Efficient, stabilized entangling gates on a trapped-ion chain

Two-qubit gates are an important building block of a universal quantum computer. On trapped-ions, two-qubit gates with high fidelity, short gate times and/or robustness against parameter drifts have been demonstrated. However, maintaining their performance while scaling to larger system sizes is challenging. Here, we present and demonstrate two scalable methods to find optimal solutions for M\o lmer-S\o rensen gates, a standard scheme to entangle trapped-ion qubits. Our methods are linear, thus allowing us to circumvent the need for non-linear optimization routines. Furthermore, with these methods, trade-offs between laser power, gate time, qubit-connectivity and robustness can be made systematically. We experimentally verify the performance of calculated pulses on a seven-ion system and find good agreement with theoretical predictions.