QuBIC: A Qubit Based on SINIS Josephson Tunnel Junctions

基于SINIS约瑟夫森隧道结的量子比特形成受控的量子态超位是量子计算的核心，执行这一功能的设备被称为“量子比特”。这里选择的实现量子比特的设备是基于双势垒SINIS约瑟夫森结（其中S是超导体，I是绝缘体，N是普通金属）。基本策略包括控制由两个最低（基态和第一激发态）Andreev束缚态（ABS）组成的2级系统中的职业，这些状态可以在SINIS结中形成。事实上，基于sinis的量子位的参数可以选择使只有上述两个ABS级别存在；这一结论独立于理论推导，与Nb/AlOxAl/AlOx/Nb双势垒结的初步实验数据一致。通过将适当的偏置电压和传输电流施加到以三端几何形状制造的器件上，可以实现对两个Andreev状态的所需控制。控制参数是通过一个垒的电压和通过一个超导层的传输电流；这些量扮演动态磁场的角色，进入相关的量子比特哈密顿量。本提案的主要目标是实现对Andreev束缚态的可控操纵，并同时推进对潜在物理机制的理解。这将包括：i)将目前制备双端SINIS器件的技术扩展到三端器件；ii)对ABS特性进行测量，包括观察两个ABS水平之间的Rabi振荡，iii)进一步发展双势垒结内局部ABS理论，以允许任意势垒透明度和任意杂质浓度在所有三个电极中，iv)对开关动力学进行详细的数值模拟；V)研究与这些设备性能相关的重组和退相干效应，最后vi)研究连接量子位以形成简单逻辑电路的策略。

EIA-0218652John KettersonNorthwestern UniversityA Qubit Based on SINIS Josephson Tunnel JunctionForming controlled super positions of quantum states lies at the heart of quantum computing and devices that perform this function have been termed "qubits". The device chosen here to realize a qubit is based on a double-barrier SINIS Josephson junction (where S is a superconductor, I is an insulator, and N is a normal metal). The basic strategy involves the controlled manipulation of the occupations in a 2-level system comprised of the two lowest (the ground and the first excited) Andreev bound states (ABS) that can form within an SINIS junction. In fact the parameters of the SINIS-based qubit can chosen such that only the above two ABS levels are present; this conclusion, which independently follows from the theory, is in agreement with preliminary experimental data taken on Nb/AlOxAl/AlOx/Nb double-barrier junctions. The required control of the two Andreev states is achieved by applying appropriate bias voltages and transport currents to a device fabricated in a three-terminal geometry. The control parameters turn out to be the voltage across one of the barriers, and the transport current across one of the super conducting layers; these quantities play the role of the dynamic magnetic fields, which enter the associated qubit Hamiltonian. The primary goal of this proposal is to achieve the controlled manipulation of the Andreev bound states and, in parallel, advance the understanding of the underlying physical mechanisms. This will include: i) extending the present technology for preparing two-terminal SINIS devices to 3-terminal devices; ii) performing measurements on the ABS characteristics, including the observation of Rabi oscillations between the two ABS levels, iii) further developing the theory of localized ABS inside double barrier junctions to allow for arbitrary barrier transparency and arbitrary impurity concentrations in all three electrodes, iv) performing detailed numerical simulations of the switching dynamics; v) studying the recombination and decoherence effects that relate to the performance of these devices, and lastly vi) examining strategies for connecting qubits to form simple logic circuits.