Publications

Titles link to full text.

For impact analysis, please refer to Researcher ID B-6733-2009.

We study the excitation dynamics of an inhomogeneously broadened spin ensemble coupled to a single cavity mode. The collective mode coupled most strongly to the cavity acquires an energy shift which may be large enough to prevent its dephasing due to the inhomogeneity in the ensemble, while other collective modes evolve in a non-trivial manner due to the joint effect of the inhomogeneity and the coupling to the cavity. Rather than identifying stationary eigenmodes we define `bare time' modes, for which the dephasing due to inhomogeneities is described exactly as a linear translation. Interaction with the cavity mode `freezes' this translation of the strongly coupled spin mode, while other collective modes experience an additional translational shift as they propagate around the frozen mode. The result is relevant for multi-mode quantum memories where qubits are encoded in different spin waves.

Preprint: arXiv:1008.5197.

@article{wesenberg10:dynamics, author ={Janus H. Wesenberg and Zoltan Kurucz and Klaus M{\o}lmer}, title = {Dynamics of the collective modes of an inhomogeneous spin ensemble in a cavity}, year = {2010}, url = {http://arxiv.org/abs/1008.5197} }

In this paper, we report the design, fabrication and preliminary testing of a 150 zone ion trap array built in a 'surface-electrode' geometry micro-fabricated on a single substrate. We demonstrate the transport of atomic ions between the legs of a 'Y'-type junction and measure the in-situ heating rates for the ions. The trap design demonstrates the use of a basic component design library that can be quickly assembled to form structures optimized for a particular experiment.

@article{amini09:scalable, author ={J. M. Amini and H. Uys and J. H. Wesenberg and S. Seidelin and J. Britton and J. J. Bollinger and D. Leibfried and C. Ospelkaus and A. P. VanDevender and D. J. Wineland}, title = {Toward scalable ion traps for quantum information processing}, journal = {New J. Phys.}, year = {2010}, volume = {12}, pages = {033031}, doi = {10.1088/1367-2630/12/3/033031} }

We report techniques for the fabrication of multizone linear radio frequency Paul traps that exploit the machinability and electrical conductivity of degenerate silicon. The approach was tested by trapping and laser cooling 24Mg+ ions in the two following trap geometries: a single-zone two-layer trap and a multizone surface-electrode trap. From the measured ion motional heating rate we determine an electric field spectral density at the ion's position of approximately $110^−10 (V/m)^2/Hz$ at $_ z/21.125 MHz$ when the ion lies 40 um above the trap surface. One application of these devices is controlled manipulation of atomic ion qubits, the basis of one form of quantum information processing.

@article{britton09:scalable, author ={J. Britton and D. Leibfried and J. A. Beall and R. B. Blakestad andJ. H. Wesenberg and D. J. Wineland}, title = {Scalable arrays of rf {P}aul traps in degenerate {S}i}, journal = {Appl. Phys. Lett.}, publisher = {AIP}, year = {2009}, volume = {95}, number = {17}, pages = {173102}, doi = {10.1063/1.3254188} }

We demonstrate the storage and retrieval of weak 10 GHz coherent excitations in distributed memories based on electron spin ensembles. Each excitation is phase encoded by a field gradient and the use of pulsed field gradients permits the stored excitations to be recalled in an arbitrary order. We have stored up to 100 weak microwave excitations in a spin ensemble and recalled them sequentially. We further demonstrate the use of a coupled nuclear spin, which can offer coherence times in excess of seconds, for even more robust storage.

@article{wu09:storage, author ={Hua Wu and Richard E. George and Arzhang Ardavan and Janus H. Wesenberg and Klaus M{\o}lmer and David I. Schuster and Robert J. Schoelkopf and Kohei M. Itoh and John J. L. Morton and G. Andrew D. Briggs}, title = {Storage of multiple coherent microwave excitations in an electron spin ensemble}, journal = {Phys. Rev. Lett.}, year = {2009}, volume = {105}, pages = {140503}, doi = {10.1103/PhysRevLett.105.140503} }

A scalable, multiplexed ion trap for quantum information processing is fabricated and tested. The trap design and fabrication process are optimized for scalability to small trap size and large numbers of interconnected traps, and for integration of control electronics and optics. Multiple traps with similar designs are tested with Cd-111(+), Mg-25(+), and Sr-88(+) ions at room temperature and with Sr-88(+) at 6 K, with respective ion lifetimes of 90 s, 300 +/- 30 s, 56 +/- 6 s, and 4.5 +/- 1.1 hours. The motional heating rate for Mg-25(+) at room temperature and a trap frequency of 1.6 MHz is measured to be 7 +/- 3 quanta per millisecond. For Sr-88(+) at 6 K and 540 kHz the heating rate is measured to be 220 +/- 30 quanta per second.

@article{leibrandt09:demonstration, author ={D. R. Leibrandt and J. Labaziewicz and R. J. Clark and I. L. Chuang and R. Epstein and C. Ospelkaus and J. Wesenberg and J. Bollinger and D. Leibfried and D. Wineland and D. Stick and J. Sterk and C. Monroe and C. -S. Pai and Y. Low and R. Frahm and R. E. Slusher}, title = {Demonstration of a scalable, multiplexed ion trap for quantum information processing}, journal = {Quant. Inf. Comput.}, year = {2009}, volume = {9}, pages = {901}, url = {http://www.rintonpress.com/journals/qicabstracts/qicabstracts9-1112.html} }

We propose to encode a register of quantum bits in different collective electron spin wave excitations in a solid medium. Coupling to spins is enabled by locating them in the vicinity of a superconducting transmission line cavity, and making use of their strong collective coupling to the quantized radiation field. The transformation between different spin waves is achieved by applying gradient magnetic fields across the sample, while a Cooper Pair Box, resonant with the cavity field, may be used to carry out one- and two-qubit gate operations.

@article{wesenberg09:quantum, author ={J. H. Wesenberg and A. Ardavan and G. A. D. Briggs and J. J. L. Morton and R. J. Schoelkopf and D. I. Schuster and K. M{\o}lmer}, title = {Quantum computing with an electron spin ensemble}, journal = {Phys. Rev. Lett.}, year = {2009}, volume = {103}, pages = {070502}, doi = {10.1103/PhysRevLett.103.070502} }

Trapped ions offer long internal state (spin) coherence times and strong inter-particle interactions mediated by the Coulomb force. This makes them interesting candidates for quantum simulation of coupled lattices. To this end it is desirable to be able to trap ions in arbitrary conformations with precisely controlled local potentials. We provide a general method for optimizing periodic planar radio-frequency electrodes for generating ion trapping potentials with specified trap locations and curvatures above the electrode plane. A linear-programming algorithm guarantees globally optimal electrode shapes requiring only a single radio-frequency voltage source for operation. The optimization method produces final electrode shapes that are smooth and exhibit low fragmentation. Such characteristics are desirable for practical fabrication of surface electrode trap lattices.

@article{schmied09:optimal, author ={Roman Schmied and Janus H. Wesenberg and Dietrich Leibfried}, title = {Optimal Surface-Electrode Trap Lattices for Quantum Simulation with Trapped Ions}, journal = {Phys. Rev. Lett.}, year = {2009}, volume = {102}, pages = {233002}, doi = {10.1103/PhysRevLett.102.233002} }

We investigate theoretically the fundamental constraints on intersecting paths of zero field in irrotational and divergence-free vector fields such as static electric or magnetic fields in source-free regions and constructively identify the lowest order multipole component allowed at an intersection point. The identified hexapole component is uniquely determined by the angle between the intersecting paths and, in the case of a right angle intersection, it has an additional line of zero field crossing the intersection point perpendicular to the tangent plane of the intersecting paths. We investigate the effects of certain implementation imperfections on the intersection. This result indicates that ideal hexapole intersections for radio-frequency ion-trap networks can only be realised for oblique angles.

@article{wesenberg08:intersecting, author ={Janus H. Wesenberg}, title = {Ideal intersections for radio-frequency trap networks}, journal = {Phys. Rev. A}, year = {2009}, volume = {79}, pages = {013416}, doi = {10.1103/PhysRevA.79.013416} }

Surface-electrode (SE) rf traps are a promising approach to manufacturing complex ion-trap networks suitable for large-scale quantum information processing. In this paper we present analytical methods for modeling SE traps in the gapless plane approximation, and apply these methods to two particular classes of SE traps. For the SE ring trap we derive analytical expressions for the trap geometry and strength, and also calculate the depth in the absence of control fields. For translationally symmetric multipole configurations (analogs of the linear Paul trap), we derive analytical expressions for electrode geometry and strength. Further, we provide arbitrarily good approximations of the trap depth in the absence of static fields and identify the requirements for obtaining maximal depth. Lastly, we show that the depth of SE multipoles can be greatly influenced by control fields.

@article{wesenberg07:analytical_theory_multipole, author ={Janus H. Wesenberg}, title = {Electrostatics of surface-electrode ion traps}, journal = {Phys. Rev. A}, year = {2008}, volume = {78}, pages = {063410}, doi = {10.1103/PhysRevA.78.063410} }

We have measured motional heating rates of trapped atomic ions, a factor that can influence multi-ion quantum logic gate fidelities. Two simplified techniques were developed for this purpose: one relies on Raman sideband detection implemented with a single laser source, while the second is even simpler and is based on time-resolved fluorescence detection during Doppler recooling. We applied these methods to determine heating rates in a microfrabricated surface-electrode trap made of gold on fused quartz, which traps ions 40 Âµm above its surface. Heating rates obtained from the two techniques were found to be in reasonable agreement. In addition, the trap gives rise to a heating rate of 300Â±30 1/s for a motional frequency of 5.25 MHz, substantially below the trend observed in other traps.

@article{epstein07:simpl_ion_heatin_rate_measur, author ={R. J. Epstein and S. Seidelin and D. Leibfried and J. H. Wesenberg and J. J. Bollinger and J. M. Amini and R. B. Blakestad and J. Britton and J. P. Home and W. M. Itano and J. D. Jost and E. Knill and C. Langer and R. Ozeri and N. Shiga and D. J. Wineland}, title = {Simplified motional heating rate measurements of trapped ions}, journal = {Phys. Rev. A}, publisher = {APS}, year = {2007}, volume = {76}, number = {3}, pages = {033411}, doi = {10.1103/PhysRevA.76.033411} }

We investigate the temporal dynamics of Doppler cooling of an initially hot single trapped atom in the weak binding regime using a semiclassical approach. We develop an analytical model for the simplest case of a single vibrational mode for a harmonic trap, and show how this model allows us to estimate the initial energy of the trapped particle by observing the fluorescence rate during the cooling process. The experimental implementation of this temperature measurement provides a way to measure atom heating rates by observing the temperature rise in the absence of cooling. This method is technically relatively simple compared to conventional sideband detection methods, and the two methods are in reasonable agreement. We also discuss the effects of RF micromotion, relevant for a trapped atomic ion, and the effect of coupling between the vibrational modes on the cooling dynamics.

@article{wesenberg07:fluor_durin_doppl_coolin_singl, author ={J. H. Wesenberg and R. J. Epstein and D. Leibfried and R. B. Blakestad and J. Britton and J. P. Home and W. M. Itano and J. D. Jost and E. Knill and C. Langer and R. Ozeri and S. Seidelin and D. J. Wineland}, title = {Fluorescence during Doppler cooling of a single trapped atom}, journal = {Phys. Rev. A}, year = {2007}, volume = {76}, number = {5}, pages = {053416}, doi = {10.1103/PhysRevA.76.053416} }

We analyze the error in trapped-ion, hyperfine qubit, quantum gates due to spontaneous scattering of photons from the gate laser beams. We investigate single-qubit rotations that are based on stimulated Raman transitions and two-qubit entangling phase gates that are based on spin-dependent optical dipole forces. This error is compared between different ion species currently being investigated as possible quantum-information carriers. For both gate types we show that with attainable laser powers the scattering error can be reduced to below current estimates of the fault-tolerance error threshold.

@article{ozeri07:errors, author ={R. Ozeri and W. M. Itano and R. B. Blakestad and J. Britton and J. Chiaverini and J. D. Jost and C. Langer and D. Leibfried and R. Reichle and S. Seidelin and J. H. Wesenberg and D. J. Wineland}, title = {Errors in trapped-ion quantum gates due to spontaneous photon scattering}, journal = {Phys. Rev. A}, publisher = {APS}, year = {2007}, volume = {75}, number = {4}, pages = {042329}, doi = {10.1103/PhysRevA.75.042329} }

Due to inhomogeneous broadening, the absorption lines of rare-earth-ion dopants in crystals are many order of magnitudes wider than the homogeneous linewidths. Several ways have been proposed to use ions with different inhomogeneous shifts as qubit registers, and to perform gate operations between such registers by means of the static dipole coupling between the ions. In this paper we show that in order to implement high-fidelity quantum gate operations by means of the static dipole interaction, we require the participating ions to be strongly coupled, and that the density of such strongly coupled registers in general scales poorly with register size. Although this is critical to previous proposals which rely on a high density of functional registers, we describe architectures and preparation strategies that will allow scalable quantum computers based on rare-earth-ion-doped crystals.

@article{wesenberg07:scalable, author ={J. H. Wesenberg and K. M{\o}lmer and L. Rippe and S. Kr{\"{o}}ll}, title = {Scalable designs for quantum computing with rare-earth-ion-doped crystals}, journal = {Phys. Rev. A}, year = {2007}, volume = {75}, pages = {012304}, doi = {10.1103/PhysRevA.75.012304} }

Proc. 2006 ICAP 103 (2006).

@inproceedings{wineland06:trapped, author ={D. Wineland and D. Leibfried and J. Bergquist and R. Blakestad and J. Bollinger and J. Britton and J. Chiaverini and R. Epstein and D. Hume and W. Itano and J. Jost and E. Knill and J. Koelemeij and C. Langer and R. Ozeri and R. Reichle and T. Rosenband and T. Schaetz and P. Schmidt and S. Seidelin and N. Shiga and J. Wesenberg}, title = {Trapped Atomic Ions and Quantum Information Processing}, booktitle = {Proc. 2006 ICAP}, year = {2006}, pages = {103} }

Individual laser-cooled 24Mg+ ions are confined in a linear Paul trap with a novel geometry where gold electrodes are located in a single plane and the ions are trapped 40 $$m above this plane. The relatively simple trap design and fabrication procedure are important for large-scale quantum information processing (QIP) using ions. Measured ion motional frequencies are compared to simulations. Measurements of ion recooling after cooling is temporarily suspended yield a heating rate of approximately 5 motional quanta per millisecond for a trap frequency of 2.83 MHz, sufficiently low to be useful for QIP.

Phys. Rev. Lett. **96**, 253003 (2006); DOI:10.1103/PhysRevLett.96.253003.

Preprint: arXiv:quant-ph/0601173.

Preprint: arXiv:quant-ph/0601173.

@article{seidelin06:microf_surfac_elect_trap_scalab, author ={S. Seidelin and J. Chiaverini and R. Reichle and J. J. Bollinger and D. Leibfried and J. Britton and J. H. Wesenberg and R. B. Blakestad and R. J. Epstein and D. B. Hume and J. D. Jost and C. Langer and R. Ozeri and N. Shiga and D. J. Wineland}, title = {A microfabricated surface-electrode ion trap for scalable quantum information processing}, journal = {Phys. Rev. Lett.}, year = {2006}, volume = {96}, pages = {253003}, doi = {10.1103/PhysRevLett.96.253003} }

We consider a method to reduce the kinetic energy in a low-order mode of a miniature cantilever. If the cantilever contributes to the capacitance of a driven RF circuit, a force on the cantilever exists due to the electric field energy stored in the capacitance. If this force acts with an appropriate phase shift relative to the motion of the cantilever, it can oppose the velocity of the cantilever, leading to cooling. Such cooling may enable reaching the quantum regime of cantilever motion.

Preprint: arXiv:quant-ph/0606180.

@unpublished{wineland07:cantilever, author ={D. J. Wineland and J. Britton and R. J. Epstein and D. Leibfried and R. B. Blakestad and K. Brown and J. D. Jost and C. Langer and R. Ozeri and S. Seidelin and J. Wesenberg}, title = {Cantilever cooling with radio frequency circuits}, year = {2007}, url = {http://arxiv.org/abs/quant-ph/0606180} }

The prospect of building a quantum information processor underlies many recent advances ion trap fabrication techniques. Potentially, a quantum computer could be constructed from a large array of interconnected ion traps. We report on a micrometer-scale ion trap, fabricated from bulk silicon using micro-electromechanical systems (MEMS) techniques. The trap geometry is relatively simple in that the electrodes lie in a single plane beneath the ions. In such a trap we confine laser-cooled 24Mg+ ions approximately 40 microns above the surface. The fabrication technique and planar electrode geometry together make this approach amenable to scaling up to large trap arrays. In addition we observe that little laser cooling light is scattered by the electrodes.

Preprint: arXiv:quant-ph/0605170.

@unpublished{britton07:microfabricated, author ={J. Britton and D. Leibfried and J. Beall and R. B. Blakestad and J. J. Bollinger and J. Chiaverini and R. J. Epstein and J. D. Jost and D. Kielpinski and C. Langer and R. Ozeri and R. Reichle and S. Seidelin and N. Shiga and J. H. Wesenberg and D. J. Wineland}, title = {A microfabricated surface-electrode ion trap in silicon}, year = {2007}, url = {http://arxiv.org/abs/quant-ph/0605170} }

The proximity between the ions results in large interactions and potentially allows fast gates, but they can still be separately addressed since different ions have different optical resonance frequency. The interaction that enables multi-qubit gates can be turned on at will and is based on that the permanent dipole moment changes as a control ion is transferred to the optically excited state which in turn Stark-shifts target qubit out of resonance. Using optical pumping, all ions within a frequency interval can be removed and then a peak of equivalent ions, each belonging to one instance of many parallel quantum computers can be positioned within the non-absorbing region. This qubit has then been efficiently transferred between different qubit states using robust complex hyperbolic secant pulses. Pairs of qubits that interact strongly have also been distilled.

; DOI:10.1109/EQEC.2005.1567534
Proc. EQEC 2005 369 (2005).

@inproceedings{rippe05:sub-nm-spaced, author ={L. Rippe and M. Nilsson and S. Kr{\"{o}}ll and J. Wesenberg and K. M{\o}lmer}, title = {Sub-nm-spaced frequency-addressed qubits}, booktitle = {Proc. EQEC 2005}, year = {2005}, pages = {369}, doi = {10.1109/EQEC.2005.1567534} }

We determine the probability distribution for the field inside a random distribution of electric or magnetic dipoles. Although the average contribution from any spherical shell around the probe position vanishes, at the center of a spherical distribution of parallel dipoles, the Levy stable distribution of the field is symmetric around a nonvanishing field amplitude. Omission of contributions from a small volume around the probe leads to a field distribution with a vanishing mean, which, in the limit of vanishing excluded volume, converges to the shifted distribution.

Phys. Rev. Lett. **93**, 143903 (2004); DOI:10.1103/PhysRevLett.93.143903.

Preprint: arXiv:quant-ph/0406178.

Preprint: arXiv:quant-ph/0406178.

@article{wesenberg04:field_insid_a_random_distr, author ={Janus H. Wesenberg and Klaus M{\o}lmer}, title = {The field inside a random distribution of parallel dipoles}, journal = {Phys. Rev. Lett.}, year = {2004}, volume = {93}, pages = {143903}, doi = {10.1103/PhysRevLett.93.143903} }

Quantum-information processing systems are often operated through time-dependent controls; choosing these controls in a way that makes the resulting operation insensitive to variations in unknown or uncontrollable system parameters is an important prerequisite for obtaining high-fidelity gate operations. In this article we present a numerical method for constructing such robust control sequences for a quite general class of quantum-information processing systems. As an application of the method we have designed a robust implementation of a phase-shift operation central to rare-earth-metal quantum computing, an ensemble quantum computing system proposed by Ohlsson et al. [Opt. Commun. 201, 71 (2002)]. In this case the method has been used to obtain a high degree of insensitivity with respect to differences between ensemble members, but it is equally well suited for quantum computing with a single physical system.

@article{wesenberg03:desig_robus_gate_implem_quant, author ={J. H. Wesenberg}, title = {Designing robust gate implementations for quantum information processing}, journal = {Phys. Rev. A}, year = {2004}, volume = {69}, pages = {042323}, doi = {10.1103/PhysRevA.69.042323} }

Robust quantum gates and a bus architecture for quantum computing with rare-earth-ion doped crystals.

We present a composite pulse controlled phase gate which, together with a bus architecture, improves the feasibility of a recent quantum computing proposal based on rare-earth-ion-doped crystals. The proposed gate operation is tolerant to variations between ions of coupling strengths, pulse lengths, and frequency shifts. In the absence of decoherence effects, it achieves worst case fidelities above $0.999$ with relative variations in coupling strength as high as $10%$ and frequency shifts up to several percent of the resonant Rabi frequency of the laser used to implement the gate. We outline an experiment to demonstrate the creation and detection of maximally entangled states in the system.

@article{wesenberg03:robus_quant_gates_a_archit, author ={J. Wesenberg and K. M{\o}lmer}, title = {Robust quantum gates and a bus architecture for quantum computing with rare-earth-ion doped crystals}, journal = {Phys. Rev. A}, year = {2003}, volume = {68}, pages = {012320}, doi = {10.1103/PhysRevA.68.012320} }

Mixed states of samples of spin s particles which are symmetric under permutations of the particles are described in terms of their total collective spin quantum numbers. We use this description to analyze the influence on spin squeezing due to imperfect initial-state preparation.

@article{wesenberg02:mixed_collec_states_many_spins, author ={J. Wesenberg and K. M{\o}lmer}, title = {Mixed collective states of many spins}, journal = {Phys. Rev. A}, year = {2002}, volume = {65}, pages = {062304}, doi = {10.1103/PhysRevA.65.062304} }

conference poster, QIP IRC Conference 2009, Oxford, United Kingdom (2009).

@misc{wesenberg09:holostrip_poster, author ={J. H. Wesenberg and A. Ardavan and G. A. D. Briggs and J. J. L. Morton and R. J. Schoelkopf and D. I. Schuster and K. M{\o}lmer}, title = {Quantum computing with an electron spin ensemble}, howpublished = {conference poster, {QIP IRC} Conference 2009, Oxford, United Kingdom}, year = {2009} }

Seminar presentation, Department of Materials, University of Oxford, Oxford, England (2008).

@misc{wesenberg08:trapfields-materials, author ={Janus H. Wesenberg}, title = {Building ion traps for {QIP}}, howpublished = {Seminar presentation, Department of Materials, University of Oxford, Oxford, England}, year = {2008} }

Seminar presentation, Institute for Quantum Computing, Georgia Tech, Atlanta, Georgia (2008).

@misc{wesenberg08:trapfields-sussex, author ={Janus H. Wesenberg}, title = {Designing surface-electrode ion-trap networks}, howpublished = {Seminar presentation, Institute for Quantum Computing, Georgia Tech, Atlanta, Georgia}, year = {2008} }

Seminar presentation, Institute for Quantum Computing, Georgia Tech, Atlanta, Georgia (2008).

@misc{wesenberg08:trapfields-georgiatech, author ={Janus H. Wesenberg}, title = {Designing surface-electrode ion-trap networks}, howpublished = {Seminar presentation, Institute for Quantum Computing, Georgia Tech, Atlanta, Georgia}, year = {2008} }

conference poster, Gordon Research Conference on Quantum Information, Big Sky, Montana (2008).

@misc{wesenberg08:trapfields-grc, author ={Janus H. Wesenberg}, title = {Ideal intersections for ion-trap networks}, howpublished = {conference poster, Gordon Research Conference on Quantum Information, Big Sky, Montana}, year = {2008} }

We present results from experiments towards realization of a scalable ion trap quantum information processor. The development of such a scalable processor depends on the ability to implement fault-tolerant techniques. These require the ability to move information around the processor while retaining the ability to perform high fidelity quantum gates. For trapped ions, a promising approach is to move the ions themselves through an array of microtraps [J. Res. Natl. Inst. Stand. Technol. 103, 259] [Nature 417, 709]. One challenge in this scheme is that the ions' motion may be heated by the transport processes. In addition, fluctuations of the electric field at the position of the ions leads to ambient heating. Since the fidelity of two qubit trapped ion gates are sensitive to the ions' temperature, it is necessary to cool the motion of the qubit ions prior to gates, while preserving the stored quantum information. In our experiments, we perform sympathetic cooling by adding coolant 24Mg ions to the 9Be qubits. We report recent work involving ground state sympathetic cooling and coherent manipulations with two-species arrays of multiple ions. In addition, we have experimentally and theoretically investigated the gate error due to spontaneous photon scattering, which represents a fundamental limit to the fidelity of logic gate operations implemented using Raman transitions. We find that in the limit where the detuning of the Raman laser from the excited states is larger than their fine structure splitting, spin-relaxation due to spontaneous Raman scattering is dramatically reduced relative to Rayleigh scattering due to an interference effect between scattering paths. In this regime, the limiting factor for two-qubit gate fidelity becomes decoherence of the motional state due to Rayleigh scattering. We show that with high laser power the error rate from this source can in theory be reduced to below 10**-4 per gate for realistic trap frequencies of >> 10 MHz, which is below current threshold estimates for fault-tolerant quantum computation [Science 279, 342] [Phys. Rev. A 68, p. 042322]. Work supported by DTO. J.H. acknowledges funding from the Lindemann Fellowship.

conference poster, ICOLS 2007, Telluride, Colorado (2007).

@misc{home07:cooling, author ={J. P. Home and J. D. Jost and C. Langer and R. Ozeri and J. Amini and J. J. Bollinger and R. B. Blakestad and J. Britton and R. J. Epstein and W. M. Itano and E. Knill and D. Leibfried and C. Ospelkaus and S. Seidelin and N. Shiga and J. H. Wesenberg and D. J. Wineland}, title = {Cooling, coherent manipulations and decoherence of two-species trapped-ion arrays for Quantum Information Processing}, howpublished = {conference poster, ICOLS 2007, Telluride, Colorado}, year = {2007} }

conference poster, DAMOP 2007, Calgary, Canada (2007).

@misc{amini07:multilayer, author ={Jason Amini and Signe Seidelin and Janus Wesenberg and Joe Britton and Brad Blakestad and Kenton Brown and Ryan Epstein and Jonathan Home and John Jost and Chris Langer and Dietrich Leibfried and Roee Ozeri and David Wineland}, title = {Multilayer {I}nterconnects for {M}icrofabricated {S}urface {E}lectrode {I}on {T}raps}, howpublished = {conference poster, {DAMOP} 2007, {C}algary, {C}anada}, year = {2007}, url = {http://meetings.aps.org/link/BAPS.2007.DAMOP.K1.17} }

conference poster, DAMOP 2007, Calgary, Canada (2007).

@misc{epstein07:ion, author ={R. J. Epstein and D. Leibfried and J. J. Bollinger and S. Seidelin and J. H. Wesenberg and N. Shiga and J. M. Amini and R. B. Blakestad and J. Britton and K. R. Brown and J. P. Home and W. M. Itano and J. D. Jost and E. Knill and C. Langer and R. Ozeri and D. J. Wineland}, title = {Ion heating rates in scalable trap architectures for quantum computation}, howpublished = {conference poster, DAMOP 2007, Calgary, Canada}, year = {2007} }

conference presentation, DAMOP 2007, Calgary, Canada (2007).

@misc{seidelin07:microfabricated, author ={S. Seidelin and J. Britton and J. Chiaverini and R. Reichle and J. J. Bollinger and D. Leibfried and J. H. Wesenberg and R. B. Blakestad and R. J. Epstein and J. M. Amini and K. R. Brown and J. P. Home and D. B. Hume and W. M. Itano and J. D. Jost and E. Knill and C. Langer and R. Ozeri and N. Shiga and D. J. Wineland}, title = {Microfabricated surface-electrode ion traps for scalable quantum information processing}, howpublished = {conference presentation, DAMOP 2007, Calgary, Canada}, year = {2007} }

conference poster, DAMOP 2007, Calgary, Canada (2007).

@misc{wesenberg07:analytical, author ={J. H. Wesenberg and J. M. Amini and R. B. Blakestad and J. Britton and K. R. Brown and R. J. Epstein and J. P. Home and W. M. Itano and J. D. Jost and C. Langer and D. Leibfried and R. Ozeri and S. Seidelin and D. J. Wineland}, title = {Analytical {M}ethods for {D}esign of {S}urface-{E}lectrode {I}on {T}raps}, howpublished = {conference poster, {DAMOP} 2007, Calgary, Canada}, year = {2007}, url = {http://meetings.aps.org/link/BAPS.2007.DAMOP.K1.12} }

conference poster, Gordon Research Conference, Atomic Physics 2007, Tilton, New Hampshire (2007).

@misc{jost07:progress, author ={J. D. Jost and J. P. Home and C. Langer and R. Ozeri and J. Amini and J. J. Bollinger and R. B. Blakestad and J. Britton and R. J. Epstein and W. M. Itano and E. Knill and D. Leibfried and C. Ospelkaus and S. Seidelin and N. Shiga and J. H. Wesenberg and D. J. Wineland}, title = {Progress towards distribution of entanglement in an ion trap array}, howpublished = {conference poster, Gordon Research Conference, Atomic Physics 2007, Tilton, New Hampshire}, year = {2007} }

conference poster, DAMOP 2006, Knoxville, Tennessee (2006).

@misc{ozeri06:steps, author ={R. Ozeri and C. Langer and J. D. Jost and R. B. Blakestad and J. Britton and J. Chiaverini and D. Hume and W. M. Itano and E. Knill and D. Leibfried and R. Reichle and S. Seidelin and J. H. Wesenberg and D. J. Wineland}, title = {Steps towards fault-tolerant quantum operations in trapped-ion Quantum information experiments}, howpublished = {conference poster, DAMOP 2006, Knoxville, Tennessee}, year = {2006} }

conference poster, SQUINT 2007, Caltech, Pasadena, California (2007).

@misc{wesenberg07:analyticala, author ={J. H. Wesenberg and J. M. Amini and R. B. Blakestad and J. Britton and K. R. Brown and R. J. Epstein and J. P. Home and W. M. Itano and J. D. Jost and C. Langer and D. Leibfried and R. Ozeri and S. Seidelin and D. J. Wineland}, title = {Analytical {M}ethods for {D}esign of {S}urface-{E}lectrode {I}on {T}raps}, howpublished = {conference poster, SQUINT 2007, Caltech, Pasadena, California}, year = {2007} }

conference poster, DAMOP 2006, Knoxville, Tennessee (2006).

@misc{wesenberg06:reducing, author ={J. H. Wesenberg and R. B. Blakestad and J. Britton and J. D. Jost and E. Knill and C. Langer and D. Leibfried and R. Ozeri and R. Reichle and S. Seidelin and D. J. Wineland}, title = {Reducing the sensitivity of the {M}{\o}lmer-{S}{\o}rensen gate for ion-trap quantum computing to unbalanced laser intensities}, howpublished = {conference poster, DAMOP 2006, Knoxville, Tennessee}, year = {2006} }

conference poster, Workshop on Trapped Ion Quantum Computing, Boulder, Colorado (2006).

@misc{wesenberg06:reduc_sensit_gate_trap_quant, author ={J. H. Wesenberg and R. B. Blakestad and J. Britton and J. D. Jost and E. Knill and C. Langer and D. Leibfried and R. Ozeri and R. Reichle and S. Seidelin and D. J. Wineland}, title = {Reducing the sensitivity of the {M}{\o}lmer-{S}{\o}rensen gate for ion-trap quantum computing to unbalanced laser intensities}, howpublished = {conference poster, Workshop on Trapped Ion Quantum Computing, Boulder, Colorado}, year = {2006}, url = {http://tf.nist.gov/ion/workshop2006/m02.pdf} }

The field at the center of a spherical shell with a uniform distribution of parallel dipoles has vanishing mean. None the less the field in the center of a sphere with a uniform spatial distribution of parallel dipoles is described by a Lorentzian distribution with nonzero center-value! The shift of the center value, which is of the order of 13% of the full width at half maximum of the Lorentz profile, has a number of interesting implications for atomic and solid state dipole interaction. We will show how this surprising result, identified first by numerical simulations, can be obtained by simple analytical methods. We subsequently discuss how, and to what degree, the conclusion is affected when a cut-off of high field values are taken into account. In this case we find always a vanishing mean shift, even though the distribution in the limiting case still approaches the shifted Lorentz distribution: a pedagogical example of why the center value of a Lorentz distribution does not constitute a proper mean value!

conference presentation, DFS Annual Meeting 2004, Nyborg, Denmark (2004).

@misc{wesenberg04:mean, author ={J. H. Wesenberg and K. M{\o}lmer}, title = {Mean mean values of dipole fields}, howpublished = {conference presentation, DFS Annual Meeting 2004, Nyborg, Denmark}, year = {2004} }

conference poster, 7th International Workshop on Atom Optics and Interferometry, Lunteren, The Netherlands (2002).

@misc{wesenberg02:squeezing, author ={J. Wesenberg and K. M{\o}lmer}, title = {Squeezing a Mixed State}, howpublished = {conference poster, 7th International Workshop on Atom Optics and Interferometry, Lunteren, The Netherlands}, year = {2002} }

Ph.D. Thesis. University of Aarhus.

The matlab code referred to in the thesis is available at halwe.dk/janus/research/opphys3_20041029.tgz. LaTeX source is available at halwe.dk/janus/research/pomfletsrc.tgz.

The matlab code referred to in the thesis is available at halwe.dk/janus/research/opphys3_20041029.tgz. LaTeX source is available at halwe.dk/janus/research/pomfletsrc.tgz.

@phdthesis{wesenberg04:quant_infor_proces_rare_earth, author ={J. H. Wesenberg}, title = {Quantum Information Processing in Rare-Earth-Ion-Doped Crystals}, school = {University of Aarhus}, year = {2004}, note = {The matlab code referred to in the thesis is available at halwe.dk/janus/research/opphys3_20041029.tgz. LaTeX source is available at halwe.dk/janus/research/pomfletsrc.tgz}, url = {http://www.halwe.dk/janus/} }

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