In this study, we use qINTERCONNECT to perform a comparative analysis of published Photonic quantum gate designs, including CNOT, Hadamard, SWAP. We introduce real-world fabrication errors via Monte Carlo simulations of key design parameters, and by analyzing the resulting means and standard deviations, we assess the relative robustness and scalability of each design under realistic conditions by comparing each design’s fidelity and probability of success. This comparison highlights key challenges facing practical implementations of quantum gates and informs design strategies for future scalable quantum computing.
In this study, we use qINTERCONNECT to perform a comparative analysis of published Photonic quantum gate designs, including CNOT, Hadamard, SWAP. We introduce real-world fabrication errors via Monte Carlo simulations of key design parameters, and by analyzing the resulting means and standard deviations, we assess the relative robustness and scalability of each design under realistic conditions by comparing each design’s fidelity and probability of success. This comparison highlights key challenges facing practical implementations of quantum gates and informs design strategies for future scalable quantum computing.
In this study, we delve into optimizing optical quantum swap gate designs, which are crucial in the advancement of quantum computing. Using qINTERCONNECT, we conduct a comparative analysis of swap gate designs, including those based on equivalent circuits like CNOT gates and others utilizing dedicated architectures. Our aim is to compare the balance between operational efficiency and error tolerance in these varying designs, so as to measure their potential for scalability. Through simulations grounded in real-world fabrication parameters, we assess the fidelity and success probabilities of each design approach. Our findings indicate that while equivalent circuit-based designs are traditionally favored in other fields of quantum computing, dedicated swap gate architectures may offer enhanced robustness and scalability in optics. This study provides a comparative understanding of different swap gate designs, elucidating the relative merits and drawbacks of current designs, and offering insights that are relevant for practical applications in quantum computing.
Abstract Integrated quantum photonic circuits are a promising approach to realizing future quantum information processing. To achieve large-scale quantum photonic circuits, as many quantum logic gates as possible are expected to be integrated on chips. This requires quantum logic gates to be as small as possible. Here, we report the implementation of super-compact universal quantum logic gates on silicon photonic chips by inverse design. The sizes for the fabricated optical controlled-NOT gate and single-qubit gates (Hadamard gate) on the chip are about one vacuum wavelength, which are the smallest optical quantum gates ever verified in the world. The quantum circuit by these cascaded fundamental gates is shrunk several orders compared to those previous quantum photonic circuits that perform arbitrary quantum processing. Our study paves the way for the realization of large-scale quantum photonic chips with integrated sources for practical quantum information processes.
Abstract Quantum technologies, such as quantum communication, quantum sensing, quantum imaging and quantum computation, need a platform which is flexible, miniaturisable and works at room temperature. Integrated photonics is a promising and fast-developing platform. This requires to develop the right tools to design and fabricate arbitrary photonic quantum devices. Here we present an algorithm which, starting from a n -mode transformation U , designs a photonic device that approximates U . Using this method we design integrated photonic devices which implement quantum gates with high fidelity. Apart from quantum computation, future applications include the design of photonic subroutines and embedded quantum devices. These custom-designed photonic chips will be able to implement a given algorithm as a single-block circuit and will be small, robust and fast compared to a fully-programmable processor.
Scaling up linear-optics quantum computing will require multi-photon gates which are compact, phase-stable, exhibit excellent quantum interference, and have success heralded by the detection of ancillary photons. We investigate the design, fabrication and characterisation of the optimal known gate scheme which meets these requirements: the Knill controlled-Z gate, implemented in integrated laser-written waveguide arrays. We show device performance to be less sensitive to phase variations in the circuit than to small deviations in the coupler reflectivity, which are expected given the tolerance values of the fabrication method. The mode fidelity is also shown to be less sensitive to reflectivity and phase errors than the process fidelity. Our best device achieves a fidelity of 0.931 ± 0.001 with the ideal 4 × 4 unitary circuit and a process fidelity of 0.680 ± 0.005 with the ideal computational-basis process.
Quantum computing has progressed from early demonstrations across superconducting, trapped ion, photonic, and spin-based platforms to increasingly integrated systems. However, transitioning from the noisy intermediate-scale quantum (NISQ) era to robust, fault tolerant implementations remain a central challenge. This paper presents a systematic review and synthesis of practical quantum computing, encompassing experimental advances, integrated photonics, error correction breakthroughs, software stack evolution, benchmarking practices, algorithmic readiness, and socio-technical dimensions. We critically assess current limitations and highlight emerging directions, including integrated photonic modules with high fidelity interconnects, real time decoders for surface code logical qubits, and hardware aware compiler strategies. Our analysis is grounded in peer-reviewed experimental data and model-based evaluations. Key findings include demonstrated logical error suppression via increased code distance, scalable photonic module prototypes, and refined resource estimates for cryptanalytic and simulation tasks. This paper concludes with a structured research agenda for 2025–2030, proposing four priority thrusts such as hardware QEC co design, reproducible cross platform benchmarking, modular/distributed architectures, and quantum networking with governance frameworks. This evidence based roadmap aims to align researchers and practitioners toward actionable milestones on the path to practical quantum computing.
This thesis investigates quantum photonic technology, proposing novel designs and photonic components towards the next generation of quantum computing and information processing. Chapter 1 introduces the history and motivation behind quantum information, and evaluates today’s most promising quantum technology platforms. Chapter 2 provides an overview of requisite linear and nonlinear classical photonic theory, introduces topological photonics and quantum photonic concepts, as well as nanofabrication principles. In chapter 3, a published novel probabilistic single photon source design is proposed, aimed at improving yield and photon purity. Chapter 4 proposes a published novel scheme for manipulating photons with the goal of enabling robust new quantum photonic gate designs. Chapter 5 introduces two works investigating a new photonic platform, lithium niobate on insulator (section 5.1), suitable for quantum photonic technology, and demonstrates the initial steps towards the development of spectral filtering on this platform (section 5.2). This thesis seeks to explore and advance future quantum photonic technology, from sources design to quantum photonic gate design and fabrication, stepping closer to the long standing dream of scalable photonic quantum computing.