25 research outputs found
Improved bounds on Lorentz violation from composite-pulse Ramsey spectroscopy in a trapped ion
In attempts to unify the four known fundamental forces in a single
quantum-consistent theory, it is suggested that Lorentz symmetry may be broken
at the Planck scale. Here we search for Lorentz violation at the low-energy
limit by comparing orthogonally oriented atomic orbitals in a
Michelson-Morley-type experiment. We apply a robust radiofrequency composite
pulse sequence in the manifold of an Yb ion, extending the
coherence time from 200 s to more than 1 s. In this manner, we fully
exploit the high intrinsic susceptibility of the state and take
advantage of its exceptionally long lifetime. We match the stability of the
previous best Lorentz symmetry test nearly an order of magnitude faster and
improve the constraints on the symmetry breaking coefficients to the 10
level. These results represent the most stringent test of this type of Lorentz
violation. The demonstrated method can be further extended to ion Coulomb
crystals
Quantum Eavesdropping without Interception: An Attack Exploiting the Dead Time of Single Photon Detectors
The security of quantum key distribution (QKD) can easily be obscured if the
eavesdropper can utilize technical imperfections of the actual implementation.
Here we describe and experimentally demonstrate a very simple but highly
effective attack which even does not need to intercept the quantum channel at
all. Only by exploiting the dead time effect of single photon detectors the
eavesdropper is able to gain (asymptotically) full information about the
generated keys without being detected by state-of-the-art QKD protocols. In our
experiment, the eavesdropper inferred up to 98.8% of the key correctly, without
increasing the bit error rate between Alice and Bob significantly. Yet, we find
an evenly simple and effective countermeasure to inhibit this and similar
attacks
Search for new bosons with ytterbium isotope shifts
The Standard Model of particle physics describes the properties of elementary
particles and their interactions remarkably well, but in particular does not
account for dark matter. Isotope-shift spectroscopy is a sensitive probe of
fifth forces and new particles that illuminate the dark matter sector. This
method sets bounds on new bosons that couple neutrons and electrons with masses
in the keV/c2 to MeV/c2 range. With increasing spectroscopic precision, such
searches are limited by uncertainties of isotope masses and the understanding
of nuclear structure. Here, we report on high-precision mass-ratio and
isotope-shift measurements of the ytterbium isotopes Yb
that exceed previous measurements by up to two orders of magnitude. From these
measurements, we extract higher-order changes in the nuclear charge
distribution along the Yb isotope chain and use these to benchmark novel ab
initio calculations. Our measurements set new bounds on the existence of the
proposed boson
Equating κ Maximum Degrees in Graphs without Short Cycles
For an integer k at least 2, and a graph G, let fk(G) be the minimum cardinality of a set X of vertices of G such that G − X has either k vertices of maximum degree or order less than k. Caro and Yuster [Discrete Mathematics 310 (2010) 742–747] conjectured that, for every k, there is a constant ck such that fk(G)≤ckn(G){f_k}\left( G \right) \le {c_k}\sqrt {n\left( G \right)} for every graph G. Verifying a conjecture of Caro, Lauri, and Zarb [arXiv:1704.08472v1], we show the best possible result that, if t is a positive integer, and F is a forest of order at most 16(t3+6t2+17t+12){1 \over 6}\left( {{t^3} + 6{t^2} + 17t + 12} \right), then f2(F ) ≤ t. We study f3(F ) for forests F in more detail obtaining similar almost tight results, and we establish upper bounds on fk(G) for graphs G of girth at least 5. For graphs G of girth more than 2p, for p at least 3, our results imply fk(G)=O(n(G)p+13p){f_k}\left( G \right) = O\left( {n{{\left( G \right)}^{{{p + 1} \over {3p}}}}} \right) . Finally, we show that, for every fixed k, and every given forest F , the value of fk(F ) can be determined in polynomial time
Host ant independent oviposition in the parasitic butterfly Maculinea alcon
Parasitic Maculinea alcon butterflies can only develop in nests of a subset of available Myrmica ant species, so female butterflies have been hypothesized to preferentially lay eggs on plants close to colonies of the correct host ants. Previous correlational investigations of host-ant-dependent oviposition in this and other Maculinea species have, however, shown equivocal results, leading to a long-term controversy over support for this hypothesis. We therefore conducted a controlled field experiment to study the egg-laying behaviour of M. alcon. Matched potted Gentiana plants were set out close to host-ant nests and non-host-ant nests, and the number and position of eggs attached were assessed. Our results show no evidence for host-ant-based oviposition in M. alcon, but support an oviposition strategy based on plant characteristics. This suggests that careful management of host-ant distribution is necessary for conservation of this endangered butterfly