Scaling up trapped ion processors with fast all-to-all entangling gates

Abstract

Trapped ions are a promising platform for large-scale quantum computation, however, they are limited by the speed and fidelity of two-qubit gates. All experimental two-qubit gates rely on adiabatic protocols, which do not scale well in multi-ion systems. Two-qubit ‘fast gates’ based on ultra-fast laser pulses are an alternative approach that bypasses the speed and scaling limitations of adiabatic gates in multi-ion systems, offering faster and larger computations. Unfortunately, fast gates are technologically limited by available laser power and control which motivates the need for error-robust gate design. Furthermore, existing fast gate protocols are only efficient for gates between neighbouring ions. This induces a significant overhead of additional gates needed to perform non-local operations which scales poorly for large systems of hundreds of ions required in computations. Therefore, while fast gates outperform current adiabatic and shuttling protocols, the limitation to nearest-neighbour operations introduces a bottleneck in achievable computation speeds. This thesis provides an alternative pathway to scalable trapped-ion quantum computing using highly connected fast gates in long ion chains. I develop a new scheme that removes artificial constraints in previous work to enable the machine design of fast gates in scalable geometries under experimentally realistic conditions. I find that this scheme is capable of designing gates that achieve higher fidelities (> 99%) with fewer pulses (< 100) in 1D quasi-uniform chains. Furthermore, I demonstrate that this scheme can be used to design gates between non-neighbouring ions with similar numbers of pulses on timescales comparable to the ion motion in arbitrarily large ion chains. This overcomes the nearest-neighbour limitation faced by current fast gate protocols and predicts close to two orders of magnitude speed up in achievable gate times compared to current experimental gates. Show more