Quantum control methods for robust entanglement of trapped ions

TL;DR

This paper reviews quantum control techniques to enhance the robustness of entangling gates in trapped ions, and demonstrates a proof-of-concept interaction resilient to both spin and motional decoherence.

Contribution

It consolidates and critically analyzes various quantum control methods for robust entanglement, and experimentally combines techniques to achieve simultaneous robustness to multiple decoherence sources.

Findings

Successful experimental realization of a robust entangling interaction

Quantum control methods can significantly mitigate decoherence effects

The approach is adaptable to different trapped ion architectures

Abstract

A major obstacle in the way of practical quantum computing is achieving scalable and robust high-fidelity entangling gates. To this end, quantum control has become an essential tool, as it can make the entangling interaction resilient to sources of noise. Nevertheless, it may be difficult to identify an appropriate quantum control technique for a particular need given the breadth of work pertaining to robust entanglement. To this end, we attempt to consolidate the literature by providing a non-exhaustive summary and critical analysis. The quantum control methods are separated into two categories: schemes which extend the robustness to (i) spin or (ii) motional decoherence. We choose to focus on extensions of the $\sigma_x\otimes\sigma_x$ Molmer-Sorensen interaction using microwaves and a static magnetic field gradient. Nevertheless, some of the techniques discussed here can be relevant to other trapped ion architectures or physical qubit implementations. Finally, we experimentally realize a proof-of-concept interaction with simultaneous robustness to spin and motional decoherence by combining several quantum control methods presented in this manuscript.