5,160 research outputs found
Designing potentials by sculpturing wires
Magnetic trapping potentials for atoms on atom chips are determined by the
current flow in the chip wires. By modifying the shape of the conductor we can
realize specialized current flow patterns and therefore micro-design the
trapping potentials. We have demonstrated this by nano-machining an atom chip
using the focused ion beam technique. We built a trap, a barrier and using a
BEC as a probe we showed that by polishing the conductor edge the potential
roughness on the selected wire can be reduced. Furthermore we give different
other designs and discuss the creation of a 1D magnetic lattice on an atom
chip.Comment: 6 pages, 8 figure
Making Sigma-Protocols Non-interactive Without Random Oracles
DamgËšard, Fazio and Nicolosi (TCC 2006) gave a transformation of Sigma-protocols, 3-move honest verifier zero-knowledge proofs, into efficient non-interactive zero-knowledge arguments for a designated verifier. Their transformation uses additively homomorphic encryption
to encrypt the verifier’s challenge, which the prover uses to compute an encrypted answer. The transformation does not rely on the random oracle model but proving soundness requires a complexity leveraging assumption.
We propose an alternative instantiation of their transformation and show that it achieves culpable soundness without complexity leveraging. This
improves upon an earlier result by Ventre and Visconti (Africacrypt 2009), who used a different construction which achieved weak culpable soundness.
We demonstrate how our construction can be used to prove validity of encrypted votes in a referendum. This yields a voting system with homomorphic tallying that does not rely on the Fiat-Shamir heuristic
Theory of the topological Anderson insulator
We present an effective medium theory that explains the disorder-induced
transition into a phase of quantized conductance, discovered in computer
simulations of HgTe quantum wells. It is the combination of a random potential
and quadratic corrections proportional to p^2 sigma_z to the Dirac Hamiltonian
that can drive an ordinary band insulator into a topological insulator (having
an inverted band gap). We calculate the location of the phase boundary at weak
disorder and show that it corresponds to the crossing of a band edge rather
than a mobility edge. Our mechanism for the formation of a topological Anderson
insulator is generic, and would apply as well to three-dimensional
semiconductors with strong spin-orbit coupling.Comment: 4 pages, 3 figures (updated figures, calculated DOS
Scrutinizing and De-Biasing Intuitive Physics with Neural Stethoscopes
Visually predicting the stability of block towers is a popular task in the
domain of intuitive physics. While previous work focusses on prediction
accuracy, a one-dimensional performance measure, we provide a broader analysis
of the learned physical understanding of the final model and how the learning
process can be guided. To this end, we introduce neural stethoscopes as a
general purpose framework for quantifying the degree of importance of specific
factors of influence in deep neural networks as well as for actively promoting
and suppressing information as appropriate. In doing so, we unify concepts from
multitask learning as well as training with auxiliary and adversarial losses.
We apply neural stethoscopes to analyse the state-of-the-art neural network for
stability prediction. We show that the baseline model is susceptible to being
misled by incorrect visual cues. This leads to a performance breakdown to the
level of random guessing when training on scenarios where visual cues are
inversely correlated with stability. Using stethoscopes to promote meaningful
feature extraction increases performance from 51% to 90% prediction accuracy.
Conversely, training on an easy dataset where visual cues are positively
correlated with stability, the baseline model learns a bias leading to poor
performance on a harder dataset. Using an adversarial stethoscope, the network
is successfully de-biased, leading to a performance increase from 66% to 88%
Switching of electrical current by spin precession in the first Landau level of an inverted-gap semiconductor
We show how the quantum Hall effect in an inverted-gap semiconductor (with
electron- and hole-like states at the conduction- and valence-band edges
interchanged) can be used to inject, precess, and detect the electron spin
along a one-dimensional pathway. The restriction of the electron motion to a
single spatial dimension ensures that all electrons experience the same amount
of precession in a parallel magnetic field, so that the full electrical current
can be switched on and off. As an example, we calculate the magnetoconductance
of a p-n interface in a HgTe quantum well and show how it can be used to
measure the spin precession due to bulk inversion asymmetry.Comment: 5 pages, 4 figures, extended versio
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Atom Chips: Fabrication and Thermal Properties
Neutral atoms can be trapped and manipulated with surface mounted microscopic
current carrying and charged structures. We present a lithographic fabrication
process for such atom chips based on evaporated metal films. The size limit of
this process is below 1m. At room temperature, thin wires can carry more
than 10A/cm current density and voltages of more than 500V. Extensive
test measurements for different substrates and metal thicknesses (up to 5
m) are compared to models for the heating characteristics of the
microscopic wires. Among the materials tested, we find that Si is the best
suited substrate for atom chips
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