Recent advances in high-dimensional mode-locked quantum frequency combs (2502.08879v2)

Abstract: High-dimensional entanglement in qudit states offers a promising pathway towards the realization of practical, large-scale quantum systems that are highly controllable. These systems can be leveraged for various applications, including advanced quantum information processing, secure communications, computation, and metrology. In this context, quantum frequency combs have a crucial role as they inherently support multiple modes in both temporal and frequency domains, while preserving a single spatial mode. The multiple temporal and frequency modes of quantum frequency combs facilitate the generation, characterization, and control of high-dimensional time-frequency entanglement in extensive quantum systems. In this review article, we provide an overview of recent technological advancements in high-dimensional energy-time entangled quantum frequency combs. We explore how these time-frequency qudits, achieved using scalable telecommunications-wavelength components, can empower the creation of large-scale quantum states. Advances in quantum frequency combs can unlock new capabilities and versatility for promising developments in quantum science and technology.

• The paper demonstrates substantial advancements in generating and stabilizing high-dimensional time-frequency entangled states using mode-locked quantum frequency combs.
• It employs nonlinear waveguides and cavity configurations to achieve enhanced, tunable entangled photon generation with a Hilbert space dimensionality of 648.
• The review emphasizes practical applications in secure quantum communications, integrated quantum systems, and quantum memory interfacing.

Advances in High-Dimensional Quantum Frequency Combs

The paper "Recent advances in high-dimensional quantum frequency combs" presents a comprehensive review of the current state and future potential of high-dimensional quantum frequency combs (QFCs) within quantum information science. The principal focus is on the generation, characterization, and application of high-dimensional time-frequency entangled states afforded by QFCs, with an emphasis on technological innovations in this domain. This review highlights the potential of QFCs to enable large-scale quantum systems using scalable telecommunications-wavelength components, uncovering new capabilities for quantum science and technology.

High-dimensional quantum systems, represented by qudit states, offer an increased complexity over conventional qubit systems by tapping into a d-dimensional Hilbert space. Such systems have inherent advantages in diverse quantum applications including quantum communications, computation, and metrology by enhancing information capacity, improving noise resilience, and supporting advanced algorithms. Photonic platforms particularly benefit from this, employing continuous-variable and discrete-variable methods to manipulate quantum information.

The introduction of mode-locked quantum frequency combs marks a significant departure from traditional methods by allowing coherent control over high-dimensional time-frequency entangled states in a single spatial mode. This is achieved through quantum frequency comb generation mechanisms utilizing nonlinear optical waveguides and cavity post-filtering. These mode-locked QFCs inherently possess dense multimode temporal and spectral structures, ideal for practical dense quantum information processing tasks.

A notable achievement reviewed in this paper is the substantial enhancement of entangled photon generation in doubly- and singly-configured cavities. These configurations, separately or in tandem, lead to improved photon pair generation that is stable, tunable, and beneficial for diverse applications without requiring complex cavity arrangements or active stabilization—important strides in practical implementations.

Strong numerical results are evident throughout the paper, demonstrating, for example, the high visibility of Franson interference revivals and the certification of high-dimensional entanglement in QFC states, where a significant Hilbert space dimensionality of 648 has been achieved. This underscores their utility in exploring and exploiting the full potential of quantum states in quantum information systems.

The implications of these advancements are substantial: QFCs present scalable pathways to large-scale integrated quantum systems, facilitating applications from purely theoretical explorations to real-world implementations like secure quantum communications through distributed quantum networks. Additionally, the integration with quantum memories promises advances in quantum repeaters, essential for achieving long-distance quantum communication.

The review encapsulates the progress made and yet to be achieved in the domain of high-dimensional QFCs, underscoring the promise they hold for future developments in quantum information processing. The continuous improvement in detector technology, such as SNSPDs with ultra-low timing jitter, indicates a trajectory towards more accessible and widely applicable high-dimensional quantum systems. As these systems continue to evolve, they are set to play pivotal roles in realizing more intricate and versatile quantum communication networks, memory systems, and computational protocols, moving closer to realizing the full potential of quantum technologies.