Southwest Quantum Information and Technology

Spontaneous emission in entangling gates for trapped ions at high magnetic fields

Presenting Author: Allison Carter, National Institute of Standards and Technology, Boulder
Contributing Author(s): Sean Muleady, Athreya Shankar, Jennifer Lilieholm, Bryce Bullock, Matthew Affolter, Ana Maria Rey, John Bollinger

Trapped ion systems have achieved some of the highest entangling gate fidelities, often limited by spontaneous emission from off-resonant lasers. Many previous treatments of spontaneous emission assume that the only contribution from elastic off-resonant light scatter to decoherence is through the recoil of the ions. This statement generally applies only to clock qubits. At the high magnetic fields required for Penning traps, however, clock qubits are often not an option. Here we consider the impact of spontaneous emission on Zeeman qubits for different types of entangling gates. In the NIST Penning trap, we have performed quantum simulations and sensing experiments on two-dimensional crystals of hundreds of beryllium ions at 4.5 T with a light-shift gate. A common alternative is the Mølmer-Sørensen gate. One advantage of the Mølmer-Sørensen gate is that it can be configured such that the driven ion motional state is less sensitive to optical phase fluctuations between the driving laser beams. This can be used to improve sensing applications and drive gates in 3-D crystals of up to tens of thousands of ions. We show that in the high-field regime, the light-shift and Mølmer-Sørensen gates perform comparably. We explore a wide variety of operating configurations for both types of gates. We also present a novel treatment of the spontaneous emission for carrier transitions for Pauli X gates, which are closely related to the Mølmer-Sørensen gate.

(Session 5 : Thursday from 5:00 pm - 7:00 pm)