Advances in High Dimensional Quantum Entanglement (1911.10006v2)

Abstract: Since its discovery in the last century, quantum entanglement has challenged some of our most cherished classical views, such as locality and reality. Today, the second quantum revolution is in full swing and promises to revolutionize areas such as computation, communication, metrology, and imaging. Here, we review conceptual and experimental advances in complex entangled systems involving many multilevel quantum particles. We provide an overview of the latest technological developments in the generation and manipulation of high-dimensionally entangled photonic systems encoded in various discrete degrees of freedom such as path, transverse spatial modes or time/frequency bins. This overview should help to transfer various physical principles for the generation and manipulation from one to another degree of freedom and thus inspire new technical developments. We also show how purely academic questions and curiosity led to new technological applications. Here fundamental research provides the necessary knowledge for coming technologies such as a prospective quantum internet or the quantum teleportation of all information stored in a quantum system. Finally, we discuss some important problems in the area of high-dimensional entanglement and give a brief outlook on possible future developments.

• The paper presents a systematic review of experimental and theoretical methods for generating and manipulating high-dimensional entangled states in photonic systems.
• It details various techniques, including path and orbital angular momentum approaches, capable of producing up to 100-dimensional entanglement.
• Emphasizing scalability and integration, the study paves the way for practical advances in quantum communication and computing technologies.

Overview of "Advances in High Dimensional Quantum Entanglement"

The paper "Advances in High Dimensional Quantum Entanglement" provides an extensive review of recent experimental and theoretical developments in the field of high-dimensional quantum entanglement, with a specific focus on photonic systems. Authored by Manuel Erhard, Mario Krenn, and Anton Zeilinger, the text explores the intricacies of creating and manipulating complex quantum states that comprise multilevel quantum particles, particularly photons. This work addresses key experimental techniques utilized to generate and measure high-dimensional entangled states across various discrete degrees of freedom (DoFs), including path, transverse spatial modes, and discrete time/frequency bins.

The authors systematically categorize advancements in high-dimensional entanglement through historical perspectives and contemporary experimental implementations. These insights set the stage for potential applications in emerging quantum technologies, such as quantum telecommunications, quantum computing, and, ultimately, the establishment of a quantum internet. Particular attention is given to the transition from academic curiosity-driven research to technological applications that could revolutionize communication and computation paradigms.

Photonic Carriers of High-Dimensional Entanglement

The researchers focus on several physical methods for generating and manipulating entanglement in photonic systems, emphasizing path DoFs, spatial modes encompassing orbital angular momentum (OAM), and discretized time and frequency modes. The path DoFs offer flexibility in arbitrary single-photon transformations with integrated optics, while OAM-based techniques exploit the helical phases and unique topological charge characteristics of photons to achieve up to 100-dimensionally entangled states.

In contrast, time and frequency mode entanglement utilize unbalanced interferometry and innovative on-chip technologies to yield significant progress in the frequency domain. Quantum frequency combs and micro-ring resonators play a pivotal role in this context, pushing forward efforts to scale quantum networks over practical distances.

Multiphoton Entanglement and Applications

The paper argues that different classes of entanglement—ranging from multi-particle states to genuinely high-dimensional multi-photon states—present vast possibilities for enhancing quantum communication protocols. Implementations classified under these categories include experimental three-dimensional quantum teleportation and entanglement swapping, which have the potential to enhance quantum network capabilities and facilitate long-distance quantum communication.

Implications and Future Directions

The paper encapsulates the theoretical implications of high-dimensional quantum entanglement, challenging conventional beaux-arts of quantum mechanics and classical physics distinctions. It highlights both the increasing experimental capabilities available to researchers today and the theoretical challenges that persist, particularly in decoding the nuanced structure of entangled multi-qudit states.

Moving forward, the authors suggest that future efforts should focus on overcoming current technological barriers, such as the development of highly efficient photonic sources and near-perfect detectors. Other areas ripe for investigation include the further exploration of non-traditional observation techniques, novel applications of high-dimensional entangled states, and the scalability and integration of quantum systems.

The paper serves as a comprehensive guide for researchers engaged in quantum technology, providing technical foundation and inspiration for further exploration of high-dimensional entangled systems. The ultimate aim remains a deeper understanding of quantum systems and the harnessing of entanglement to power next-generation quantum applications.