This PDF file contains the front matter associated with SPIE Proceedings Volume 12692, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Enabling large-scale and high-speed quantum computation is a key to practical quantum computation. Continuous-variable approach in optical systems offer advantages in scalability and speed by leveraging their temporal degree of freedom and inherent large carrier frequency. In this paper, we investigate the generation and manipulation of quantum entanglement through a time-domain multiplexing approach. By employing time-domain multiplexing, we generate a two-dimensional cluster state—a universal resource for large-scale quantum computation—and perform quantum operations in the time domain with cluster state. Additionally, our ongoing research focuses on the generation and measurement of broadband optical quantum entanglement through an optical parametric oscillator, which holds potential as a foundation for high-speed quantum computing surpassing limitations of existing systems. By further engineering the quantum entanglement, we have also theoretically formulated a practical teleportation-based architectures for quantum computation in time domain. These advancements form the groundwork for the development of practical optical quantum computation.

By simultaneously measuring individual and coincidence counts of two single photon detectors connected to a fiber-based entangled photon source and fitting the results with a theoretical model of the photon generation rates, we determine the average number of polarization-entangled photon pairs generated by four-wave mixing and the average number of noise photons generated by Raman scattering and self-phase modulation of the pump as a function of power. In contrast to previous efforts to characterize fiber-based entangled photon sources, this method does not require additional coherence-based measurements to distinguish SPM photons from FWM and Raman-scattered photons.

Quantum contextuality can be observed in three path interferometers, suggesting a fundamental contradiction between wave propagation and particle propagation inherent in the wave-particle dualism. Here, we investigate this contradiction in a three path interferometer specifically designed to illustrate the paradoxical aspects of single particle interference. A particularly clear violation of non-contextual assumptions is obtained when interference effects suppress detection probabilities to zero in paths that seem to be necessary to explain the observation of photons in the output. This contradiction between detection probabilities in the paths and detection probabilities in the output cannot be explained by any assignment of photon paths through the interferometer, demonstrating a fundamental incompatibility of wave propagation and particle propagation.

We designed and fabricated a -0.64 dB loss hybrid coupling platform for silicon chips. The coupler is also stable enough to maintain within +-0.1 dB coupling fluctuation against 20 um fiber holder movement. This feature allows a constant photon stream over ten days with no active alignment mechanism. Furthermore, the fiber is engineered with centimeterlong small-core fiber spliced on the tip. This minimizes Raman noise and provides high stability compared with other coupling solutions based on ordinary UHNA fibers or lensed fibers.

We aim to study quantum illumination using two-mode squeezed light. When quantum illumination is applied to outdoor radar applications, one of the light waves in the quantum entangled state is emitted toward the atmospheric disturbance. Therefore, it is extremely important to investigate the effect of atmospheric disturbance on the propagation characteristics and quantum nature of the lightwave. In this study, we focus on thermal fluctuations and air ow as atmospheric disturbances. First, the effect of atmospheric disturbance on the propagation characteristics and interferometry of light waves are investigated using laser light. Then, the effect of atmospheric disturbance on the quantum properties of single-mode squeezed light is investigated. We found that when the squeezed light passes through thermal fluctuations, the optical axis and intensity distribution are affected and the observed squeezing level fluctuates significantly. This may be due to the fact that the propagation of the squeezed light was affected by the thermal fluctuation and the interference efficiency with the local oscillator light fluctuated. On the other hand, when the squeezed light passed through the air ow, the propagation was affected very little. The observed squeezing levels remained almost unchanged.

Photonic quantum computing has been dramatically scaled up recently by the promising approach of combining the continuous-variable" and time-multiplexing" schemes. We report on our recent development of time-multiplexed programmable continuous-variable photonic quantum computing, including a programmable loop-based quantum processor for single-mode multi-step Gaussian gates and a programmable time-multiplexed squeezed light source for initial state preparation. Our works pave the way to large-scale programmable continuous-variable quantum computing.

We investigate the use of a spatially distributed beam of entangled photons for applications of wavefront division interferometry. Using a fiber-based spontaneous parametric down conversion process, which redirect the signal and idler into a common single-mode fiber, we generate a Gaussian beam of colinear entangled photons randomly distributed in space. Coincidence measurements carried by wavefront division demonstrate quantum interference patterns, including classical single photon fringes, two-photon interferences and the Hong-Ou-Mandel effect. Our results are relevant for detecting transverse variations in the statistical properties of weak turbulence.

Very-long baseline interferometry has been one of the major astronomical imaging techniques used in the last century for tasks ranging from measuring diameters of stars to imaging black holes at the center of galaxies. However, the usual heterodyne technique is typically limited to radio wavelengths for the longest baselines due to fundamental noise from the local oscillator, which is used to measure the collected electric field in time at each aperture. Further, the visible and near-infrared (V-NIR) wavelengths do not easily allow such measurements due to their higher frequency; so, for optimal performance, the collected fields must be directly interfered with each other to measure the spatial correlation of the stellar light between each aperture. This implies, at V-NIR wavelengths, a practical limitation on the distance between the receivers and the brightness of stellar sources since bringing the fields together is lossy. Several theoretical proposals have promised reduction of this loss by using single photons along with quantum networks and/or quantum memories. We demonstrate a proof-of-principle, table-top experiment of one proposal by interfering path-entangled single photons generated from parametric down conversion and the light collected from a quasi-thermal source occupying a single spectral-temporal mode representing light from a star. The interference signal was then used to recover the spatial autocorrelation of two source distributions: 1 and 2 mm separated double slits. We compare this to a theoretical model and see good agreement. This model allows further comparison to other weak, non-single-photon, local-oscillator sources such as coherent states.

Optical tomography can reveal the intrinsic structure of complex objects with high accuracy. Cold atoms are an excellent model physical system for designing new protocols. By combining the gradient echo memory protocol with spatial homodyne detection, our experiment achieved micron-level resolution and excellent shot-noise limited sensitivity for interrogating atomic coherence. We also demonstrated three-dimensional imaging of an external magnetic field, and plan to extend the scheme to ultra-sensitive three-dimensional imaging of microwave fields using Rydberg atoms. Our work pushes the boundaries of quantum sensing for weak fields and unexplored three-dimensional tomographic imaging. The method may also be applied to hot atoms or solid-state probes, such as color centers, or ions, embedded in an interrogated medium.

We present integrated sources of polarization entanglement built on portable platforms for quantum communication. We employ type-II degenerate spontaneous parametric down conversion processes in periodically poled potassium titanyl phosphate (PPKTP) waveguides to generate pairs of orthogonally polarized photons at near-infrared wavelengths. We use balanced non-polarizing beam splitter (NPBS) to generate post-selected polarization-entangled states via coincidence measurements and investigate the power and spectral tunability of the system. The small size of the waveguides allows the installation of several units on the same platform, and thereby the generation of multiple entangled states simultaneously. We built a separate platform containing a computer-controlled tomography system to characterize the produced states and another NPBS is installed to combine photons from adjacent waveguides and assess their interferability, a prerequisite to entanglement swapping. The overall experiment is compact and requires little alignment when set, making it an attractive option for local quantum networking using mobile platforms, e.g., drones or satellites.

This paper considers an application of the quantum stream cipher (QSC) Y-00. QSC Y-00 can provide secure long-haul and high-capacity data transmission in optical networks. Post-quantum cryptography (PQC) can provide quantum-resistant authentication and key-establishment. We propose a secure link architecture for optical communication networks using QSC Y-00 and PQC. Further, we report a field experiment using the optical fibers embedded along a railway truck between two train stations to demonstrate user authentication, key-establishment, and secure data communication with the intensity modulation-based Y-00 transceivers and PQC. Finally, we discuss the further applications of the proposed secure link architecture.

The primary focus of this paper is high-performance quantum communication systems that facilitate secure data transfer via free-space links. We consider an approach that uses correlated photon pairs generated in such a way that their polarizations are entangled and can be used to support quantum encryption protocols. However, when deployed in free space, these links can be affected by channel distortion, primarily via the spatial and temporal fields of the refractive index along the propagation path. In classical links, these fields alter the optical wave front characteristics; however, this mechanism does not directly apply to the quantum states utilized in single-photon or entangled photon protocols. Transmitting signals with quantum-based encryption creates a realm of problems, not related to wave front distortions, but rather to integrity of the quantum states after the signals propagate over free-space channels. We study these phenomena by implementing a laboratory testbed capable of creating a turbulent environment using atmospheric chambers developed by the AFRL. It is then used for experimental investigation of quantum entanglement after photon pairs are propagated both collinearly and via separate paths.

In this work we investigate the modeling of optical structures, such as optical fibers and crystalline lattices, whose optical potential exhibit a certain type of symmetry known as parity-time (PT) symmetry. These optical potentials describe the scattering of light in the structure by modulating the refractive index of the system and thus generating a nonlinear optical beam that propagates along the waveguide. These optical beams have low dispersion and low energy loss, and maintain their shape during propagation. Due to such properties these nonlinear optical pulses can be applied in the development of optical filters, as well as in the transmission and processing of nonlinear optical signals. These systems, which exhibit well-defined band structure, can be employed in integrated optics, incorporating the possibilities generated from quantum and nonlinear optics. Such applications can also innovate the perspectives and demands of quantum computing.

Interference measurements with undetected photons employ entangled photon pairs in order to overcome classical limitations in measurement sensitivity. With the undetected photon technique, one photon (signal) interacts with an object, and the signature of the interaction is stored in its entangled counterpart (idler): the interacting photon remains undetected, while the detection is performed on the photon that did not interact with the object. While the signal photon can be chosen in any spectral region suitable for the interaction, the idler photon is generated in a spectral region where detectors are efficient, scalable, and cheap. To date, the configurations proposed are in bulk setups. In this work, we propose a novel configuration on an integrated device, with the advantages of the reduced dimension, the lower cost and the robustness to alignment. In our experiment, we pumped a silicon-on-silica integrated circuit with a classical beam at a wavelength of 1.568 μm. Via intermodal spontaneous four-wave mixing, we generated highly non-degenerate time-energy entangled signal and idler photons at 1.99 μm and 1.29 μm, respectively. As we have integrated two identical sources of entangled photons in series, the photon pairs generated in the two sources are indistinguishable, and controlling the phase of the pump beam and the phase of the signal photons after the first nonlinear source, we observed interference patterns with 24% maximum visibility in the idler photon counts. We successfully measured the dephasing induced on the signal photons by measuring only the idler ones.

Transient wavelength and power stability of two DFBLDs with sub-MHz linewidth are compared to provide differential logarithmic wavelength and power variations within 1×10^-5% (▵lnλ) and 0.03% (▵lnP), respectively, for high-security DPS phase-shift-keying encoding/decoding at 200Mbit/s.