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Novel Ion Traps for Enhanced Fluorescence Collections and Single Photon Sources Based on Barium Ions

Gang Shu

Published Nov 1, 2010• 1 citation
OpenAlex

Abstract

Efficient ion-photon interface is critical for ion-photon and ion-ion entanglement generation, which are the fundamental building blocks for loophole-free Bell inequality violation tests based on ion qubits, and for the quantum computer architecture based on ion-photon networks. As one approach to address the problem, the feasibility of integrating reflective optics into ion trap to increase free-space photon interception is studied. The development and operation of two novel ion traps are demonstrated: one integrates a spherical mirror with a linear quadrapole trap, and the other combines the optical surface with the RF electrode. The possibility of using aspherical optics to improve ion images is studied and partially implemented. A continuously excited single photon source based on 138Ba+ ion is demonstrated and calibrated. Methods of scaling up current design are also discussed.

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Efficient ion-photon interface is critical for ion-photon and ion-ion entanglement generation, which are the fundamental building blocks for loophole-free Bell inequality violation tests based on ion qubits, and for the quantum computer architecture based on ion-photon networks. As one approach to address the problem, the feasibility of integrating reflective optics into ion trap to increase free-space photon interception is studied. The development and operation of two novel ion traps are demonstrated: one integrates a spherical mirror with a linear quadrapole trap, and the other combines the optical surface with the RF electrode. The possibility of using aspherical optics to improve ion images is studied and partially implemented. A continuously excited single photon source based on 138Ba+ ion is demonstrated and calibrated. Methods of scaling up current design are also discussed.
We improved photon collection efficiency from single trapped ions by integrating a high numerical aperture spherical mirror into a linear Paul trap. Satisfactory single ion images were achieved by compensating the large spherical aberration of the mirror by a specially designed aspheric corrector. We also designed a new RF ion trap with the metallic spherical mirror acting as one of the trap electrodes. This trap will greatly increase the efficiency of ion fluorescence collection for ion-photon and remote ion entanglement.
Efficient collection of fluorescence from trapped ions is crucial for quantum optics and quantum computing applications, specifically for qubit state detection and in generating single photons for ion-photon and remote ion entanglement. In a typical setup, only a few percent of the ion fluorescence is intercepted by the aperture of the imaging optics. We employ a simple metallic spherical mirror integrated with a linear Paul ion trap to achieve a photon collection efficiency of at least 1010%10 from a single Ba+{}^{+}+ ion. An aspheric corrector is used to reduce the aberrations caused by the mirror and achieve high image quality.
Trapped, laser-cooled atoms and ions produce intense fluorescence of the order 107~108 photons per second. Detection of this fluorescence enables efficient measurement of the quantum state of qubits based on trapped atoms. It is desirable to collect a large fraction of the photons to make the detection faster and more reliable. Additionally, efficient fluorescence collection can improve the speed and fidelity of remote ion entanglement and quantum gates. Refractive and reflective optics, and optical cavities have all been used to collect the trapped ion fluorescence with up to about 10% efficiency. Here we show a novel ion trap design that incorporates a metallic spherical mirror as the integral part of the trap itself, being its RF electrode. The mirror geometry enables up to 35% solid angle collection of trapped ion fluorescence. The movable central pin electrode of this trap allows precise placement of the ion at the focus of the reflector. We characterize the performance of the mirror, and measure 25% collection efficiency, likely limited by the imperfections of the mirror surface. We also study the properties of the images of single ions formed by the spherical mirror and apply aberration correction with an aspherical element placed outside the vacuum system. Owing to the simplicity of its design, this trap structure can be adapted for microfabrication and integration into more complex trap architectures.
Abstract. Efficient collection and analysis of trapped ion qubit fluorescence is essential for robust qubit state detection in trapped ion quantum computing schemes. We discuss simple techniques of improving photon collection efficiency using high numerical aperture (N.A.) reflective optics. To test these techniques we placed a spherical mirror with an effective N.A. of about 0.9 inside a vacuum chamber in the vicinity of a linear Paul trap. We demonstrate stable and reliable trapping of single barium ions, in excellent agreement with our simulations of the electric field in this setup. While a large N.A. spherical mirror introduces significant spherical aberration, the ion image quality can be greatly improved by a specially designed aspheric corrector lens located outside the vacuum system. Our simulations show that the spherical mirror/corrector design is an easy and cost-effective way to achieve high photon collection rates when compared to a more sophisticated parabolic mirror setup.
Efficient collection and analysis of trapped ion qubit fluorescence is essential for robust qubit state detection in trapped ion quantum computing schemes. We discuss simple techniques of improving photon collection efficiency using high numerical aperture (N.A.) reflective optics. To test these techniques we placed a spherical mirror with an effective N.A. of about 0.9 inside a vacuum chamber in the vicinity of a linear Paul trap. We demonstrate stable and reliable trapping of single barium ions, in excellent agreement with our simulations of the electric field in this setup. While a large N.A. spherical mirror introduces significant spherical aberration, the ion image quality can be greatly improved by a specially designed aspheric corrector lens located outside the vacuum system. Our simulations show that the spherical mirror/corrector design is an easy and cost-effective way to achieve high photon collection rates when compared to a more sophisticated parabolic mirror setup.
Photonic interconnects between quantum systems will play a central role in both scalable quantum computing and quantum networking. Entanglement of remote qubits via photons has been demonstrated in many platforms; however, improving the rate of entanglement generation will be instrumental for integrating photonic links into modular quantum computers. We present an ion trap system that has the highest reported free-space photon collection efficiency for quantum networking. We use a pair of in-vacuum aspheric lenses, each with a numerical aperture of 0.8, to couple 10(1)% of the 493 nm photons emitted from a 138Ba+ ion into single-mode fibers. We also demonstrate that proximal effects of the lenses on the ion position and motion can be mitigated.