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European Frequency and Time Forum

Ultracold molecular hydrogen ions in a linear radiofrequency trap: Novel systems for molecular frequency metrology

Bernhard Roth, H. Daerr, Jeroen C. J. Koelemeij, Alexander Yu. Nevsky, Stephan Schiller

Published Mar 27, 2006• 1 citation
OpenAlex

Abstract

We have measured the ro-vibrational infrared transition (v = 0, J = 2) → (v = 4, J = 1) in ultracold HD+ molecular ions embedded inside Be+ Coulomb crystals, by 1+1 REMPI spectroscopy. The molecular ions, trapped in a linear radiofrequency trap, were cooled to temperatures of few tens of mK, via sympathetic cooling using laser-cooled Be+ ions. For detection, we have used secular excitation of the HD+ ions to monitor their loss rate. The transition frequency agrees with a theoretical prediction.

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We have measured the ro-vibrational infrared transition (v = 0, J = 2) → (v = 4, J = 1) in ultracold HD+ molecular ions embedded inside Be+ Coulomb crystals, by 1+1 REMPI spectroscopy. The molecular ions, trapped in a linear radiofrequency trap, were cooled to temperatures of few tens of mK, via sympathetic cooling using laser-cooled Be+ ions. For detection, we have used secular excitation of the HD+ ions to monitor their loss rate. The transition frequency agrees with a theoretical prediction.
Narrow ro-vibrational transitions in ultracold molecules are excellent candidates for frequency references in the near-IR to visible spectral domain and interesting systems for fundamental tests of physics, in particular for a satellite test of the gravitational redshift of clocks. We have performed laser spectroscopy of several ro-vibrational overtone transitions υ = 0 → υ = 4 in HD+ ions at around 1.4 μm. 1+1 REMPD was used as a detection method, followed by measurement of the number of remaining molecules. The molecular ions were stored in a linear radiofrequency trap and cooled to millikelvin temperatures, by sympathetic cooling using laser-cooled Be+ ions simultaneously stored in the same trap.
Narrow ro-vibrational transitions in ultracold molecules are excellent candidates for frequency references in the near-IR to visible spectral domain and interesting systems for fundamental tests of physics, in particular for a satellite test of the gravitational redshift of clocks. We have performed laser spectroscopy of several ro-vibrational overtone transitions υ = 0 → υ = 4 in HD + ions at around 1.4 μm. 1+1 REMPD was used as a detection method, followed by measurement of the number of remaining molecules. The molecular ions were stored in a linear radiofrequency trap and cooled to millikelvin temperatures, by sympathetic cooling using laser-cooled Be + ions simultaneously stored in the same trap.
We report a method of efficiently generating ultracold hydrogen molecular ions HD+ in a segmented linear ion trap. HD+ ions are created by [2+1′] resonance-enhanced multiphoton ionization (REMPI) of an HD supersonic molecular beam, and sympathetically cooled by laser-cooled Be+ ions. The HD+ ions are generated species-selectively using 201 nm and 395 nm pulse lasers with energies of 0.08 mJ (5.1 × 106 W/cm2) and 1.5 mJ (9.5 × 107 W/cm2) respectively. The average loading rate of 4.3(2) HD+ ions per second in the ion trap is determined by comparing the experimental images with the simulated images of Be+-HD+ bi-component Coulomb crystals. This method paves a way to produce the state-selected HD+ ions, which can improve the signal strengths of the selected rovibrational transitions of HD+ ions.
A single, trapped and ultracold molecular hydrogen ion is an attractive quantum system for exploring various aspects of fundamental physics, such as the determination of fundamental constants and testing their time-independence. Here we demonstrate, for the first time, controlled loading, sympathetic cooling, mass spectrometric identification, and vibrational excitation of ultracold single HD+ ions trapped in a tightly confining radiofrequency trap using single laser-cooled Be+ ions for sympathetic cooling. The apparatus can be used also for preparing other single ions, both lighter and heavier than the coolant ion.
We have cooled ensembles of the molecular hydrogen ions H2+, H3+, and all their deuterated variants to temperatures of a few mK in a radio frequency trap, by sympathetic cooling with laser-cooled beryllium ions. The molecular ions are embedded in the central regions of Coulomb crystals. Mass spectroscopy and molecular dynamics simulations were used to accurately characterize the properties of the ultracold multispecies crystals. We demonstrate species-selective purification of multispecies ensembles. These molecules are of fundamental importance as the simplest of all molecules, and have the potential to be used for precision tests of molecular structure theory, tests of Lorentz invariance, and measurements of electron to nuclear mass ratios and their time variation.
We report a high-resolution spectroscopic study of molecular ions at millikelvin temperatures. We measured several rovibrational infrared transitions in HD+\mathrm{H}{\mathrm{D}}^{+}HD+ molecular ions, stored in a radio-frequency trap and sympathetically cooled to $\ensuremath{\approx}20\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ by laser-cooled Be+{\mathrm{Be}}^{+}Be+ ions. We observed hyperfine splitting of the lines, in good agreement with theoretical predictions. The transitions were detected by monitoring the decrease in ion number after selective photodissociation of HD+\mathrm{H}{\mathrm{D}}^{+}HD+ ions in the upper vibrational state. The method described here is expected to be generally applicable.