Decoherence in Excited Atoms by Low-Energy Scattering

We describe a new mechanism of decoherence in excited atoms that arise from particle scattering by the atomic nucleus. It is based on the idea that the scattering will produce a sudden displacement of the nucleus which will be perceived by the electron of the atom as an instant shift in the electrostatic potential. This will leave the atom’s wavefunction partially projected into lower-energy states which will lead to the decoherence of the atomic state. The decoherence is calculated to increase with the excitation of the atom, making observations of the effect easier in Rydberg atoms. We estimate the order of the decoherence for photons and massive particles scattering, analyzing several commonly presented scenarios. By maximizing the order of the effect it can be used for detection of weakly-interacting particles, like those which may be the constituents of Dark Matter, through applying very precise atomic spectroscopy

Quantum secrecy in thermal states II

In this paper we consider a scheme for cryptographic key distribution based on a variation of continuous variable quantum key distribution called central broadcast. In the continuous variable central broadcast scheme, security arises from discord present in the Hanbury Brown and Twiss effect from a thermal source. The benefit of this scheme is that it expands the range of frequencies into the microwave regime. Longer wavelengths—where the thermal photon number is higher and correlations remain robust over long distances—may even be preferable to optical wavelengths. Assuming that Alice controls the source but not the distribution of the light (e.g. satellite broadcasts), then we demonstrate that the central broadcast scheme is robust to an entangling cloner attack. We establish the security of the protocol both experimentally and theoretically

A portable diagnostic device for cardiac magnetic field mapping

In this paper we present a portable magnetocardiography device. The focus of this development was delivering a rapid assessment of chest pain in an emergency department. The aim was therefore to produce an inexpensive device that could be rapidly deployed in a noisy unshielded ward environment. We found that induction coil magnetometers with a coil design optimized for magnetic field mapping possess sufficient sensitivity (104fT /√ Hz noise floor at 10Hz) and response (813fT /µV at 10Hz) for cycle averaged magnetocardiography and are able to measure depolarisation signals in an unshielded environment. We were unable to observe repolarisation signals to a reasonable fidelity. We present the design of the induction coil sensor array and signal processing routine along with data demonstrating performance in a hospital environment

Climbing the Jaynes-Cummings Ladder and Observing its Sqrt(n) Nonlinearity in a Cavity QED System

The already very active field of cavity quantum electrodynamics (QED), traditionally studied in atomic systems, has recently gained additional momentum by the advent of experiments with semiconducting and superconducting systems. In these solid state implementations, novel quantum optics experiments are enabled by the possibility to engineer many of the characteristic parameters at will. In cavity QED, the observation of the vacuum Rabi mode splitting is a hallmark experiment aimed at probing the nature of matter-light interaction on the level of a single quantum. However, this effect can, at least in principle, be explained classically as the normal mode splitting of two coupled linear oscillators. It has been suggested that an observation of the scaling of the resonant atom-photon coupling strength in the Jaynes-Cummings energy ladder with the square root of photon number n is sufficient to prove that the system is quantum mechanical in nature. Here we report a direct spectroscopic observation of this characteristic quantum nonlinearity. Measuring the photonic degree of freedom of the coupled system, our measurements provide unambiguous, long sought for spectroscopic evidence for the quantum nature of the resonant atom-field interaction in cavity QED. We explore atom-photon superposition states involving up to two photons, using a spectroscopic pump and probe technique. The experiments have been performed in a circuit QED setup, in which ultra strong coupling is realized by the large dipole coupling strength and the long coherence time of a superconducting qubit embedded in a high quality on-chip microwave cavity.Comment: ArXiv version of manuscript published in Nature in July 2008, 5 pages, 5 figures, hi-res version at http://www.finkjohannes.com/SqrtNArxivPreprint.pd

Determining the Depth and Location of Buried Pipeline by Magnetometer Survey

This paper proposes a new approach to determine the depth and location of buried pipelines using the remote magnetic field measured by aboveground magnetometer surveys. Calculation is presented and verified by the experimental results on 152-mm (6-in.). steel vessels. Performance of the technique is also evaluated through field trials against industrial pipe locators. The depth calculated from the measured magnetic field using this proposed technique agreed within the tolerance interval representing the confidence level of 99.7% of the depth determined by the industrial devices and was able to trend changes of the buried depth. In addition, it was possible to map the target pipeline using the survey route coordinates by calculating the lateral position of the survey route relative to the pipeline centerline from the measured magnetic field. So far, the depth measured by this proposed technique has shown a potential error of 8%. By producing a three-dimensional profile of buried pipelines through quick aboveground surveys, the proposed technique can be considered as a screening technique for asset and integrity management such as monitoring geohazard conditions

Solving the inverse problem of magnetisation-stress resolution

Magnetostriction in various metals has been known since 1842, recently the focus has shifted away from ferrous metals, towards materials with a straightforward or exaggerated stress magnetostriction relationship. However, there is an increasing interest in understanding ferrous metal relationships, especially steels, because of its widespread use in building structures, transportation infrastructure, and pipelines. The aim of this paper is to solve the inverse problem of determining stress from an observed magnetic field which implies a given magnetic structure and to demonstrate that theoretical calculations using a multi-physics modeling technique agree with this experimental observation

Quantum Secrecy in Thermal States II

In this paper we consider a scheme for cryptographic key distribution based on a variation of continuous variable quantum key distribution called central broadcast. In the continuous variable central broadcast scheme, security arises from discord present in the Hanbury Brown and Twiss effect from a thermal source. The bene t of this scheme is that it expands the range of frequencies into the microwave regime. Longer wavelengths—where the thermal photon number is higher and correlations remain robust over long distances—may even be preferable to optical wavelengths. Assuming that Alice controls the source but not the distribution of the light (e.g. satellite broadcasts), then we demonstrate that the central broadcast scheme is robust to an entangling cloner attack. We establish the security of the protocol both experimentally and theoretically