Integrated optical quantum manipulation and measurement of trapped ions

Individual atomic ions confined in designed electromagnetic potentials and manipulated via lasers are strong candidates as physical bases for quantum information processing (QIP). This is in large part due to their long coherence times, indistinguishability, and strong Coulomb interactions. Much work in recent years has utilized these properties to implement increasingly precise quantum operations essential for QIP, as well as to conduct increasingly sophisticated experiments on few-ion systems. Many questions remain however regarding how to implement the significant classical apparatus required to control and measure many ions (and indeed any physical qubit under study) in a scalable way that furthermore does not compromise qubit quality.

This work draws on techniques in integrated optics to address this question. Planar-fabricated waveguides and gratings integrated with planar ion traps are demonstrated to allow optical addressing of individual ⁸⁸Sr ⁺ions 50 µm above the chip surface with diffraction-limited focused beams, with advantages in stability and scalability. Motivated by the requirement for low crosstalk in qubit addressing, we show also that intuitively designed devices can generate precisely tailored intensity profiles at the ion locations, with diffraction-limited sidelobe intensities characterized to the 5 x 10^-6 level in relative intensity up to 25 µm from the focus. Such devices can be implemented alongside complex systems in complementary metal-oxide-semiconductor (CMOS) processes. We show in addition that the multiple patternable metal layers present in CMOS processes can be used to create complex planar ion traps with performance comparable to simple single-layer traps, and that CMOS silicon avalanche photodiodes may be employed for scalable quantum state readout. Finally we show initial results on integrated electro-optic modulators for visible light.

These results open possibilities for experiments with trapped ions in the short term, and indicate routes to achieving large-scale systems of thousands or more ions in the future. Though ion qubits may seem isolated from scalable solid-state technologies, it appears this apparent isolation may uniquely allow a cooperation with complex planar-fabricated optical and electronic systems without introducing additional decoherence. (Copies available exclusively from MIT Libraries, libraries.mit.edu/docs - [email protected])