing tasks to realize practical quantum computer. In this regard, continuous-variable optical systems have shown many promising progresses such as generation of enormous cluster states, resources for measurement-based quantum computation, using minimal resources. In this talk, I will explain the concepts of continuous-variable quantum computation with the focuses on the quantum computation based on quantum teleportation. It turns out that the quantum teleportation protocol, a basic protocol that is equivalent to the identity operation, contains many essences of the quantum computation. I will discuss the recent experimental progresses with the main focuses on the time-domain multiplexing approach and how these progresses are paving the path toward large-scale fault-tolerant universal quantum computation.

Photonics is an effective platform for engineering quantum states of many photons that can be harnessed for applications in information processing tasks, ranging from secure communications to enhanced sensors to efficient simulation of physical or other systems. I will discuss recent developments and some challenges to achieving this promise. Building and measuring multi-photon quantum states suitable for these applications demands a means for them to interfere and for detection at the level of individual photons. Photonic integrated circuits are well suited to these tasks at a scale that is not possible by other means. Advances in the design and utilization of circuits and detectors enable quantum advantage, and indeed provide new opportunities for classical optical systems.

Quantum sensors have been named a top 10 emerging technology by the World Economic Forum in 2020. This is mainly driven by their imminent application potential and the ability to open up qualitatively new sensing areas, such as sensing into the ground, or seeing the brain at work. We are now just one step away from commercial breakthrough applications in civil engineering and clinical trials. With this success, the next step will be to develop integrated photonics components to open up mass markets in water, navigation and gaming. I will provide an overview of the working principle of an atomic quantum sensor and lay out the parameter needs for photonic integration.

The use of quantum properties of light has paved new avenues in the field of imaging. Quantum illumination and ghost-imaging protocols have shown exciting promise in addressing the issues inherent in classical imaging, such as background noise and a high level of required illumination. Moreover, quantum metrological schemes analyzing the modal content of light would address the resolution limits of direct imaging, promising enhancement beyond the Rayleigh limit. Augmenting these novel techniques with machine learning, particularly deep learning architectures such as Convolutional Neural Networks (CNNs), one strives to see significant improvements in image reconstruction and object identification in quantum imaging protocols. In my talk, I present recent progress and development on reconstructing the image of different objects with quantum sources, employing a high degree of spatial correlation between photon pairs and autoencoder deep learning architecture.

Single-photon detection when used in picosecond resolution time-correlated mode is now a candidate technology for a number of depth imaging applications in the visible, near-infrared and short-wave infrared regions. This approach has been used in a range of challenging sensing scenarios including imaging though highly scattering underwater conditions, free-space imaging through obscurants such as smoke or fog, and depth imaging of complex multiple surface scenes. I will review recent developments in this field and describe recent experiments and computational imaging approaches that highlight the long-term potential of this work.

We are developing technologies based on nitrogen-vacancy centres (NVCs) in diamond for both quantum computing and magnetometry. Here I will focus on the latter: our fibre-coupled NVC-ensemble magnetometer has an unshielded sensitivity of 100 pT/√Hz in the frequency range of 10 150 Hz at room temperature. Fibre coupling means the sensor can be conveniently brought within 2 mm of the object under study. We aim to detect the magnetic fields created by the heart for medical diagnostics: magnetocardiography. By modifying our magnetometer we have imaged damage in steel which could be useful for finding corrosion.

Atom-based sensors have generated a lot of attention in the past several years because of their many possible advantages over other conventional technologies. NIST and other groups have made great progress in the development of Rydberg atom-based radio-frequency (RF) E-field sensors/receivers. These sensors have the capability of measuring amplitude, polarization, and phase of the RF field. As such, various applications are beginning to emerge: SI-traceable E-field probes, power-sensors, voltage standards, receivers for communication signals (AM/FM modulated and digital phase modulation signals), and even recording musical instruments. In fact, this new atom-based technology has allowed for interesting and unforeseen applications. In this talk, I will summarize this work and discuss various applications.

The spatial degree of freedom of quantum states of light can offer new possibilities for imaging and sensing applications, such as enhanced optical resolution, noiseless image amplification, and enhanced beam positioning. In order to take full advantage of the spatial degree of freedom for practical applications, it is necessary to control the quantum correlations between the spatial modes that make up a quantum state of light. In this talk, I will present our study of the spatial quantum correlations in bright entangled twin beams and show that it is possible to obtain full control over their distribution.

Silicon integrated photonics has grown in the last decade to fill the market with classical devices that offer tremendous SWaP benefits over conventional bulk optics or fiber components. For quantum systems the material and device losses present were still too large to allow for larger scaling of systems at the single and low photon level. Over the last couple years, both industry and government laboratories have worked closely with commercial foundries to drop the optical losses to levels that now can scale quantum systems. This research area, the results, and the next steps forward for integrating other materials and qubit systems into the platform will be the subject of my talk.

In this talk, I will describe a number of open source photonic simulation packages developed in our group for modeling large scale classical and quantum photonic circuits. These include Simphony, a high speed photonic circuit simulator; SiPANN, a photonic simulation package based on neural networks; and EMEPy, an eigenmode expansion package. Direct integration with quantum photonic circuit solvers, such as Strawberry Fields, allows for quantum photonic circuit simulation that is hardware-aware and device-specific.

Efficient and low-noise distribution of photons is essential for quantum technology networks. Current strategies focus on low-loss distribution channels or the use of quantum repeaters. I will present a surprising alternate strategy: transporting photons stored in a quantum hard drive. Recent results demonstrate the potential for such a device in rare-earth ion crystals with coherence lifetimes greater than 6 hours. With a sufficiently high photonic storage capacity, quantum hard drives will enable new regimes of science, such as optical astronomy below 1 µas resolution using very long baseline interferometry.

A rising photonic platform, aluminum gallium arsenide on insulator (AlGaAsOI), has led to remarkable breakthroughs in integrated photonics over last few years. In this talk, we will introduce the key progress on this platform, including development of low loss AlGaAsOI waveguide, many record-breaking efficient nonlinear processes enabled by ultra-high Q resonators, as well as the recent demonstration of the brightest entangled photon pair generation on chip. We will discuss the potential AlGaAsOI holds for realizing high performance quantum photonics devices and fully integrated photonic quantum circuits in the future.

Trapped atomic ions manipulated by laser beams is a leading candidate to construct scalable and practical quantum computers. Fully programmable quantum computers have been constructed using this technology, offering the highest performance quantum computing in commercial setting. Controlling atomic qubits with lasers is at the heart of constructing reliable trapped ion quantum computers. In this talk, I will discuss the stringent requirement for the optical systems required to build high performance trapped ion quantum computers, and prospect for constructing scalable systems in the future.

We develop quantum devices for the generation, manipulation and detection of light at the single photon level. Quantum dot devices allow for the generation of single and entangled photons at various frequencies including telecom wavelengths. We also develop single photon detectors with high efficiency based on NbTIN superconducting nanostructures, low noise and high time resolution to enable a range of applications including quantum communication, quantum sensing and integrated photonics. To allow for complex systems, integrated quantum optics circuits where we combine quantum sources and superconducting detectors are under development.

The role of governments in quantum technology

Women in Quantum Panel Session

Workforce and Education Panel

Polarization entanglement based cryptography uses the photon pairs generated in a spontaneous paramet- ric down-conversion process and guarantees the security through the violation of Bell’s inequality. Certain experimental parameters affects the entanglement fidelity and leads to a possible information leakage. The optical path difference of photons born at different crystals contributes to reduced fidelity, due to the extra birefringence of the nonlinear crystal. Although previous studies suggested methods to erase the distinguishability of photons by introducing compensation crystals, the phase difference, which is due to the lateral ray distribution is not studied. We used two commercially available collection optics; an aspheric and an achromatic lens. With these collection optics, the effect of collection optics on the entanglement fidelity is studied. We developed a simulation of such a system and found that aspheric collection optics is more suitable to achieve high fidelity.

Hardware of modern quantum computing (QC) platforms is based mainly on superconductors and ion traps. It demands ultra-low temperature and high vacuum. Practicality and scaling up thus remain questionable. This work analyzes the alternative based on the micro- and nanoparticles of the compounds of Rare Earth (RE) elements, such as phosphors NaYF₄: X³⁺ (X stands for Tm, Er, etc.), embedded in polymer matrices. The qubits in these systems correspond to the quantum levels of 4f electrons of RE ions, and they have optical frequencies. Qubit formation is supported by the properties of RE ions: (a) weak interaction with the environment, (b) strong inhomogeneous crystal field, and (c) the ability of neighboring ions, being in some 4f states, to interact with each other through the mechanism of Stark blockade. The latter is required for quantum conditional gate operations, such as Controlled NOT (CNOT – the basic block of a quantum computer circuit). Optical spectroscopy indicated that CNOT gate can be implemented, for instance, using the transitions in for-level system of Tm³⁺ ions |³H₆> (ground state), |³H₄> (state 0), |¹D₂> (state 1), and |¹I₆> (auxiliary state 1’) activated with conventional tunable lasers at 451, 653, 798, and 1459 nm. We also considered the PT- and anti-PT-symmetry on the decoherence rate of the qubits. PT-symmetric Hamiltonian H(x) has its real part symmetric versus x-coordinate, and the anti-PT-symmetric one is anti-symmetric. Anti-PT symmetric qubits tend to be more decoherence stable than the others. It was suggested that the anti-PT-symmetry can be introduce via coupling of the qubits to anti-PT-symmetric cavities using RE-doped compounds as gain media.

Quantum optical memories are a key component in a variety of quantum information applications, from extending quantum communication channels to building high-efficiency single-photon sources to enabling protocols requiring multiple synchronized qubits. However, most current photon storage systems utilize light-matter interactions and are therefore not broadband; meanwhile the available broader-bandwidth photon storage systems operate with somewhat shorter storage times or require cryogenic operation. Here we develop a system with multiplexed free-space storage cavities, able to store single photons with high efficiency over variable delays, up to 12.5 µs, and over multiple nanometers bandwidth at room temperature. The system can store multiple qubits encoded in various degrees of freedom (e.g., time-bin, and polarization) simultaneously. The work presented here has demonstrated storage of polarization states for 1.25 µs and retrieval through single-mode fiber with a state fidelity >99% and efficiency 82%.

We introduce a new generation of 3D imaging devices based on quantum plenoptic imaging. Position-momentum entanglement and photon number correlations are exploited to provide a scan-free 3D image after post-processing of the collected light intensity signal. We explore the steps toward designing and implementing quantum plenop- tic cameras with dramatically improved performances, unattainable in standard plenoptic cameras, such as diffraction-limited resolution, large depth of focus, and ultra-low noise. However, to make these new types of devices attractive to end-users, two main challenges need to be tackled: the reduction of the acquisition times, that for the commercially available high-resolution cameras would be from tens of seconds to a few minutes, and a speed-up in processing the large amount of data that are acquired, in order to retrieve 3D reconstructions or refocused 2D images. To address these challenges, we are employing high-resolution SPAD (single photon avalanche diode) arrays and high-performance low-level programming of ultra-fast electronics, combined with compressive sensing and quantum tomography algorithms, with the aim of reducing both the acquisition and the elaboration time by one or possibly two orders of magnitude. Moreover, in order to achieve the quantum limit and further increase the volumetric resolution beyond the Rayleigh diffraction limit, we explored dedicated pro- tocols based on quantum Fisher information. Finally, we discuss how this new generation of quantum plenoptic devices could be exploited in different fields of research, such as 3D microscopy and space imaging.

We use the IBMQ machine to implement a quantum database circuit. The database is made of a single multi- column table with multiple superposed records using Toffoli, CNOT and single quantum qubit gates. We present an optimized quantum circuit which allows us to select an item from the table, according to a specific oracle. Our circuit is based only on a single auxiliary qubit to perform the Selective Inversion (SI) and the Inversion Around the Average (IAA), which constitute the Grover operator. We analyze the difference between the generated transpired circuits while executing the original circuit on different IBMQ machines, namely the Melbourne and Athens quantum machines. We discuss the physical constraints causing the difference between the simulation on the composer and the executions of the circuits on the real IBMQ devices.

In recent years, deep learning algorithms have shown promising results for different image analyzing tasks, particularly in remote sensing image processing. Inspired by the success of remote sensing sensors in geo-located imagery, many studies have been carried out on remote sensing sensors for image processing, which brings a new approach into intelligent remote sensing and photogrammetric computer vision. At the same time, algorithms for quantum processors have been shown to efficiently solve some issues that are intractable on conventional, classical processors. This study summarizes the novel techniques of deep learning and quantum deep learning and its research progress and real-world applications in remote sensing image processing, introduces the current main challenges in processing and its development of geo-located datasets, focuses on the analysis and elaboration of the research status of quantum deep learning in sensing and imaging, and on this basis, summarizes the intelligent remote sensing applications and their application effects in scene understanding.

Photoacoustic microscopy has high spatial resolution and unique high optical contrast, so it has attracted the attention of a large number of medical imaging researchers, and has made great progress in the past decade. At present, the most widely used photoacoustic microscopy uses point-by-point scanning imaging method. Although this system has high imaging accuracy, it has low imaging efficiency. Therefore, this paper proposes virtual photoacoustic microscopy based on single-pixel imaging using K-Wave to realize a wide-field imaging without motion. This method is based on the principles of photoacoustic imaging and Fourier single pixel imaging. According to the principle of Fourier single-pixel imaging, any image is a weighted superposition of a sequence of cosine stripes of different spatial frequencies, and the weight coefficients of these stripes can be obtained to reconstruct the image. Therefore, a series of spatial frequency stripes are used to illuminate the sample, and the photoacoustic signal obtained by a single ultrasonic transducer is the Fourier spectral coefficient of the sample corresponding to the spatial frequency, all the Fourier spectral coefficients are obtained, and finally the inverse Fourier transform to obtain high-resolution images. In order to verify the feasibility of this method, this paper uses the K-Wave simulation tool to build a single-pixel photoacoustic microscopic imaging simulation model, and uses this model to image blood vessels. The results show that the lateral resolution of large-scale imaging without point scanning can reach 17 microns, demonstrating that this method can achieve a wide-field imaging with high-resolution.

Photoacoustic imaging technology is a three-dimensional imaging method based on the photoacoustic effect, which has the characteristics of high resolution, high contrast and high penetration depth. This technology provides a very important means to study the structure, metabolism, physiological and pathological characteristics of biological tissue, so photoacoustic imaging has a great application prospect in biomedicine. However, because of the high-resolution Nyquist sampling rate and large amount of data, it will cause great pressure on the storage equipment and make data transmission difficult. Generally, the problem of large amount of data is solved by compressed sensing. Compressed sensing theory can make the sampling speed determined by the internal structure and content of the signal, rather than by the bandwidth, thus reducing the amount of data. Build the virtual simulation platform of photoacoustic imaging based on k-wave, and use the BP reconstruction algorithm of compressed sensing to restore the original image. The results show that it can restore the original image with high quality while reducing the amount of data.

In recent years, the emerging non-harmful photoacoustic imaging technology has attracted extensive attention. This technology combines the advantages of high resolution and rich contrast of optical imaging with the advantages of high penetration depth of acoustic imaging. As a branch of photoacoustic imaging field, the photoacoustic microscopic technology, based on its unique focusing method, can achieve higher resolution, such as imaging of individual red blood cells, therefore, photoacoustic microscopy is widely used in the medical field. However, complex structure of the photoacoustic microscopy, expensive equipments of the photoacoustic microscopy, high cost of study of the photoacoustic microscopy, and complicated experimental operation steps cause the development of this technology to be limited. Therefore, it is necessary to combine simulation technology to build a photoacoustic microscopy simulation platform. In order to achieve this goal, in this paper, we build a simulation platform for photoacoustic microscopy based on K-Wave simulation toolbox. This simulation platform avoids the cost of equipment in real photoacoustic microscopy, which saves the research cost. Each module of the system (optical, Acoustics, etc.) can be easily adjusted and only need to modify the various system parameters to analyze the performance of the system. We measures the performance of the constructed photoacoustic microscopy by three-dimensional imaging of the blood vessel. A-Scan, B-Scan and C-Scan were simulated. The performance of the system was measured, with a lateral resolution of approximately 4.176 μm, an axial resolution of 27.056 μm. The establishment of the simulation platform has a significance for the theoretical research of photoacoustic microscopy and its application in biomedicine.

Photoacoustic imaging technology is an emerging functional imaging method in the field of biomedical applications. It combines the light absorption characteristics of tissues with the advantages of ultrasonic detection, and has the advantages of strong contrast, high sensitivity, and deep imaging depth. Therefore, this article uses the finite element software COMSOL Multiphysics to study the relationship between ultrashort laser pulses and the generated photoacoustic signals. In COMSOL, a laser with a pulse width of 5 ps is used as the excitation light source. Use mathematics module, heat transmission module, etc. to simulate the process of photothermal conversion-thermal expansion-generation of ultrasound in the photoacoustic imaging of the tissue-absorber system. In this way, the photoacoustic signal and its image are obtained. This study provides a theoretical basis for the application of picosecond laser pulses in photoacoustic imaging.

In this work, we combine an on-chip, telecom, broadband polarization-entangled photon source with industry-grade flexible wavelength management techniques to build a reconfigurable entanglement distribution quantum network over up to 75 km between up to 8 users. As an application, we implement a multi-user QKD protocol (BBM92) over our network.

Single photon emitters play a central role in the rapidly developing field of quantum technologies. Therefor new single photon sources are highly sought after. Understanding their properties is essential for their applications in integrated quantum technologies. Defect centers in hexagonal boron nitride (hBN) have become prominent candidates as single photon sources during the last years due to their highly favorable properties, like bright emission, narrow linewidth, and high photostability at even at room-temperature. Several recent studies have shown a spectral dependency on the excitation wavelength of fluorescence behavior of these emitters^1,2. In general, both the intensity and second order autocorrelation function, as well as the emission spectrum, vary with the excitation wavelength. By tuning the excitation over a broad range inside the visible spectrum and performing measurements regarding the quantum nature as well as the spectral decomposition of the emission light, we gain further insight to the characteristic properties and energy level schemes of these defect centers. Especially interesting for the energetic investigation of individual emitters is the appearance of additional sharp emission lines at higher excitation frequencies. These lines can be interpreted as higher order excited states of the same quantum system. To verify the assumption of a single system as the origin of these additional states, spectral cross correlations between individual lines are measured in a free beam HBT setup. Further analysis of these excited states can be done by performing fluorescence life time measurements, as well as comparison between the emission rates in order to determine the efficiency of the different decay channels.

We present a new technique for performing three-dimensional optical microscopy based on correlation plenoptic imaging. This approach, named Correlation Plenoptic Microscopy (CPM), exploits correlations between intensity fluctuations of pseudo-thermal light to retrieve plenoptic information about the sample, i. e. both spatial information about the intensity distribution of light and angular information about the propagation direction of the light rays. This leads to an enhancement of the depth of field, overcoming the sacrifice of lateral resolution required in conventional plenoptic microscopy. The intrinsic capability to refocus out-of-focus planes of the sample enables scanning-free three-dimensional reconstruction with the resolution kept at the diffraction limit. We show a setup to perform CPM with a microscope objective and present calculations of the correlation function for this specific case. Moreover we demonstrate with simulations that CPM improves the resolution, for a given depth of field, with respect to conventional optical microscopy.

Trapped ions, as one of the pillars of progress in frequency metrology and quantum optics, require a complex experimental environment with well-defined conditions. We present that a feature called dark resonance, provided by the trapped ion itself, can be used as a versatile sensor for enhanced in-situ analysis of interacting fields. The dark resonance is formed in the lambda-type energy level scheme of a laser cooled ⁴⁰Ca⁺ ion and corresponds to a fluorescence quenching. The method uses an analysis of the detection times of photons emitted from the upper energy level, which is excited via two optical dipole transitions. The two excitation lasers are phase locked to an optical frequency comb to reduce their linewidths and for precise control of their optical frequencies within the dark resonance. The amplitudes of interacting fields are obtained using the Fourier transform of the ion fluorescence or photon correlation measurements. This paper shows that the method can be applied for sensing of electric, magnetic and electromagnetic fields. Firstly, we present the potential for frequency analysis of the secular motion of a few-ion Coulomb crystal, which corresponds to the axial static electric field of a linear ion trap. Secondly, we demonstrate the optical frequency analysis of the employed lasers driving the two transitions. In the last case we show the analysis of an alternating magnetic field at the position of single ion.