Publications
129 results found
Tarlton JE, Thompson RC, Lucas DM, 2023, Surface-electrode ion trap design for near-field microwave quantum gates, APPLIED PHYSICS B-LASERS AND OPTICS, Vol: 129, ISSN: 0946-2171
Lee C, Webster SC, Toba JM, et al., 2023, Measurement-based ground-state cooling of a trapped-ion oscillator, PHYSICAL REVIEW A, Vol: 107, ISSN: 2469-9926
Corfield O, Lishman J, Lee C, et al., 2021, Certifying multilevel coherence in the motional state of a trapped ion, PRX Quantum, Vol: 2, ISSN: 2691-3399
Quantum coherence is the foundation of almost all departures from classical physics and is exhibited when a quantum system is in a superposition of different basis states. Here, the coherent superposition of three motional Fock states of a single trapped ion is experimentally certified, with a procedure that does not produce false positives. As the motional state cannot be directly interrogated, our scheme uses an interference pattern generated by projective measurement of the coupled qubit state. The minimum number of coherently superposed states is inferred from a series of threshold values based on analysis of the interference pattern. This demonstrates that high-level coherence can be verified and investigated with simple nonideal control methods that are well suited to noisy intermediate-scale quantum devices.
Barontini G, Blackburn L, Boyer V, et al., 2021, Measuring the stability of fundamental constants with a network of clocks, Publisher: arXiv
The detection of variations of fundamental constants of the Standard Modelwould provide us with compelling evidence of new physics, and could lift theveil on the nature of dark matter and dark energy. In this work, we discuss howa network of atomic and molecular clocks can be used to look for suchvariations with unprecedented sensitivity over a wide range of time scales.This is precisely the goal of the recently launched QSNET project: A network ofclocks for measuring the stability of fundamental constants. QSNET will includestate-of-the-art atomic clocks, but will also develop next-generation molecularand highly charged ion clocks with enhanced sensitivity to variations offundamental constants. We describe the technological and scientific aims ofQSNET and evaluate its expected performance. We show that in the range ofparameters probed by QSNET, either we will discover new physics, or we willimpose new constraints on violations of fundamental symmetries and a range oftheories beyond the Standard Model, including dark matter and dark energymodels.
Jarlaud V, Hrmo P, Joshi MK, et al., 2021, Coherence properties of highly-excited motional states of a trapped ion, Journal of Physics B: Atomic, Molecular and Optical Physics, Vol: 54, Pages: 1-12, ISSN: 0953-4075
We present a study of the coherence properties of a variety of motional states of a single ion confined in a Penning ion trap. We demonstrate that the motion of the ion has a coherence time of the order of 1 s, using Ramsey interferometry. We introduce a technique for preparing the ion in an incoherent superposition of highly-excited motional states using a simple modification of optical sideband cooling. Coherent manipulation of these states allows measurements of optical and motional coherence to be carried out. We show that these highly-excited motional state superpositions have long coherence times despite the incoherent preparation of the states. Such states can be useful for sensitive motional dephasing measurements.
Hrmo P, Joshi MK, Jarlaud V, et al., 2019, Sideband cooling of the radial modes of motion of a single ion in a Penning trap, Physical Review A, Vol: 100, ISSN: 2469-9926
Doppler and sideband cooling are long-standing techniques that have been used together to prepare trapped atomic ions in their ground state of motion. In this paper we study how these techniques can be extended to cool both radial modes of motion of a single ion in a Penning trap. We numerically explore the prerequisite experimental parameters for efficient Doppler cooling in the presence of an additional oscillating electric field to resonantly couple the radial modes. The simulations are supported by experimental data for a single 40Ca+ ion Doppler cooled to ∼100 phonons in both radial modes at a magnetron frequency of 52 kHz and a modified cyclotron frequency of 677 kHz. For these frequencies, we then show that mean phonon numbers of 0.35(5) for the modified cyclotron and 1.7(2) for the magnetron motions are achieved after 68 ms of sideband cooling.
Nörtershäuser W, Ullmann J, Skripnikov LV, et al., 2019, The hyperfine puzzle of strong-field bound-state QED, Hyperfine Interactions, Vol: 240, ISSN: 0304-3843
The hyperfine splitting in heavy highly charged ions provide the means to test QED in extremely strong magnetic fields. In order to provide a meaningful test, the splitting has to be measured in H-like and Li-like ions to remove uncertainties from nuclear structure. This has been achieved at the experimental storage ring ESR but a discrepancy to the theoretical prediction of more than 7σ was observed. We report on these measurements as well as on NMR measurements that were performed to solve this issue.
Hannen V, Vollbrecht J, Andelkovic Z, et al., 2019, Lifetimes and g-factors of the HFS states in H-like and Li-like bismuth, Journal of Physics B: Atomic, Molecular and Optical Physics, Vol: 52, ISSN: 0953-4075
Journal of Physics B: Atomic, Molecular and Optical PhysicsPaper • The following article is OPEN ACCESSLifetimes and g-factors of the HFS states in H-like and Li-like bismuthVolker Hannen1, Jonas Vollbrecht1, Zoran Andelkovic2, Carsten Brandau2,3, Andreas Dax4, Wolfgang Geithner2, Christopher Geppert5,6, Christian Gorges5,6, Michael Hammen6,7, Simon Kaufmann5Show full author listPublished 2 April 2019 • © 2019 IOP Publishing LtdJournal of Physics B: Atomic, Molecular and Optical Physics, Volume 52, Number 8Download Article PDFFiguresReferences264 Total downloadsArticle has an altmetric score of 1Turn on MathJaxShare this article Share this content via email Share on Facebook Share on Twitter Share on Google+ Share on CiteULike Share on MendeleyArticle informationAbstractThe LIBELLE experiment performed at the experimental storage ring at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt, Germany, has successfully determined the ground state hyperfine (HFS) splittings in hydrogen-like (${}^{209}{\mathrm{Bi}}^{82+}$) and lithium-like (${}^{209}{\mathrm{Bi}}^{80+}$) bismuth. The study of HFS transitions in highly charged ions enables precision tests of QED in extreme electric and magnetic fields otherwise not attainable in laboratory experiments. Besides the transition wavelengths the time-resolved detection of fluorescence photons following the excitation of the ions by a pulsed laser system also allows the extraction of lifetimes of the upper HFS levels and g-factors of the bound 1s and 2s electrons for both charge states. While the lifetime of the upper HFS state in ${}^{209}{\mathrm{Bi}}^{82+}$ has already been measured in earlier experiments, an experimental value for lifetime of this state in ${}^{209}{\mathrm{Bi}}^{80+}$ is reported for the first time in this work.
Joshi MK, Hrmo P, Jarlaud V, et al., 2019, Population dynamics in sideband cooling of trapped ions outside the Lamb-Dicke regime, Physical Review A, Vol: 99, ISSN: 1050-2947
We present the results of simulations of optical sideband cooling of atomic ions in a trap with a shallow potential well. In such traps, an ion cannot be Doppler cooled near to the Lamb-Dicke regime [η2(2⟨n⟩+1)≪1]. Outside the Lamb-Dicke regime, the sideband cooling dynamics are altered by the existence of various Fock states with weak coupling where the cooling becomes very slow. A 40Ca+ion trapped in our Penning trap realizes such a situation; hence single stage cooling is inefficient to prepare the ion in the motional ground state. For these systems, it is necessary to study the cooling dynamics in detail and we show that it is possible to implement an optimized cooling sequence to achieve efficient ground-state cooling. We also present the simulated cooling dynamics of two ions trapped in a Penning trap, where the presence of an additional motional mode requires a complicated cooling sequence in order to cool both axial modes to the ground state simultaneously. Additionally, we demonstrate the dissipative preparation of Fock states outside the Lamb-Dicke regime by sideband heating a single ion in a Penning trap.
Beige A, Freegarde T, Thompson R, 2018, Special issue in memory of Prof Danny Segal (1960-2015), Journal of Modern Optics, Vol: 65, Pages: 481-481, ISSN: 0950-0340
Thompson RC, 2018, Professor Danny Segal - scientist and scholar, Journal of Modern Optics, Vol: 65, Pages: 485-489, ISSN: 0950-0340
Schmidt S, Murbock T, Andelkovic Z, et al., 2018, Sympathetic cooling in two-species ion crystals in a Penning trap, Journal of Modern Optics, Vol: 65, Pages: 538-548, ISSN: 0950-0340
We have studied the formation and properties of two-species ion Coulomb crystals in the Penning trap of the SpecTrap experiment. These crystals have been formed by injection of admixture ions from an external source into a previously confined and laser-cooled cloud of magnesium ions. This kind of study, performed over a range of the admixture ions’ charge-to-mass ratios, indicates the conditions for their sympathetic cooling and the formation of two-species ion crystals. This mechanism allows efficient cooling of the admixed species such as highly charged ions which do not feature suitable laser-cooling transitions, and thus make them accessible to high-resolution laser spectroscopy.
Stutter G, Hrmo P, Jarlaud V, et al., 2017, Sideband cooling of small ion Coulomb crystals in a Penning trap, Journal of Modern Optics, Vol: 65, Pages: 64-74, ISSN: 0950-0340
We have recently demonstrated the laser cooling of a single 40 Ca + ion to the motional ground state in a Penning trap using the resolved-sideband cooling technique on the electric quadrupole transition S 1/2 ↔ D 5/2 . Here we report on the extension of this technique to small ion Coulomb crystals made of two or three 40 Ca + ions. Efficient cooling of the axial motion is achieved outside the Lamb-Dicke regime on a two-ion string along the magnetic field axis as well as on two- and three-ion planar crystals. Complex sideband cooling sequences are required in order to cool both axial degrees of freedom simultaneously. We measure a mean excitation after cooling of n COM for the centre of mass (COM) mode and n B for the breathing mode of the two-ion string with corresponding heating rates of 11(2)s -1 and 1(1)s -1 at a trap frequency of 162 kHz. The occupation of the ground state of the axial modes (n tilt = n COM = 0) is above 75% for the two-ion planar crystal and the associated heating rates 0.8(5)s -1 at a trap frequency of 355 kHz.
Ullmann J, Andelkovic Z, Brandau C, et al., 2017, High precision hyperfine measurements in Bismuth challenge bound-state strong-field QED, Nature Communications, Vol: 8, ISSN: 2041-1723
Electrons bound in highly charged heavy ions such as hydrogen-like bismuth 209Bi82+ experience electromagnetic fields that are a million times stronger than in light atoms. Measuring the wavelength of light emitted and absorbed by these ions is therefore a sensitive testing ground for quantum electrodynamical (QED) effects and especially the electron–nucleus interaction under such extreme conditions. However, insufficient knowledge of the nuclear structure has prevented a rigorous test of strong-field QED. Here we present a measurement of the so-called specific difference between the hyperfine splittings in hydrogen-like and lithium-like bismuth 209Bi82+,80+ with a precision that is improved by more than an order of magnitude. Even though this quantity is believed to be largely insensitive to nuclear structure and therefore the most decisive test of QED in the strong magnetic field regime, we find a 7-σ discrepancy compared with the theoretical prediction.
Sanchez R, Lochmann M, Joehren R, et al., 2017, Laser spectroscopy measurement of the 2s-hyperfine splitting in lithium-like bismuth, Journal of Physics B - Atomic Molecular and Optical Physics, Vol: 50, ISSN: 0953-4075
We have recently reported on the first direct measurement of the $2s$ hyperfine transition in lithium-like bismuth (209Bi80+) at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany. Combined with a new measurement of the $1s$ hyperfine splitting (HFS) in hydrogen-like (209Bi82+) the so-called specific difference ${\rm{\Delta }}^{\prime} E=-61.37(36)$ meV could be determined and was found to be in good agreement with its prediction from strong-field bound-state quantum electrodynamics. Here we report on additional investigations performed to estimate systematic uncertainties of these results and on details of the experimental setup. We show that the dominating uncertainty arises from insufficient knowledge of the ion beam velocity which is determined by the electron-cooler voltage. Two routes to obtain a cooler-voltage calibration are discussed and it is shown that agreement can be reached either between the experimental ${\rm{\Delta }}^{\prime} E$ and the theoretical result, or between the two measurements of the HFS in hydrogen-like bismuth, but not both at the same time.
Murboeck T, Schmidt S, Birkl G, et al., 2016, Rapid crystallization of externally produced ions in a Penning trap, Physical Review A, Vol: 94, ISSN: 2469-9926
We have studied the cooling dynamics, formation process, and geometric structure of mesoscopic crystals ofexternally produced magnesium ions in a Penning trap. We present a cooling model and measurements for acombination of buffer gas cooling and laser cooling which has been found to reduce the ion kinetic energy byeight orders of magnitude from several hundreds of eV to μeV and below within seconds. With ion numbersof the order of 1 × 103 to 1 × 105, such cooling leads to the formation of ion Coulomb crystals which displaya characteristic shell structure in agreement with the theory of non-neutral plasmas. We show the productionand characterization of two-species ion crystals as a means of sympathetic cooling of ions lacking a suitablelaser-cooling transition.
Goodwin JF, Stutter G, Thompson RC, et al., 2016, Resolved-sideband laser cooling in a penning trap, Physical Review Letters, Vol: 116, ISSN: 1079-7114
We report the laser cooling of a single ^{40}Ca^{+} ion in a Penning trap to the motional ground state in one dimension. Cooling is performed in the strong binding limit on the 729-nm electric quadrupole S_{1/2}↔D_{5/2} transition, broadened by a quench laser coupling the D_{5/2} and P_{3/2} levels. We find the final ground-state occupation to be 98(1)%. We measure the heating rate of the trap to be very low with n[over ¯][over ˙]≈0.3(2) s^{-1} for trap frequencies from 150-400 kHz, consistent with the large ion-electrode distance.
Vogel M, Andelkovic Z, Birkl G, et al., 2015, Penning-trap experiments for spectroscopy of highly-charged ions at HITRAP., Physica Scripta, Vol: T166, ISSN: 0031-8949
Highly charged ions offer the possibility to measure electronic fine structures and hyperfine structures with precisions of optical lasers. Microwave spectroscopy of transitions between Zeeman substates further yields magnetic moments (g-factors) of bound electrons, making tests of calculations in the framework of bound-state QED possible in the strong-field regime. We present the SPECTRAP and ARTEMIS experiments, which are currently being commissioned with highly charged ions in the framework of the HITRAP facility at GSI, Germany. We present the scientific outline, the experimental setups and first results with confined ions.
Sanchez R, Ullmann J, Vollbrecht J, et al., 2015, Hyperfine transition in Bi-209(80+)-one step forward, PHYSICA SCRIPTA, Vol: T166, ISSN: 0031-8949
Goodwin JF, Brown BJ, Stutter G, et al., 2015, Trapped-ion quantum error-correcting protocols using only global operations, Physical Review A, Vol: 92, Pages: 032314-1-032314-7, ISSN: 1094-1622
Quantum error-correcting codes are many-body entangled states used to robustly store coherent quantum statesover long periods of time in the presence of noise. Practical implementations will require efficient entanglingprotocols that minimize the introduction of noise during encoding or readout. We propose an experiment thatuses only global operations to encode information to either the five-qubit repetition code or the five-qubit code ona two-dimensional ion Coulomb crystal architecture. We show we can prepare, read out, and acquire syndromeinformation for these two codes by using only six and ten global entangling pulses, respectively. We provide anerror analysis, estimating we can achieve a sixfold improvement in coherence time with as much as 1% noise inthe control parameters for each entangling operation.
Ullmann J, Andelkovic Z, Dax A, et al., 2015, An improved value for the hyperfine splitting of hydrogen-like Bi-209(82+), JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 48, ISSN: 0953-4075
Thompson RC, 2015, Ion Coulomb crystals, CONTEMPORARY PHYSICS, Vol: 56, Pages: 63-79, ISSN: 0010-7514
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Vollbrecht J, Andelkovic Z, Dax A, et al., 2015, Laser spectroscopy of the ground-state hyperfine structure in H-like and Li-like bismuth, 17th International Conference on the Physics of Highly Charged Ions, Publisher: IOP Publishing Ltd, Pages: 012002-012002, ISSN: 1742-6588
The LIBELLE experiment performed at the experimental storage ring (ESR) at the GSI Helmholtz Center in Darmstadt aims for the determination of the ground state hyperfine (HFS) transitions and lifetimes in hydrogen-like (209Bi82+) and lithium-like (209Bi80+) bismuth. The study of HFS transitions in highly charged ions enables precision tests of QED in extreme electric and magnetic fields otherwise not attainable in laboratory experiments. While the HFS transition in H-like bismuth was already observed in earlier experiments at the ESR, the LIBELLE experiment succeeded for the first time to measure the HFS transition in Li-like bismuth in a laser spectroscopy experiment.
Thompson RC, Mavadia S, Goodwin JF, et al., 2015, Control of the Conformations of Ion Coulomb Crystals in a Penning Trap, 11th International Workshop on Non-Neutral Plasmas, Publisher: AMER INST PHYSICS, ISSN: 0094-243X
Lochmann M, Joehren R, Geppert C, et al., 2014, Observation of the hyperfine transition in lithium-like bismuth <SUP>209</SUP>Bi<SUP>80+</SUP> : Towards a test of QED in strong magnetic fields, PHYSICAL REVIEW A, Vol: 90, ISSN: 2469-9926
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Fisher E, Thompson R, 2014, Enjoy Writing Your Science Thesis Or Dissertation!, ISBN: 9781783264216
This book is a step by step illustrated guide to planning and writing dissertations and theses for undergraduate and graduate science students.
Fobelets K, Utke I, 2014, Nano Fabrication 2013 Preface, MICROELECTRONIC ENGINEERING, Vol: 121, Pages: VII-VII, ISSN: 0167-9317
Thompson RC, Knoop M, Madsen N, 2014, Physics With Trapped Charged Particles, Publisher: Imperial College Press, ISBN: 9781783264049
This book is a collection of articles on Physics with Trapped Charged Particles by speakers at the Les Houches Winter School.
Mavadia S, Stutter G, Goodwin JF, et al., 2014, Optical sideband spectroscopy of a single ion in a Penning trap, Physical Review A, Vol: 89, ISSN: 1050-2947
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