Scalable arrays of micro-Penning traps for quantum computing and simulation

We propose the use of 2-dimensional Penning trap arrays as a scalable platform for quantum simulation and quantum computing with trapped atomic ions. This approach involves placing arrays of micro-structured electrodes defining static electric quadrupole sites in a magnetic field, with single ions trapped at each site and coupled to neighbors via the Coulomb interaction. We solve for the normal modes of ion motion in such arrays, and derive a generalized multi-ion invariance theorem for stable motion even in the presence of trap imperfections. We use these techniques to investigate the feasibility of quantum simulation and quantum computation in fixed ion lattices. In homogeneous arrays, we show that sufficiently dense arrays are achievable, with axial, magnetron and cyclotron motions exhibiting inter-ion dipolar coupling with rates significantly higher than expected decoherence. With the addition of laser fields these can realize tunable-range interacting spin Hamiltonians. We also show how local control of potentials allows isolation of small numbers of ions in a fixed array and can be used to implement high fidelity gates. The use of static trapping fields means that our approach is not limited by power requirements as system size increases, removing a major challenge for scaling which is present in standard radio-frequency traps. Thus the architecture and methods provided here appear to open a path for trapped-ion quantum computing to reach fault-tolerant scale devices.Comment: 21 pages, 10 figures Changes include adding section IX (Implementation Example) and substantially rewriting section X (Scaling

Robust dynamical exchange cooling with trapped ions

We investigate theoretically the possibility for robust and fast cooling of a trapped atomic ion by transient interaction with a pre-cooled ion. The transient coupling is achieved through dynamical control of the ions' equilibrium positions. To achieve short cooling times we make use of shortcuts to adiabaticity by applying invariant-based engineering. We design these to take account of imperfections such as stray fields, and trap frequency offsets. For settings appropriate to a currently operational trap in our laboratory, we find that robust performance could be achieved down to $6.3$ motional cycles, comprising $14.2\ \mathrm{\mu s}$ for ions with a $0.44\ \mathrm{MHz}$ trap frequency. This is considerably faster than can be achieved using laser cooling in the weak coupling regime, which makes this an attractive scheme in the context of quantum computing.Comment: 34 pages, 9 figures; added reference, changed title to emphasize robustnes

WHIPLASH: The possible impact of context on diagnosis

This study explores the importance of context when diagnosing Whiplash Associated Disorders (WAD). Whiplash is a complex injury and there is considerable variation in its diagnosis and treatment. Research has focussed on RTAs, whilst there is a paucity of evidence relating to WAD in sport. It is unclear whether WAD is simply not occurring in sport, or if such injuries are occurring but are not identified as WAD. In the current study, 87 postgraduate physiotherapists were asked to classify an injury reported in a short vignette. Two parallel vignettes were used, which were identical except for the context of the injury (one being an RTA and the other being within sport). Each participant responded to only one of these. It was found that, even within a sample of experienced physiotherapists, the injury environment impacted on diagnosis, despite the symptoms being identical. A significantly higher proportion of therapists diagnosed WAD within the RTA context than within the sporting context. Additionally, there were differences between the two context groups in relation to the diagnostic terminology used by participants. Most respondents had heard of the CSP whiplash guidelines but only a minority had actively used these. The majority of respondents were also aware of the litigation aspects of RTAs

NMR analogues of the quantum Zeno effect

We describe Nuclear Magnetic Resonance (NMR) demonstrations of the quantum Zeno effect, and discuss briefly how these are related to similar phenomena in more conventional NMR experiments.Comment: 8 pages including 4 figures; intended as a possible answer to Malcolm Levitt's question at the 2005 Magnetic Resonanace GRC: "What is the NMR analogue of the quantum Zeno effect?". In press at Physics Letters

Probing the limits of correlations in an indivisible quantum system

We employ a trapped ion to study quantum contextual correlations in a single qutrit using the 5-observable Klyachko,Can,Binicio˘glu,andShumovskyinequality,whichisarguablythemostfundamentalnoncontextuality inequality for testing quantum mechanics (QM). We quantify the effect of systematics in our experiment by purposely scanning the degree of signaling between measurements, which allows us to place realistic bounds on the nonclassicality of the observed correlations. Our results violate the classical bound for this experiment by up to 25 standard deviations, while being in agreement with the QM limit. In order to test the prediction of QM that the contextual fraction increases with the number of observables, we gradually increase the complexity of our measurements from 5 up to 121 observables. We find stronger-than-classical correlations in all prepared scenarios up to 101 observables, beyond which experimental imperfections blur the quantum-classical divide