The Standard Model of particle physics is known to be incomplete. Extensions to the Standard Model, such as weak-scale supersymmetry, posit the existence of new particles and interactions that are asymmetric under time reversal (T) and nearly always predict a small yet potentially measurable electron electric dipole moment (EDM), d(e), in the range of 10(-27) to 10(-30) e·cm. The EDM is an asymmetric charge distribution along the electron spin (S(→)) that is also asymmetric under T. Using the polar molecule thorium monoxide, we measured d(e) = (-2.1 ± 3.7stat ± 2.5syst) × 10(-29) e·cm. This corresponds to an upper limit of |d(e)| < 8.7 × 10(-29) e·cm with 90% confidence, an order of magnitude improvement in sensitivity relative to the previous best limit. Our result constrains T-violating physics at the TeV energy scale.

We recently set a new limit on the electric dipole moment of the electron (eEDM) (J Baron et al and ACME collaboration 2014 Science 343 269-272), which represented an order-of-magnitude improvement on the previous limit and placed more stringent constraints on many charge-parityviolating extensions to the standard model. In this paper we discuss the measurement in detail. The experimental method and associated apparatus are described, together with the techniques used to isolate the eEDM signal. In particular, we detail the way experimental switches were used to suppress effects that can mimic the signal of interest. The methods used to search for systematic errors, and models explaining observed systematic errors, are also described. We briefly discuss possible improvements to the experiment. 9 Note that the limit we report here uses an updated value for  = 78 eff GV cm −1 which is obtained by averaging the results from [29, 30]. 10 A detailed discussion of the sign convention for this Hamiltonian term is provided in section appendix A.3 1 states have very small magnetic moments [58] since the d 3 2 orbital valence electron serves to nearly cancel the magnetic moment of the s 1 2 orbital. The actual magnetic moment of H deviates from zero primarily because of mixing with other states [59]. We express ThO molecule states using the basis Wñ |Y J M , , , , where Y is the electronic state, J is the total angular momentum, M is the projection of J onto the laboratoryẑ-axis, and Ω 1 (V cm −1 ) −1 [67]; this permits full (>99%) polarisation of the state in small applied electric fields,   10 V cm −1 , allowing us to take full advantage of the huge  eff in ThO. The Ω-doublet structure is also useful in rejecting systematic errors since it allows for spectroscopic reversal of  µ -n eff by addressing different  states without reversing the applied electric field [68]. This is discussed in greater detail in section 5.4.The H state in ThO is metastable with a lifetime »1.8 ms [69], limiting our measurement time to t » 1 ms. We note that this is comparable to previous beam-based eEDM measurements where the atomic/molecular states used had significantly longer lifetimes [20,69,70]. 1 (V cm −1 ) −1 (black arrow/lines) is the expectation value of the molecular electric dipole moment in these states [60]. Additionally, a magnetic field   causes a Zeeman shift  m »-Mg z 1 B , with m p » -ǵ 2 6kHz 1 B G −1 (red arrow/lines) [59, 64]. A nonzero eEDM would result in an additional energy shift   »-M d e eff (blue arrow/lines) where  = -1 (+1) when the applied  field is (is not) reversed. The orientation of   eff (green arrows), the spin of the electron in the σ orbital (black arrow next to molecule), the external electric field  , and the external magnetic field   are shown relative to the laboratoryẑ direction which is oriented upwards on the page. Diagram not to scale. 11 Throughout the paper, we give numerical values of energies (with  = 1) in terms of angular frequencies by using the notation p´f 2 , where f ...

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The divide between the realms of atomic-scale quantum particles and lithographically-defined nanostructures is rapidly being bridged. Hybrid quantum systems comprising ultracold gas-phase atoms and substrate-bound devices already offer exciting prospects for quantum sensors 1,2 , quantum information 3 and quantum control 4 . Ideally, such devices should be scalable, versatile and support quantum interactions with long coherence times. Fulfilling these criteria is extremely challenging as it demands a stable and tractable interface between two disparate regimes. Here we demonstrate an architecture for atomic control based on domain walls (DWs) in planar magnetic nanowires that provides a tunable atomic interaction, manifested experimentally as the reflection of ultracold atoms from a nanowire array. We exploit the magnetic reconfigurability of the nanowires to quickly and remotely tune the interaction with high reliability. This proof-of-principle study shows the practicability of more elaborate atom chips based on magnetic nanowires being used to perform atom optics on the nanometre scale.The position, internal state and interactions of quantum particles can be precisely controlled by a variety of techniques utilising combinations of electric, magnetic and optical fields 5,6 . These methods have been enhanced by exploiting the advances in modern nanofabrication techniques, giving rise to a wide array of miniaturised atom chip experiments 7 . Previous studies using micron-scale atom chips have demonstrated robust and exquisite control over atoms through increasingly complex networks of traps, guides and other atom-optical elements. Further miniaturisation of such devices to the nanoscale offers the tantalising prospect of the precise manipulation of the position and internal state of individual atoms.Magnetic atom chips can be roughly divided into devices based on current-carrying wires 8 and those based on permanent magnetic material 9 . Atom chips based on current-carrying wires can suffer from technical noise which induces spin-flip losses 10 and causes inhomogeneities in the magnetic potentials. Care must also be taken to ensure sufficient power dissipation, which can limit the precision of the fields created. On the other hand, lithographically fabricated permanent magnets far surpass the feature size limits of atom chips based on current-carrying wires 11-13 and offer greater flexibility of design, whilst allowing the creation of significantly stronger fields. This has enabled the creation of atom traps with exceptionally high trap frequencies [14][15][16] . However, permanent magnets suffer from the inability to be switched off or reconfigured once the device has been fabricated, limiting the realisation of dynamic behaviour.Here we demonstrate an atom chip based on nanomagnetic technology that exhibits the benefits of patterned magnetic materials whilst maintaining reconfigurability. The small characteristic size of our magnetic nanostructures provides exquisite control over the magnetic configuration and...

We present a new approach to calculating magnetic fringing fields from head-to-head type domain walls in planar magnetic nanowires. In contrast to calculations based on micromagnetically simulated structures the descriptions of the fields are for the most part analytic and thus significantly less time and resource intensive. We begin with an intuitive picture of domain walls, which is built upon in a phenomenological manner. The resulting models require no a priori knowledge of the magnetization structure, and facilitate calculation of fringing fields without any free parameters. Comparisons with fields calculated using micromagnetic methods show good quantitative agreement. arXiv:1104.2249v2 [cond-mat.mtrl-sci]