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arXiv:2112.06816 · Scientific Reports

A fully fiber-integrated ion trap for portable quantum technologies

Xavier Fernandez-Gonzalvo, Matthias Keller

Published Jan 10, 2023• 8 citations
arXivHTMLPDF

Abstract

Abstract Trapped ions are a promising platform for the deployment of quantum technologies. However, traditional ion trap experiments tend to be bulky and environment-sensitive due to the use of free-space optics. Here we present a single-ion trap with integrated optical fibers directly embedded within the trap structure, to deliver laser light as well as to collect the ion’s fluorescence. This eliminates the need for optical windows. We characterise the system’s performance and measure the ion’s fluorescence with signal-to-background ratios on the order of 50, which allows us to perform internal state readout measurements with a fidelity over 99% in 600 $$\upmu$$ μ s. We test the system’s resilience to thermal variations in the range between 22 and 53 $$^{\circ }$$ ∘ C, and the system’s vibration resilience at 34 Hz and 300 Hz and find no effect on its performance. The combination of compactness and robustness of our fiber-coupled trap makes it well suited for applications in, as well as outside, research laboratory environments, and in particular for highly compact portable quantum technologies, such as portable optical atomic clocks. While our system is designed for trapping 40Ca+ ions the fundamental design principles can be applied to other ion species.

DOI
10.1038/s41598-022-27193-9

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Abstract Trapped ions are a promising platform for the deployment of quantum technologies. However, traditional ion trap experiments tend to be bulky and environment-sensitive due to the use of free-space optics. Here we present a single-ion trap with integrated optical fibers directly embedded within the trap structure, to deliver laser light as well as to collect the ion’s fluorescence. This eliminates the need for optical windows. We characterise the system’s performance and measure the ion’s fluorescence with signal-to-background ratios on the order of 50, which allows us to perform internal state readout measurements with a fidelity over 99% in 600 \upmu\upmu\upmu μ s. We test the system’s resilience to thermal variations in the range between 22 and 53 ∘^{\circ }∘ ∘ C, and the system’s vibration resilience at 34 Hz and 300 Hz and find no effect on its performance. The combination of compactness and robustness of our fiber-coupled trap makes it well suited for applications in, as well as outside, research laboratory environments, and in particular for highly compact portable quantum technologies, such as portable optical atomic clocks. While our system is designed for trapping 40Ca+ ions the fundamental design principles can be applied to other ion species.
We have realized a compact system to efficiently couple the fluorescent light emitted by a single trapped ion to two opposing optical fibers. The fibers are tightly integrated in the center electrodes of a miniature endcap trap. They capture light from the ion with a numerical aperture of 0.34 each, corresponding to 6% of the solid angle in total. The high collection efficiency and high signal-to-background ratio make the setup an ideal quantum light source. We have observed strong antibunching of the photons emitted from the two fibers. The system has a range of applications from single-ion state detection in quantum information processing to strong coupling cavity-QED with ions.
Monolithic integration of control technologies for atomic systems presents a promising route to the development of quantum computers and portable quantum sensors. Trapped atomic ions form the basis of high-fidelity quantum information processors and high-accuracy optical clocks, but currently rely on free-space optics for ion control, limiting portability and scalability. Here we demonstrate a surface-electrode ion trap which delivers all wavelengths required for ionization, cooling, coherent operations, and quantum-state preparation and detection of Sr+^{+}+ qubits using integrated waveguides and grating couplers. Laser light from the violet to the infrared is coupled onto the chip via an optical-fiber array, creating an inherently stable optical path that we use to demonstrate qubit coherence resilient to platform vibrations. This demonstration of CMOS-compatible integrated-photonic surface-trap fabrication, robust packaging, and enhanced qubit coherence represents a key advance in the development of portable trapped-ion quantum sensors and clocks, and it lights the way toward the complete, individual control of larger numbers of ions in quantum information processing systems.
Trapped ions hold promise as the basis of highly accurate clocks and other quantum sensors. However, many real-world applications for quantum sensing require miniaturized, environmentally robust devices that can operate in the field. The significant experimental overhead imposed by free-space optics for control laser light delivery and collection has been an impediment to truly compact trapped-ion based clocks and sensors. The use of integrated technologies—including photonic waveguides, single-photon avalanche detectors (SPADs) and integrated electronics—provides a potential pathway towards overcoming these obstacles. I will discuss MIT Lincoln Laboratory’s recent efforts in this area, including demonstrations of integrated trapped-ion light delivery and collection and prospects for combining these technologies into a single chip-based trapped-ion reference.
Abstract Monolithic integration of control technologies for atomic systems is a promising route to the development of quantum computers and portable quantum sensors1–4. Trapped atomic ions form the basis of high-fidelity quantum information processors5, 6 and high-accuracy optical clocks7. However, current implementations rely on free-space optics for ion control, which limits their portability and scalability. Here we demonstrate a surface-electrode ion-trap chip8, 9 using integrated waveguides and grating couplers, which delivers all the wavelengths of light required for ionization, cooling, coherent operations and quantum state preparation and detection of Sr+ qubits. Laser light from violet to infrared is coupled onto the chip via an optical-fibre array, creating an inherently stable optical path, which we use to demonstrate qubit coherence that is resilient to platform vibrations. This demonstration of CMOS-compatible integrated photonic surface-trap fabrication, robust packaging and enhanced qubit coherence is a key advance in the development of portable trapped-ion quantum sensors and clocks, providing a way towards the complete, individual control of larger numbers of ions in quantum information processing systems.
Abstract Practical and useful quantum information processing requires substantial improvements with respect to current systems, both in the error rates of basic operations and in scale. The fundamental qualities of individual trapped-ion1 qubits are promising for long-term systems2, but the optics involved in their precise control are a barrier to scaling3. Planar-fabricated optics integrated within ion-trap devices can make such systems simultaneously more robust and parallelizable, as suggested by previous work with single ions4. Here we use scalable optics co-fabricated with a surface-electrode ion trap to achieve high-fidelity multi-ion quantum logic gates, which are often the limiting elements in building up the precise, large-scale entanglement that is essential to quantum computation. Light is efficiently delivered to a trap chip in a cryogenic environment via direct fibre coupling on multiple channels, eliminating the need for beam alignment into vacuum systems and cryostats and lending robustness to vibrations and beam-pointing drifts. This allows us to perform ground-state laser cooling of ion motion and to implement gates generating two-ion entangled states with fidelities greater than 99.3(2) per cent. This work demonstrates hardware that reduces noise and drifts in sensitive quantum logic, and simultaneously offers a route to practical parallelization for high-fidelity quantum processors5. Similar devices may also find applications in atom- and ion-based quantum sensing and timekeeping6.
Integrated photonics in trapped-ion systems are critical for the realization of applications such as portable optical atomic clocks and scalable quantum computers. However, system-level integration of all required functionalities remains a key challenge. In this work, we demonstrate an autonomously operating optical clock having a short-term frequency instability of 3.14(5)×10−14/τ3.14(5)\times 10^{-14} / \sqrtτ3.14(5)×10−14/τ​ using an ensemble of four 171Yb+^{171}\textrm{Yb}^{+}171Yb+ ions trapped in a multi-site surface-electrode trap at room temperature. All clock operations are performed with light delivered via on-chip waveguides. We showcase the system's resilience through sustained, autonomous operation featuring automated ion shuttling and reloading to mitigate ion loss during interleaved clock measurements. This work paves the way beyond component-level functionality to establish a viable and robust architecture for the next generation of portable, multi-ion quantum sensors and computers.