Chip-based photon quantum state sources using nonlinear optics (1706.04300v1)

Abstract: The ability to generate complex optical photon states involving entanglement between multiple optical modes is not only critical to advancing our understanding of quantum mechanics but will play a key role in generating many applications in quantum technologies. These include quantum communications, computation, imaging, microscopy and many other novel technologies that are constantly being proposed. However, approaches to generating parallel multiple, customisable bi- and multi-entangled quantum bits (qubits) on a chip are still in the early stages of development. Here, we review recent developments in the realisation of integrated sources of photonic quantum states, focusing on approaches based on nonlinear optics that are compatible with contemporary optical fibre telecommunications and quantum memory infrastructures as well as with chip-scale semiconductor technology. These new and exciting platforms hold the promise of compact, low-cost, scalable and practical implementations of sources for the generation and manipulation of complex quantum optical states on a chip, which will play a major role in bringing quantum technologies out of the laboratory and into the real world.

• The paper demonstrates novel chip-based quantum state sources employing nonlinear optics, integrating SPDC and SFWM methods for quantum photon generation.
• It provides a comparative analysis of SPDC and SFWM approaches by evaluating key metrics such as brightness, purity, and heralding efficiency on silicon-based platforms.
• The study highlights challenges like pump wavelength filtering while paving the way for scalable quantum communication and computing applications.

Chip-based Photon Quantum State Sources Using Nonlinear Optics

The paper authored by Caspani et al. presents a comprehensive overview of recent advancements in developing integrated photonic sources for generating quantum states, focusing on nonlinear optics principles. This research addresses the burgeoning demand for scalable, cost-effective solutions to produce complex quantum optical states directly on-chip. Such innovations are particularly relevant for advancing quantum technologies in communication, computing, and various quantum-enabled applications.

Key Findings and Methodologies

The paper encapsulates various methodologies and material systems employed to construct chip-based photon quantum state sources, emphasizing the crucial role of nonlinear optical processes. Among these methods, the paper predominantly reviews spontaneous parametric down-conversion (SPDC) and spontaneous four-wave mixing (SFWM), both pivotal for generating entangled and single photons. These quantum states are foundational for implementing secure quantum communication protocols and quantum computing frameworks.

The authors highlight the distinct differences between SPDC and SFWM. While SPDC processes rely on second-order nonlinearities, SFWM exploits third-order nonlinear interactions, each catering to specific frequency generation requirements dictated by conservation laws. The research underscores that SPDC demands signal and idler photons at symmetrical frequencies with respect to the pump, whereas SFWM's flexibility lies in generating spectrally adjacent photon pairs around the pump's frequency.

Performance and Challenges

This paper presents a detailed comparison across various integrated quantum sources, utilizing materials such as silicon, Hydex, and silicon nitride (Si3N4), which are compatible with complementary metal-oxide-semiconductor (CMOS) technology. The performance metrics assessed include brightness, coincidence-to-accidental ratio (CAR), purity, and heralding efficiency, critical for practical quantum technological applications.

One significant challenge discussed is efficiently filtering out the pump wavelength due to its spectral proximity to generated photons in SFWM processes. The research highlights recent innovations achieving high pump suppression levels and points out the integration potential with high-Q microresonators to enhance photon generation efficiency further.

Implications and Future Directions

Caspani et al.'s examination reveals promising implications for deploying quantum technologies beyond laboratory settings into widespread practical use. Moreover, the potential for integrating these chip-based quantum sources with existing fiber-optic networks underscores their utility in quantum communication. The advancement towards deterministic photon sources through heralding and multiplexing techniques represents an essential echo of progress, promising enhancements in heralded single-photon quality and yield.

The paper also discusses future avenues, such as fully leveraging high-dimensional entangled states and cluster states on-chip, which could unlock unprecedented efficiencies and capabilities in quantum information processing and computation. Additionally, improved integration methods and material engineering might address current limitations, such as photon indistinguishability and multiphoton probabilities.

In conclusion, this comprehensive paper signals a crucial step towards economically viable, scalable quantum photonic systems. The seamless integration of these systems with existing semiconductor and fiber technologies could precipitate a new era of applications facilitated by quantum mechanics' intrinsic properties, such as superposition and entanglement, across modern communication and computation landscapes.