Coulomb Crystallization Advances Control of Xenon Highly Charged Ions in Traps
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The pursuit of increasingly precise measurements demands innovative approaches to isolating and controlling individual atoms, and now, highly charged ions. Leonid Prokhorov, Aaron A. Smith, and Mingyao Xu, alongside colleagues from the University of Birmingham and the Max-Planck-Institut für Kernphysik, demonstrate a groundbreaking technique for achieving this control by sympathetically cooling and crystallizing xenon highly charged ions within a matrix of laser-cooled calcium ions. This achievement allows researchers to precisely manipulate and study these exotic ions, creating ordered structures with dark voids visible in fluorescence images, and opens exciting possibilities for optical frequency searches, investigations into fundamental physics, and advancements in information science. By combining the established control techniques for calcium ions with the unique properties of highly charged xenon, the team establishes a resourceful platform for exploring the boundaries of atomic and ionic control.
Cryogenic Ion Traps and Highly Charged Ions This collection of research details advancements in high-precision metrology, ion trapping, and quantum sensing, focusing on highly charged ions (HCIs). The work explores core technologies, including Paul traps and Penning traps for confining ions, and linear Paul traps for manipulating ion chains. These traps operate at extremely low temperatures, typically below 4 Kelvin, to minimize noise and enhance signal clarity. HCIs are central to this research, offering unique advantages for precision measurements due to their sensitivity to fundamental constants and potential for revealing new physics. Sympathetic cooling is a crucial technique employed to cool HCIs, as direct cooling methods are often limited. This process utilizes laser-cooled ions, such as calcium or strontium, to transfer energy to the HCI. Quantum logic spectroscopy further enhances precision by using a laser-cooled ion as a quantum gate to manipulate and measure the HCI’s state. The ordered arrangement of ions within the trap, known as a Coulomb crystal, is carefully controlled to facilitate manipulation and measurement.
Electron Beam Ion Traps (EBITs) produce and trap HCIs, providing a source for these precision experiments. Research extends to developing highly accurate optical clocks based on trapped ions, with HCIs offering the potential for even greater precision. Scientists are employing HCIs to test fundamental constants and search for evidence of new physics, including dark matter and new fundamental forces. Trapped ions are also being explored as qubits for quantum computing, with researchers developing multi-qubit logic gates and quantum sensors for high-precision measurements of electric and magnetic fields. The study of molecular ions within these traps offers opportunities for quantum simulation and advanced metrology. Current trends focus on miniaturizing ion traps for field applications, integrating technologies into compact systems, and scaling up the number of trapped ions for quantum computing and sensing. Sympathetic Cooling of Highly Charged Xenon Ions Scientists engineered a system to produce, cool, and trap highly charged xenon ions (HCIs) by sympathetically cooling them with laser-cooled calcium ions. The study pioneered a method where HCIs, generated in a compact electron beam ion trap and subjected to charge selection and deceleration, are injected into a cryogenic linear Paul trap. Within this trap, the HCIs are captured into Coulomb crystals formed by calcium ions, co-crystallizing within the calcium matrix and creating visible dark voids in fluorescence images. This technique allows for precise control over the number of trapped ions and HCIs, enabling the creation of mixed-species crystals with defined ordering patterns. Researchers developed a method for manipulating crystal composition by selectively expelling calcium ions using a blue-detuned cooling laser. The rate of ion removal is inversely proportional to crystal size, and the presence of an HCI accelerates this process for larger crystals. To maintain crystal integrity when removing multiple calcium ions, the trapping frequencies are reduced to melt the crystal before applying minimal cooling laser power, allowing for single-atom precision in constructing mixed Coulomb crystals.
The team demonstrated this capability, creating crystals containing up to seven HCIs. To characterize the HCIs, scientists measured the frequencies of the lowest normal axial modes of linear mixed-species crystals. By modulating the amplitude of the radio frequency drive of the Paul trap, they excited axial motion within the crystal, detecting changes in fluorescence signal. The observed mode frequencies were then compared to theoretical calculations, confirming the assigned charge and mass of the HCIs. Measurements of the separation between calcium ions yielded a value of approximately 52. 5μm for a xenon 11+ ion, aligning with experimental observations.
The team determined an average lifetime of 27 minutes for the Xe11+ HCI, inferring a pressure of 2 × 10−14 mbar within the 4 Kelvin shield. This innovative approach represents a significant advancement towards realizing xenon-based HCI optical clocks and precision tests of fundamental physics.
Mixed Species Crystals with Highly Charged Ions Scientists have achieved sympathetic cooling and Coulomb crystallization of highly charged xenon ions (HCIs) alongside laser-cooled calcium ions, demonstrating a novel platform for precision measurements. The research team successfully captured HCIs produced in a compact electron beam ion trap, decelerated them, and injected them into a cryogenic linear Paul trap where they were co-crystallized within calcium Coulomb crystals. This process creates visible dark voids within the calcium fluorescence images, confirming the presence and localization of the HCIs. Experiments reveal precise control over the number of trapped ions and HCIs, enabling the creation of mixed-species crystals with specifically engineered ordering patterns. The decelerated HCI bunches exhibited mean energies of approximately 160 qeV, demonstrating effective energy control.
The team applied voltages to the electrodes of the Paul trap to provide radial confinement, utilizing the same pseudopotential to confine hundreds of calcium ions. This sympathetic cooling process allows the HCIs to crystallize within the calcium Coulomb crystal, a process confirmed by the observation of dark voids in the fluorescence images. This breakthrough delivers a resourceful platform for optical frequency searches and precision tests of fundamental physics, paving the way for future HCI-based optical clocks. Xenon and Calcium, Mixed-Species Coulomb Crystals Form Researchers have successfully demonstrated the sympathetic cooling and Coulomb crystallization of highly charged xenon ions alongside laser-cooled calcium ions within a cryogenic linear Paul trap. This achievement involves capturing highly charged ions, produced using a compact electron beam ion trap, within the Coulomb crystals formed by calcium ions, creating observable dark voids in fluorescence images. By carefully controlling the number of ions, the team created mixed-species crystals with defined ordering patterns and investigated the interactions between the xenon and calcium ions, confirming charge states and measuring lifetimes. This work establishes a resourceful platform combining the established control of calcium ions with the unique atomic properties of highly charged xenon ions. 👉 More information 🗞 Coulomb crystallization of xenon highly charged ions in a laser-cooled Ca+ matrix 🧠 ArXiv: https://arxiv.org/abs/2512.12266 Tags: