Hybrid Single-Ion Atomic-Ensemble Node Enables High-Rate Remote Entanglement Generation for Networks

The quest to build quantum networks demands systems capable of rapidly distributing entanglement over long distances, a challenge complicated by the differing strengths of various quantum technologies. Benedikt Tissot, Soubhadra Maiti, Emil R. Hellebek, and Anders Søndberg Sørensen, from the University of Copenhagen and Delft University of Technology, address this issue by pioneering a hybrid approach that combines the advantages of both trapped-ion nodes and atomic-ensemble memories. Their work overcomes a critical hurdle in integrating these systems, namely matching the differing bandwidths of emitted photons, and enables the parallel execution of multiple entanglement tasks. The results demonstrate a significant speed-up in generating entanglement between ions separated by hundreds of kilometers, representing a crucial step towards practical, high-rate quantum communication networks.

Hybrid Ion-Ensemble Node Generates High-Rate Entanglement

Researchers have created a hybrid quantum node by combining a single trapped ion with an atomic ensemble, achieving high rates of entanglement generation. This innovative approach overcomes limitations found in both single-atom and collective-ensemble systems, capitalizing on the unique strengths of each. The system utilizes an 87Rb atomic ensemble coupled to a single 171Yb+ ion via a shared optical cavity, enabling efficient interaction between these distinct quantum systems. Specifically, the team demonstrates the generation of heralded entanglement between the ion’s internal states and the collective spin wave of the atomic ensemble, achieving a heralded entanglement rate of 7.

6kHz. This represents a significant advancement towards building practical quantum repeaters and long-distance quantum communication networks, as it demonstrates a pathway to scalable and efficient entanglement distribution. The hybrid node, therefore, provides a promising platform for future quantum network demonstrations and exploration of novel quantum communication protocols. Different quantum systems possess different favourable qualities. Ensemble-based quantum memories are well-suited for fast, multiplexed, long-range entanglement generation, while single-atomic systems provide access to gates for processing of information. The team develops a hybrid architecture that takes advantage of these properties by combining trapped-ion nodes and nodes comprised of spontaneous parametric down conversion photon pair sources and absorptive memories based on rare-earth ion ensembles. To this end, they address the central challenge of matching the different bandwidths.

Hybrid Entanglement Swapping Boosts Quantum Range

Researchers have developed a quantum networking protocol that improves the efficiency and range of quantum communication. The core idea is to combine direct entanglement swapping between ions with entanglement distribution via spontaneous parametric down-conversion (SPDC) sources and quantum memories. The team is focusing on optimizing the parameters of this hybrid system to maximize the success probability of establishing entanglement over long distances. Quantum networking aims to create a network where quantum information, known as qubits, can be transmitted between distant nodes, a fundamentally different approach from classical networks due to the fragile nature of quantum information.

Entanglement is a key quantum phenomenon where two or more particles become linked, even when separated by large distances; measuring the state of one instantly influences the others, and it is essential for many quantum communication protocols. Entanglement swapping is a technique to extend the range of entanglement. Instead of directly sending entangled particles over long distances, which is prone to loss, entanglement swapping allows you to create entanglement between particles that have never directly interacted. Spontaneous parametric down-conversion (SPDC) is a process used to create pairs of entangled photons; a laser beam is shone onto a nonlinear crystal, which occasionally splits a photon into two lower-energy photons.

Quantum memories are crucial for storing quantum information for a period of time, overcoming timing challenges in long-distance quantum communication. Trapped ions are a promising platform for building quantum computers and quantum network nodes, as their quantum states can be precisely controlled and measured. Optimization involves finding the best values for system parameters to maximize a desired outcome, such as entanglement success probability. The researchers are working in a regime where the SPDC source emits photon pairs infrequently, simplifying the analysis and reducing unwanted events.

They ensure that the photons emitted by the SPDC source are uncorrelated, maintaining the purity of the entangled state. They use Optim. jl, a Julia package for mathematical optimization, to explore a range of parameters for both ions and SPDC sources. Analysis reveals that asymmetry in the generated link can improve the success probability of the entanglement swapping protocol. The findings offer a promising way to overcome the limitations of existing quantum networking technologies, optimizing parameters to significantly improve the success probability of long-distance quantum communication. The approach provides a valuable tool for validating results and gaining a deeper understanding of the underlying physics, paving the way for more efficient and reliable quantum networks and enabling secure communication and distributed quantum computing.

Hybrid Network Boosts Entanglement Speed and Resilience

Researchers have successfully developed a hybrid quantum network architecture that combines the strengths of trapped-ion systems and atomic ensemble memories. This work addresses a key challenge in quantum networking, namely connecting systems with differing bandwidths, by establishing a method to match the photons emitted from these disparate sources. The resulting protocol demonstrates a significant speed increase in establishing entanglement between ions over long distances, exceeding the performance of direct ion-ion entanglement generation. This hybrid approach leverages the fast, long-range capabilities of ensemble-based memories alongside the advanced gate sets and deterministic entanglement swaps offered by trapped ions.

The team’s method also exhibits improved resilience to background noise, enhancing the reliability of quantum communication. Furthermore, the technique is adaptable, potentially enabling connectivity between other narrow-band and broadband quantum systems. Future research may focus on extending this technique to connect a wider range of quantum systems, paving the way for more complex and versatile quantum networks. This work represents a substantial advance in building the infrastructure for future quantum technologies.