A mistake in the computer program performing the power law fit of the numerical computation of the hadron attenuation ratio R M has been detected. The mistake affects all fits which include the Xe nucleus. Below we present corrected results for table 2 and Figs. 8-10.Based on the corrected calculation we revise our conclusion in ref. [1]. The A 2/3 power law for 1 − R M in the absorption model remains also after including the Xe nucleus in the (c,α) fit.
For successful realization of a quantum computer, its building blocks (qubits) should be simultaneously scalable and sufficiently protected from environmental noise. Recently, a novel approach to the protection of superconducting qubits has been proposed. The idea is to prevent errors at the "hardware" level, by building a fault-free (topologically protected) logical qubit from "faulty" physical qubits with properly engineered interactions between them. It has been predicted that the decoupling of a protected logical qubit from local noises would grow exponentially with the number of physical qubits. Here we report on the proof-of-concept experiments with a prototype device which consists of twelve physical qubits made of nanoscale Josephson junctions. We observed that due to properly tuned quantum fluctuations, this qubit is protected against magnetic flux variations well beyond linear order, in agreement with theoretical predictions. These results demonstrate the feasibility of topologically protected superconducting qubits. 6 .
Since the original invention by Samuel P. Langley in 1878 5 , bolometers have gone a long way of improving the sensitivity and expanding the frequency range, from X-rays and optical/UV radiation to the submillimeter waves. The latter range contains approximately half the total luminosity of the Universe and 98% of all the photons emitted since the Big Bang 6 .Because the performance of ground-based THz telescopes is severely limited by a strong absorption of THz radiation in the Earth atmosphere, the development of space-based THz telescopes will be crucial for better understanding of the Universe evolution. Active cooling of primary mirrors on these telescopes will reduce the mirror emission below the cosmic background level (Fig. 1) and greatly expand the range of observable faint objects. The development of advanced detectors with background-limited sensitivity for such telescopes poses a significant challenge. Indeed, the photon flux N ph , which corresponds to the cosmic background fluctuations, is very weak: at ν > 1 THz, the photon flux in a diffraction-limited beam does not exceed 100 photons/s for typical extragalactic emission lines with ν/δν ~ 1000. The noise equivalent power (NEP) of a background-limited detector should be less than NEP ph = hν 2N ph ~ 10 -20 W/Hz 1/2 , which is a factor of 100 lower than that of state-of-the-art bolometers.Although new detector concepts are coming into play nowadays 7,8 , bolometers still have a great potential for achieving the most challenging goals. Realization of the ultra-high sensitivity requires an unprecedented thermal isolation of a bolometer. Indeed, in the fluxintegrating regime (the bolometric time constant τ >> N ph -1 ), the minimum NEP is determined by the thermal energy fluctuations in a bolometer, and the corresponding value ofG is controlled by the thermal conductance G between the bolometer and its environment. In a traditional (the so-called "geometrically isolated") bolometer, G is determined by the number of relevant phonon and photon "channels" (modes) participating in thermal transport between the sensor and its environment. It has been shown recently for both photons 3,9 and phonons 10 that the thermal conductance of a short single channel is determined by the universal value G Q = π Despite a relatively small size of this micromachined device, the heat capacity C was still rather large, which resulted in a slow bolometric response with the time constant τ = C/G =1-10 s.Here we present a novel approach that enables a significant increase of the bolometer sensitivity and, at the same time, reduction of its response time. Fast response in a well isolated bolometer requires a very small heat capacity C and, thus, the nanoscale dimensions of a sensor.To overcome the limitation of fast phonon exchange, we realized the hot-electron regime 11, , 12 13 in superconducting nanobolometers at sub-Kelvin temperatures. In this case, a weak electronphonon coupling, which governs the effective thermal conductance, dramatically improves the thermal isola...
Self-assembled monolayers (SAMs) are widely used in a variety of emerging applications for surface modification of metals and oxides. Here, we demonstrate a new type of molecular self-assembly: the growth of organosilane SAMs at the surface of organic semiconductors. Remarkably, SAM growth results in a pronounced increase of the surface conductivity of organic materials, which can be very large for SAMs with a strong electron-withdrawing ability. For example, the conductivity induced by perfluorinated alkyl silanes in organic molecular crystals approaches 10(-5) S per square, two orders of magnitude greater than the maximum conductivity typically achieved in organic field-effect transistors. The observed large electronic effect opens new opportunities for nanoscale surface functionalization of organic semiconductors with molecular self-assembly. In particular, SAM-induced conductivity shows sensitivity to different molecular species present in the environment, which makes this system very attractive for chemical sensing applications.
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