Shaping entangled photons through thick scattering media using an advanced wave beacon (2403.18324v1)

Abstract: Entangled photons provide transformative new paths in the fields of communication, sensing, and computing. However, when entangled photons propagate through a complex medium such as a biological tissue or a turbulent atmosphere, their correlations are scrambled. Using wavefront shaping to compensate for the scattering and retrieve the two-photon correlations is challenging due to the low signal-to-noise ratio of the two-photon signal. While previous works partly addressed this challenge by using feedback from a strong classical laser beam that co-propagates with the entangled photons, such methods frequently depend on assumptions about the complex medium, limiting the applicability of quantum wavefront shaping. In this work, we propose and demonstrate a new feedback mechanism that is inspired by Klyshko's advanced wave picture, in which the classical laser beam counter-propagates with one of the entangled photons and co-propagates with the other. The new Klyshko feedback allows compensation of scattering in thick samples and even in situations where each photon propagates through a different scattering medium. Since the advanced wave picture applies whenever optical reciprocity is valid, such Klyshko optimization can be utilized across a wide range of configurations, offering a robust and alignment-free setup. We therefore believe this protocol will open the door for real-world applications of quantum wavefront shaping.

• The paper introduces a Klyshko beam feedback mechanism that optimally enhances entangled photon correlations without needing detailed assumptions about the scattering medium.
• It employs spatial light modulators for wavefront shaping, significantly boosting coincidence detection rates even in thick and heterogeneous scatterers.
• The study paves the way for robust quantum communication by showcasing scalable techniques to control entangled photons through complex environments.

Shaping Entangled Photons through Complex Media

The research presented in the paper "Shaping entangled photons through thick scattering media using an advanced wave beacon" addresses advanced modes of controlling entangled photon propagation through complex media. The transformation of entangled photons holds considerable potential in quantum communication, sensing, and computing. However, these photons' interactions with complex media such as biological tissues or turbulent atmospheres often scramble their correlations, presenting a formidable problem for their practical application.

Methods and Technique

The paper introduces an innovative feedback mechanism inspired by Klyshko's advanced wave picture (AWP). Traditional feedback systems for the correction of entangled photon scattering rely on a co-propagating classical laser beam. This approach is often impeded by assumptions regarding the complex medium, which reduce its generalizability. In stark contrast, the authors propose employing a counter-propagating classical beam (referred to as the "Klyshko beam") that aligns with optical reciprocity principles. The Klyshko beam, when introduced into the experimental configuration, optimally enhances entangled photon correlations without necessitating detailed assumptions about the scattering medium.

The experimental setup employs spatial light modulators (SLMs) to perform wavefront shaping, enhancing the fidelity of spatially entangled photons even when subjected to distinct scatterers. Notably, it does so efficiently for both thick samples and configurations wherein individual photons traverse disparate scattering media.

Experimental Results

The robust alignment of the detector configurations allows for significant ease of use, resulting in substantial enhancements in the coincidence detection rate of the entangled photons. The results demonstrate that localized two-photon correlations can be achieved even outside the memory-effect range of the scattering medium. This circumvents a major limitation associated with using a single, copropagating shaping laser for scattering compensation.

Interestingly, the research includes the measurement of the angular memory effect with the application of the advanced wave picture. This illustrates that the Klyshko beam and entangled photon pairs exhibit very similar dynamics under scattering conditions, providing empirical support to theoretical models of wave-like behavior of quantum states through complex media.

Implications and Outlook

The paper substantially contributes to quantum information science by expanding the toolkit available for manipulating quantum states in non-ideal conditions. Practically, the application of the Klyshko feedback for shaping entangled photons has wide implications for quantum communications, particularly in enhancing the resilience of transmitted quantum information over large distances and through complex media.

On a theoretical level, the adoption of Klyshko's AWP presents a foundational advancement in quantum optics, potentially aiding in the design of quantum circuits that are resistant to scattering-induced information degradation. This area may see further development, as technical refinements in implementing AWP with diverse beam shapes and crystal configurations could broaden its applicability.

Future research directions could involve extending these methodologies to other quantum systems and exploring the scalability of the setup in more intricate networks with higher-dimensional entanglement. Combining Klyshko optimization with developing technologies like high-dimensional quantum cryptography could facilitate real-world implementations and contribute to advancing secure quantum communications.

In conclusion, the work opens up avenues of exploration for the utilization of entangled photons in complex environments, thus offering a promising approach to overcoming limitations posed by scattering media. By pushing the boundaries of how quantum states interact with and are manipulated by their environment, this research forwards the trajectory of quantum technology development.