Towards Quantum Error Correction with Dual Isotopes in a Cryogenic Trapped-Ion Experiment

Trapped-ion systems have been used to realize quantum error correction due to their long coherence times and high gate fidelity. The protection of logical quantum information is performed by the redundant encoding of many so-called "data" qubits. Error correction is implemented by in-sequence periodic detection of ancilla qubits to enable the appropriate conditional feedback pulses applied to the data qubits. We propose and demonstration experiments towards using two isotopes of calcium ions for the purpose of data and ancilla qubits. The spectral separation between isotopes allows for the in-sequence readout of ancilla qubits while preserving coherence of the data qubits. In addition, these ancilla qubits can be used to sympathetically re-cool motional modes of the ion string to enable high fidelity gates. The similar masses of isotopes results in strong coupling between the radial motion of ions, which is used as a quantum bus for entanglement between ions. Our system consists of a cryogenic ultra-high vacuum apparatus to allow for the stable trapping of long linear ion strings in a segmented-electrode micro-fabricated ion trap. Individual control of ions is provided by a multi-core fiber focused perpendicular to the string axis, and an EMCCD camera providing low latency individual readout for fast feedback.