Ultracold atom-ion collisions are an emerging field of research that can ultimately lead to their precise quantum control. In collisions in which the ion is prepared in an excited state, previous studies showed that the dominant reaction pathway was charge exchange. Here, we explored the outcome products and the energy released from a single ultracold collision between a single $^{88}\mathrm{Sr}^{+}$ ion and a single $^{87}\mathrm{Rb}$ atom prepared in excited metastable and ground electronic states, respectively, with control over their relative spins. We found that the ion's long-lived ${D}_{5/2}$ and ${D}_{3/2}$ states quench after roughly three collisions, acquiring immense kinetic energy in the process. By performing single-shot thermometry on the ion after the collision, we identified two dominant reaction pathways: electronic excitation exchange and spin-orbit change. In contrast to previous experiments, we observed no charge-exchange events. These processes are theoretically understood to occur through Landau-Zener avoided crossings leading to the observed reaction pathways. We also found that spin orientation has almost no effect on the reaction pathways, due to strong Coriolis-spin mixing. Our results provide a deeper understanding of ultracold atom-ion inelastic collisions and offer additional quantum control tools for the cold chemistry field.Ultracold atom-ion collisions are an emerging field of research that can ultimately lead to their precise quantum control. In collisions in which the ion is prepared in an excited state, previous studies showed that the dominant reaction pathway was charge exchange. Here, we explored the outcome products and the energy released from a single ultracold collision between a single $^{88}\mathrm{Sr}^{+}$ ion and a single $^{87}\mathrm{Rb}$ atom prepared in excited metastable and ground electronic states, respectively, with control over their relative spins. We found that the ion's long-lived ${D}_{5/2}$ and ${D}_{3/2}$ states quench after roughly three collisions, acquiring immense kinetic energy in the process. By performing single-shot thermometry on the ion after the collision, we identified two dominant reaction pathways: electronic excitation exchange and spin-orbit change. In contrast to previous experiments, we observed no charge-exchange events. These processes are theoretically understood to occur through Landau-Zener avoided crossings leading to the observed reaction pathways. We also found that spin orientation has almost no effect on the reaction pathways, due to strong Coriolis-spin mixing. Our results provide a deeper understanding of ultracold atom-ion inelastic collisions and offer additional quantum control tools for the cold chemistry field.

arXiv:1907.06736Physical Review ASep 16, 202011 citations

Excited State Atom-Ion Charge-Exchange

Ming Li, Constantinos Makrides, Alexander A. Petrov +1 more

Bulletin of the American Physical SocietyJun 6, 20170 citations

Controlled quantum-state-resolved chemistry to enable quantum logic with molecular ions

Michael Charles Mills

This dissertation describes experiments performed in the MOTion trap, a hybrid atom--ion trap comprised of a magneto-optical trap (MOT) and a linear Paul trap with an integrated time-of-flight mass spectrometer (ToF-MS).We aim to sympathetically cool the vibrational and rotational degrees of freedom of a BaCl $^+$ molecular ion by overlapping a cold ( $\\sim4$ ~mK) Ca MOT.\nThis sympathetic cooling can prepare a molecular ion in its rovibrational quantum ground state, providing a method for state preparation for applications in molecular ion quantum logic.\nWhile collisions between the molecular ion and the cold atoms can cool the internal degrees of freedom, chemical reactions are also possible for electronically excited atoms.\nAs such, we study these excited-state atom--ion reactions at low temperature $<1$ ~K and develop tools to control these collisions.\nWe make the first experimental observation of reaction blockading, an effect that suppresses excited-state reactions at low temperature, and develop a method to reverse this suppression if desired with the addition of a catalyst laser, providing a means to optically control such reactions.Beyond its intended purpose of studying and achieving sympathetic cooling, we find that this apparatus is a powerful tool for chemical studies.By imaging the ions, we can observe reactions occurring one atom at a time.\nWe can precisely tune the collision energy or temperature down to the mK regime to as high as $\\sim$10~K using techniques described in this dissertation, allowing controlled interrogation of these low-temperature reactions.\nFurther, using lasers to address electronic transitions, we can precisely control the quantum state of the reactants, and we can measure the reaction products with the ToF-MS.\nA testament to the value of this apparatus is the study of BaOCa$^+$ described in this dissertation.\nUsing the tools of the MOTion trap, we were able to identify the production of BaOCa $^+$ , the first observation of a mixed hypermetallic oxide, and determine the path of reaction as BaOCH $_3^+$ + Ca( $4s4p$ ~ $^3P_J$ ) $\\rightarrow$ BaOCa $^+$ + CH $_3$ .In addition to developing control of these atom--ion interactions towards sympathetic cooling of molecular ions, we also work towards further developing new quantum logic schemes for molecular ions, such as dipolar quantum logic, dipole--phonon quantum logic (DPQL), and electric-field gradient gates (EGGs).Specifically, we propose a class of molecules particularly well-suited for DPQL, the alkaline earth monoxide cations, that can also be added to existing atomic ion experiments with minimal additional experimental complexity.\nWe further develop the techniques for DPQL and propose methods for single- and two-qubit gates, outlining a path towards universal quantum computation with molecular ions.This dissertation describes experiments performed in the MOTion trap, a hybrid atom--ion trap comprised of a magneto-optical trap (MOT) and a linear Paul trap with an integrated time-of-flight mass spectrometer (ToF-MS).We aim to sympathetically cool the vibrational and rotational degrees of freedom of a BaCl$^+$ molecular ion by overlapping a cold ($\\sim4$~mK) Ca MOT.\nThis sympathetic cooling can prepare a molecular ion in its rovibrational quantum ground state, providing a method for state preparation for applications in molecular ion quantum logic.\nWhile collisions between the molecular ion and the cold atoms can cool the internal degrees of freedom, chemical reactions are also possible for electronically excited atoms.\nAs such, we study these excited-state atom--ion reactions at low temperature $<1$~K and develop tools to control these collisions.\nWe make the first experimental observation of reaction blockading, an effect that suppresses excited-state reactions at low temperature, and develop a method to reverse this suppression if desired with the addition of a catalyst laser, providing a means to optically control such reactions.Beyond its intended purpose of studying and achieving sympathetic cooling, we find that this apparatus is a powerful tool for chemical studies.By imaging the ions, we can observe reactions occurring one atom at a time.\nWe can precisely tune the collision energy or temperature down to the mK regime to as high as $\\sim$10~K using techniques described in this dissertation, allowing controlled interrogation of these low-temperature reactions.\nFurther, using lasers to address electronic transitions, we can precisely control the quantum state of the reactants, and we can measure the reaction products with the ToF-MS.\nA testament to the value of this apparatus is the study of BaOCa$^+$ described in this dissertation.\nUsing the tools of the MOTion trap, we were able to identify the production of BaOCa$^+$, the first observation of a mixed hypermetallic oxide, and determine the path of reaction as BaOCH$_3^+$ + Ca($4s4p$~$^3P_J$) $\\rightarrow$ BaOCa$^+$ + CH$_3$.In addition to developing control of these atom--ion interactions towards sympathetic cooling of molecular ions, we also work towards further developing new quantum logic schemes for molecular ions, such as dipolar quantum logic, dipole--phonon quantum logic (DPQL), and electric-field gradient gates (EGGs).Specifically, we propose a class of molecules particularly well-suited for DPQL, the alkaline earth monoxide cations, that can also be added to existing atomic ion experiments with minimal additional experimental complexity.\nWe further develop the techniques for DPQL and propose methods for single- and two-qubit gates, outlining a path towards universal quantum computation with molecular ions.

Jan 1, 20200 citations

Quantum-state-controlled reactions between molecular radicals and ions

J. M. Greenberg, Philipp Christoph Schmid, Mikhail I. Miller +2 more

Chemical reactions between ions and molecular radicals are important in both terrestrial and extraterrestrial environments. However, due to the challenge of creating dense, pure samples of both species, very few studies have been performed in the laboratory. We present the first measurement of a state-controlled reaction between a radical and an ion, where the ${\mathrm{Ca}}^{+}$ cation and the NO radical molecule combine to form ${\mathrm{CaO}}^{+}$ and a nitrogen atom. The charge transfer between ${\mathrm{Ca}}^{+}$ and NO is simultaneously observed. We utilize a linear Paul ion trap coupled to a time-of-flight mass spectrometer to make direct, simultaneous measurements of multiple ionic product channels. We demonstrate control over the reaction rates by tuning of the excited-state population of the laser cooled $^{40}\mathrm{Ca}^{+}$ . This control, coupled with a sensitive detection technique, enables precise measurement of the rate constants and branching ratios for this reaction.Chemical reactions between ions and molecular radicals are important in both terrestrial and extraterrestrial environments. However, due to the challenge of creating dense, pure samples of both species, very few studies have been performed in the laboratory. We present the first measurement of a state-controlled reaction between a radical and an ion, where the ${\mathrm{Ca}}^{+}$ cation and the NO radical molecule combine to form ${\mathrm{CaO}}^{+}$ and a nitrogen atom. The charge transfer between ${\mathrm{Ca}}^{+}$ and NO is simultaneously observed. We utilize a linear Paul ion trap coupled to a time-of-flight mass spectrometer to make direct, simultaneous measurements of multiple ionic product channels. We demonstrate control over the reaction rates by tuning of the excited-state population of the laser cooled $^{40}\mathrm{Ca}^{+}$. This control, coupled with a sensitive detection technique, enables precise measurement of the rate constants and branching ratios for this reaction.

Physical Review ASep 13, 201823 citations

Catching a Molecule in an Excited State

Tim Wogan

PhysicsMar 13, 20153 citations

^{88}\mathrm{Sr}^{+}

ion and a single

^{87}\mathrm{Rb}

atom prepared in excited metastable and ground electronic states, respectively, with control over their relative spins. We found that the ion's long-lived

{D}_{5/2}

and

{D}_{3/2}

states quench after roughly three collisions, acquiring immense kinetic energy in the process. By performing single-shot thermometry on the ion after the collision, we identified two dominant reaction pathways: electronic excitation exchange and spin-orbit change. In contrast to previous experiments, we observed no charge-exchange events. These processes are theoretically understood to occur through Landau-Zener avoided crossings leading to the observed reaction pathways. We also found that spin orientation has almost no effect on the reaction pathways, due to strong Coriolis-spin mixing. Our results provide a deeper understanding of ultracold atom-ion inelastic collisions and offer additional quantum control tools for the cold chemistry field.

^+

molecular ion by overlapping a cold (

\\sim4

~mK) Ca MOT.\nThis sympathetic cooling can prepare a molecular ion in its rovibrational quantum ground state, providing a method for state preparation for applications in molecular ion quantum logic.\nWhile collisions between the molecular ion and the cold atoms can cool the internal degrees of freedom, chemical reactions are also possible for electronically excited atoms.\nAs such, we study these excited-state atom--ion reactions at low temperature

<1

~K and develop tools to control these collisions.\nWe make the first experimental observation of reaction blockading, an effect that suppresses excited-state reactions at low temperature, and develop a method to reverse this suppression if desired with the addition of a catalyst laser, providing a means to optically control such reactions.Beyond its intended purpose of studying and achieving sympathetic cooling, we find that this apparatus is a powerful tool for chemical studies.By imaging the ions, we can observe reactions occurring one atom at a time.\nWe can precisely tune the collision energy or temperature down to the mK regime to as high as $\\sim$10~K using techniques described in this dissertation, allowing controlled interrogation of these low-temperature reactions.\nFurther, using lasers to address electronic transitions, we can precisely control the quantum state of the reactants, and we can measure the reaction products with the ToF-MS.\nA testament to the value of this apparatus is the study of BaOCa$^+$ described in this dissertation.\nUsing the tools of the MOTion trap, we were able to identify the production of BaOCa

^+

, the first observation of a mixed hypermetallic oxide, and determine the path of reaction as BaOCH

_3^+

+ Ca(

4s4p

^3P_J

)

\\rightarrow

BaOCa

^+

+ CH

_3

.In addition to developing control of these atom--ion interactions towards sympathetic cooling of molecular ions, we also work towards further developing new quantum logic schemes for molecular ions, such as dipolar quantum logic, dipole--phonon quantum logic (DPQL), and electric-field gradient gates (EGGs).Specifically, we propose a class of molecules particularly well-suited for DPQL, the alkaline earth monoxide cations, that can also be added to existing atomic ion experiments with minimal additional experimental complexity.\nWe further develop the techniques for DPQL and propose methods for single- and two-qubit gates, outlining a path towards universal quantum computation with molecular ions.

{\mathrm{Ca}}^{+}

cation and the NO radical molecule combine to form

{\mathrm{CaO}}^{+}

and a nitrogen atom. The charge transfer between

{\mathrm{Ca}}^{+}

and NO is simultaneously observed. We utilize a linear Paul ion trap coupled to a time-of-flight mass spectrometer to make direct, simultaneous measurements of multiple ionic product channels. We demonstrate control over the reaction rates by tuning of the excited-state population of the laser cooled

^{40}\mathrm{Ca}^{+}

. This control, coupled with a sensitive detection technique, enables precise measurement of the rate constants and branching ratios for this reaction.