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Science

Scaling the Ion Trap Quantum Processor

Christopher R. Monroe, Jungsang Kim

Published Mar 7, 2013• 785 citations
Publisher

Abstract

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.

DOI
10.1126/science.1231298

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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.
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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.
Scaling up controlled quantum systems to involve large numbers of qubits remains one of the outstanding challenges of quantum information science. One path toward scalability is the use of a modular architecture where adjacent qubits may be entangled with applied electromagnetic fields, and remote qubits may be entangled using photon interference. Trapped atomic ion qubits are one of the most promising platforms for scaling up quantum systems by combining long coherence times with high fidelity entangling operations between proximate and remote qubits. In this thesis, I present experimental progress on combining entanglement between remote atomic ions separated by 1 meter with near-eld entanglement between atomic ions in the same ion trap. I describe the experimental improvements to increase the remote entanglement rate by orders of magnitude to nearly 5 per second. This is the first experimental demonstration where the remote entanglement rate exceeds the decoherence rate of the entangled qubits. The flexibility of creating remote entanglement through photon interference is demonstrated by using the interference of distinguishable photons without sacrificing remote entanglement rate or fidelity. Next I describe the use of master clock in combination with a frequency comb to lock the phases of all laser-induced interactions between remote ion traps while removing optical phase stability requirements. The combination of both types of entanglement gates to create a small quantum network are described. Finally, I present ways to mitigate cross talk between photonic and memory qubits by using different trapped ion species. I show preliminary work on performing state detection of nuclear spin 0 ions by using entanglement between atomic ion spin and photon polarization. These control techniques may be important for building a large-scale modular quantum system.
Trapped atomic ions are standards for quantum information processing, as all of the fundamental quantum operations have been demonstrated in small collections of atoms. Current work is concentrated on scaling ion traps to larger numbers of interacting qubits and the generation of massive entangled states. We discuss progress in the quantum networking of trapped atomic ions, using the Coulomb interaction for demonstrations of simple quantum simulations of magnetism, ultrafast laser pulses for entanglement, and finally probabilistic photonic interactions to bridge entanglement over long distances. © Published under licence by IOP Publishing Ltd.
Trapped atomic ions are standards for quantum information processing, as all of the fundamental quantum operations have been demonstrated in small collections of atoms. Current work is concentrated on scaling ion traps to larger numbers of interacting qubits and the generation of massive entangled states. We discuss progress in the quantum networking of trapped atomic ions, using the Coulomb interaction for demonstrations of simple quantum simulations of magnetism, ultrafast laser pulses for entanglement, and finally probabilistic photonic interactions to bridge entanglement over long distances. © Published under licence by IOP Publishing Ltd.
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