Identification of molecular quantum states using phase-sensitive forces

Spatial and Temporal Detection of Ions Ejected from Coulomb Crystals

Coulomb crystals have proven to be powerful and versatile tools for the study of ion-molecule reactions under cold and controlled conditions. Reactions in Coulomb crystals are typically monitored through a combination of in situ fluorescence imaging of the laser-cooled ions and destructive time-of-flight mass spectrometry measurements of the ejected ions. However, neither of these techniques is able to provide direct structural information on the positions of nonfluorescing "dark" ions within the crystal. In this work, structural information is obtained using a phosphor screen and a microchannel plate detector in conjunction with a Timepix3 camera. The Timepix3 camera simultaneously records the spatial and temporal distribution of all ions that strike the phosphor screen detector following crystal ejection at a selected reaction time. A direct comparison can be made between the observed Timepix3 ion distributions and the distributions established from SIMION simulations of the ion trajectories through the apparatus and onto the detector. Quantitative agreement is found between the measured Timepix3 signal and the properties of Coulomb crystals assigned using fluorescence imaging─independently confirming that the positions and numbers of nonfluorescing ions within Coulomb crystals can be accurately determined using molecular dynamics simulations. It is anticipated that the combination of high-resolution spatial and temporal data will facilitate new measurements of the ion properties within Coulomb crystals.

Scheme for Quantum-Logic Based Transfer of Accuracy in Polarizability Measurement for Trapped Ions Using a Moving Optical Lattice

Optical atomic clocks based on trapped ions suffer from systematic frequency shifts of the clock transition due to interaction with blackbody radiation from the environment. These shifts can be compensated if the blackbody radiation spectrum and the differential dynamic polarizability is known to a sufficient precision. Here, we present a new measurement scheme, based on quantum logic that allows a direct transfer of precision for polarizability measurements from one species to the other. This measurement circumvents the necessity of calibrating laser power below the percent level, which is the limitation for state-of-the-art polarizability measurements in trapped ions. Furthermore, the presented technique allows one to reference the polarizability transfer to hydrogenlike ions for which the polarizability can be calculated with high precision.

Amplifying a Zeptonewton Force with a Single-Ion Nonlinear Oscillator

Nonlinear mechanical resonators display rich and complex dynamics and are important in many areas of fundamental and applied sciences. Here, we present a general strategy to generate mechanical nonlinearities for trapped particles by transverse driving in a funnel-shaped potential. Employing a trapped ion platform, we study the nonlinear oscillation, bifurcation, and hysteresis of a single calcium ion and demonstrate a 20-fold enhancement of the signal from a zeptonewton-magnitude harmonic force through the effect of vibrational resonance. Our results represent a first step in combining the rich nonlinear dynamics with the precision control over mechanical motions offered by atomic physics and open up possibilities for exploiting nonlinear mechanical phenomena in the quantum regime.

Design and characterization of a cryogenic linear Paul ion trap for ion-neutral reaction studies

Ultra-high vacuum conditions are ideal for the study of trapped ions. They offer an almost perturbation-free environment, where ions confined in traps can be studied for extended periods of time-facilitating precision measurements and allowing infrequent events to be observed. However, if one wishes to study processes involving molecular ions, it is important to consider the effect of blackbody radiation (BBR). The vast majority of molecular ions interact with BBR. At 300 K, state selection in trapped molecular ions can be rapidly lost (in a matter of seconds). To address this issue, and to maintain state selectivity in trapped molecular ions, a cryogenic ion trap chamber has been constructed and characterized. At the center of the apparatus is a linear Paul ion trap, where Coulomb crystals can be formed for ion-neutral reaction studies. Optical access is provided, for lasers and for imaging of the crystals, alongside ion optics and a flight tube for recording time-of-flight mass spectra. The ion trap region, encased within two nested temperature stages, reaches temperatures below 9 K. To avoid vibrations from the cryocooler impeding laser cooling or imaging of the ions, vibration-damping elements are explicitly included. These components successfully inhibit the coupling of vibrations from the cold head to the ion trap-confirmed by accelerometer measurements and by the resolution of images recorded at the trap center (at 9 and 295 K). These results confirm that the cryogenic ion trap apparatus meets all requirements for studying ion-neutral reactions under cold, controlled conditions.

From megahertz to terahertz qubits encoded in molecular ions: theoretical analysis of dipole-forbidden spectroscopic transitions in N2. Phys Chem Chem Phys 2020;22:23083-23098. [PMID: 33048077 DOI: 10.1039/d0cp03906c]

Recent advances in quantum technologies have enabled the precise control of single trapped molecules on the quantum level. Exploring the scope of these new technologies, we studied theoretically the implementation of qubits and clock transitions in the spin, rotational, and vibrational degrees of freedom of molecular nitrogen ions including the effects of magnetic fields. The relevant spectroscopic transitions span six orders of magnitude in frequency, illustrating the versatility of the molecular spectrum for encoding quantum information. We identified two types of magnetically insensitive qubits with very low ("stretched"-state qubits) or even zero ("magic" magnetic-field qubits) linear Zeeman shifts. The corresponding spectroscopic transitions are predicted to shift by as little as a few mHz for an amplitude of magnetic-field fluctuations on the order of a few mG, translating into Zeeman-limited coherence times of tens of minutes encoded in the rotations and vibrations of the molecule. We also found that the Q(0) line of the fundamental vibrational transition is magnetic-dipole allowed by interaction with the first excited electronic state of the molecule. The Q(0) transitions, which benefit from small systematic shifts for clock operation and is thus well suited for testing a possible variation in the proton-to-electron mass ratio, were so far not considered in single-photon spectra. Finally, we explored possibilities to coherently control the nuclear-spin configuration of N2+ through the magnetically enhanced mixing of nuclear-spin states.