Researchers at South China Normal University in Guangzhou have demonstrated a quantum memory capable of storing high-dimensional qudits, using an approach different from single-qubit methods. Operating on 11-dimensional spatial modes, the memory achieves over 80% efficiency and greater than 99% qubit storage fidelity. This high-performance system, developed with affiliations at the Guangdong-Hong Kong Joint Laboratory of Quantum Matter and the Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area, estimates a distribution of 3.56 ± 0.16 bits of quantum information over 1000 kilometers in one minute.

Quantum Interconnect Rate Quantifies Memory Performance

A new quantum memory developed by researchers at South China Normal University achieves over 80% efficiency while storing qubits with greater than 99% fidelity, a performance level expected to accelerate the development of scalable quantum networks. This system introduces a metric designed to comprehensively evaluate quantum memories by integrating multimode capacity, efficiency, and fidelity into a single quantifiable value.

The need for such a metric arose from the limitations of assessing quantum memories based on individual performance aspects, which hindered the creation of truly practical systems for long-distance quantum communication. The team, affiliated with the Key Laboratory of Atomic and Subatomic Structure and Quantum Control, operates on 11-dimensional spatial modes to maximize data density within the memory.

Researchers estimate that, utilizing this memory, 3.56 ± 0.16 bits of quantum information could be distributed over a 1000-kilometer repeater link in just one minute. Establishing a unified benchmark for quantum memory performance proved challenging, as excelling in one metric often came at the expense of others. The authors write that benchmarking and building a practical quantum memory that simultaneously optimizes multiple performance metrics poses two key challenges, highlighting the complexity of balancing these competing demands.

Previous advancements in quantum memory have demonstrated high efficiency, extended lifetimes, and improved fidelities, but rarely have these qualities been combined in a single device. The introduction of quantum interconnect rate aims to address this gap, providing a holistic measure of a memory’s suitability for real-world quantum interconnects.

Quantum memories are essential components of quantum repeaters, which synchronize photonic qubits and enable entanglement swapping, thereby extending the range of quantum networks. Single photons, the preferred carriers of quantum information, are susceptible to loss in transmission, and efficient quantum memories are vital to mitigating this issue.

High-Dimensional Qubit Storage with 11 Spatial Modes

Quantum memories capable of storing information across eleven spatial modes represent an advance in the architecture of quantum networks, according to work from South China Normal University. These memories, developed by a team of Shan-Chao Zhang and Hui Yan, address a critical bottleneck in long-distance quantum communication: photon loss. Single photons, ideal for transmitting quantum information, degrade in signal strength over distance, necessitating quantum repeaters to synchronize and amplify the signal.

The team’s approach moves beyond storing qubits as simple on/off states, instead leveraging the potential of high-dimensional qudits. By encoding information within eleven distinct spatial modes of light, the memory substantially increases the amount of quantum information that can be stored and transmitted through a single channel. This memory achieves a uniform efficiency exceeding 80% and qubit storage fidelities above 99%, enabling the efficient storage of these high-dimensional qudits.

Achieving 80% Efficiency in Multimode Quantum Memory

This advance addresses a critical bottleneck in the development of scalable quantum networks, where transmitting quantum information over long distances requires overcoming signal loss. This focus on high-dimensional qubits represents an approach different from many current quantum memory designs, which primarily focus on single-qubit storage. By encoding information across multiple spatial modes, the researchers effectively increase the density of information that can be transmitted and processed within a quantum network.

The implications extend to channel capacity; the team estimates a distribution of 3.56 ± 0.16 bits of quantum information. The researchers write, “Single photons serve as the fundamental carriers of quantum information in communication networks and quantum interconnects,” emphasizing the foundational role of their memory in future quantum infrastructure.

99% Fidelity for Storing High-Dimensional Qudits

This memory distinguishes itself by using an approach different from many current methods for storing information encoded in high-dimensional qudits. The developed system achieves a uniform efficiency exceeding 80% across these 11 dimensions, demonstrating a notable balance of these critical features. Their calculations estimate a distribution of 3.56 ± 0.16 bits of quantum information over a 1000-km repeater link in one minute, a figure that suggests a potential pathway toward scalable quantum interconnects.

Single Photons as Carriers in Quantum Networks

Researchers at South China Normal University are using an approach different from many current methods to redefine the capacity of quantum memories, moving beyond single-qubit storage to harness the potential of high-dimensional qudits. The researchers recognized that assessing a memory’s performance requires considering not just efficiency or fidelity in isolation, but a unified measure encompassing multimode capacity, efficiency, and fidelity.

This holistic approach allows for meaningful comparison between different memory technologies and guides the development of systems optimized for real-world applications. The implications of this high-performance memory extend to the practical realization of long-distance quantum communication.

Scalable Quantum Interconnects via Repeaters

Unlike many current approaches focused on single-qubit storage, this memory leverages high-dimensional qudits, potentially increasing data density and processing capabilities within future quantum infrastructures. This combination of high efficiency and fidelity is crucial for maintaining the integrity of quantum states over extended distances, a persistent challenge in quantum communication. The team introduced a new metric to comprehensively quantify quantum memories, acknowledging that assessing performance requires consideration of multiple characteristics simultaneously.

Establishing a unified benchmark is essential because excelling in a single metric, such as efficiency, lifetime, or fidelity, is insufficient for practical quantum interconnects. The ability to store multiple entangled states simultaneously, enabled by the multimode capacity, provides a direct boost to entanglement distribution rates, a key factor in building a functional quantum internet. Single photons, the fundamental carriers of quantum information, benefit from this improved memory capacity, as they can transmit information with minimal decoherence when entangled with stationary matter qubits.

The work builds on existing prototypes of high-performance quantum key distribution and metropolitan-scale quantum networks, marking steady progress toward a global quantum internet. The researchers’ focus on maximizing multiple performance characteristics simultaneously addresses a critical bottleneck in the field.

👉 More information
🗞 High-Performance Quantum Memory for Quantum Interconnects
✍️ Hao-Xuan Luo et al.
🧠 DOI: http://link.aps.org/doi/10.1103/k35f-7k9s

More like this