Anti-Zeno Effect for Quantum Transport in Disordered Systems

We demonstrate that repeated measurements in disordered systems can induce quantum anti-Zeno effect under certain condition to enhance quantum transport. The enhancement of energy transfer is really exhibited with a simple model under repeated measurements. The optimal measurement interval for the anti-Zeno effect and the maximal efficiency of energy transfer are specified in terms of the relevant physical parameters. Since the environment acts as frequent measurements on the system, the decoherence-induced energy transfer, which has been discussed recently for photosynthetic complexes, may be interpreted in terms of the anti-Zeno effect. We further find an interesting phenomenon, where local decoherence or repeated measurements may even promote entanglement generation between the non-local sites.Comment: 5pages, 3 figures; v2: published versio

Cluster-based architecture for fault-tolerant quantum computation

We present a detailed description of an architecture for fault-tolerant quantum computation, which is based on the cluster model of encoded qubits. In this cluster-based architecture, concatenated computation is implemented in a quite different way from the usual circuit-based architecture where physical gates are recursively replaced by logical gates with error-correction gadgets. Instead, some relevant cluster states, say fundamental clusters, are recursively constructed through verification and postselection in advance for the higher-level one-way computation, which namely provides error-precorrection of gate operations. A suitable code such as the Steane seven-qubit code is adopted for transversal operations. This concatenated construction of verified fundamental clusters has a simple transversal structure of logical errors, and achieves a high noise threshold ~ 3 % for computation by using appropriate verification procedures. Since the postselection is localized within each fundamental cluster with the help of deterministic bare controlled-Z gates without verification, divergence of resources is restrained, which reconciles postselection with scalability.Comment: 16 pages, 34 figure

Successive phase transitions at finite temperatures of the supersolid in the three-dimensional extended Bose-Hubbard model

We study the finite temperature properties of the extended Bose-Hubbard model on a cubic lattice. This model exhibits the so-called supersolid state. To start with, we investigate ordering processes by quantum Monte Carlo simulations, and find successive superfluid and solid phase transitions. There, we find that the two order parameters compete with each other. We obtain the finite temperature phase diagram, which contains the superfluid, the solid, the supersolid and the disordered phase. We develop a mean-field theory to analyze the ordering processes and compare the result with that obtained by simulations, and discuss the mechanism of the competition of these two orders. We also study how the supersolid region shrinks as the on-site repulsion becomes strong.Comment: 6 pages, 6 figure

Development of measuring method for softness of epidermis using rotational step response

We have proposed a new measuring method for the softness of epidermis using rotational step response. It can be proceeded that horizontal torsional step is given periodically to the human skin surface by rotational step motor. Then dynamically epidermal characteristic is abstracted selectively from the human skin minimizing influence of the subcutaneous tissue. The cylindrical rotor is attached to the shaft of step motor and its external area is surrounded by the cylindrical guard ring; therefore, only human skin surface of inside the guard ring is screwed periodically by its rotor. At this moment, viscoelasticity of the epidermis is evaluated from analyzing the inducting coil of the step motor. The waveform of voltage of inducing coil can be characterized by overshoot P1, damping ratio D and undamped natural frequency &#969;n. The softness Ks that indicates viscoelasticity of the epidermis can be calculated from these parameters. Many experimental results showed that the softness Ks corresponds to the human sense and it is rational as a parameter for the human skin characteristics. This system is very useful as the measurement can be done easily, in vivo, and non-invasively. It also can be constructed simply without special mechanical sensor because step motor acts as not only driving but also sensing </p