It is well established that the collective motion of ion crystals can be used as a quantum bus for multi-qubit entanglement. However, as the number of ions increases, it becomes difficult to directly entangle ions far apart and resolve all motional modes of the ion crystal. We introduce a scalable and flexible scheme for efficient entanglement between any pair of ions within a large ion chain, using an evenly distributed 50-ion crystal as an example. By performing amplitude and frequency modulation, we find high-fidelity pulse sequences that primarily drive a transverse motional mode with a wavelength of 4 ion spacings. We present two 500μs pulses that can in theory suppress gate errors due to residual motion to below 10−4, and observe a trade-off between gate power and robustness against unwanted frequency offsets.
@article{arxiv.1808.02555,
title = {Entangling an arbitrary pair of qubits in a long ion crystal},
author = {Pak Hong Leung and Kenneth R. Brown},
journal= {arXiv preprint arXiv:1808.02555},
year = {2018}
}