Quantum Logic Spectroscopy with Ions in Thermal Motion.

J J Wu,S D Erickson,A C Wilson,D Kienzler,D J Wineland,D Leibfried,Y Wan

doi:10.1103/physrevx.10.021012

Abstract

A mixed-species geometric phase gate has been proposed for implementing quantum logic spectroscopy on trapped ions, which combines probe and information transfer from the spectroscopy to the logic ion in a single pulse. We experimentally realize this method, show how it can be applied as a technique for identifying transitions in currently intractable atoms or molecules, demonstrate its reduced temperature sensitivity, and observe quantum-enhanced frequency sensitivity when it is applied to multi-ion chains. Potential applications include improved readout of trapped-ion clocks and simplified error syndrome measurements for quantum error correction.

Highlights

Quantum logic spectroscopy (QLS) can be used for internal-state preparation and readout of atomic and molecular ion species that lack a suitable electronic level structure to directly implement these tasks [1,2,3,4]
We demonstrate the basic features of this method on a mixed-species ion pair of electronic ground-state hyperfine qubits composed of one spectroscopy ion” (SI) (25Mgþ with the two-level system defined as j↑Mgi 1⁄4 j3; 1i and j↓Mgi 1⁄4 j2; 0i, with a frequency splitting ωMg ≈ 2π × 1.7632 GHz at the applied magnetic field of B ≈ 11.9 mT) and one logic ion” (LI) (9Beþ with j↑Bei 1⁄4 j1; 1i, j↓Bei 1⁄4 j2; 0i, with a frequency splitting ωBe ≈ 2π × 1.2075 GHz at the same magnetic field)
We perform Rabi- and Ramsey-type experiments with both axial modes of motion initially cooled to the ground state, while the LI is prepared in j↑i and the SI in either j↑i or j↓i

Summary

INTRODUCTION

Quantum logic spectroscopy (QLS) can be used for internal-state preparation and readout of atomic and molecular ion species that lack a suitable electronic level structure to directly implement these tasks [1,2,3,4]. That is often used in quantum information processing for multiqubit entangling gates This type of geometric phase gate has previously been used on a mixed-species ion pair to implement quantum logic readout with reduced temperature sensitivity as part of a controlled-NOT operation [10]. We explore a technique, using only a Mølmer-Sørensen (MS) interaction [11,12,13,14,15], to simultaneously implement both the spectroscopy operation and transfer of SI state information to the LI for readout. This technique reduces temperature sensitivity compared to traditional QLS [16]. While our technique shares some features with previous work, which implements Heisenberg-limited Ramsey [19,20] and Rabi spectroscopy [21], it extends metrology that takes advantage of entanglement to a wider range and number of spectroscopy ions [9]

Basic operations

Heisenberg scaling

Influence of LI properties on the protocol

Basic method

Robustness of the method

Application to four ions

Applications in quantum information processing

CONCLUSION

State preparation and readout