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IEEE/LEOS Summer Topical Meetings

Quantum Repeaters Based on Two-Species Trapped Ions

Sreraman Muralidharan, Siddhartha Santra, Liang Jiang, Christopher R. Monroe, Vladimir S. Malinovsky

Published Jul 1, 2018• 2 citations
Publisher

Abstract

Trapped ions technology is the most promising candidate for construction of the large-scale quantum computers, quantum repeaters and quantum networks. Quantum networks require matter qubits with fast quantum gates and measurement, efficient coupling to photons and low gate error rates. There was growing progress in two-species ion trapping [1], where one ion acts as a communication qubit that can be efficiently entangled to photon and the other one used as excellent quantum memories allowing efficient local processing. However, the photonic interface needed for communication ions must not affect the state of the quantum memory ion. In a recent experimental breakthrough, the isolation between quantum memory ion (171Yb+) and communication ion (138Ba+) was achieved and a quantum state transfer between the ions has been demonstrated.

DOI
10.1109/phosst.2018.8456727

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Trapped ions technology is the most promising candidate for construction of the large-scale quantum computers, quantum repeaters and quantum networks. Quantum networks require matter qubits with fast quantum gates and measurement, efficient coupling to photons and low gate error rates. There was growing progress in two-species ion trapping [1], where one ion acts as a communication qubit that can be efficiently entangled to photon and the other one used as excellent quantum memories allowing efficient local processing. However, the photonic interface needed for communication ions must not affect the state of the quantum memory ion. In a recent experimental breakthrough, the isolation between quantum memory ion (171Yb+) and communication ion (138Ba+) was achieved and a quantum state transfer between the ions has been demonstrated.
Abstract We examine the viability of quantum repeaters based on two-species trapped ion modules for long-distance quantum key distribution. Repeater nodes comprised of ion-trap modules of co-trapped ions of distinct species are considered. The species used for communication qubits has excellent optical properties while the other longer lived species serves as a memory qubit in the modules. Each module interacts with the network only via single photons emitted by the communication ions. Coherent Coulomb interaction between ions is utilized to transfer quantum information between the communication and memory ions and to achieve entanglement swapping between two memory ions. We describe simple modular quantum repeater architectures realizable with the ion-trap modules and numerically study the dependence of the quantum key distribution rate on various experimental parameters, including coupling efficiency, gate infidelity, operation time and length of the elementary links. Our analysis suggests crucial improvements necessary in a physical implementation for co-trapped two-species ions to be a competitive platform in long-distance quantum communication.
Trapped atomic ions are standards for quantum information processing, serving as quantum memories, hosts of quantum gates in quantum computers and simulators, and nodes of quantum communication networks. Quantum bits based on trapped ions enjoy a rare combination of attributes: They have exquisite coherence properties, they can be prepared and measured with nearly 100% efficiency, and they are readily entangled with each other through the Coulomb interaction or remote photonic interconnects. The outstanding challenge is the scaling of trapped ions to hundreds or thousands of qubits and beyond, at which scale quantum processors can outperform their classical counterparts in certain applications. We review the latest progress and prospects in that effort, with the promise of advanced architectures and new technologies, such as microfabricated ion traps and integrated photonics.
Trapped atomic ions constitute one of the leading physical platforms for building the quantum repeater nodes to realize large-scale quantum networks. In a long-distance trapped-ion quantum network, it is essential to have crosstalk-free dual-type qubits: one type, called the communication qubit, to establish an entangling interface with telecom photons; and the other type, called the memory qubit, to store quantum information immune from photon scattering under entangling attempts. Here, we report the first experimental implementation of a telecom-compatible and crosstalk-free quantum network node based on two trapped ^{40}Ca^{+} ions. The memory qubit is encoded on a long-lived metastable level to avoid crosstalk with the communication qubit encoded in another subspace of the same ion species, and a quantum wavelength conversion module is employed to generate heralded ion-photon entanglement over a 12 km fiber. Our work therefore constitutes an important step toward the realization of quantum repeaters and long-distance quantum networks.
Trapped ions constitute a promising platform for implementation of a quantum network. Recently, a dual-type qubit scheme has been realized in a quantum network node where communication qubits and memory qubits are encoded in different energy levels of the same ion species, such that the generation of ion-photon entanglement on the communication qubits has negligible cross-talk error on the preloaded quantum information in the memory qubits. However, to achieve versatile applications of a quantum network, a crucial component of the dual-type node, namely, the entangling gate between the communication and the memory qubits, is still missing. Here, we report a dual-type quantum network node equipped with ion-photon entanglement generation, cross-talk-free quantum memory, and entangling gates between dual-type qubits simultaneously. We demonstrate its practical applications including the passive quantum-state teleportation and the preparation of multipartite entangled state. Our work achieves the necessary components of a dual-type quantum network node.