Second-Scale $^9\text{Be}^+$ Spin Coherence in a Compact Penning Trap

Abstract

We report microwave spectroscopy of co-trapped 9 Be + and 40 Ca + within a compact permanent-magnetbased Penning ion trap. The trap is constructed with a reconfigurable array of NdFeB rings providing a 0.654 T magnetic field that is near the 0.6774-T magnetic-field-insensitive hyperfine transition in 9 Be + . Performing Ramsey spectroscopy on this hyperfine transition, we demonstrate nuclear spin coherence with a contrast decay time of > 1 s. The 9 Be + is sympathetically cooled by a Coulomb crystal of 40 Ca + , which minimizes 9 Be + illumination and thus mitigates reactive loss. Introducing a unique high-magnetic-field optical detection scheme for 40 Ca + , we perform spin state readout without a 729 nm shelving laser. We record a fractional trap magnetic field instability below 20 ppb (< 13 nT) at 43 s of averaging time with no magnetic shielding and only passive thermal isolation. We discuss potential applications of this compact, reconfigurable Penning trap.