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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Multimode quantum networking with trapped ions

Victor L. Krutyanskiy, Vojtech Krcmarsky, M. Canteri, Martin Meraner, Josef Schupp, B. P. Lanyon

Published Jun 21, 2021• 0 citations
Publisher

Abstract

Envisioned large-scale quantum networks demand the ability to rapidly distribute and store entanglement between remote matter-based nodes using photons [1] . The minimum time required to distribute entanglement between two nodes is the time it takes light to travel between them, which over 100 km distance already 0.33 ms. The speed of light thus sets a fundamental limit on the achievable entanglement distribution rate: with a single quantum emitter in a node, one has to wait for the photon travel time before trying again with a new photon for any application that would require also classical communication (e.g. to realize a quantum repeater) [2] . Over 100 km of fiber, this limits the entanglement distribution attempt rate to 2 kHz and, given 1.5% transmission in the best telecom fibres, a success rate of 30 Hz. This is a general problem for entanglement distribution over long distances as far higher rates are critical for the practical realisation of quantum networks and their applications. To overcome this limit, several entanglement distribution attempts have to be done in parallel. This requires multiple modes of the node (memory qubits) to couple selectively to the multiple modes of the link.

DOI
10.1109/cleo/europe-eqec52157.2021.9542557

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Envisioned large-scale quantum networks demand the ability to rapidly distribute and store entanglement between remote matter-based nodes using photons [1] . The minimum time required to distribute entanglement between two nodes is the time it takes light to travel between them, which over 100 km distance already 0.33 ms. The speed of light thus sets a fundamental limit on the achievable entanglement distribution rate: with a single quantum emitter in a node, one has to wait for the photon travel time before trying again with a new photon for any application that would require also classical communication (e.g. to realize a quantum repeater) [2] . Over 100 km of fiber, this limits the entanglement distribution attempt rate to 2 kHz and, given 1.5% transmission in the best telecom fibres, a success rate of 30 Hz. This is a general problem for entanglement distribution over long distances as far higher rates are critical for the practical realisation of quantum networks and their applications. To overcome this limit, several entanglement distribution attempts have to be done in parallel. This requires multiple modes of the node (memory qubits) to couple selectively to the multiple modes of the link.
A three-qubit quantum network node based on trapped atomic ions is presented. The ability to establish entanglement between each of the qubits in the node and a separate photon that has travelled over a 101km-long optical fiber is demonstrated. By sending those photons through the fiber in close succession, a remote entanglement rate is achieved that is greater than when using only a single qubit in the node. Once extended to more qubits, this multimode approach can be a useful technique to boost entanglement distribution rates in future long-distance quantum networks of light and matter.
Abstract When shared between remote locations, entanglement opens up fundamentally new capabilities for science and technology. Envisioned quantum networks use light to distribute entanglement between their remote matter-based quantum nodes. Here we report on the observation of entanglement between matter (a trapped ion) and light (a photon) over 50 km of optical fibre: two orders of magnitude further than the state of the art and a practical distance to start building large-scale quantum networks. Our methods include an efficient source of ion–photon entanglement via cavity-QED techniques (0.5 probability on-demand fibre-coupled photon from the ion) and a single photon entanglement-preserving quantum frequency converter to the 1550 nm telecom C band (0.25 device efficiency). Modestly optimising and duplicating our system would already allow for 100 km-spaced ion–ion heralded entanglement at rates of over 1 Hz. We show therefore a direct path to entangling 100 km-spaced registers of quantum-logic capable trapped-ion qubits, and the optical atomic clock transitions that they contain.
Quantum networks, integrating quantum communication, quantum metrology, and distributed quantum computing, could provide secure and efficient information transfer, high-resolution sensing, and an exponential speed-up in information processing. Deterministic entanglement distribution over long distances is a prerequisite for scalable quantum networks, enabling the utilization of device-independent quantum key distribution (DI-QKD) and quantum teleportation to achieve secure and efficient information transfer. However, the exponential photon loss in optical fibres prohibits efficient and deterministic entanglement distribution. Quantum repeaters, incorporating entanglement swapping and entanglement purification with quantum memories, offer the most promising means to overcome this limitation in fibre-based quantum networks. Despite numerous pioneering efforts toward realizing quantum repeaters, a critical bottleneck remains, as remote memory-memory entanglement suffers from decoherence more rapidly than it can be established and purified over long distances. We overcome this by developing long-lived trapped-ion memories, an efficient telecom interface, and a high-visibility single-photon entanglement protocol. This allows us to establish and maintain memory-memory entanglement over a 10 km fibre within the average entanglement establishment time for the same distance. As a direct application, we demonstrate metropolitan-scale DI-QKD, distilling 1,917 secret keys out of 4.05*10^5 Bell pairs over 10 km. We further report a positive key rate over 101 km in the asymptotic limit, extending the achievable distance by more than two orders of magnitude. Our work provides a critical building block for quantum repeaters and marks an important step toward scalable quantum networks.
A three-qubit quantum network node based on trapped atomic ions is presented.The ability to establish entanglement between each individual qubit in the node and a separate photon that has traveled over a 101km-long optical fiber is demonstrated.By sending those photons through the fiber in close succession, a remote entanglement rate is achieved that is greater than when using only a single qubit in the node.Once extended to more qubits, this multimode approach can be a useful technique to boost entanglementdistribution rates in future long-distance quantum networks of light and matter.
Quantum networks and quantum repeaters represent the promising avenues for building large-scale quantum information systems, serving as foundational infrastructure for distributed quantum computing, long-distance quantum communication, and networked quantum sensing. A critical step in realizing a functional quantum network is the efficient and high-fidelity establishment of heralded entanglement between remote quantum nodes. A multimode entangling scheme offers a powerful strategy to accelerate remote entanglement distribution, particularly over long optical fibers. Here, we experimentally demonstrate multimode-enhanced heralded entanglement between two trapped-ion quantum network nodes. By harnessing ten temporal photonic modes, we achieve a 4.59-fold speedup in ion-ion entanglement generation and attain an entanglement fidelity of 95.9%±1.5% over 1.2 km of fiber. Employing a dual-type architecture, our system is readily scalable to multiple nodes, thereby establishing a key building block for future large-scale quantum networks.
Single photons are the flying qubits of choice for distributing entanglement in a quantum internet. Quantum memories embedded in quantum repeaters are crucial to overcome transmission loss and enhance the rate of quantum communication. A multimode memory can further boost the channel capacity. However, benchmarking and building a practical quantum memory that simultaneously optimizes multiple performance metrics poses two key challenges. Here, we introduce quantum interconnect rate to comprehensively quantify quantum memories, and further demonstrate a high-performance quantum memory that simultaneously integrates three essential criteria at once: large multimode capacity, high efficiency, and high fidelity. Operating on 11-dimensional spatial modes, our memory achieves a uniform efficiency exceeding 80% and qubit storage fidelities above 99%, enabling the efficient storage of high-dimensional qudits. Based on these capabilities, we estimate a distribution of 3.56 bits of quantum information over a 1000-km repeater link in one minute, highlighting a practical pathway toward scalable quantum interconnects and quantum networks.