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• Journal article
  Hrmo P, Joshi MK, Jarlaud V, Corfield O, Thompson RCet 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.

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• Journal article
  Joshi MK, Hrmo P, Jarlaud V, Oehl F, Thompson RCet 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.

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• Journal article
  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
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• Journal article
  Thompson RC, 2018,

  Professor Danny Segal - scientist and scholar

  , Journal of Modern Optics, Vol: 65, Pages: 485-489, ISSN: 0950-0340
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• Journal article
  Schmidt S, Murbock T, Andelkovic Z, Birkl G, Konig K, Nortershauser W, Thompson RC, Vogel Met 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.

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• Journal article
  Stutter G, Hrmo P, Jarlaud V, Joshi MK, Goodwin JF, Thompson RCet 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.

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• Journal article
  Murboeck T, Schmidt S, Birkl G, Noertershaeuser W, Thompson RC, Vogel Met 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.

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• Journal article
  Goodwin JF, Stutter G, Thompson RC, Segal DMet 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.

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• Journal article
  Goodwin JF, Brown BJ, Stutter G, Dale H, Thompson RC, Rudolph Tet 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.

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• Journal article
  Mavadia S, Stutter G, Goodwin JF, Crick DR, Thompson RC, Segal DMet 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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• Journal article
  Asprusten M, Worthington S, Thompson RC, 2014,

  Theory and simulation of ion Coulomb crystal formation in a Penning trap

  , Applied Physics B - Lasers and Optics, Vol: 114, Pages: 157-166, ISSN: 0946-2171
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• Journal article
  Mavadia S, Goodwin JF, Stutter G, Bharadia S, Crick DR, Segal DM, Thompson RCet al., 2013,

  Control of the conformations of ion Coulomb crystals in a Penning trap

  , Nature Communications, Vol: 4, ISSN: 2041-1723
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• Conference paper
  Noertershaeuser W, Lochmann M, Joehren R, Geppert C, Andelkovic Z, Anielski D, Botermann B, Bussmann M, Dax A, Froemmgen N, Hammen M, Hannen V, Kuehl T, Litvinov YA, Volbrecht J, Stoehlker T, Thompson RC, Weinheimer C, Wen W, Will E, Winters D, Sanchez RMet al., 2013,

  First observation of the ground-state hyperfine transition in Bi-209(80+)

  , 16th International Conference on the Physics of Highly Charged Ions (HCI), Publisher: IOP PUBLISHING LTD, ISSN: 0031-8949
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  • Citations: 24
• Journal article
  Andelkovic Z, Cazan R, Noertershaeuser W, Bharadia S, Segal DM, Thompson RC, Joehren R, Vollbrecht J, Hannen V, Vogel Met al., 2013,

  Laser cooling of externally produced Mg ions in a Penning trap for sympathetic cooling of highly charged ions

  , PHYSICAL REVIEW A, Vol: 87, ISSN: 1050-2947
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  • Citations: 34
• Journal article
  Segal DM, Vogel M, Thompson RC, Bharadia Set al., 2012,

  Dynamics of laser-cooled Ca+ ions in a Penning trap with a rotating wall

  , Applied Physics B: lasers and optics

  We have performed systematic measurements of the dynamics of laser-cooled 40Ca+ ions confined in a Penning trap and driven by a rotating dipole field (‘rotating wall’). The trap used is a copy of the one used in the SPECTRAP experiment located at the HITRAP facility at GSI, Germany. The size and shape of the ion cloud has been monitored using a CCD camera to image the fluorescence light resulting from excitation by the cooling laser. We have varied the experimental conditions such as amplitude and frequency of the rotating wall drive as well as the trapping parameters. The rotating wall can be used for a radial compression of the ion cloud thus increasing the ion density in the trap. We have also observed plasma mode excitations in agreement with theoretical expectations. This work will allow us to define the optimum parameters for high compression of the ions as needed for precision spectroscopy of forbidden transitions.

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• Journal article
  Skoff SM, Hendricks RJ, Sinclair CDJ, Hudson JJ, Segal DM, Sauer BE, Hinds EA, Tarbutt MRet al., 2011,

  Diffusion, thermalization, and optical pumping of YbF molecules in a cold buffer-gas cell

  , PHYSICAL REVIEW A, Vol: 83, ISSN: 1050-2947
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  • Citations: 30
• Journal article
  Crick DR, Donnellan S, Segal DM, Thompson RCet al., 2010,

  Magnetically induced electron shelving in a trapped Ca+ ion

  , PHYSICAL REVIEW A, Vol: 81, ISSN: 1050-2947
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  • Citations: 13
• Journal article
  Crick DR, Donnellan S, Ananthamurthy S, Thompson RC, Segal DMet al., 2010,

  Fast shuttling of ions in a scalable Penning trap array

  , REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 81, ISSN: 0034-6748
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  • Citations: 10
• Journal article
  Skoff SM, Hendricks RJ, Sinclair CDJ, Tarbutt MR, Hudson JJ, Segal DM, Sauer BE, Hinds EAet al., 2009,

  Doppler-free laser spectroscopy of buffer-gas-cooled molecular radicals

  , NEW JOURNAL OF PHYSICS, Vol: 11, ISSN: 1367-2630
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  • Citations: 17
• Journal article
  Thompson RC, Donnellan S, Crick DR, Segal DMet al., 2009,

  Applications of laser cooled ions in a Penning trap

  , JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 42, ISSN: 0953-4075
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  • Citations: 15
• Journal article
  Retzker A, Thompson RC, Segal DM, Plenio MBet al., 2008,

  Double Well Potentials and Quantum Phase Transitions in Ion Traps

  , PHYSICAL REVIEW LETTERS, Vol: 101, ISSN: 0031-9007
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  • Citations: 76
• Journal article
  Phillips ES, Hendricks RJ, Abdulla AM, Ohadi H, Crick DR, Koo K, Segal DM, Thompson RCet al., 2008,

  Dynamics of axialized laser-cooled ions in a Penning trap

  , PHYSICAL REVIEW A, Vol: 78, ISSN: 1050-2947
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  • Citations: 6
• Journal article
  Crick DR, Ohadi H, Bhatti I, Thompson RC, Segal DMet al., 2008,

  Two-ion Coulomb crystals of Ca+ in a Penning trap

  , OPTICS EXPRESS, Vol: 16, Pages: 2351-2362, ISSN: 1094-4087
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  • Citations: 18
• Journal article
  Hendricks RJ, Phillips ES, Segal DM, Thompson RCet al., 2008,

  Laser cooling in the Penning trap: an analytical model for cooling rates in the presence of an axializing field

  , JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 41, ISSN: 0953-4075
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  • Citations: 9
• Journal article
  Brownnutt M, Letchumanan V, Wilpers G, Thompson RC, Gill P, Sinclair AGet al., 2007,

  Controlled photoionization loading of Sr-88(+) for precision ion-trap experiments

  , APPLIED PHYSICS B-LASERS AND OPTICS, Vol: 87, Pages: 411-415, ISSN: 0946-2171
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  • Citations: 37
• Journal article
  Castrejon-Pita JR, Ohadi H, Crick DR, Winters DFA, Segal DM, Thompson RCet al., 2007,

  Novel designs for Penning ion traps

  , JOURNAL OF MODERN OPTICS, Vol: 54, Pages: 1581-1594, ISSN: 0950-0340
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  • Citations: 15
• Journal article
  Brownnutt M, Wilpers G, Gill P, Thompson RC, Sinclair AGet al., 2006,

  Monolithic microfabricated ion trap chip design for scaleable quantum processors

  , NEW JOURNAL OF PHYSICS, Vol: 8, ISSN: 1367-2630
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  • Citations: 27
• Journal article
  Winters DFA, Vogel M, Segal DM, Thompson RCet al., 2006,

  Electronic detection of charged particle effects in a Penning trap

  , JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, Vol: 39, Pages: 3131-3143, ISSN: 0953-4075
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  • Citations: 20
• Journal article
  Vogel M, Winters DFA, Segal DM, Thompson RCet al., 2005,

  Proposed precision laser spectrometer for trapped, highly charged ions

  , REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 76, ISSN: 0034-6748
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  • Citations: 36
• Journal article
  Castrejon-Pita JR, Thompson RC, 2005,

  Proposal for a planar Penning ion trap - art. no. 013406

  , PHYSICAL REVIEW A, Vol: 72, ISSN: 2469-9926
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  • Citations: 21

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