Detection of motional ground state population of a trapped ion using delayed pulses

F Gebert,Y Wan,F Wolf,Jan C Heip,Piet O Schmidt

doi:10.1088/1367-2630/18/1/013037

Abstract

Efficient preparation and detection of the motional state of trapped ions is important in many experiments ranging from quantum computation to precision spectroscopy. We investigate the stimulated Raman adiabatic passage (STIRAP) technique for the manipulation of motional states in a trapped ion system. The presented technique uses a Raman coupling between two hyperfine ground states in 25Mg+, implemented with delayed pulses, which removes a single phonon independent of the initial motional state. We show that for a thermal probability distribution of motional states the STIRAP population transfer is more efficient than a stimulated Raman Rabi pulse on a motional sideband. In contrast to previous implementations, a large detuning of more than 200 times the natural linewidth of the transition is used. This approach renders STIRAP suitable for atoms in which resonant laser fields would populate nearby fluorescing excited states and thus impede the STIRAP process. We use the technique to measure the wavefunction overlap of excited motional states with the motional ground state. This is an important application for force sensing applications using trapped ions, such as photon recoil spectroscopy, in which the signal is proportional to the depletion of motional ground state population. Furthermore, a determination of the ground state population enables a simple measurement of the ion's temperature.

Highlights

Progress in trapped-ion quantum information processing [1, 2, 3, 4], quantum simulation [5, 6], and precision spectroscopy experiments [7, 8, 9, 10, 11, 12] is largely based on advances in the ability to control and manipulate the quantum states of the system
Spontaneous emission from light fields coupling to states not involved in the stimulated Raman adiabatic passage (STIRAP) process is suppressed, allowing STIRAP to be implemented in multi-level systems such as the 25Mg+ ion used in our work
The relative populations of the two qubit states during the STIRAP sequence, together with the relative strength of the involved couplings of these states to the auxiliary magnetic sub-states [48], explain the asymmetry with respect to the pulse order seen in the experiment

Summary

Introduction

Progress in trapped-ion quantum information processing [1, 2, 3, 4], quantum simulation [5, 6], and precision spectroscopy experiments [7, 8, 9, 10, 11, 12] is largely based on advances in the ability to control and manipulate the quantum states of the system. Sequences of laser or microwave pulses are applied to prepare a desired state or implement operations for state manipulation. Mostly square pulses with a fixed length and frequency are employed that rotate the atomic qubit and – depending on the experimental implementation – change the motional state. The effect of undesired frequency components in square-shaped pulses has previously been reduced by employing amplitude-shaped pulses with a smooth rising and falling slope [13, 14, 15]. Composite pulses, first developed in the context of nuclear magnetic resonance [16, 17, 18], are used in trapped ion systems to implement complex algorithms [19, 20] or operations that are less sensitive to variations of the experimental parameters [21, 22, 23, 24]

Methods

Results

Conclusion