Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Nature

Coherent spectroscopy with a single antiproton spin

B. M. Latacz, Stefan Erlewein, M. Fleck, J. I. Jäger, F. Abbass, B. P. Arndt, P Geissler, Tomoka Imamura, Marc Leonhardt, P. Micke, Andreas H. Mooser, D. Schweitzer, F. Voelksen, E. Wursten, H. Yildiz, K. Blaum, J. A. Devlin, Y. Matsuda, C. Ospelkaus, W. Quint, A. Sótér, J. Walz, Y. Yamazaki, C. Smorra, S. Ulmer

Published Jul 23, 2025• 9 citations
Publisher

Abstract

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.

DOI
10.1038/s41586-025-09323-1

Related papers

Probing Trapped Antihydrogen. In Situ Diagnostics and Observations of Quantum Transitions

Tim Friesen

Antihydrogen, the bound state of a positron and an antiproton, is the simplest pure anti-atomic system and an excellent candidate to test the symmetry between matter and antimatter. This thesis focuses on the magnetic confinement of antihydrogen and the first ever resonant interaction with trapped antihydrogen, as performed by the ALPHA collaboration. The ALPHA apparatus and the techniques that have been developed to form, trap, probe, and detect antihydrogen atoms will be described in detail. The first successful demonstration of trapped antihydrogen will then be described. In the initial demonstrations, 38 trapped antihydrogen atoms were detected after being confined for at least 172 ms. Since then, over 400 antihydrogen atoms have been trapped and confinement times of 1000 s (over 15 minutes) have been demonstrated. Spectroscopy of these trapped antihydrogen atoms is the next major step forward. As an initial proof-of-principle demonstration, ALPHA induced and observed reso- nant positron spin flip (PSR) transitions between the ground states of antihydrogen. Because of the strong magnetic field dependence of these transition frequencies, the success of this experiment relied heavily on the ability to measure the magnetic field seen by the antihydrogen atoms. A novel method to measure the magnetic field in situ by detecting the cyclotron resonance of a trapped electron plasma is presented. This method allowed ALPHA to measure the magnetic field strength at the minimum of the magnetic antihydrogen trap to within 1.4 parts in 103. Hardware improvements and further study should allow this resolution to be improved by several orders of magnitude. The cyclotron resonance measurements can also be applied as a roughdiagnostic of a microwave field within the ALPHA apparatus. This allowed for important diagnostics of the microwave field used to excite the PSR transitions. Finally, the experimental results demonstrating resonant PSR transitions in antihydrogen are presented. This experiment is the first ever spectroscopic measurement of antihydrogen and an important step towards future precision spectroscopy.

•Jan 31, 2014•1 citation

Observation of individual spin quantum transitions of a single antiproton

C. Smorra, Andreas H. Mooser, M. Besirli +15 more

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.

arXiv:1703.07096•Physics Letters B•Mar 17, 2017•25 citations

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

M. J. Borchert, Pascal E. Blessing, J. A. Devlin +15 more

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.

arXiv:1901.09860•Physical Review Letters•Jan 28, 2019•29 citations

High-resolution spectroscopy of single nuclear spins via sequential weak measurements

Matthias Pfender, Ping Wang, Hitoshi Sumiya +8 more

Abstract Nuclear magnetic resonance (NMR) of single spins have recently been detected by quantum sensors. However, the spectral resolution has been limited by the sensor’s relaxation to a few kHz at room temperature. This can be improved by using quantum memories, at the expense of sensitivity. In contrast, classical signals can be measured with exceptional spectral resolution by using continuous measurement techniques, without compromising sensitivity. When applied to single-spin NMR, it is critical to overcome the impact of back action inherent of quantum measurement. Here we report sequential weak measurements on a single 13C nuclear spin. The back-action causes the spin to undergo a quantum dynamics phase transition from coherent trapping to coherent oscillation. Single-spin NMR at room-temperature with a spectral resolution of 3.8 Hz is achieved. These results enable the use of measurement-correlation schemes for the detection of very weakly coupled single spins.

arXiv:1806.02181•Nature Communications•Feb 5, 2019•94 citations

Optical Atomic Coherence at the 1-Second Time Scale

Martin M. Boyd, Tanya Zelevinsky, Andrew D. Ludlow +4 more

Highest-resolution laser spectroscopy has generally been limited to single trapped ion systems because of the rapid decoherence that plagues neutral atom ensembles. Precision spectroscopy of ultracold neutral atoms confined in a trapping potential now shows superior optical coherence without any deleterious effects from motional degrees of freedom, revealing optical resonance linewidths at the hertz level with a good signal-to-noise ratio. The resonance quality factor of 2.4 x 10(14) is the highest ever recovered in any form of coherent spectroscopy. The spectral resolution permits direct observation of the breaking of nuclear spin degeneracy for the 1S0 and 3P0 optical clock states of 87Sr under a small magnetic bias field. This optical approach for excitation of nuclear spin states allows an accurate measurement of the differential Landé g factor between 1S0 and 3P0. The optical atomic coherence demonstrated for collective excitation of a large number of atoms will have a strong impact on quantum measurement and precision frequency metrology.

arXiv:physics/0610096•Science•Nov 30, 2006•159 citations

Quantum spectroscopy of single spins assisted by a classical clock

Tuvia Gefen, Maxim Khodas, Liam Paul McGuinness +2 more

Quantum spectroscopy with single two-level systems has considerably improved our ability to detect weak signals. Recently it was realized that for classical signals, precision and resolution of quantum spectroscopy is limited mainly by coherence of the signal and the stability of the clock used to measure time. The coherence time of the quantum probe, which can be significantly shorter, is not a major limiting factor in resolution measurements. Here, we address a similar question for spectroscopy of quantum signals, for example, a quantum sensor is used to detect a single nuclear spin. We present and analyze a novel correlation spectroscopy technique with performance that is limited by the coherence time of the target spins and the stability of the clock.

arXiv:1612.07225•Physical Review A•Jul 27, 2018•20 citations
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.
Antihydrogen, the bound state of a positron and an antiproton, is the simplest pure anti-atomic system and an excellent candidate to test the symmetry between matter and antimatter. This thesis focuses on the magnetic confinement of antihydrogen and the first ever resonant interaction with trapped antihydrogen, as performed by the ALPHA collaboration. The ALPHA apparatus and the techniques that have been developed to form, trap, probe, and detect antihydrogen atoms will be described in detail. The first successful demonstration of trapped antihydrogen will then be described. In the initial demonstrations, 38 trapped antihydrogen atoms were detected after being confined for at least 172 ms. Since then, over 400 antihydrogen atoms have been trapped and confinement times of 1000 s (over 15 minutes) have been demonstrated. Spectroscopy of these trapped antihydrogen atoms is the next major step forward. As an initial proof-of-principle demonstration, ALPHA induced and observed reso- nant positron spin flip (PSR) transitions between the ground states of antihydrogen. Because of the strong magnetic field dependence of these transition frequencies, the success of this experiment relied heavily on the ability to measure the magnetic field seen by the antihydrogen atoms. A novel method to measure the magnetic field in situ by detecting the cyclotron resonance of a trapped electron plasma is presented. This method allowed ALPHA to measure the magnetic field strength at the minimum of the magnetic antihydrogen trap to within 1.4 parts in 103. Hardware improvements and further study should allow this resolution to be improved by several orders of magnitude. The cyclotron resonance measurements can also be applied as a roughdiagnostic of a microwave field within the ALPHA apparatus. This allowed for important diagnostics of the microwave field used to excite the PSR transitions. Finally, the experimental results demonstrating resonant PSR transitions in antihydrogen are presented. This experiment is the first ever spectroscopic measurement of antihydrogen and an important step towards future precision spectroscopy.
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.
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.
Abstract Nuclear magnetic resonance (NMR) of single spins have recently been detected by quantum sensors. However, the spectral resolution has been limited by the sensor’s relaxation to a few kHz at room temperature. This can be improved by using quantum memories, at the expense of sensitivity. In contrast, classical signals can be measured with exceptional spectral resolution by using continuous measurement techniques, without compromising sensitivity. When applied to single-spin NMR, it is critical to overcome the impact of back action inherent of quantum measurement. Here we report sequential weak measurements on a single 13C nuclear spin. The back-action causes the spin to undergo a quantum dynamics phase transition from coherent trapping to coherent oscillation. Single-spin NMR at room-temperature with a spectral resolution of 3.8 Hz is achieved. These results enable the use of measurement-correlation schemes for the detection of very weakly coupled single spins.
Highest-resolution laser spectroscopy has generally been limited to single trapped ion systems because of the rapid decoherence that plagues neutral atom ensembles. Precision spectroscopy of ultracold neutral atoms confined in a trapping potential now shows superior optical coherence without any deleterious effects from motional degrees of freedom, revealing optical resonance linewidths at the hertz level with a good signal-to-noise ratio. The resonance quality factor of 2.4 x 10(14) is the highest ever recovered in any form of coherent spectroscopy. The spectral resolution permits direct observation of the breaking of nuclear spin degeneracy for the 1S0 and 3P0 optical clock states of 87Sr under a small magnetic bias field. This optical approach for excitation of nuclear spin states allows an accurate measurement of the differential Landé g factor between 1S0 and 3P0. The optical atomic coherence demonstrated for collective excitation of a large number of atoms will have a strong impact on quantum measurement and precision frequency metrology.
Quantum spectroscopy with single two-level systems has considerably improved our ability to detect weak signals. Recently it was realized that for classical signals, precision and resolution of quantum spectroscopy is limited mainly by coherence of the signal and the stability of the clock used to measure time. The coherence time of the quantum probe, which can be significantly shorter, is not a major limiting factor in resolution measurements. Here, we address a similar question for spectroscopy of quantum signals, for example, a quantum sensor is used to detect a single nuclear spin. We present and analyze a novel correlation spectroscopy technique with performance that is limited by the coherence time of the target spins and the stability of the clock.