A Chip-Scale Quantum Information Processor Using Atomic Ions and Photonic Circuits

Driven by the intractability of classical simulation of complex quantum systems, the execution of algorithms pertaining to encryption and certain search problems, quantum state engineering has proven a fruitful field in recent years. Atomic ions are a leading approach to development of quantum information processors. Typically experiments have been limited to a few ions because of the reliance on optical beams propagating in free space for control and readout of the ions. Difficulties with the usual optics approach pose formidable barriers to the useful application of the wealth of promising basic ideas that have been developed in recent years.

This work seeks to devise nanophotonic devices and systems in which light is controlled on chip in a fashion allowing thousands of independent optical beams, which can be integrated with electrode structures that confine the ions above the chip. The work would lead to optical control and readout of individual ions at dramatically larger scales than possible with current technology; additionally, integration as proposed would bring certain performance advantages, including lower power requirements on the laser beams due to tighter focusing on individual ions, and reduced noise due to stability of the beams' phase and location with respect to ions. The approach would advance basic capabilities in the field of integrated photonics, and bring closer the goals of arbitrary quantum state manipulation in atomic systems large enough to allow exploration of physics, as well as useful computations, beyond what can be done on current classical computers.

Realizing the systems proposed requires developments in a variety of basic photonic devices, and approaches to systems implementations. Ions of interest have transitions spanning the visible spectrum (for 88Sr+, 422-1097 nm), and the impact of the approach is greatest if all wavelengths are guided with low loss in the same dielectric layer. Grating couplers will be developed that convert light propagating in single-mode dielectric waveguides into focused beams propagating towards the ions. Electro-optic devices using integrated non-linear materials as the active core material for high-extinction (>40 dB) modulation of beams used for qubit control and readout will be designed and fabricated as well. In addition, we will pursue a post-processing technique whereby devices such as these could be created in chips made in standard CMOS foundries; this would open the possibility for systems bringing together beam-forming optics, modulators and avalanche photodetectors together with trap electrodes and control electronics for control of trapped ion systems with unprecedented scale. A critical advantage of CMOS foundry-made chips as a platform for science and engineering research is the intrinsic reproducibility and ease of dissemination for the experimental devices. For the first time, students of atomic physics and visible photonics will be able to leverage the multi-billion dollar infrastructure of CMOS. By drawing deeply on ideas both in integrated photonics and atomic physics, this work additionally creates new opportunities for interdisciplinary education and collaboration for the undergraduates, graduate students and researchers involved; and in addition to the capabilities for trapped ion systems offered by the work proposed here, we expect cross-fertilization between the two areas will make fertile ground for unforeseen ideas.