Quantum computation using photons offers one possible route towards the long-standing goal of scalable, fault-tolerant quantum computing. Within this realm, measurement-based quantum computing offers a promising approach exploiting many of the advantages of photons. Implementing photonic measurement-based architectures relies upon the deterministic generation of graph states composed of many entangled photons. Semiconductor quantum dots (QDs) are sources of indistinguishable single photons and hosts of solid-state spins, marking them desirable platforms for controlled entanglement generation. Such a platform consisting of a single charged QD coupled to a photonic cavity has been proven for the generation of multipartite spin-photon graph states. This dissertation will present advancements in the versatility and coherence of such entanglement generation. First, background on quantum dots, single photon generation, spin control, and entanglement will be introduced. Then, sources of error and decoherence will be addressed using control of the hole g-factor and dynamical decoupling techniques. The aim of versatility is advanced through results on the generation of four-partite graph states with on-demand reconfigurability of the type of state produced. Finally, a different paradigm using quantum dot molecules will be introduced, and novel estimation of important physical parameters in this system is developed.
Quantum computation using photons offers one possible route towards the long-standing goal of scalable, fault-tolerant quantum computing. Within this realm, measurement-based quantum computing offers a promising approach exploiting many of the advantages of photons. Implementing photonic measurement-based architectures relies upon the deterministic generation of graph states composed of many entangled photons. Semiconductor quantum dots (QDs) are sources of indistinguishable single photons and hosts of solid-state spins, marking them desirable platforms for controlled entanglement generation. Such a platform consisting of a single charged QD coupled to a photonic cavity has been proven for the generation of multipartite spin-photon graph states. This dissertation will present advancements in the versatility and coherence of such entanglement generation. First, background on quantum dots, single photon generation, spin control, and entanglement will be introduced. Then, sources of error and decoherence will be addressed using control of the hole g-factor and dynamical decoupling techniques. The aim of versatility is advanced through results on the generation of four-partite graph states with on-demand reconfigurability of the type of state produced. Finally, a different paradigm using quantum dot molecules will be introduced, and novel estimation of important physical parameters in this system is developed.
Semiconductor quantum dots (QDs) have emerged as a premier solid-state platform for the deterministic generation of nonclassical light, offering a compelling pathway toward scalable quantum photonic systems. While single-photon emission from QDs has reached a high level of maturity, the realization of high-fidelity entangled photon-pair sources remains an active and rapidly evolving frontier. In this review, we survey the recent progress in QD-based entangled photon sources, highlighting the conceptual evolution from the established biexciton-exciton cascade to the emerging paradigm of spontaneous two-photon emission. We further examine how advances in nanophotonic architectures and coherent control strategies are redefining fundamental performance limits, enabling concurrent improvements in source brightness, coherence, and entanglement fidelity. Finally, we discuss the key physical and technological challenges that must be addressed to bridge the gap between laboratory demonstrations and large-scale deployment. We conclude by outlining the future opportunities for integrating QD-based entangled photon sources into practical quantum communication, computation, and sensing platforms.
Semiconductor quantum dots (QDs) have emerged as a premier solid-state platform for the deterministic generation of nonclassical light, offering a compelling pathway toward scalable quantum photonic systems. While single-photon emission from QDs has reached a high level of maturity, the realization of high-fidelity entangled photon-pair sources remains an active and rapidly evolving frontier. In this review, we survey the recent progress in QD-based entangled photon sources, highlighting the conceptual evolution from the established biexciton–exciton cascade to the emerging paradigm of spontaneous two-photon emission. We further examine how advances in nanophotonic architectures and coherent control strategies are redefining fundamental performance limits, enabling concurrent improvements in source brightness, coherence, and entanglement fidelity. Finally, we discuss the key physical and technological challenges that must be addressed to bridge the gap between laboratory demonstrations and large-scale deployment. We conclude by outlining the future opportunities for integrating QD-based entangled photon sources into practical quantum communication, computation, and sensing platforms.
Hybrid photonic quantum computers, combining stationary matter qubits and flying photonic qubits, offer an intrinsically networked and resource-efficient route to large-scale, error-corrected quantum computation. Their core components are cavity-coupled matter qubits that act as light--matter interfaces, enabling: high-efficiency on-demand single-photon generation, stable near-unity photon indistinguishability and spin--multi-photon entanglement. Semiconductor quantum dots in microcavities are a leading platform for realizing such devices. Yet reaching the performance, reproducibility and spin-coherence thresholds for large-scale error correction remains a major challenge requiring industrial fabrication and control. Here we report thousands of monolithic semiconductor quantum-dot devices fabricated using a III--V pilot production-line process compatible with large-scale deployment. Systematic control of source parameters yields state-of-the-art efficiency and supports a path to optical losses below fault-tolerance thresholds. Using field-quadrature state reconstruction as a stringent joint test of efficiency and indistinguishability, we observe near-unity photon quantum purity stable over tens of minutes and a record single-photon Wigner-function negativity. We further demonstrate seven-partite spin--multi-photon entanglement and spin coherence extendable to microsecond timescales in the low-magnetic-field regime. Finally, photons from distant sources are as indistinguishable as photons emitted successively by a single source. These results establish foundry-compatible III--V quantum dots as a scalable platform for hybrid photonic quantum computing.
Measurement-based quantum computing offers a promising route towards scalable, universal photonic quantum computation. This approach relies on the deterministic and efficient generation of photonic graph states in which many photons are mutually entangled with various topologies. Recently, deterministic sources of graph states have been demonstrated with quantum emitters in both the optical and microwave domains. In this work, we demonstrate deterministic and reconfigurable graph state generation with optical solid-state integrated quantum emitters. Specifically, we use a single semiconductor quantum dot in a cavity to generate caterpillar graph states, the most general type of graph state that can be produced with a single emitter. By using fast detuned optical pulses, we achieve full control over the spin state, enabling us to vary the entanglement topology at will. We perform quantum state tomography of two successive photons, measuring Bell state fidelities up to 0.80 ± 0.04 and concurrences up to 0.69 ± 0.09, while maintaining high photon indistinguishability. This simple optical scheme, compatible with commercially available quantum dot-based single photon sources, brings us a step closer to fault-tolerant quantum computing with spins and photons. Quantum emitters have recently been identified as efficient sources of graph states, which are entangled states crucial for photonic quantum computation. Here the authors demonstrate deterministic and reconfigurable generation of caterpillar graph states using a semiconductor quantum dot in a cavity.
Quantum mechanics endows light with properties that have no classical analogue - superposition, entanglement, and non-classical photon statistics, that can be harnessed as resources for computing, communication, sensing, and simulation. After decades of foundational research, quantum states of light can now be generated, manipulated, and measured with sufficient precision that their non-classical properties are no longer merely curiosities, but engineerable resources. Integrated photonics offers a compelling path forward. By confining light in lithographically defined waveguides on a chip, it replaces fragile bulk optical assemblies with compact, phase-stable, and reproducible circuits. Semiconductor quantum dots embedded in photonic nanostructures provide bright, on-demand single-photon emission compatible with waveguide integration, while superconducting nanowire single-photon detectors provide the efficiency and timing precision that quantum optical measurements demand. A particularly powerful frontier is reconfigurability: programmable photonic circuits whose functionality is defined in software can serve as versatile quantum photonic processors without any physical modification. This dissertation presents work on engineering quantum light across the full chain of generation, control, and detection using integrated photonic platforms. It covers coherent control of nanowire quantum dot emitters, generation of multipartite entangled states on a silicon nitride chip, and the use of programmable silicon-on-insulator interferometers as reconfigurable quantum optical processors for simulating quantum systems.
Photonic cluster states are fundamental resource for measurement-based quantum computing (MBQC), which is a promising approach for scalable quantum computing. These highly entangled states enable computation with applying local measurements rather than gate operations, which makes them essential for fault-tolerant quantum computing. Generation of the photonic cluster states requires high-quality entanglement and stability, which can be done by making use of cavity quantum electrodynamics (cavity QED), which is embedding quantum dots (QDs) into photonic microcavities. This method enables controlled single-photon emission and the entanglement of them, helping with key challenges in generating photonic cluster states. Enhancing the generation of the photonic cluster state requires improvement in the quality factor (Q-factor) and therefore, cooperativity of cavity and QD systems. A high Q-factor helps with reduction in photon loss and decoherence, ensuring more stable and high-fidelity quantum states. It also enables better light-matter interactions, improving cluster state quality. Cooperativity, which is a measure for the light-matter coupling strength relative to dissipation, directly impacts photon emission efficiency. Optimization of these parameters improves entanglement generation, which is essential for producing high-quality photonic cluster states. Therefore, optimized cavities are essential for improving the generation of the photonic cluster states. Scalability is also an important parameter for the generation of the large-scale cluster states used in quantum computing. In this paper, after reviewing MBQC, cluster states, and the generation of the photonic cluster states, we investigate the deterministic generation of the photonic cluster state resource for the purpose of MBQC, and highlights the importance of the inverse design techniques for this goal.