Resolution of Single Spin-Flips of a Single Proton

The spin magnetic moment of a single proton in a cryogenic Penning trap was coupled to the particle's axial motion with a superimposed magnetic bottle. Jumps in the oscillation frequency indicate spin-flips and were identified using a Bayesian analysis.Comment: accepted for publication by Phys. Rev. Lett., submitted 6.June.201

Demonstration of the Double Penning Trap Technique with a Single Proton

Spin flips of a single proton were driven in a Penning trap with a homogeneous magnetic field. For the spin-state analysis the proton was transported into a second Penning trap with a superimposed magnetic bottle, and the continuous Stern-Gerlach effect was applied. This first demonstration of the double Penning trap technique with a single proton suggests that the antiproton magnetic moment measurement can potentially be improved by three orders of magnitude or more

Constraining General Two Higgs Doublet Models by the Evolution of Yukawa Couplings

We study how general two Higgs doublet models can be constrained by considering their properties under renormalization group evolution of the Yukawa couplings. We take into account both the appearance of a Landau pole as well as off-diagonal Yukawa couplings leading to flavour changing neutral currents in violation with experimental constraints at the electroweak scale. We find that the latter condition can be used to limit the amount of Z2 symmetry breaking allowed in a given model.Comment: 28 pages, 10 figures, added discussion of evolution from high to low scales, to be published in JHE

The magnetic moments of the proton and the antiproton

Recent exciting progress in the preparation and manipulation of the motional quantum states of a single trapped proton enabled the first direct detection of the particle's spin state. Based on this success the proton magnetic moment $\mu_p$ was measured with ppm precision in a Penning trap with a superimposed magnetic field inhomogeneity. An improvement by an additional factor of 1000 in precision is possible by application of the so-called double Penning trap technique. In a recent paper we reported the first demonstration of this method with a single trapped proton, which is a major step towards the first direct high-precision measurement of $\mu_p$. The techniques required for the proton can be directly applied to measure the antiproton magnetic moment $\mu_{\bar{p}}$. An improvement in precision of $\mu_{\bar{p}}$ by more than three orders of magnitude becomes possible, which will provide one of the most sensitive tests of CPT invariance. To achieve this research goal we are currently setting up the Baryon Antibaryon Symmetry Experiment (BASE) at the antiproton decelerator (AD) of CERN

Catalyst Interface Engineering for Improved 2D Film Lift-Off and Transfer

The mechanisms by which chemical vapor deposited (CVD) graphene and hexagonal boron nitride (h-BN) films can be released from a growth catalyst, such as widely used copper (Cu) foil, are systematically explored as a basis for an improved lift-off transfer. We show how intercalation processes allow the local Cu oxidation at the interface followed by selective oxide dissolution, which gently releases the 2D material (2DM) film. Interfacial composition change and selective dissolution can thereby be achieved in a single step or split into two individual process steps. We demonstrate that this method is not only highly versatile but also yields graphene and h-BN films of high quality regarding surface contamination, layer coherence, defects, and electronic properties, without requiring additional post-transfer annealing. We highlight how such transfers rely on targeted corrosion at the catalyst interface and discuss this in context of the wider CVD growth and 2DM transfer literature, thereby fostering an improved general understanding of widely used transfer processes, which is essential to numerous other applications.We acknowledge funding from the ERC (InsituNANO, grant 279342). R.W. acknowledges an EPSRC Doctoral Training Award (EP/M506485/1). During this work, S.T. was supported in parts by a DFG research fellowship under grant TA 1122/1-1:1. J.A.A.-W. acknowledges a Research Fellowship from Churchill College, Cambridge. Z.A.V.V. acknowledges funding from ESPRC grant EP/L016087/1. P.B. and B.S.J. thank the Danish National Research Foundation Centre for Nanostructured graphene, DNRF103, and EU Horizon 2020 “Graphene Flagship” 696656. T.J.B. and P.R.W. acknowledge financial support from EU FP7-6040007 “GLADIATOR” and Innovation Fund Denmark Da-Gate 0603-005668B. P.R.K. acknowledges a Lindemann Trust Fellowship

Extrinsic Cation Selectivity of 2D Membranes

From a systematic study of the concentration driven diffusion of positive and negative ions across porous 2D membranes of graphene and hexagonal boron nitride (h-BN), we prove their cation selectivity. Using the current−voltage characteristics of graphene and h-BN monolayers separating reservoirs of different salt concentrations, we calculate the reversal potential as a measure of selectivity. We tune the Debye screening length by exchanging the salt concentrations and demonstrate that negative surface charge gives rise to cation selectivity. Surprisingly, h-BN and graphene membranes show similar characteristics, strongly suggesting a common origin of selectivity in aqueous solvents. For the first time, we demonstrate that the cation flux can be increased by using ozone to create additional pores in graphene while maintaining excellent selectivity. We discuss opportunities to exploit our scalable method to use 2D membranes for applications including osmotic power conversion.This work was supported by the EPSRC Cambridge NanoDTC, EP/G037221/1, and EPSRC grant GRAPHTED, EP/K016636/1. R.S.W. acknowledges a Research Fellowship from St. John’s College, Cambridge, and a Marie SkłodowskaCurie Individual Fellowship (Global) under Grant ARTIST (No. 656870) from the European Union’s Horizon 2020 research and innovation programme. V.S. acknowledges funding from the Commonwealth Scholarship Commission in the UK. S.C. acknowledges funding from EPSRC (doctoral training award). U.F.K. was partly supported by an ERC consolidator grant DesignerPores 647144

Graphene-Integrated Metamaterial Device for All-Electrical Polarization Control of Terahertz Quantum Cascade Lasers

Optoelectronic modulators that operate by the electrical tuning of plasmonic resonator structures have demonstrated fast (>MHz) manipulation of terahertz (THz) radiation for communications, imaging, and spectroscopy applications. Among this class of THz device, chiral metamaterial-based polarization modulators have attracted increasing attention due to the importance of THz polarization control for chemistry, biology, and spectroscopy applications, as well as for THz communication protocols. In this paper, active polarization modulation of a THz quantum cascade laser is demonstrated by the electrical tuning of a 2D chiral metamaterial array. The operating principle of this device is based on an electromagnetically induced transparency analogue, produced by the coupling between a bright resonator and two dark resonators. The orientation of these resonators is such that a radiating electric dipole orthogonal to the incident electric field polarization is induced, causing a rotation of the polarization angle of the transmitted radiation. By variably dampening the dark resonators using graphene, the coupling condition is electrically modulated such that continuous tuning of the transmitted polarization angle is achieved. This device, operating at room temperature, can be readily implemented as a fast, optoelectronic, polarization modulator with a maximum tuning range of 20 degrees at 1.75 THz, with demonstrated reconfiguration speeds of >5 MHz

General Analysis of Antideuteron Searches for Dark Matter

Low energy cosmic ray antideuterons provide a unique low background channel for indirect detection of dark matter. We compute the cosmic ray flux of antideuterons from hadronic annihilations of dark matter for various Standard Model final states and determine the mass reach of two future experiments (AMS-02 and GAPS) designed to greatly increase the sensitivity of antideuteron detection over current bounds. We consider generic models of scalar, fermion, and massive vector bosons as thermal dark matter, describe their basic features relevant to direct and indirect detection, and discuss the implications of direct detection bounds on models of dark matter as a thermal relic. We also consider specific dark matter candidates and assess their potential for detection via antideuterons from their hadronic annihilation channels. Since the dark matter mass reach of the GAPS experiment can be well above 100 GeV, we find that antideuterons can be a good indirect detection channel for a variety of thermal relic electroweak scale dark matter candidates, even when the rate for direct detection is highly suppressed.Comment: 44 pages, 15 Figure

Bolometric detection of terahertz quantum cascade laser radiation with graphene-plasmonic antenna arrays

We present a fast room temperature terahertz detector based on graphene loaded plasmonic antenna arrays. The antenna elements, which are arranged in series and are shorted by graphene, are contacting source and drain metallic pads, thus providing both the optical resonant element and the electrodes. The distance between the antenna's arms of approximately 300 nm allows a strong field enhancement in the graphene region, when the incident radiation is resonant with the antennas. The current passing through the source and drain is dependent on the graphene's conductivity, which is modified by the power impinging onto the detector as well as from the biasing back-gate voltage. The incident radiation power is thus translated into a current modification, with the main detection mechanism being attributed to the bolometric effect. The device has been characterized and tested with two bound to continuum terahertz quantum cascade lasers emitting at a single frequency around 2 THz and 2.7 THz yielding a maximum responsivity of ~2 mA W$^{−1}$.RD, HEB and DAR acknowledge financial support from the Engineering and Physical Sciences Research Council (Grant No. EP/J017671/1, Coherent Terahertz Systems). SH acknowledges funding from EPSRC (Grant No. EP/K016636/1, GRAPHTED). KN acknowledges the University of Cambridge Nanoscience Doctoral Training Centre (EPSRC EP/G037221/1) for financial support