This PDF file contains the front matter associated with SPIE Proceedings Volume 12517, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

The use of rare earth ions (REIs)—typically embedded as atomic defects in solids—has emerged as a promising strategy for practical quantum memories. In particular, the Er ion has garnered significant attention due to its telecom C-band optical transition, which makes it a suitable candidate for integration into existing optical fiber networks without the need for photon wavelength conversion. However, successful scalability of such a quantum memory platform would benefit greatly from employing a host material that is fully compatible with silicon and modern CMOS fabrication processes. In this study, we present the synthesis of Er-doped TiO₂ thin films directly on standard silicon or silicon-on-insulator (SOI) substrates using atomic layer deposition (ALD). Our thin film exhibits favorable emitter properties at cryogenic temperatures (T = 3.5 K), including a narrow inhomogeneous linewidth and optical lifetime approaching that of bulk values. Additionally, the ALD process provides ample opportunities for device fabrication and integration with other components, further enhancing its potential for practical applications. Overall, our findings suggest that Er-doped TiO₂ thin films synthesized via ALD represent a promising approach for developing practical quantum memories that can be seamlessly integrated with silicon photonics. This work lays a foundation for the development of quantum technologies with potential applications in communication, computing, and cryptography.

Cryogenic photoluminescence spectroscopy is a versatile tool to locally probe the defects in diverse material platforms as well as to observe modifications of the underlying electronic band structure in novel two-dimensional quantum materials such as the monolayer transition metal dichalcogenides (TMDs) (e.g. MoS₂, WS₂, WSe₂, and MoSe₂) and their heterostructures. These monolayer TMDs feature direct bandgaps and excitons with high binding energies due to quantum confinement which are conducive towards optoelectronic applications. We present our latest results on the characterization of monolayer TMDs and heterostructures based on monolayer TMDs using our newly developed fiber optic-based cryogenic photoluminescence setup in the Quantum Engineered Nano Devices Laboratory (QENDL) at the Naval Information Warfare Center Pacific (NIWC Pacific) towards their future implementation in quantum applications. Specifically, we investigate the temperature dependence of photoluminescence (PL) for Chemical Vapor Deposition (CVD) and Molecular Beam Epitaxy (MBE) grown monolayer TMDs on sapphire (0001) substrates; CVD monolayer WS₂-MoS₂ heterostructure on sapphire (0001) substrate; CVD monolayer WSe₂-MoSe₂ heterostructure on sapphire (0001) substrate; CVD monolayer MoS₂ on CVD monolayer hexagonal boron nitride (hBN) on SiO₂-silicon substrate; and CVD monolayer WS₂ on CVD monolayer hBN on sapphire (0001) substrate. We observed a significant temperature dependent direct bandgap red shift in CVD and MBE monolayer MoSe₂ on sapphire (0001), MBE monolayer WS₂ on sapphire (0001), and MBE monolayer WSe₂ on sapphire (0001) substrate. We estimated the exciton binding energy in MBE monolayer WSe₂ on sapphire (0001) by fitting the peak PL intensity values to the Arrhenius equation. Furthermore, we observed quite different temperature dependence of PL spectra from the monolayer CVD WS₂-MoS₂ heterostructure on sapphire (0001) substrate, which suggests the existence of spatial inhomogeneity across the sample. We also observed a temperature dependent PL peak red shift in both monolayer CVD WS₂-MoS₂ heterostructure on sapphire (0001) and monolayer CVD WSe₂-MoSe₂ heterostructure on sapphire (0001) substrate. Finally, we observed significant variability in the PL peak wavelength dependence on temperature for the transferred monolayer CVD MoS₂ on transferred monolayer CVD hBN on SiO2-silicon substrate as well as for the transferred monolayer CVD WS₂ on transferred monolayer CVD hBN on sapphire (0001) substrate.

We introduce a novel QKD protocol which utilizes the intrinsic temporal correlations found in photon pairs from a two-mode squeezed vacuum (TMSV) state. Upon generation, the idler photons are measured right away by Alice, and their time stamps recorded. This idler detection heralds the corresponding signal photons traveling in the channel towards Bob, which ensures the temporal configuration of the photons is identical between the two sets of photons when Bob measures them as a later time. By converting the time intervals between these photons into an uniformly-distributed integer stream, we generate two matching streams of integers which can be used to generate a secure key. The security of this key-generation scheme is discussed and investigated, as well as the utilization of this system in a real-world environment. The introduction of dropped photons and dark counts requires the use of non-standard error correcting codes. We discuss the use of Marker codes in the system and how correction and privacy amplification can occur without allowing knowledge of the full key to transmit to an eavesdropper.

Random number generators (RNG) are essential elements in many cryptographic systems. True random number generators (TRNG) rely upon sources of randomness from natural processes such as those arising from quantum mechanics phenomena. We demonstrate that a quantum computer can serve as a high-quality, weakly random source for a generalized user-defined probability mass function (PMF). Specifically, QC measurement implements the process of variate sampling according to a user-specified PMF resulting in a word comprised of electronic bits that can then be processed by an extractor function to address inaccuracies due to non-ideal quantum gate operations and other system biases. We introduce an automated and flexible method for implementing a TRNG as a programmed quantum circuit that executes on commercially-available, gate-model quantum computers. The user specifies the desired word size as the number of qubits and a definition of the desired PMF. Based upon the user specification of the PMF, our compilation tool automatically synthesizes the desired TRNG as a structural OpenQASM file containing native gate operations that are optimized to reduce the circuit’s quantum depth. The resulting TRNG provides multiple bits of randomness for each execution/measurement cycle; thus, the number of random bits produced in each execution is limited only by the size of the QC. We provide experimental results to illustrate the viability of this approach.

Several prominent quantum computing algorithms—including Grover’s search algorithm and Shor’s algorithm for finding the prime factorization of an integer—employ subcircuits termed ‘oracles’ that embed a specific instance of a mathematical function into a corresponding bijective function that is then realized as a quantum circuit representation. Designing oracles, and particularly, designing them to be optimized for a particular use case, can be a non-trivial task. For example, the challenge of implementing quantum circuits in the current era of NISQ-based quantum computers generally dictates that they should be designed with a minimal number of qubits, as larger qubit counts increase the likelihood that computations will fail due to one or more of the qubits decohering. However, some quantum circuits require that function domain values be preserved, which can preclude using the minimal number of qubits in the oracle circuit. Thus, quantum oracles must be designed with a particular application in mind. In this work, we present two methods for automatic quantum oracle synthesis. One of these methods uses a minimal number of qubits, while the other preserves the function domain values while also minimizing the overall required number of qubits. For each method, we describe known quantum circuit use cases, and illustrate implementation using an automated quantum compilation and optimization tool to synthesize oracles for a set of benchmark functions; we can then compare the methods with metrics including required qubit count and quantum circuit complexity.

Quantum Random Number Generators (QRNG) are quantum cryptographic protocols that distill secure random bit strings from quantum sources. One of the main research challenges in this area is to improve their random bit generation rates. Here we investigate several possible post processing strategies for QRNG protocols, showing when they help and when they hinder. We also look at the trade-offs to using these methods as some require a larger amount of initial randomness. Finally, we comment on some interesting future problems that remain open.

Quantum systems are entering a crucial stage of technology development where it is critical that design automation tools are co-developed along with the technology itself. Electronics design ecosystem provides tools which may be extended towards simulation and verification, critical steps towards large-scale certifiable designs of such quantum systems. SPICE simulations provide an appropriate level of abstraction that is both physical, in terms of custom designed physical components, and simulation approach, i.e. differential-algebraic equations. In this work we describe our efforts in modeling quantum + classical systems within SPICE. We first present our highly successful spintronics platform that has allowed us to model a multitude of spintronic effects including transport in tunnel-junctions, full lifecycle of quasi-quantum topological objects such as skyrmions, and transport in topological materials (TI, Weyl Semimetals). We demonstrate the extension of this platform towards simulations of circuits built using spin-qubits made from Josephson junctions, and a more emergent platform of Majorana Zero Modes (MZMs). We describe our approach that allows us to abstract away microscopic details, while capturing device and circuit behavior using controlled sources and custom components. We describe our approach to embed full dynamic solutions of alternate non-electrical state variables and indeed abstract quantities within the framework of SPICE. Our approach interplays well with more “fundamental” modeling approaches such as quantum master equations and non-equilibrium Green’s functions, as well as more “system” level modeling approaches such as SystemVerilog, thereby bridging both these worlds for exploration, analysis, simulation, and verification of scaled quantum systems.

Novel multiphoton entangled states have been developed, which offer utility for sensors. These states are linear combinations of M&N states (LCMNS). Closed form expressions for the coefficients have been derived that result in states offering sensitivities far greater than those found in the literature. Adaptive optics procedures have been conceived that permit these coefficients to be determined. LCMNS can also be used to generate high quality hyperentangled states. Various states generated by this process are developed. The utility of these procedures for quantum interferometry and RF signal detection is examined. The susceptibility to loss of the various interferometry and RF detection approaches is examined using an open systems analysis. The novel quantum interferometer uses adaptive optics, which offers a huge improvement in phase sensitivity over previous interferometers, while greatly reducing the number of photons used. Large numbers of photons can contribute to vibration reducing sensitivity. The approach based on entanglement presented here, even in the presence of loss can reduce the number of photons used significantly, while enhancing phase sensitivity. The new interferometer simultaneously minimizes phase error, maximizes visibility and greatly reduces the number of photons used. When the interferometer employing LCMNS is combined with an atomic RF antenna, E-field sensitivity is increased to a value nearly 400,000 times that found in the literature. Extensive numerical results are provided comparing phase sensitivity, visibility and E-field sensitivity for LCMNS, N00N states, and non-entangled states. LCMNS offer huge improvements in sensitivity compared to other approaches.

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 [5s₂ ¹S_0-5p¹P₁] 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.