Movies of Quantum Decoherence
Complex superpositions of photonic quantum states that display strong
quantum interference have been “filmed” as they evolve and decohere in
time, allowing detailed observations of their decay as they interact with
their environment.
Using a superconducting phase qubit, experimenters at UC Santa Barbara
have created a range of quantum superpositions of photon states in a
microwave resonator. They can analyze the photon states by employing a
technique known as Wigner tomography, from which two-dimensional Wigner
quasiprobability functions can be calculated; these display the
artistically appealing characteristics of quantum interference. By
performing tomography on the states as they evolve in time, the
experimenters can construct “movies” of the state evolution, providing
striking illustrations of the decoherence and decay of the delicate
quantum states in the resonator. These detailed measurements also allow
the experimenters to extract the time-dependent density matrix for the
resonator, with non-zero on- and off-diagonal elements, and they find good
agreement with theory for the detailed time evolution of every element in
the density matrix. This paper and its accompanying movies present an
appealing and intuitive demonstration of quantum state evolution and
decay.
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BG11217
Atomic configuration, conductance and tensile force of platinum wires with single-atom width
An atomic-scale direct visual experiment was realized for possible smallest artificial structures, i.e., single-atom-width wires. Only six platinum atoms were pulled out from a substrate in line using a nanotip. For individual atomic wires, the dynamic process was directly observed by transmission electron microscopy while simultaneous measurement of electric conductance and mechanical strength. Thus, now, our method allowed us to produce smallest artificial structures, to observe them, and to analyze electrical and mechanical properties one by one. Metallic atom wires have been classified into two large groups: those which exhibit the quantization of conductance or not. Platinum atomic wires typify non-quantized conductance group. Due to deficiency of method, the picture of wires exhibiting non-quantized conductance have not been imaged, although their electricity have been intensively studied. The present study demonstrated an experimental evidence for the picture of atomic wires exhibiting non-quantized conductance.
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AH10402
Magic travel on "Poincare sphere"
Researchers recently investigated evolution of the optical polarization in periodically poled optical superlattice with electric field by observing polarization trajectories on Poincare sphere and novel behaviors of optical polarization were surprisingly discovered.
Optical polarization which reflects the vector nature of the electromagnetic field has been attracting researchers' curiosity for centuries and many remarkable effects regarding optical polarization has been discovered. Recently, researchers from Shanghai Jiao Tong University introduced such striking topic into an optical superlattice. Here, the superlattice functioned as a "magic box" which was able to flexibly manipulate the polarization of a light through electric field. To get an insight into such "magic", researchers observed the evolution trajectories of polarization using "Poincare sphere".
Experiments have revealed that after passing through the "magic box", optical polarization of some wavelengths motivated by electric fields will travel along a closed path parallel to the equator of Poincare sphere like planets around stars; perturbation of the initial optical polarization may force the evolution to take a different orbit. More interestingly, optical polarization of other wavelengths will however travel along a series of discrete paths with a common point of tangency. Here, the superlattice provides a spaceship for polarization and the electric field functions as an energy booster which supports the travel.
This study will promote a novel method for precise and flexible polarization control and may find applications in many scientific realms.
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[BBR1149] R19942PRB
Doppler-Effect in Superconductivity
If waves like light or sound are reflected from a moving surface a shift of wavelength and frequency occurs, which is known as the Doppler-effect. In a recent experiment, we demonstrated that the Doppler shift also occurs in the wave mechanics of electrons, i.e. in the Andreev reflection at a normal-metal/superconductor interface. Andreev reflection means that the incoming electron is reflected as a hole, while a Cooper pair joins the superconducting condensate. Andreev reflections allow supercurrent flow through a Josephson junction formed by normal metal sandwiched between two superconducting contacts. If the condensate in the contacts is set in motion, e.g., by an external magnetic field, the wavelength of the reflected hole is drastically affected. As a consequence the allowed energy levels in the normal metal shift. In our experiment the Doppler-shift results in an unanticipated sensitivity of the supercurrent capacity of the junctions and other properties, which may be exploited in the construction of ultra-sensitive magnetic field detectors.
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LJ11730
Dark matter nuggets shine brightly in gamma-rays
Ultracompact nuggets of dark matter formed when the Universe was in its infancy could be detected by existing high-energy telescopes. If the nuggets (“ultracompact minihalos”) are made of weakly-interacting massive particles (WIMPs), they should produce gamma-rays when WIMPs annihilate with one another. Our paper shows that depending on exactly when the nuggets formed, they could produce enough gamma-rays today to be detected by the Large Area Telescope aboard the Fermi satellite, or existing ground-based gamma-ray observatories such as the HESS telescope, in Namibia.
Dark matter makes up almost a quarter of the Universe, but so far we have no idea what it really is; WIMPs are the leading theoretical candidate. A detection of gamma-rays from WIMP annihilation would not only solve the dark matter problem, but revolutionise our current understanding of particle physics. Ultracompact minihalos are a recently-proposed dark matter structure; our paper shows that their compactness results in very strong gamma-ray signals.
