On the genesis and evolution of Integrated Quantum Optics (1108.3162v1)

Abstract: Applications of Integrated Optics to quantum sources, detectors, interfaces, memories and linear optical quantum computing are described in this review. By their inherent compactness, efficiencies, and interconnectability, many of the demonstrated individual devices can clearly serve as building blocks for more complex quantum systems, that could also profit from the incorporation of other guided wave technologies.

• The paper demonstrates how integrated optics drives quantum development by leveraging nonlinear interactions and optimized device design.
• It highlights advanced techniques for generating heralded single photons and entangled states, paving the way for scalable quantum computing.
• The review outlines challenges in fiber coupling and future directions using emerging integrated technologies to enhance quantum networks.

Integrated Quantum Optics: Developments and Applications

The field of integrated quantum optics has undergone significant advancements, as discussed in this comprehensive review paper. This work serves as a detailed exposition on how integrated optics (IO) influences and drives developments in quantum optics, with applications ranging from quantum communication to computing.

Genesis and Development of Integrated Quantum Optics

Integrated optics has served as a bridging technology, connecting the realms of photonics and quantum mechanics. The initial motivation came from the shift towards exploiting the fundamental quantum properties such as uncertainty and multiparticle superposition (entanglement) in the early 1990s. Leveraging technological advances from fiber optic telecommunications has further accelerated this integration, enabling widespread applications in quantum optics and information.

Quantum Devices and Systems through IO

The paper thoroughly reviews the use of IO in quantum sources, detectors, interfaces, memories, and quantum computing. The compactness, efficiency, and interconnectability of these components allow for sophisticated quantum systems, offering potential beyond individual device capabilities. Key developments and applications addressed include:

1. Quantum Sources and Nonlinear Optical Interactions: Highly efficient integrated optical sources for generating quantum states, leveraging nonlinear interactions like spontaneous parametric down-conversion (SPDC) in periodically poled lithium niobate (PPLN) waveguides. The optimized efficiency and mode overlap provided by PPLN offer significant advantages over traditional bulk optics systems.
2. Heralded Single Photon Sources and Entangled Photon-Pair Generation: Advanced techniques for creating heralded single photon sources (HSPSs) and sources of entangled photons, pivotal for quantum key distribution and other communication protocols. These developments lay the foundation for devices that operate at telecommunications wavelengths, crucial for integration into existing fiber networks.
3. Quantum Relay and Repeater Technologies: The discussion includes quantum relays and repeaters that extend the reach of quantum communications, overcoming limitations of direct communication channels. Integrated optics facilitates the realization of entanglement swapping and teleportation protocols necessary for these operations.
4. Single Photon Detectors and Quantum Interfaces: The advancement of up-conversion detectors that improve detection capability for telecom photons by converting them to wavelengths suitable for silicon detectors, thus enhancing detection efficiency and reducing dark counts. The paper elaborates on coherence-preserving quantum interfaces that transpose qubits across wavelength domains, essential for quantum network operations involving atomic storage materials.
5. Quantum Memories: Integration of optical waveguides in quantum memory systems, particularly those based on rare-earth doped crystals. These devices show promise for future quantum networks by enabling storage and retrieval of quantum information with high fidelity and efficiency.
6. Quantum Computing on an Integrated Platform: The review illuminates linear optical quantum computing realized through integrated waveguide platforms, highlighting advancements in scalability and complex circuit executions. Notably, integrated photonics is shown to have executed small-scale algorithms, such as Shor's algorithm, demonstrating feasibility for scalable quantum information processing.

Challenges and Future Directions

While the review acknowledges the strides made with IO in quantum optics, challenges remain, particularly in achieving efficient coupling between fiber and integrated devices. Future developments could focus on further functional integration to minimize losses and harness the full potential of IO technologies. The incorporation of emerging technologies such as silicon nano-wire and photonic crystal circuits may herald further breakthroughs. Moreover, the design of more sophisticated integrated devices like on-chip quantum relays underscores the direction towards an extensive utility of integrated optics in practical quantum applications.

In conclusion, this review provides a critical synthesis of the various facets of integrated quantum optics. It offers a roadmap for future research directions, underscoring both the challenges and opportunities inherent in leveraging integrated technologies for advanced quantum applications. The paper's detailed exploration of current capabilities and future prospects makes it an invaluable resource for researchers in the field of quantum optics.