Scalable quantum logic spectroscopy using a Schrӧdinger cat interferometer*

Quantum logic spectroscopy[1] (QLS) is a technique that allows for precision spectroscopy of atomic or molecular ions that lack suitable transitions for laser cooling and detection. However, due to the requirements such as ground state cooling, this technique does not scale easily to large numbers of spectroscopy ions. Here we present a method that extends QLS to larger numbers of spectroscopy ions based on the Schrӧdinger cat interferometer[2]. We have demonstrated this method on linear and non-linear chains of up to 6 ions. Similar to what has been used for the detection of single-photon scattering events[3], ²⁵Mg⁺ions are employed to sense a state-dependent driving force applied to the co-trapped ²⁷Al⁺ions. Our results show an improved measurement speed of the ¹S₀ →³P₀ transition in ²⁷Al⁺with increased number of ²⁵Mg⁺ions under Doppler cooling, which opens the way of improving the clock stability by using multiple ²⁷Al⁺ions.

[1] P. O. Schmidt et al., Science 309, 749 (2005).

[2] Q. A. Turchette et al., Phys. Rev. A 62, 053807 (2000).

[3] C. Hempel et al., Nat. Photonics 7, 630 (2013).