MEMS Based Optical Beam Steering System with Applications in Quantum Information Processing - Michael Feng

In an effort to create a scalable ion trap quantum architecture, a micro-electro-mechanical (MEMS) based optical beam steering system has been developed to provide individual addressability of an array of trapped atoms. This optical system is used to guide laser beams to address specific locations in that array using MEMS mirrors. These mirrors are able to tilt along one axis with an applied voltage, and this tilt is converted to a lateral shift via optics. By characterizing the different physical parameters of the mirrors, we have been able to optimize the design for optical characteristics, speed, reliability, and manufacturability. In addition, I have been involved the implementation and integration of the full MEMS system. Due to the specific application for our system, the control electronics required are highly specialized. Using an FPGA based platform, I have been developing a custom scalable control system capable of meeting both the voltage and speed requirements for mirror control, as well as other applications. This system, consisting of a computer based interface, actuation electronics, and high voltage amplifiers, will allow for a multiple beam system to conduct an experiment on a real-time level. Introduction Quantum computers have the potential to speed up computation for a number of problems, the classic examples being factorization and cryptography. One potential implementation uses trapped atoms as qubits, with quantum information being stored in the electrical states of each atom. I have, over the past two years in conjunction with Dr. Jungsang Kim, been involved in the development of a microelectro-mechanical systems (MEMS) based architecture to improve the scalability of ion trap quantum information processing. In ion trap architectures, lasers are used to manipulate and read qubits. In order to address an array of atoms, we must be able to shift the laser beams to different physical locations corresponding to the atom locations. To achieve this optical shift, a MEMS system consisting of tilting mirrors are used. These mirrors must be fast, reliable, controllable, and must be of high optical quality. The mirrors are fabricated by either MEMSCAP via the polyMUMPS process, or more recently Sandia’s SUMMiT process. These processes allow us to fabricate complex multi-level polysilicon designs. The mirrors are circular and suspended at two points by mechanical springs, allowing for tilt along one axis. The tilt is achieved through electrostatic force; the applied voltage at one of the electrodes induces an attractive force between the electrode and the mirror plate. The mirror plate is coated in a reflective metal (Gold, silver, or aluminum) to minimize optical losses at each mirror. Shown in Figure 1 is the basic physical design of the mirrors. 1 See C. Knoernschild, C. Kim, F. P. Lu and J. Kim, Multiplexed Broadband Beam Steering System utilizing High Speed MEMS Mirrors, Optics Express 17, pp 7233 (2009): http://arxiv.org/abs/0902.1574v1 (2009). 2 See http://www.memscap.com/en_mumps.html for more information 3 See http://mems.sandia.gov/tech-info/summit-v.html for more information Figure 1 : MEMS Mirror Physical Design. A side view is shown on the left, and a top view on the right. Image courtesy of Caleb Knoernschild The MEMS mirrors are arranged in an optical system that uses two mirrors to tilt the incoming beam in two orthogonal planes, which is later converted into a lateral shift by means of a lens. By adjusting the tilt, we may adjust the lateral shift, thus allowing different lattice locations to be addressed, as shown in Figure 2. Figure 2 : MEMS Optical Beam Steering System. The tilt of the MEMS mirrors is translated into a lateral shift through an optical system, thus allowing the laser to address specific locations in a 2-D lattice. Source : C. Knoernschild, C. Kim, F. P. Lu and J. Kim, Multiplexed Broadband Beam Steering System utilizing High Speed MEMS Mirrors, Optics Express 17, pp 7233 (2009): http://arxiv.org/abs/0902.1574v1 (2009). Mirror Design and Characterization In order to understand and improve the mirror design, a lot of work has been put into thorough characterization of both mechanical and electrical properties of our mirrors. Basic characterization g V GND GND GND GND t βR αR