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arXiv:2203.16933 · Physical Review A

Formation of two-ion crystals by injection from a Paul-trap source into a high-magnetic-field Penning trap

J. Berrocal, E. Altozano, F. Domínguez, M. J. Gutiérrez, Javier Cerrillo, F. J. Fernández, M. Block, C. Ospelkaus, D. Rodríguez

Published May 16, 2022• 0 citations
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Abstract

Two-ion crystals constitute a platform for investigations of quantum nature that can be extended to any ion species or charged particle provided one of the ions in the crystal can be directly laser cooled and manipulated with laser radiation. This paper presents the formation of two-ion crystals for quantum metrology in a 7-tesla open-ring Penning trap. $^{40}\mathrm{Ca}^{+}$ ions are produced either internally by photoionization or externally in a (Paul-trap) source, transported through the strong magnetic field gradient of the superconducting solenoid, and captured in-flight with a mean kinetic energy of a few electronvolts with respect to the minimum of the Penning-trap potential well. Laser cooling of the two-ion crystal in a strong magnetic field towards reaching the quantum regime is also presented, with particular emphasis on the cooling of the radial modes.

DOI
10.1103/physreva.105.052603

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Two-ion crystals constitute a platform for investigations of quantum nature that can be extended to any ion species or charged particle provided one of the ions in the crystal can be directly laser cooled and manipulated with laser radiation. This paper presents the formation of two-ion crystals for quantum metrology in a 7-tesla open-ring Penning trap. 40Ca+^{40}\mathrm{Ca}^{+}40Ca+ ions are produced either internally by photoionization or externally in a (Paul-trap) source, transported through the strong magnetic field gradient of the superconducting solenoid, and captured in-flight with a mean kinetic energy of a few electronvolts with respect to the minimum of the Penning-trap potential well. Laser cooling of the two-ion crystal in a strong magnetic field towards reaching the quantum regime is also presented, with particular emphasis on the cooling of the radial modes.
Two-ion crystals constitute a platform for investigations of quantum nature that can be extended to any ion \nspecies or charged particle provided one of the ions in the crystal can be directly laser cooled and manipulated \nwith laser radiation. This paper presents the formation of two-ion crystals for quantum metrology in a 7-tesla \nopen-ring Penning trap. 40Ca+ ions are produced either internally by photoionization or externally in a (Paul-trap) \nsource, transported through the strong magnetic field gradient of the superconducting solenoid, and captured \nin-flight with a mean kinetic energy of a few electronvolts with respect to the minimum of the Penning-trap \npotential well. Laser cooling of the two-ion crystal in a strong magnetic field towards reaching the quantum \nregime is also presented, with particular emphasis on the cooling of the radial modes.
We have studied the formation and properties of two-species ion Coulomb crystals in the Penning trap of the SpecTrap experiment. These crystals have been formed by injection of admixture ions from an external source into a previously confined and laser-cooled cloud of magnesium ions. This kind of study, performed over a range of the admixture ions’ charge-to-mass ratios, indicates the conditions for their sympathetic cooling and the formation of two-species ion crystals. This mechanism allows efficient cooling of the admixed species such as highly charged ions which do not feature suitable laser-cooling transitions, and thus make them accessible to high-resolution laser spectroscopy.
We propose to measure the six motional frequencies of an unbalanced two-ion crystal in a Penning trap using a scheme that has been demonstrated in a quantum-metrology experiment with a single ion in a linear Paul trap. To study the feasibility, we derive the quantum Hamiltonian for the unbalanced crystal formed by a target and a sensor ion ( 40 Ca , and deduce characteristic coordinates , and , associated to the amplitudes of the displacement operator , and , respectively, when a dipolar time-varying field is applied. The final state after excitation is read out using rapid adiabatic passage. We also present the status of the 7 tesla open-ring Penning trap where first experiments on the 232 Th Ca crystal, cooled to the ground state, are foreseen in the short-term future. Finally, we underline possible experiments with this unique platform.
We have studied the cooling dynamics, formation process, and geometric structure of mesoscopic crystals of externally produced magnesium ions in a Penning trap. We present a cooling model and measurements for a combination of buffer gas cooling and laser cooling which has been found to reduce the ion kinetic energy by eight orders of magnitude from several hundreds of eV to $\ensuremath{\mu}\mathrm{eV}$ and below within seconds. With ion numbers of the order of $1\ifmmode\times\else\texttimes\fi{}{10}^{3}$ to $1\ifmmode\times\else\texttimes\fi{}{10}^{5}$, such cooling leads to the formation of ion Coulomb crystals which display a characteristic shell structure in agreement with the theory of non-neutral plasmas. We show the production and characterization of two-species ion crystals as a means of sympathetic cooling of ions lacking a suitable laser-cooling transition.
We report on the sympathetic cooling and Coulomb crystallization of xenon highly charged ions (HCIs) with laser-cooled Ca+^++ ions. The HCIs are produced in a compact electron beam ion trap, then charge selected, decelerated, and finally injected into a cryogenic linear Paul trap. There, they are captured into 40^{40}40Ca+^++ Coulomb crystals, and co-crystallized within them, causing dark voids in their fluorescence images. Fine control over the number of trapped ions and HCIs allows us to realize mixed-species crystals with arbitrary ordering patterns. By investigating Xeq+^{q+}q+--Ca+^++ strings, we confirm the HCI charge states, measure their lifetime and characterize the mixed-species motional modes. Our system effectively combines the established quantum control toolbox for Ca+^++ with the rich set of atomic properties of Xe highly charged ions, providing a resourceful platform for optical frequency metrology, searches for signatures of new physics, and quantum information science.
We demonstrate the Doppler laser cooling of 40Ca+^{40}\mathrm{Ca}^{+}40Ca+ ions confined in a segmented linear Paul trap in the presence of a strong quadrupolar magnetic field generated by two permanent ring magnets. Magnetic field gradients of 800 to 1600 G/mm give rise to a highly position-dependent Zeeman shift on the energy levels of the trapped ions. Efficient laser cooling is demonstrated using two 397 nm cooling laser beams with appropriate wavelengths and polarizations and one 866 nm repumper laser beam. Coulomb crystals of ions are found to exhibit similar secular temperatures to those trapped in absence of the magnetic field. In addition, the position dependency of the Zeeman effect is used to generate a map of the field strength. This work forms the basis for developing hybrid trapping experiments for cold ions and neutral molecules that consist of an ion and a magnetic trap to study cold interactions between these species, and opens up new possibilities for quantum-science experiments that employ trapped ions in inhomogeneous magnetic fields.