This PDF file contains the front matter associated with SPIE Proceedings Volume 12238, including the Title Page, Copywrite information, Table of Contents, and Conference Committee Page.

We will show that photon correlations can be employed to overcome the typical limitations of conventional plenoptic imaging devices, thus leading to quantum-enhanced plenoptic imaging. In particular, we will show an unprecedented combination of resolution and depth of field combined with refocusing capability and depth extension. We will show experimental results obtained in different application scenarios, ranging from microscopy to photography-like protocols. Significant advances in acquisition speed will also be discussed, as achieved by both hardware (e.g., use of SPAD arrays, as opposed to common CMOS and CCD cameras) and software (e.g., compressive sensing, quantum tomography) solutions.

Quantum ghost imaging is an alternative imaging technique which utilises pairs of entangled photons to reconstruct an image. Due to the scanning nature of spatially resolving detectors and the inherent low light levels of quantum experiments, imaging speeds are inefficient and scale quadratically with the required resolution. We leveraged artificial intelligence capabilities to achieve early object recognition and to super-resolve the reconstructed image. We achieved a 5x reduction in image acquisition times and super-resolved the images to a resolution 4x greater than the measured resolution. Leading to efficient image acquisition times without losing fine details of the image.

There is a great deal of interest in highly sensitive sensing technology that utilizes the quantum entanglement of quantum light. Light wave sensing based on the quantum illumination theory is expected to be used outdoors with atmospheric disturbances. For the realization of such technology, it is extremely important to know the fundamental properties of quantum light propagation under various atmospheric conditions. In this study, we first investigated the propagation characteristics of laser light in fog. Next, we investigated the effects of fog on the quantum properties of single-mode squeezed light. It was found that when the fog density increases, not only the light energy is attenuated, but also the noise is superimposed on the intensity distribution. It was also found that the effect of fog on the squeezed light is mainly energy attenuation.

Optical time-domain reflectometry (OTDR) is one of the most used techniques for nondestructive characterization of optical fiber links. Although conventional OTDR exhibits good performance in classical network applications, photoncounting OTDR (ν-OTDR) offers a promising way for in-situ optical channel characterization of quantum network fibers where single-photon detectors are present. ν-OTDR has been demonstrated at the telecommunication wavelengths of 1310 and 1550 nm. Here, we present our hyperspectral ν-OTDR measurement covering a wavelength range from 1150 nm to 1800 nm. The results show low attenuation in SMF-28 fiber between 1150 nm and 1700 nm of less than 0.5 dB/km. However, we show that connector loss can worsen significantly for wavelengths greater than 1550 nm.

We present a novel approach to three-dimensional optical microscopy, named correlation light-field microscopy (CLM). This approach is based on correlation plenoptic imaging and exploits correlations between intensity fluctuations, intrinsic in chaotic light, to retrieve both spatial information about the intensity distribution of light on the sample and angular information about the directions of propagation of the light rays. Such a plenoptic (or light-field) information about the sample enables an extension of the natural depth of field, while avoiding the intrinsic loss of spatial resolution occurring in conventional light-field microscopy. We discuss the capability of CLM of refocusing out-of-focus planes of the sample, paving the way to scanning-free three-dimensional reconstruction while keeping the at-focus resolution at the diffraction limit showing a brief comparison with light-field microscopy. Finally we discuss the perspective of improvements in CLM acquisition speed by the integration of SPAD array sensors in the setup.

Quantum search algorithms show quadratic speedups over their classical counterparts, and the speedup also turns out to be optimal. They share the common structure that an iteration contains two inversions, one with respect to a target state and the other to an initial state, and such iterations are applied O( √ N) times for an unsorted database of N items. In this work, we present the characterization to an iteration that leads to exact quantum search with a quadratic speedup. We show that the fixed-point quantum search algorithm with a quadratic speedup contains iterations that are not QAAOs whereas exact quantum algorithms are sequences of QAAOs. We also demonstrate 3-qubit QAAOs in cloud-based quantum computing services, IBMQ and IonQ.

It is commonly assumed that interference patterns contain no information about the path taken by the individual photons. Surprisingly, recent results based on the analysis of weak interactions with probe qubits suggest that this may be a misconception. Here we show that the fluctuations of detection events in quantum interference patterns are correlated with the fluctuations of particle presence in the paths. It is pointed out that this correlation is a general feature of quantum fluctuations that distinguishes them from classical noise.

Quantum computation has made considerable progress in the last decade with multiple emerging technologies providing proof-of-principle experimental demonstrations of such calculations. However, these experimental demonstrations of quantum computation face technical challenges due to the noise and errors that arise from imperfect implementation of the technology. Here, we frame the concepts of computational accuracy, result reproducibility, device reliability and program stability in the context of quantum computation. We provide intuitive definitions for these concepts in the context of quantum computation that lead to operationally meaningful bounds on program output. Our assessment highlights the continuing need for statistical analyses of quantum computing program to increase our confidence in the burgeoning field of quantum information science.

Recent advances in quantum machine learning and quantum state embedding are integrated, providing a resource efficient framework for solutions of linear systems on Noisy Intermediate Scale Quantum (NISQ) machines. A divide and conquer algorithm is used to embed the indexing vector after which the Coherent Variational Quantum Linear Solver (CVQLS) algorithm is used to invert the problem matrix. This integrated procedure has an improved complexity scaling in the quantum resources needed to execute and produces solutions which agree with what is found classically.

Entangled photon sources are fundamental building blocks for quantum communication and quantum networks. Recently, silicon carbide emerged as a promising material for integrated quantum devices since it is CMOS compatible with favorable mechanical, electrical and photonic properties. In this work, we report the progress on the entangled photon pair generation at the telecom wavelength (1550 nm), which is achieved by implementing the spontaneous four-wave mixing process in a compact silicon carbide microring resonator. We will present the design principle, experimental set-up, and results of this work.

Quantum devices have the potential to revolutionize applications in computing, communications, and sensing; however, current state-of-art resources must operate at extremely low temperatures, making the routing of microwave control and readout signals challenging to scale. Interest in microwave photonic solutions to this problem has grown in recent years, in which control signals are delivered to the cold stage via optical fiber, where they are converted to electrical signals through photodetection. Overall link performance depends strongly on the characteristics of the photodiode, yet detailed measurements of many detector properties remain lacking at cold temperatures. In this work, we examine and compare the performance of a modified uni-traveling carrier photodiode (MUTC-PD) at both room (300 K) and liquid nitrogen (80 K) temperatures, focusing in particular on responsivity, bandwidth, and linearity. In line with previous work, we find a sharp reduction in responsivity at 1550 nm as temperature decreases, while RF bandwidth remains steady. Interestingly, our linearity tests reveal that the RF output saturates more quickly at 80 K, suggesting reduced linearity with lower temperature, the cause of which is still under investigation. Our results should help contribute to the understanding and future design of highly linear cryogenic quantum links.

Quantum entanglement is critical to build the backbone of all quantum technologies. Quantum networks, quantum computations, and quantum communication networking is based on long-range distribution of entangled photons and teleportation of photon qubit states. In order to understand quantum entanglement, characterization of atmospheric turbulence and its effects on propagating quantum states in free-space is essential. One method of photon entanglement is using a photon’s polarization. In this paper, we report results using polarization entangled signal and idler photons. The results may be applicable to support various quantum computing, encryption, and other qubit based high-performance communication protocols. Classically, the degradation of beam quality occurs due to many factors but primarily due to the distortion of spatial and temporal fields of refractive index. However, behavior of single photons through similar turbulent media creates a different set of challenges pointing to integrity of quantum states during propagation. We study this behavior by analyzing quantum states and the degree of entanglement in real-time and correlating it to known atmospheric models, (refractive index structure parameter), and relevant propagation path parameters. This experimental study was performed initially in a controlled laboratory environment, and then devised to be implemented outdoors over a 100-meter free space communication link.

Quantum key distribution (QKD) is a promising technology to enable secure cryptography after quantum computers have been developed. It allows for a key growing protocol that permits creating absolutely random keys to be used in the onetime pad codification scheme. Enabling a global QKD network is one of the final goals of the field. However, to do this with conventional optical fibres presents a fundamental limitation due to their intrinsic loss. Free-space, and specifically satellite links, have been proposed as an alternative and have gathered a lot of interest in recent years. They are considered one of the best candidates to enable a global network. Free-space QKD implementations are dominated by polarisation encoding protocols due to the relative transparency of the atmosphere to polarization. Nonetheless, time-bin and phase codifications offer some advantages and can be practical thanks to new passive interferometer designs. In this paper, the first free-space Coherent One-Way (COW) implementation is reported, some design considerations are commented, and the results of the experiment are shown. These show how time-bin/phase codifications are interesting candidates for free-space QKD.

Edge computing network and quantum network are two emerging technologies in current communication fields. Edge computing has emerged to support the computational demand of delay-sensitive applications in which substantial computing and storage are deployed at the network edge close to data sources. Quantum network supports distributed quantum computing, which could provide exponentially computation capabilities for certain problems. The vision of a hybrid quantum-edge is to provide a fundamentally new computing paradigm by expanding the computing capabilities and security of edge computing with quantum computing and quantum communications. The distributed nature of edge computing networks will also enable new scalable quantum networking schemes and applications. Such a hybrid computing paradigm will achieve unparalleled capabilities that are provably impossible by using only classical computing or quantum computing schemes alone. In this paper, we introduce the concept of hybrid quantum-edge computing network and discuss its challenges and opportunities.

Nonlocal dispersion compensation facilitated over standard ITU-T G.652/7 telecommunication fiber provides the simplest solution for the preservation of pair-wise timing correlations of broadband spontaneous parametric down converted photons. Its reliance on key parameters such as the relative spectral property of the down converted photons and pump wavelength were studied, providing important insights for an effective use of this scheme. We also raise the benefit of using modern ITU-T G.655 telecommunication fiber to complement this scheme. We preserved the timing correlations of photons distributed over a cumulative distance of 40km to within 60ps, with only 2km of extra G.655 fiber.

This contribution focuses on experimental verification of the QKD system deployment in a multi-domain network environment managed by Czech and Polish National Research and Educational Network (NREN) operators. We demonstrate full functionality of such a solution for transmission of secret keys in boundary conditions, and with this we open up new possibilities for further use of extremely secure communication between two neighboring network entities, and the services built upon it. Moreover, we have shared the cross-border link among strong QKD service channels, accurate time, and classical data channels together with weak quantum channel to reduce the total number of optical fibers needed for transmission. To our knowledge, this is the first shared cross-border QKD transmission in the region of Central and Eastern Europe (CEE).

A quantum network will consist of many physically separated nodes connected by quantum communication channels that distribute entanglement between them. Such nodes will require mechanisms for the generation, routing, and measurement of quantum states to fulfill various quantum communication protocols between any two quantum nodes. An aim of our quantum network metrology program is to develop portable, low-cost, robust, and reliable tools that can be deployed anywhere into a quantum network testbed for these purposes. The prototype source and receiver systems described here will serve as benchmarking devices for the implementation of quantum network metrology in real-life testbeds and are, by-design, integrated into a 19” rack to allow for the easy deployment into anywhere with standard networking infrastructure. Measurements performed using this toolset have shown a fidelity of more than 0.98 with a polarization entanglement visibility of 0.97.