Robust Integrable Quantum Optical Sources, Constructed by Topological Boundary States, Are Crucial for the on-chip Quantum Information Processing. However, Limited by the Bulk-edge Correspondence, the Implementation of Topological Boundary Channels Necessitates a Substantial Number of Bulk Sites, Which Notably Diminishes the Ratio of Ring Resonators to Generate Quantum Sources. How to Achieve Topologically-protected Quantum Sources With the Extremely Enhanced Utilization Efficiency of Optical Resonators Remains a Challenge. Here, the First Realization of Hyperbolic Topological Quantum Sources is reported, Which Possess a Dominated Number of Boundary Resonators Than That in the Bulk Domain. Specifically, Hyperbolic Topological Quantum Sources Require Fewer Resources (i.e., the number of ring resonators) to Achieve the Same Level of Brightness Compared With Euclidean Topological Quantum Sources. Furthermore, the Robust Correlated- and Entangled-photon Pairs Are Measured. The Work Possesses Potential Applications in Integrable Quantum Circuits and Suggests a Novel Way on the Exploration of Quantum Physics in Non-Euclidean Space.
Robust Integrable Quantum Optical Sources, Constructed by Topological Boundary States, Are Crucial for the on-chip Quantum Information Processing. However, Limited by the Bulk-edge Correspondence, the Implementation of Topological Boundary Channels Necessitates a Substantial Number of Bulk Sites, Which Notably Diminishes the Ratio of Ring Resonators to Generate Quantum Sources. How to Achieve Topologically-protected Quantum Sources With the Extremely Enhanced Utilization Efficiency of Optical Resonators Remains a Challenge. Here, the First Realization of Hyperbolic Topological Quantum Sources is reported, Which Possess a Dominated Number of Boundary Resonators Than That in the Bulk Domain. Specifically, Hyperbolic Topological Quantum Sources Require Fewer Resources (i.e., the number of ring resonators) to Achieve the Same Level of Brightness Compared With Euclidean Topological Quantum Sources. Furthermore, the Robust Correlated- and Entangled-photon Pairs Are Measured. The Work Possesses Potential Applications in Integrable Quantum Circuits and Suggests a Novel Way on the Exploration of Quantum Physics in Non-Euclidean Space.
Abstract Entanglement, a fundamental concept in quantum mechanics, plays a crucial role as a valuable resource in quantum technologies. The practical implementation of entangled photon sources encounters obstacles arising from imperfections and defects inherent in physical systems and microchips, resulting in a loss or degradation of entanglement. The topological photonic insulators, however, have emerged as promising candidates, demonstrating an exceptional capability to resist defect-induced scattering, thus enabling the development of robust entangled sources. Despite their inherent advantages, building bright and programmable topologically protected entangled sources remains challenging due to intricate device designs and weak material nonlinearity. Here we present an advancement in entanglement generation achieved through a non-magnetic and tunable resonance-based anomalous Floquet insulator, utilizing an optical spontaneous four-wave mixing process. Our experiment demonstrates a substantial enhancement in entangled photon pair generation compared to devices reliant solely on topological edge states and outperforming trivial photonic devices in spectral resilience. This work marks a step forward in the pursuit of defect-robust and bright entangled sources that can open avenues for the exploration of cascaded quantum devices and the engineering of quantum states. Our result could lead to the development of resilient quantum sources with potential applications in quantum technologies.
The generation and manipulation of robust quantum entanglement are paramount for advancing quantum technologies, including quantum computing, communication, and sensing. Traditional methods often suffer from environmental decoherence and fabrication imperfections, limiting their scalability and fidelity. This paper explores the potential of topological diffractive elements (TDEs) to overcome these challenges by leveraging principles of topological protection. TDEs, drawing inspiration from topological photonics and metamaterials, exploit non-trivial topological properties to create wave propagation channels that are inherently robust against disorder and defects. We review the theoretical underpinnings of topological phases in optical systems, detailing how concepts such as Berry curvature and topological invariants can be harnessed in the design of diffractive structures. Specific attention is given to the generation of orbital angular momentum (OAM) entangled photons, where the topological charge plays a crucial role. We discuss various design methodologies for TDEs, including those based on photonic crystals, metasurfaces, and quasi-bound states in the continuum, and their application in creating stable and efficient sources of entangled photons. The paper highlights how the robustness afforded by topological protection can significantly enhance the fidelity and coherence lifetime of quantum entanglement, paving the way for more resilient quantum information processing systems. We also consider the experimental feasibility and potential applications of these advanced diffractive elements in integrated quantum circuits and remote entanglement distribution.
Entanglement is a valuable resource in quantum information technologies. The practical implementation of entangled photon sources faces obstacles from imperfections and defects inherent in physical systems, resulting in a loss or degradation of entanglement. The topological photonic insulators, however, have emerged as promising candidates, demonstrating an exceptional capability to resist defect-induced scattering, thus enabling the development of robust entangled sources. Despite their inherent advantages, building programmable topologically protected entangled sources remains challenging due to complex device designs and weak material nonlinearity. Here, we present a development in entangled photon-pair generation achieved through a nonmagnetic and tunable anomalous Floquet insulator, utilizing an optical spontaneous four-wave-mixing process. We verify the nonclassicality and time-energy entanglement of the photons generated by our topological system. Our experiment demonstrates a substantial enhancement in nonclassical photon-pair generation compared to devices reliant only on topological edge states. Our results could lead to the development of resilient quantum sources with potential applications in quantum technology. Published by the American Physical Society 2024
Abstract High-dimensional quantum entanglement is an important resource for emerging quantum technologies such as quantum communication and quantum computation. The scalability of metres-long experimental setups limits high-dimensional entanglement in bulk optics. Advancements in quantum technology hinge on reproducible, and reconfigurable quantum devices—including photon sources, which are challenging to achieve in a scalable manner using bulk optics. Advances in nanotechnology and CMOS-compatible integration techniques have enabled the generation of entangled photons on millimeter-scale chips, significantly enhancing scalability, stability, replicability, and miniaturization for real-world quantum applications. In recent years we have seen several chip-scale demonstrations with different discrete degrees of freedom including path, frequency-bin, time-bin, and transverse modes, on many material platforms. A complete quantum photonic integrated circuit requires the generation, manipulation, and detection of quantum states, involving various active and passive quantum photonic components which further increase the degree of complexity. Here, we focus on the high-dimensional versions of qubits—qudits—and review the nonlinear optical processes that facilitate on-chip high-dimensional entangled photon sources, and the currently used material platforms. We discuss a range of current implementations of on-chip high-dimensional entangled photon sources and demonstrated applications. We comment on the current challenges due to the limitations of individual material platforms and present future opportunities in hybrid and heterogeneous integration strategies for the next generation of integrated quantum photonic chips.
Quantum entanglement, as the strictly non-classical phenomena, is the kernel of quantum computing and quantum simulation, and has been widely applied ranging from fundamental tests of quantum physics to quantum information processing. The decoherence of quantum states restricts the capability of building quantum simulators and quantum computers in a scalable fashion. Meanwhile, the topological phase is found inherently capable of protecting physical fields from unavoidable fabrication-induced disorder, which inspires the potential application of topological protection on quantum states. Here, we present the first experimental demonstration of topologically protected quantum polarization entangled states on a photonic chip. The process tomography shows that quantum entanglement can be well preserved by the boundary states even when the chip material substantially introduces relative polarization rotation in phase space. Our work links topology, material and quantum physics, opening the door to wide applications of topological enhancement in genuine quantum regime.
Abstract Entanglement and topology both portray nature at the fundamental level but in different manners. Entangled states of quantum particles are intrinsically sensitive to environment, whereas topological phases of matters represent natural robustness against environmental perturbations. Harnessing topology physics to protect entanglement thus has a great potential for reliable quantum applications. However, generating topologically-protected entanglement remains a significant challenge, which requires operating complex quantum devices in combined extreme conditions. Here we report topologically-protected quantum entanglement emitters, that emit topological Einstein-Podolsky-Rosen entangled state and topological multiphoton entangled state from a monolithically-integrated plug-and-play silicon-photonic chip in ambient conditions. The device emulating a photonic anomalous Floquet insulator allows the generation of up to four-photon topological entangled states at nontrivial edge modes. More importantly, we show that the Einstein-Podolsky-Rosen entanglement emitters can be topologically protected against artificial structure defects, by comparing tomographically measured fidelities of 0.968 ± 0.004 and 0.951 ± 0.01 for the perfect and defected emitters, respectively. Our topologically-protected entanglement emitters may find applications in photonic quantum computation and quantum simulation, and in the study of quantum topological physics.