419 research outputs found

    Proximity-induced Josephson effect and its application to heavy fermion superconductor UBe13

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    A new effect between a superconductor with superconducting transition temperature T(,cs) and a normal metal N (T(,cn)) (or another superconductor with T(,cn) \u3c T(,cs)) has been experimentally observed and theoretically explained. That is when S and N are brought together to form a weak link the Josephson effect can occur in this SN system even in the temperature range T(,cn) \u3c T \u3c T(,cs), when the N side is in the normal state. This Josephson effect is believed to happen between the S and a region of proximity-induced super- conductivity in N near the contact with S. We call this effect the proximity-induced Josephson effect. The temperature dependence of the Josephson critical current I(,c)(T) of the SN point contact junc- tions have been studied experimentally. The experiments have been performed on Ta/Mo, Ta/UBe(,13) and Nb/Ta point contacts etc. The theoretical model is based on the linearized Gor\u27kov equation (or linearized Ginzburg-Landau equation) combined with de Gennes boundary conditions. This model is applicable only in the vicinity of the T(,c) of the SN system. Thus, we studied I(,c)(T) of the SN junctions near their T(,c). Good agreement between experimental data and theoretical result is obtained;Along with the recent discovery of the superconductivity in heavy fermion materials CeCu(,2)Si(,2), UBe(,13) and UPt(,3) the old question of p-wave pairing superconductivity is raised again (in case of the exist- ence of strong spin-orbit scattering, it should be called odd parity superconductivity, since in that case the wave function of Cooper pairs cannot be separated into spin part and orbit part). These rare-earth and actinide compounds exhibit properties which cannot be explained by the conventional isotropic s-wave pairing supercon- ductivity (or BCS superconductivity) but are consistent with the varieties of p-wave (or odd parity) superconductivity. Among these three heavy fermion superconductors UBe(,13) is thought to be the best candidate for odd parity pairing for the reasons in Chapter 5 of this work. The proximity-induced Josephson effect is employed;to investigate the pairing state of UBe(,13). The results are found to favor an odd parity bulk superconducting ground state in UBe(,13); *DOE Report IS-T-1244. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy

    Extracting an arbitrary relative phase from a multiqubit two-component entangled state

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    We show that an arbitrary relative phase can be extracted from a multiqubit two-component (MTC) entangled state by local Hadamard transformations and measurements along a single basis only. In addition, how to distinguish a MTC entangled state with an arbitrary entanglement degree and relative phase from a class of multiqubit mixed states is discussed.Comment: 4 pages, REVTEX, accepted by Physical Review

    Efficient many-party controlled teleportation of multi-qubit quantum information via entanglement

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    We present a way to teleport multi-qubit quantum information from a sender to a distant receiver via the control of many agents in a network. We show that the original state of each qubit can be restored by the receiver as long as all the agents collaborate. However, even if one agent does not cooperate, the receiver can not fully recover the original state of each qubit. The method operates essentially through entangling quantum information during teleportation, in such a way that the required auxiliary qubit resources, local operation, and classical communication are considerably reduced for the present purpose

    Rapid optimization of working parameters of microwave-driven multi-level qubits for minimal gate leakage

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    We propose an effective method to optimize the working parameters (WPs) of microwave-driven quantum logical gates implemented with multi-level physical qubits. We show that by treating transitions between each pair of levels independently, intrinsic gate errors due primarily to population leakage to undesired states can be estimated accurately from spectroscopic properties of the qubits and minimized by choosing appropriate WPs. The validity and efficiency of the approach are demonstrated by applying it to optimize the WPs of two coupled rf SQUID flux qubits for controlled-NOT (CNOT) operation. The result of this independent transition approximation (ITA) is in good agreement with that of dynamic method (DM). Furthermore, the ratio of the speed of ITA to that of DM scales exponentially as 2^n when the number of qubits n increases.Comment: 4pages, 3 figure

    A n-qubit controlled phase gate with superconducting quantum interference devices coupled to a resonator

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    We present a way to realize a nn-qubit controlled phase gate with superconducting quantum interference devices (SQUIDs) by coupling them to a superconducting resonator. In this proposal, the two logical states of a qubit are represented by the two lowest levels of a SQUID. An intermediate level of each SQUID is utilized to facilitate coherent control and manipulation of quantum states of the qubits. It is interesting to note that a nn-qubit controlled phase gate can be achieved with nn SQUIDs by successively applying a ŌÄ/2\pi /2 Jaynes-Cummings pulse to each of the n‚ąí1n-1 control SQUIDs before and after a ŌÄ\pi Jaynes-Cummings pulse on the target SQUID.Comment: 9 pages, 4 figures, 1 table, RevTeX, Resubmitted to Phys. Rev.

    Anti-Theft Travel Bag Design: Advantage, Interest, and Satisfaction

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    Theft around the world continues to rise (Travelling Overseas, 2012). Tourists have always been easy targets for thieves (Holcomb & Pizam, 2006). Data released by the U.S. Office of Travel and Tourism Industries (OTTI) show that the total number of U.S. citizens travelling abroad in 2011 increased by 76% since 2001
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