Surface-electrode trap with an integrated permanent magnet for   generating a magnetic-field gradient at trapped ions
  We report on a surface-electrode trap with SmCo magnets arranged in a quadrupole configuration underneath the trap electrode. Because the distance between the magnets and the trapped ions can be as little as several hundred micrometers, a large magnetic field is produced without any heat management. The magnetic-field gradient was measured using the Zeeman splitting of a single trapped $^{40}$Ca$^+$ ion at several positions, and a field gradient of 36 T/m was obtained. Such a field gradient is useful for the generation of a state-dependent force, which is important for quantum simulation and/or quantum gate operation using radio-frequency or microwave radiation. 
Yuji Kawai, Kenji Shimizu, Atsushi Noguchi, Shinji Urabe and Utako   Tanaka
physics.atom-ph quant-ph