Establishing and storing of deterministic quantum entanglement among three distant atomic ensembles (1712.01470v1)

Abstract: It is crucial for physical realization of quantum information networks to first establish entanglement among multiple space-separated quantum memories and then at a user-controlled moment to transfer the stored entanglement to quantum channels for distribution and conveyance of information. Here we present an experimental demonstration on generation, storage and transfer of deterministic quantum entanglement among three spatially separated atomic ensembles. The off-line prepared multipartite entanglement of optical modes is mapped into three distant atomic ensembles to establish entanglement of atomic spin waves via electromagnetically-induced-transparency light-matter interaction. Then the stored atomic entanglement is transferred into a tripartite quadrature entangled state of light, which is space-separated and can be dynamically allocated to three quantum channels for conveying quantum information. The existence of entanglement among released three optical modes verifies that the system has capacity of preserving multipartite entanglement. The presented protocol can be directly extended to larger quantum networks with more nodes.

• The paper achieved deterministic generation and storage of tripartite entanglement among atomic ensembles using an off-line prepared optical entangled state mapped via EIT.
• The experimental setup employed balanced homodyne detection to verify entanglement retrieval after a controlled 2.6-meter storage period.
• The findings advance scalable quantum networks while highlighting challenges in mapping efficiency and losses in optical-to-atomic interfaces.

Overview of Deterministic Quantum Entanglement Among Distant Atomic Ensembles

The paper examines the experimental generation, storage, and transfer of deterministic quantum entanglement among three spatially separated atomic ensembles. It addresses the critical requirement for quantum information networks to establish entanglement between multiple distant quantum memories before transferring this entanglement to quantum channels. The research employs continuous-variable (CV) entanglement and demonstrates the storage and retrieval of tripartite entanglement, enhancing our understanding of quantum information processing capacities.

Key Findings and Methodology

1. Entanglement Generation and Storage: The research team achieved entanglement among three distant atomic ensembles using a multipartite entangled state of optical modes, which was subsequently mapped into atomic spin waves via electromagnetically-induced-transparency (EIT) interaction. The experiment documented successful storage and retrieval of this entanglement over a distance of 2.6 meters.
2. Experimental Setup: The setup involved off-line preparation of a tripartite optical entangled state, which interacted with three atomic ensembles located at different nodes. Post interaction, entanglement among the atomic ensembles was verified by transferring the stored entanglement back into optical channels.
3. Verification of Entanglement: The researchers used balanced homodyne detectors to measure the entanglement among the released optical submodes after a controlled storage period. The presence of entanglement among the submodes was confirmed by violation of tripartite inseparability criteria, showing entanglement even after storage.
4. Performance Metrics: The crucial performance metrics included the squeezing parameters of the input optical modes and the total mapping efficiency from optical submodes to atomic ensembles and back. The efficiency was notably affected by various factors including transmission loss and the inherent properties of the atomic media.

Implications and Challenges

This research provides important insights into the practical realization of quantum information networks. By successfully demonstrating multipartite entanglement among atomic nodes, it paves the way for more complex quantum network architectures. How this entanglement is achieved and managed, especially the methodology of using EIT for efficient light-matter interaction, is especially noteworthy for future developments.

However, several challenges remain—particularly in enhancing the mapping efficiency which is currently limited by optic losses and some internal noise processes within the atomic media. The experiment also highlights the difficulty in minimizing these noises while maintaining high transmission and storage efficiencies.

Future Prospects

The experiment's semi-automated architecture provides a template for scaling up to more extensive quantum networks involving multiple nodes. Enhancements in squeezing parameters and reduction in noise can improve the robustness of quantum memories. Advances in technology, such as better optical elements or enhanced cavity configurations, could be leveraged to increase mapping and storage efficiencies.

Ultimately, this research contributes substantially to the foundational work necessary for the development of a quantum network infrastructure. The potential to network entangled states across distant memories opens up opportunities for progress in quantum computation and quantum secure communications. As experimental setups and theoretical models continue to evolve, the viability of large-scale quantum networks becomes increasingly realistic.