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arXiv:1901.09860 · Physical Review Letters

Measurement of Ultralow Heating Rates of a Single Antiproton in a Cryogenic Penning Trap

M. J. Borchert, Pascal E. Blessing, J. A. Devlin, James A. Harrington, Takashi Higuchi, Jonathan Morgner, C. Smorra, E. Wursten, M. Bohman, M. Wiesinger, Andreas H. Mooser, K. Blaum, Y. Matsuda, C. Ospelkaus, W. Quint, J. Walz, Y. Yamazaki, S. Ulmer

Published Jan 28, 2019• 29 citations
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Abstract

We report on the first detailed study of motional heating in a cryogenic Penning trap using a single antiproton. Employing the continuous Stern-Gerlach effect we observe cyclotron quantum transition rates of $6(1)\text{ }\text{ }\mathrm{quanta}/\mathrm{h}$ and an electric-field noise spectral density below $7.5(3.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\text{ }\text{ }{\mathrm{V}}^{2}\text{ }{\mathrm{m}}^{\ensuremath{-}2}\text{ }{\mathrm{Hz}}^{\ensuremath{-}1}$, which corresponds to a scaled noise spectral density below $8.8(4.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\text{ }\text{ }{\mathrm{V}}^{2}\text{ }{\mathrm{m}}^{\ensuremath{-}2}$, results which are more than 2 orders of magnitude smaller than those reported by other ion-trap experiments.

DOI
10.1103/physrevlett.122.043201

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We report on the first detailed study of motional heating in a cryogenic Penning trap using a single antiproton. Employing the continuous Stern-Gerlach effect we observe cyclotron quantum transition rates of 6(1)  quanta/h6(1)\text{ }\text{ }\mathrm{quanta}/\mathrm{h}6(1)  quanta/h and an electric-field noise spectral density below 7.5(3.4)\ifmmode×\else\texttimes\fi10\ensuremath−20  V2 m\ensuremath−2 Hz\ensuremath−17.5(3.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\text{ }\text{ }{\mathrm{V}}^{2}\text{ }{\mathrm{m}}^{\ensuremath{-}2}\text{ }{\mathrm{Hz}}^{\ensuremath{-}1}7.5(3.4)\ifmmode×\else\texttimes\fi10\ensuremath−20  V2 m\ensuremath−2 Hz\ensuremath−1, which corresponds to a scaled noise spectral density below 8.8(4.0)\ifmmode×\else\texttimes\fi10\ensuremath−12  V2 m\ensuremath−28.8(4.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\text{ }\text{ }{\mathrm{V}}^{2}\text{ }{\mathrm{m}}^{\ensuremath{-}2}8.8(4.0)\ifmmode×\else\texttimes\fi10\ensuremath−12  V2 m\ensuremath−2, results which are more than 2 orders of magnitude smaller than those reported by other ion-trap experiments.
Abstract Coherent quantum transition spectroscopy is a powerful tool in quantum-sensing and metrology (1), quantum information processing (2), accurate magnetometry (3), high-precision tests of the fundamental laws of nature, and searches for physics beyond the Standard Model (4). In atomic physics measurements, it was applied with great success in proton and deuteron magnetic moment measurements (5), which culminated for example in MASER spectroscopy with sub-parts per trillion resolution (6), in record-constraints on the neutron electric dipole moment (7), and many other experiments at the forefront of physics. All these experiments were performed on macroscopic ensembles of particles, while the coherent spectroscopy of a “quasifree” single nuclear spin has never been reported before. In this manuscript, we demonstrate the first non-destructive coherent quantum transition spectroscopy of the spin of a single trapped antiproton, stored in a cryogenic Penning-trap system. We apply a multi-trap technique (8), detect the antiproton spin-state using the continuous Stern-Gerlach-effect (9), and transport the particle to the homogeneous and stabilized magnetic field of a precision trap (PT). Here, we induce the coherent dynamics, and analyze the result by a quantum-projection measurement in the analysis trap (10). In our measurements, we observe for the first time Rabi-oscillations of a single nuclear magnetic moment, and achieve in time series measurements spin inversion probabilities above 80% at spin coherence times of ≈ 50s. Scans of single-particle spin resonance spectra show inversions > 70%, at transition line-widths 16 times narrower than in our previous measurements (8), limited by cyclotron frequency measurement decoherence. This achievement marks a major step towards at least 10-fold improved measurements of the proton and antiproton magnetic moments, and thus, substantially improved tests of matter/antimatter symmetry in the baryon-sector.
We demonstrate efficient sub-thermal cooling of the modified cyclotron mode of a single trapped antiproton and reach particle temperatures T+=E+/kBT_+=E_+/k_\text{B}T+​=E+​/kB​ below 200 200\,200mK in preparation times shorter than 500 500\,500s. This corresponds to the fastest resistive single-particle cyclotron cooling to sub-thermal temperatures ever demonstrated. By cooling trapped particles to such low energies, we demonstrate the detection of antiproton spin transitions with an error-rate <0.000025<0.000025<0.000025, more than three orders of magnitude better than in previous best experiments. This method will have enormous impact on multi-Penning-trap experiments that measure magnetic moments with single nuclear spins for tests of matter/antimatter symmetry, high-precision mass-spectrometry, and measurements of electron ggg-factors bound to highly-charged ions that test quantum electrodynamics.
We demonstrate efficient subthermal cooling of the modified cyclotron mode of a single trapped antiproton and reach particle temperatures T_{+}=E_{+}/k_{B} below 200 mK in preparation times shorter than 500 s. This corresponds to the fastest resistive single-particle cyclotron cooling to subthermal temperatures ever demonstrated. By cooling trapped particles to such low energies, we demonstrate the detection of antiproton spin transitions with an error rate <0.000 023, more than 3 orders of magnitude better than in previous best experiments. This method has enormous impact on multi-Penning-trap experiments that measure magnetic moments with single nuclear spins for tests of matter and antimatter symmetry, high-precision mass spectrometry, and measurements of electron g factors bound to highly charged ions that test quantum electrodynamics and establish standards for magnetometry.
The comparison of the g-factors of the proton and the antiproton is a stringent test of CPT invariance. The state-of-the-art method for the determination of the (anti-)proton's g-factor is the application of the continuous Stern-Gerlach effect. With this method, precisions in the low parts per billion regime could be achieved. However, preparation times for cold enough particles are on the order of minutes to hours. The implementation of sympathetic cooling using a co-trapped atomic ion could lead to preparation times in the milliseconds regime. Furthermore, the applicability of sympathetic cooling would enable an alternative readout scheme using quantum logic methods. This thesis presents a Penning trap system that is designed for ground state cooling, adiabatic transport, and motional coupling of single 9Be+ ions. It has been built in a modular manner, giving the option of adapting it for motional coupling and sympathetic cooling of single (anti-)protons. In the course of this work, the prerequisites for motional coupling of 9Be+ ions have been fulfilled: A cloud of 9Be+ ions was cooled to a temperature of 1.7~mK applying Doppler cooling. The achieved temperature is about three times the Doppler limit which is 0.5~mK for beryllium ions. Furthermore, a scheme for reproducible loading of the trap and reducing the particle number was developed. Finally, first transport in our apparatus was demonstrated with clouds of beryllium ions. The method used for that is directly applicable to single ions. The results of this work pave the way towards adiabatic transport of single 9Be+ ions, which is crucial for sympathetic cooling of (anti-)protons in a double-well potential as well as for implementing quantum logic spectroscopy with single (anti-)protons.
We present measurements of the motional heating rate of a trapped ion at different trap frequencies and temperatures between $\ensuremath{\sim}0.6$ and 1.5 MHz and $\ensuremath{\sim}4$ and 295 K. Additionally, we examine the possible effect of adsorbed surface contaminants with boiling points below $\ensuremath{\sim}105{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ by measuring the ion heating rate before and after locally baking our ion trap chip under ultrahigh vacuum conditions. We compare the heating rates presented here to those calculated from available electric-field noise models. We can tightly constrain a subset of these models based on their expected frequency and temperature scaling interdependence. Discrepancies between the measured results and predicted values point to the need for refinement of theoretical noise models in order to more fully understand the mechanisms behind motional trapped-ion heating.
We report on the first observation of the continuous Stern-Gerlach effect on an electron bound in an atomic ion. The measurement was performed on a single hydrogenlike ion ( 12C5+) in a Penning trap. The measured g factor of the bound electron, g = 2.001 042(2), is in excellent agreement with the theoretical value, confirming the relativistic correction at a level of 0.1%. This proves the possibility of g-factor determinations on atomic ions to high precision by using the continuous Stern-Gerlach effect. The result demonstrates the feasibility of conducting experiments on single heavy highly charged ions to test quantum electrodynamics in the strong electric field of the nucleus.