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Spectroscopy is a key analytical tool that provides valuable insight into molecular structure and is widely used to identify chemical samples. Action spectroscopy combines spectroscopic methods with mass spectrometry, enabling the analysis of low-density gas phase molecular ions. So far, commonly reported action spectroscopy techniques destructively record spectra of ensembles of molecular ions, where the presence of multiple chemical and isomeric species greatly complicates the interpretation of the spectra. Here, we extend the action spectroscopy to the purest possible sample: a single gas phase molecule. The resulting single molecule vibrational spectroscopy is initially demonstrated by the first recorded spectrum of a single gas phase polyatomic molecule to our knowledge. This thesis presents the experimental setup, method, and results of the achieved single-molecule vibrational spectroscopy. The apparatus centers around a cryogenic ion trap, where a single molecular ion is confined after being mass-selected by a quadrupole mass filter. A laser-cooled 88Sr+ ion is co-trapped with the molecular ion. The two ions are sympathetically cooled to a Coulomb crystal at milliKelvin temperatures. We developed nondestructive mass spectrometry based on the crystal's secular motion frequencies. This technique enables ``tagging'' spectroscopy with a single molecular ion, where vibrational transitions are monitored by a nitrogen molecule tag. The single molecule vibrational spectra are deduced based on the vibration-induced de-tagging rate. We showed this single molecule vibrational spectroscopy is generalizable to a broad class of molecular ions and is a powerful analytical tool for the nondestructive identification of single molecules.

The long-term goal of the Penning trap system for the heavy ion accelerator named RAON in Korea is to obtain an order of magnitude higher mass accuracy for short-lived rare isotopes. For that purpose, we are developing a sympathetic cooler for highly charged ions by exploiting laser-cooled Ca+ ions. We installed a prototype octagon chamber with a calcium atom source, a Paul trap, and a helical resonator for the high-voltage RF supply. The laser system is composed of three extended cavity diode lasers (423, 397, 866 nm) plus one UV diode laser (375 nm). The optical frequency stabilization setup is made up of a wavelength meter, a multichannel fiber switch and a PXI system with an 8-channel analog output module. After having obtained a resonant ionization signal from the calcium atomic beam, we applied the RF voltage to the trap electrodes and illuminated the cooling lasers at the center of the trap. We successfully observed a laser-cooled ion bunch and a linearly aligned ion string by using imaging optics and an electron multiplying charge coupled device (EMCCD) camera. In addition to the experimental effort, we performed a simulation study for cooling 132Sn10+ ions inside a laser-cooled 40Ca+ Coulomb crystal by using a parallel computation technique.

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 t...

The positron, the antiparticle of the electron, predicted by Dirac in 1931 and discovered by Anderson in 1933, plays a key role in many scientific and everyday endeavours. Notably, the positron is a constituent of antihydrogen, the only long-lived neutral antimatter bound state that can currently be synthesized at low energy, presenting a prominent system for testing fundamental symmetries with high precision. Here, we report on the use of laser cooled Be+ ions to sympathetically cool a large and dense plasma of positrons to directly measured temperatures below 7 K in a Penning trap for antihydrogen synthesis. This will likely herald a significant increase in the amount of antihydrogen available for experimentation, thus facilitating further improvements in studies of fundamental symmetries., Positrons are key to the production of cold antihydrogen. Here the authors report the sympathetic cooling of positrons by interacting them with laser-cooled Be+ ions resulting in a three-fold reduction of the temperature of positrons for antihydrogen synthesis.

We propose an experimental architecture where an array of optical tweezers affords site-dependent control over the confining potential of a conventional radio-frequency ion trap. The site-dependent control enables programmable manipulation of phonon modes of ions, with many potential applications in quantum information processing (QIP) and thermodynamics. We describe protocols for programming the array of optical tweezers to attain a set of target phonon modes with high accuracy. We propose applications of such controls in simulating quantum thermodynamics of a particle of programmable effective mass via Jarzynski's equality and improving the efficiency of sympathetic cooling and quantum logic gates in a multi-species ion system of disparate masses. We discuss the required optical parameters in a realistic ion trap system and potential adverse effects of optical tweezers in QIP. Our scheme extends the utility of trapped-ions as a platform for quantum computation and simulation.

Trapped atomic ions find wide applications ranging from precision measurement to quantum information science and quantum computing. Beryllium ions are widely used due to the light mass and convenient atomic structure of beryllium; however, conventional ion loading from thermal ovens exerts undesirable gas loads for a prolonged duration. Here, we demonstrate a method to rapidly produce pure linear chains of beryllium ions with pulsed laser ablation, serving as a starting point for large-scale quantum information processing. Our method is fast compared to thermal ovens, reduces the gas load to only 10−12 Torr (10−10 Pa) level, yields a short recovery time of a few seconds, and also eliminates the need for a deep ultraviolet laser for photoionization. We also study the loading dynamics, which show non-Poissonian statistics in the presence of sympathetic cooling. In addition, we apply feedback control to obtain defect-free ion chains with desirable lengths.

A microwave ion clock based on 113Cd+ ions at Tsinghua University has been carried out for eleven years. To improve the performance of the ion clock with lower second-order Doppler frequency shift and suppressed Dick effect, a high-performance scheme for sympathetically cooling 113Cd+ ions based on molecular dynamics simulation is reported.

We demonstrate key multi-qubit quantum logic primitives in a dual-species trapped-ion system based on $^{40}$Ca+ and $^{88}$Sr+ ions, using two optical qubits with quantum-logic-control frequencies in the red to near-infrared range. With all ionization, cooling, and control wavelengths in a wavelength band similar for the two species and centered in the visible, and with a favorable mass ratio for sympathetic cooling, this pair is a promising candidate for scalable quantum information processing. Same-species and dual-species two-qubit gates, based on the Moelmer-Soerensen interaction and performed in a cryogenic surface-electrode trap, are characterized via the fidelity of generated entangled states; we achieve fidelities of 98.8(2)% and 97.5(2)% in Ca+ - Ca+ and Sr+ - Sr+ gates, respectively. For a similar Ca+ - Sr+ gate, we achieve a fidelity of 94.3(3)%, and carrying out a Sr+ - Sr+ gate performed with a Ca+ sympathetic cooling ion in a Sr+ - Ca+ - Sr+ crystal configuration, we achieve a fidelity of 95.7(3)%. These primitives form a set of trapped-ion capabilities for logic with sympathetic cooling and ancilla readout or state transfer for general quantum computing and communication applications., 12 pages, 4 figures, 2 tables

An ion in a radiofrequency (rf) trap sympathetically cooled by a simultaneously trapped neutral buffer gas exhibits deviations from thermal statistics caused by collision-induced coupling of the rf field to the ion motion. For a uniform density distribution of the buffer gas, the energy distribution of the ion can be described by Tsallis statistics. Moreover, runaway heating of the ion occurs if the buffer gas particles are sufficiently heavy relative to the ion. In typical experiments, however, ultracold buffer gases are confined in traps resulting in localised, non-uniform density distributions. Using a superstatistical approach, we develop an analytical model for an ion interacting with a localised buffer gas. We demonstrate theoretically that limiting collisions to the centre of the ion trap enables cooling at far greater mass ratios than achievable using a uniform buffer gas, but that an upper limit to the usable mass ratio exists even in this case. Furthermore, we analytically derive the energy distribution for an ion interacting with a buffer gas held in a harmonic potential. The analytical distribution obtained is found to be in excellent agreement with the results of numerical simulations., Comment: 27 pages, 6 figures

Trapped ions are one of the leading platforms in quantum information science. For quantum computing with large circuit depth and quantum simulation with long evolution time, it is of crucial importance to cool large ion crystals at runtime without affecting the internal states of the computational qubits, thus the necessity of sympathetic cooling. Here, we report multi-ion sympathetic cooling on a long ion chain using a narrow cooling beam focused on two adjacent ions, and optimize the choice of the cooling ions according to the collective oscillation modes of the chain. We show that, by cooling a small fraction of ions, cooling effects close to the global Doppler cooling limit can be achieved. This experiment therefore demonstrates an important enabling step for quantum information processing with large ion crystals.

Efficient cooling of trapped charged particles is essential in many fundamental physics experiments, for high-precision metrology, and for quantum technology. Until now, ion-ion coupling for sympathetic cooling or quantum state control has been limited to ion species with accessible optical transitions or has required close-range Coulomb interactions. To overcome this limitation and further develop scalable quantum control techniques, there has been a sustained desire to extend laser-cooling techniques to particles in macroscopically separated traps, opening quantum control techniques to previously inaccessible particles such as highly charged ions, molecular ions, and antimatter particles. Here, we demonstrate sympathetic cooling of a single proton by laser cooled Be+ ions stored in a spatially separated Penning trap. The two traps are connected by a superconducting LC circuit that enables energy exchange over a distance of 9 cm. We simultaneously demonstrate the cooling of a resonant mode of a macroscopic LC circuit with laser-cooled ions and sympathetic cooling of an individually trapped proton, reaching temperatures far below the environment temperature. Importantly, as this technique does not rely on the direct Coulomb interaction but rather on image-current interactions, it can be easily applied to an experiment with antiprotons, facilitating improved precision in matter-antimatter comparisons and dark matter searches.

We report the production of quantum degenerate Bose-Bose mixtures of Cs and Yb with both attractive (Cs + $^{174}$Yb) and repulsive (Cs + $^{170}$Yb) interspecies interactions. Dual-species evaporation is performed in a bichromatic optical dipole trap that combines light at 1070 nm and 532 nm to enable control of the relative trap depths for Cs and Yb. Maintaining a trap which is shallower for Yb throughout the evaporation leads to highly efficient sympathetic cooling of Cs for both isotopic combinations at magnetic fields close to the Efimov minimum in the Cs three-body recombination rate at around 22 G. For Cs + $^{174}$Yb, we produce quantum mixtures with typical atom numbers of $N_\mathrm{Yb} \sim 5 \times 10^4$ and $N_\mathrm{Cs} \sim 5 \times 10^3$. We find that the attractive interspecies interaction (characterised by the scattering length $a_\mathrm{CsYb} = -75\,a_0$) is stabilised by the repulsive intraspecies interactions. For Cs + $^{170}$Yb, we produce quantum mixtures with typical atom numbers of $N_\mathrm{Yb} \sim 4 \times 10^4$, and $N_\mathrm{Cs} \sim 1 \times 10^4$. Here, the repulsive interspecies interaction ($a_\mathrm{CsYb} = 96\,a_0$) can overwhelm the intraspecies interactions, such that the mixture sits in a region of partial miscibility., Comment: 12 pages, 10 figures. v2: minor changes to figures, text and references following review

We present protocols for dissipative entanglement of three trapped-ion qubits and discuss a scheme that uses sympathetic cooling as the dissipation mechanism. This scheme relies on tailored destructive interference to generate any one of six entangled W states in a three-ion qubit space. Using a beryllium–magnesium ion crystal as an example system, we theoretically investigate the protocol's performance and the effects of likely error sources, including thermal secular motion of the ion crystal, calibration imperfections, and spontaneous photon scattering. We estimate that a fidelity of ~98% may be achieved in typical trapped ion experiments with ~1 ms interaction time. These protocols avoid timescale hierarchies for faster preparation of entangled states., New Journal of Physics, 23 (7), ISSN:1367-2630

This study proposes a method to achieve stable confinement and efficient sympathetic cooling of a mixed ion system in dual radiofrequency (RF) traps by numerical simulations. The dynamic coupling behavior, sympathetic cooling mechanism, and efficiency-affecting factors of the dual RF ion trap system were quantitatively analyzed by molecular dynamics simulations, yielding the stable confinement conditions of three-dimensional (3D) cold ion system in dual RF confinement fields and the characteristics of 3D correlation coupling between intrinsic micromotion and secular motion. The transient processes of ion intrinsic micromotion were also investigated. Herein, a reasonable second trapping potential contributed to the efficient cooling of the ion system and suppression of its micromotion. The effects of the dual RF trapping field strength on the spatial configuration and the dynamic coupling process of sympathetic cooling were investigated in mixed 3D ion crystals with a large mass-to-charge ratio (M/Q) difference, which reveals that simultaneous stable trapping and matching dynamic modes are the key to achieving efficient sympathetic cooling in the two-component ion system. These results are applicable to studies such as quantum logic manipulation, antimatter synthesis, dark ion detection, regulation of ultracold chemical reaction processes, and precision spectral measurements based on sympathetic cooling.

Efficient cooling of trapped charged particles is essential to many fundamental physics experiments1,2, to high-precision metrology3,4 and to quantum technology5,6. Until now, sympathetic cooling has required close-range Coulomb interactions7,8, but there has been a sustained desire to bring laser-cooling techniques to particles in macroscopically separated traps5,9,10, extending quantum control techniques to previously inaccessible particles such as highly charged ions, molecular ions and antimatter. Here we demonstrate sympathetic cooling of a single proton using laser-cooled Be+ ions in spatially separated Penning traps. The traps are connected by a superconducting LC circuit that enables energy exchange over a distance of 9 cm. We also demonstrate the cooling of a resonant mode of a macroscopic LC circuit with laser-cooled ions and sympathetic cooling of an individually trapped proton, reaching temperatures far below the environmental temperature. Notably, as this technique uses only image–current interactions, it can be easily applied to an experiment with antiprotons1, facilitating improved precision in matter–antimatter comparisons11 and dark matter searches12,13., A single electromagnetically trapped proton is sympathetically cooled to below ambient temperature by coupling it through a superconducting LC circuit to a laser-cooled cloud of Be+ ions stored in a spatially separated trap.

Current precision experiments with single (anti)protons to test CPT symmetry progress at a rapid pace, but are complicated by the need to cool particles to sub-thermal energies. We describe a cryogenic Penning-trap setup for $^9$Be$^+$ ions designed to allow coupling of single (anti)protons to laser-cooled atomic ions for sympathetic cooling and quantum logic spectroscopy. We report on trapping and laser cooling of clouds and single $^9$Be$^+$ ions. We discuss prospects for a microfabricated trap to allow coupling of single (anti)protons to laser-cooled $^9$Be$^+$ ions for sympathetic laser cooling to sub-mK temperatures on ms time scales., Comment: Presented at the Eighth Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, May 12-16, 2019

Laser-cooled ions have been used to substantially lower the temperature of a proton located several centimetres away. This technique could be useful in ultraprecise measurements of the properties of antimatter particles. Sympathetic cooling of a trapped proton by ions in a separate trap.

International audience; We report on the production of cold, state-selected H$_2^+$ molecular ions in a linear RF trap. The ions are produced by (3+1) resonance-enhanced multi-photon ionisation (REMPI) of H$_2$, and sympathetically cooled by laser-cooled Be$^+$ ions. After demonstrating and characterizing the REMPI process, we use photodissociation by a deep UV laser at 213~nm to verify the high vibrational purity of the produced H$_2^+$ ion samples. Moreover, the large difference between the photodissociation efficiencies of ions created in the $v=0$ and $v=1$ levels provides a way to detect a $v=0 \to 1$ transition. These results pave the way towards high-resolution vibrational spectroscopy of H$_2^+$ for fundamental metrology applications.

We present a characterization of the ions&rsquo, translational energy distribution in a multipole ion trap. A linear mapping between the energy distribution of the trapped ions onto the ions&rsquo, time-of-flight (TOF) to a detector is demonstrated. For low ion temperatures, a deviation from linearity is observed and can be attributed to the emergence of multiple potential minima. The potential landscape of the trapped ions is modeled via the finite element method, also accounting for subtleties such as surface-charge accumulation. We demonstrate the validity of our thermometry method by simulating the energy distribution of the ion ensemble thermalized with buffer gas using a Molecular Dynamics (MD) simulation. A comparison between the energy distribution of trapped ions in different multipole trap configurations&mdash, i.e., with hyperbolic rods, cylindrical rods, and cylindrical wires&mdash, is provided. With these findings, one can map the temperature of the trapped ions down to the Kelvin regime using their TOF distributions. This enables future studies on sympathetic cooling and chemical reactions involving ions in multipole traps.

Typical quantum cavity optomechanics allows cooling and detection of a single mechanical degree of freedom with its motion along the cavity axis. However, a recent breakthrough using cavities populated solely by coherent scattering (CS) allowing quantum ground-state cooling of levitated nanoparticles [U. Delic et al., Science 367, 892 (2020)], is uniquely three dimensional (3D) in character, with coupling along all three spatial axes. We present a reanalysis of current experiments and show that the underlying behavior is far from the addition of independent one dimensional spectral components and that cooling and sensing analysis must consider, to date neglected, nontrivial 3D hybridization effects arising from interferences between the x , y , z modes as well as the optical modes. These lead to new heating and sympathetic cooling channels and modify phonon occupancies. Unique to these systems, we find a close relation between cavity-mediated and direct hybridization terms that can completely suppress the 3D behavior.

We study the relaxation dynamics of temperature anisotropy between longitudinal and transverse motions of $^{87}\mathrm{Rb}$ atoms in a one-dimensional optical lattice. The temperature imbalance is established by Raman sideband cooling applied along the lattice axis. At low temperature, a large difference between the longitudinal and transverse vibration frequencies limits the relaxation. We transform the trap potential by phase modulating the lattice beam to reduce the anisotropy and thereby enhance cross-dimensional sympathetic cooling. An extension of classical theory, which incorporates the quantization of the atomic motion, explains the experimental results well. We also report that effects of trap anharmonicity and atomic vector polarizability on broadening of the Raman sideband cancel each other at a particular lattice depth, which greatly facilitates sideband cooling.

Precision measurements comparing the fundamental properties of conjugate particles and antiparticles constitute stringent tests of CPT invariance. We review recent precision measurements of the BASE collaboration, which improved the uncertainty of the proton and antiproton magnetic moments and the comparison of the proton-to-antiproton charge-to-mass ratio. These measurements constitute the most stringent tests of CPT invariance with antiprotons. Further, we discuss the improved limit on the antiproton lifetime based on the storage of a cloud of antiprotons in the unique BASE reservoir trap. Based on these recent advances, we discuss ongoing technical developments which comprise a coupling trap for the sympathetic cooling of single (anti-)protons with laser-cooled beryllium ions, a transportable trap to relocate antiproton measurements into a high-precision laboratory, and a new experiment to measure the magnetic moment of helium-3 ions, which will improve absolute precision magnetometry., ICPEAC 2019 conference proceedings