November_EDFA_Digital ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 23 NO . 4 28 FAILURE MODES IN MICROFABRICATED ION TRAP DEVICES FOR QUANTUM INFORMATION SCIENCE Matthew G. Blain, Raymond A. Haltli, and Melissa Revelle Sandia National Laboratories, Albuquerque, New Mexico EDFAAO (2021) 4:28-37 1537-0755/$19.00 ©ASM International ® INTRODUCTION Although viewed by some as a bit of a dark horse for large-scale quantum computing (QC), trapped ions are in fact one of the leading technology platforms for pursuing applications inquantuminformation science (QIS), includ- ing noisy intermediate scale quantum (NISQ) computing. Quantum information is the quantum mechanical ana- logue to classical binary information. A classical computer utilizes physical quantities, such as the two voltage levels in transistor logic, to represent the two logic states 1 and 0. QIS, however, describes binary information using a multilevel (can be two levels or more) quantum system, such as distinct polarization states of a photon or internal energy levels of an atom (e.g., |↑) or |↓)). In a quantum system, a single bit is called a qubit. Unlike a classical system, a qubit can exist in some fraction of each level at the same time. This super-position of states of the qubits means that Nqubits can perform2 N operations simultane- ously, an extraordinarily large number of computations. Logical operations on two or more qubits are affected by the precise, coherent control of the qubits such that the changing of the state of one qubit depends on the quantum state of another qubit. A good introduction to the subject may be found in Stolze. [1] In addition to QC, other applications of QIS includequantumcommunication (e.g., quantumkey distribution) and quantummetrology, which promises increasedmeasurement precision over its classical counterpart. Exciting advances have been made and concerted efforts undertaken to realize quantum systems that show supremacy over classical computing systems. Trapped ion systems are one of the leading technology platforms being used, [2-4] however there are still many technical challenges that must be addressed to demonstrate an ion-basedNISQ-scale computer. An excellent reviewof the status and challenges of trapped ion QC may be found in Bruzewicz. [5] Importantly, Sandia National Laboratories has a technology platform to address these challenges and to evince the promise of an ion-based QIS system: the Quantum Scientific Computing Open User Testbed (QSCOUT). [2] Building ion trap devices for this functional, operating QIS system is one avenue that is providing the opportunity to discover and address the failure modes of these devices. This article illustrates how the unique construction requirements anddemanding operating and environmen- tal conditions of the trap can combine to create unique failure modes. Some of these modes have been analyzed and mitigated, but others need more investigation or are just beginning to emerge. Three specific examples of fail- ures for packaged trap chips in either their rendering or use, and the resulting technical challenges, are discussed. WHAT IS NEEDED TO TRAP AN ION? While ion traps are key for ion-basedquantumcomput- ing, surrounding them is a large infrastructure of vacuum pumps, optics, lasers, and control electronics. Figure 1a shows an example of an ion trapping chamber during assembly. Inside the chamber (shown in Fig. 1b) is the ion trap and an ion source (for example ytterbium, Yb). The control voltages for the ion trap are routed from the device through a vacuum chamber feed-through. To trap andmanipulate the ions requires anRF source,microwave generation, and many lasers, all of which are precisely aligned to the ion. Removing the chamber and replacing an ion trap is usually a risky and time-consuming process entailing the removal of external systems for access to the trap, hence confidence in awell behaved, properly operat- ing trap is highly desirable. To achieve high fidelity qubits, the ions are cooled to the quantumground state, an extremely lowenergy state. Any collision with a background gas has the possibility to