Reversing hydride-ion formation in quantum-information experiments withBe+

Abstract

We demonstrate photodissociation of BeH + ions within a Coulomb crystal of thousands of 9 Be + ions confined in a Penning trap. Because BeH + ions are created via exothermic reactions between trapped, laser-cooled Be + ( 2 P 3/2 ) and background H2 within the vacuum chamber, they represent a major contaminant species responsible for infidelities in large-scale trapped-ion quantum information experiments. The rotational-state-insensitive dissociation scheme described here makes use of 157 nm photons to produce Be + and H as products, thereby restoring Be + ions without the need for reloading. This technique facilitates longer experiment runtimes at a given background H2 pressure, and may be adapted for removal of MgH + and AlH + impurities.PACS numbers: 52.27. Jt, 33.80.Gj, 34.50.Lf, Crystals of laser-cooled atomic ions form the basis of many experimental realizations of quantum logic gates [1][2][3] and simulations of quantum many-body physics [4][5][6]. In room-temperature vacuum systems, collisions with neutral background gas molecules limit quantum coherences and quantum logic operations [7]. Here we focus on inelastic (i.e. reactive) collisions where exothermic chemical reactions with background gas molecules can generate, in both Penning and rf traps, co-trapped molecular ions over a wide range of trapping conditions and crystal geometries [6][7][8][9]. These contaminants alter ion-crystal eigenfrequencies and can complicate quantum logic interactions [10]. Impurities may be resonantly ejected from both radiofrequency and Penning traps, but this technique is least efficient when the impurities are similar in mass to the qubit ion [11]. The rate of impurity ion formation increases linearly with the number of ion qubits in the register, and the time required for loading new ions and recalibrating the register increases with the size of the system. Therefore, experimental techniques to prevent or reverse qubit-ion chemistry will be a key tool for many-ion quantum information platforms. [18]. Given the difficulty of detecting scattered photons from dilute molecular-ion samples, rotational-state-selective PD has emerged as a critical tool for molecular ion spectroscopy [15,19] and precision measurements [16,20], while rotationally-insensitive dissociation schemes provide valuable tests of molecular * Electronic address: brian.sawyer@boulder.nist.gov ) after 9000 pulses of 157 nm photodissociation light at 1.6 mJ/pulse. We measure an increase in the Be + fraction from 81% to 97% of the constant total ion number in the crystal. Each image is 1.2 mm × 1.2 mm.

Simulating generic spin-boson models with matrix product states

“…In order to exemplify the power and generality of our approach compared to these other methods, we thus consider a case in which the center of mass mode is no longer spatially uniform. In particular, we simulate the case of an ion crystal in which some atomic ions have converted to heavier mass molecular ions through collisions with background gas, focusing on a crystal of Be + ions with BeH + impurities as a particular example [90]. Impurity molecular ions have a heavier mass than the atomic ions, and so move to the edge of the rotating crystal due to centrifugal forces.…”

Ultra-low-vibration closed-cycle cryogenic surface-electrode ion trap apparatus

“…Kinetic collisions with background gas will most likely not be a source of ion loss and therefore cannot be used to reach conclusions about the background gas density. A useful method to characterize vacuum quality under these conditions was presented in [92]: The main loss channel for Doppler cooled 9 Be + ions in a cryogenic trap is a chemical reaction with hydrogen. The reaction of a hydrogen molecule with an ion is endothermic and will not happen without supplying an activation energy.…”

“…Assuming that this is the only relevant loss channel [92], the effective ion lifetime τ is inversely proportional to the number density of hydrogen. The proportionality factor is the inverse reaction rate k −1 L :…”

Second-Scale $^9\text{Be}^+$ Spin Coherence in a Compact Penning Trap

“…40 Ca + SPECTROSCOPY Trapped 40 Ca + is useful for characterizing the Penning trap magnetic field environment due to the high sensitivity (∼ 28.025 MHz/mT) of its |S 1/2 , +1/2 → |S 1/2 , −1/2 electronspin resonance (ESR) transition [36]. Also, in contrast to Be + and Mg + , Ca + does not exhibit long-term loss from chemical reactions with residual H 2 molecules [26,37]. We regularly maintain a 40 Ca + crystal for weeks.…”