Coherent control of a flux qubit by phase-shifted resonant microwave pulses

The quantum state of a flux qubit was successfully pulse-controlled by using a resonant microwave. We observed Ramsey fringes by applying a pair of phase-shifted pi/2 microwave pulses without introducing detuning. With this method, the qubit state can be rotated on an arbitrary axis in the x-y plane of the Bloch sphere in a rotating frame. We obtained a qubit signal from a coherent oscillation with an angular velocity of up to 2pi*11.4 Grad/s. In combination with Rabi pulses, this method enables us to achieve full control of single qubit operation. It also offers the possibility of orders of magnitude increases in the speed of the arbitrary unitary gate operation.Comment: 3 pages, 3 figure

Impact of multiple modes on the evolution of self-interacting axion condensate around rotating black holes

Ultra-light particles, such as axions, form a macroscopic condensate around a highly spinning black hole by the superradiant instability. Due to its macroscopic nature, the condensate opens the possibility of detecting the axion through gravitational wave observations. However, the precise evolution of the condensate must be known for the actual detection. For future observation, we numerically study the influence of the self-interaction, especially interaction between different modes, on the evolution of the condensate in detail. First, we focus on the case when condensate starts with the smallest possible angular quantum number. For this case, we perform the non-linear calculation and show that the dissipation induced by the mode interaction is strong enough to saturate the superradiant instability, even if the secondary cloud starts with quantum fluctuations. Our result indicates that explosive phenomena such as bosenova do not occur in this case. We also show that the condensate settles to a quasi-stationary state mainly composed of two modes, one with the smallest angular quantum number for which the superradiant instability occurs and the other with the adjacent higher angular quantum number. We also study the case when the condensate starts with the dominance of the higher angular quantum number. We show that the dissipation process induced by the mode coupling does not occur for small gravitational coupling. Therefore, bosenova might occur in this case.Comment: 29 pages, 25 figures, 1 tabl

How Do Scale Insects Settle into the Nests of Plant-Ants on Macaranga Myrmecophytes? Dispersal by Wind and Selection by Plant-Ants

This report elucidates the process of settlement by Coccus scale insects into Crematogaster plant-ant nests formed inside the hollow stems of a myrmecophytic species, Macaranga bancana, in a tropical rain forest. We collected wafting scale insect nymphs from the canopy using sticky traps and characterized the DNA sequence of the trapped nymphs. In addition, we experimentally introduced first-instar nymphs of both symbiotic and nonsymbiotic scale insects to M. bancana seedlings with newly formed plant-ant colonies. Nymphs of symbiotic species were generally carried by ants into their nests within a few minutes of introduction. Most nymphs of nonsymbiotic species were thrown to the ground by ants. Our results suggest that in Crematogaster-Macaranga myrmecophytism, symbiotic coccids disperse by wind onto host plant seedlings at the nymphal stage, and plant-ants actively carry the nymphs landing on seedlings into their nests in discrimination from nonsymbiotic scale insects.ArticleSOCIOBIOLOGY. 59(2):435-446 (2012)journal articl

On the existence of a static black hole on a brane

We study a static black hole localized on a brane in the Randall-Sundrum (RS) II braneworld scenario. To solve this problem numerically, we develop a code having the almost 4th-order accuracy. This code derives the highly accurate result for the case where the brane tension is zero, i.e., the spherically symmetric case. However, a nonsystematic error is detected in the cases where the brane tension is nonzero. This error is irremovable by any systematic methods such as increasing the resolution, setting the outer boundary at more distant location, or improving the convergence of the numerical relaxation. We discuss the possible origins for the nonsystematic error, and conclude that our result is naturally interpreted as the evidence for the nonexistence of solutions to this setup, although an "approximate" solution exists for sufficiently small brane tension. We discuss the possibility that the black holes produced on a brane may be unstable and lead to two interesting consequences: the event horizon pinch and the brane pinch.Comment: 26 pages, 9 figures, submitted to JHE