Coherence Time Improvements for Error Correction and Logical Entangling Gates with ⁴⁰Ca⁺ Single-Ion Logical Qubits

Quantum error correction (QEC) is essential for quantum computers to perform useful algorithms, but large-scale fault-tolerant computation remains out of reach due to demanding requirements on operation fidelity and the number of controllable quantum bits (qubits). While traditional QEC schemes involve encoding each logical qubit into many physical qubits, in this work we explore a complementary approach by performing error correction and entangling gates on logical qubits encoded in multi-level trapped ion systems. To achieve coherence times much longer than the gate time, we present an interferometer-based vibration cancellation system that monitors and compensates for mechanical vibrations of our cryostat via feedforward to the Raman lasers that generate the entangling interaction. To further reduce phase noise, the optical fiber length between the laser system and the experiment is minimized. In parallel, a new laser architecture for Raman transition-based control of ⁴⁰Ca⁺ metastable states is implemented. This new system is based on a cost-effective seed laser and tapered amplifier at 895 nm and substantially increases the detuning and available laser power to achieve gates with low scattering error.