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arXiv:1703.07096 · Physics Letters B

Observation of individual spin quantum transitions of a single antiproton

C. Smorra, Andreas H. Mooser, M. Besirli, M. Bohman, M. J. Borchert, James A. Harrington, Takashi Higuchi, Hiroki Nagahama, Georg L. Schneider, Stefan Sellner, T. Tanaka, K. Blaum, Y. Matsuda, C. Ospelkaus, W. Quint, J. Walz, Y. Yamazaki, S. Ulmer

Published Mar 17, 2017• 25 citations
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Abstract

We report on the detection of individual spin quantum transitions of a single trapped antiproton in a Penning trap . The spin-state determination, which is based on the unambiguous detection of axial frequency shifts in presence of a strong magnetic bottle, reaches a fidelity of 92.1 % . Spin-state initialization with > 99.9 % fidelity and an average initialization time of 24 min are demonstrated. This is a major step towards an antiproton magnetic moment measurement with a relative uncertainty on the part-per-billion level.

DOI
10.1016/j.physletb.2017.03.024

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We report on the detection of individual spin quantum transitions of a single trapped antiproton in a Penning trap . The spin-state determination, which is based on the unambiguous detection of axial frequency shifts in presence of a strong magnetic bottle, reaches a fidelity of 92.1 % . Spin-state initialization with > 99.9 % fidelity and an average initialization time of 24 min are demonstrated. This is a major step towards an antiproton magnetic moment measurement with a relative uncertainty on the part-per-billion level.
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 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.
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.
Electronic feedback is used to self-excite the axial oscillation of a single electron in a Penning trap. Large, stable, easily detected oscillations arise even in an anharmonic potential. Amplitudes are controlled by adjusting the feedback gain, and frequencies can be made nearly independent of amplitude fluctuations. Quantum jump spectroscopy of a perpendicular cyclotron motion reveals the absolute temperature and amplitude of the self-excited oscillation. The possibility to quickly measure parts per billion frequency shifts could open the way to improved measurements of e(-), e(+), p, and (-)p magnetic moments.
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 $7.5(3.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\text{ }\text{ }{\mathrm{V}}^{2}\text{ }{\mathrm{m}}^{\ensuremath{-}2}\text{ }{\mathrm{Hz}}^{\ensuremath{-}1}$, 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.