Experimental investigation of quantum coherence in Josephson circuits with superconductor-ferromagnet-superconductor pi-junctions

超导-铁磁体-超导π结约瑟夫森电路中量子相干性的实验研究

基本信息

批准号：
63915341
负责人：
Professor Dr. Alexey V. Ustinov, Ph.D.
金额：
--
依托单位：
Physikalisch-Technische Bundesanstalt (PTB)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2008
资助国家：
德国
起止时间：
2007-12-31 至 2014-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/63915341?language=en
关键词：
Experimental investigation quantum coherence Josephson

项目摘要

Using of superconductor-ferromagnet-superconductor (SFS) π-junctions having inverted currentphase relation, can open new possibilities for superconducting micro- and nanoelectronic circuits. In the first phase of this project we have shown that the Josephson π-junctions based on Nb (S) and CuNi (F) materials can be naturally integrated with available Nb technology, enabling both digital and quantum circuits. In particular, no degradation of quantum coherence, related to presence of a π-junction, was observed at least on the time scale of several nanoseconds, typical for Nb phase qubits of conventional design. Motivated by this success, in this proposal we would like to explore the decoherence limits of SFS-based π-junction phase shifters by measuring the energy relaxation and dephasing induced by these devices at microwave frequencies. We will elaborate on recent improvement of coherence in the Nb qubits with symmetric potential and new ideas on optimal design of the Josephson qubits. Our final goal will be to integrate and characterize the SFS π-junctions with Josephson ux- and quartic phase qubits. These two types of qubit are able to operate and readout in a symmetry (magic) point and, therefore, they are potentially more immune to various decoherence factors. A longer coherence time of these qubits should allow concluding about possible effect of the π-junctions ensuring in these circuits necessary phase bias. These results will be compared with those obtained in a model of noise in these junctions, physical parameters for which will be found experimentally. We hope that our experiments will open the way towards broad use of SFS π-junctions in quantum information circuits.

使用具有倒电流相关的超导体 - ferromagnet-supoducductor（SFS）π界面，可以为超导微型和纳米电路电路打开新的可能性。在该项目的第一阶段中，我们已经表明，基于NB（S）和CUNI（F）材料的JosephsonπJunctions可以与可用的NB技术自然整合，从而使数字电路和量子电路都可以。特别是，至少在几个纳秒的时间尺度上观察到与存在π结的存在有关的量子相干性的降解，这是常规设计的NB相位值的典型特征。在这一提议中，我们希望通过测量这些设备在微波频率下诱导的能量弛豫和脱位，从而探索基于SFS的π结相移位器的破坏限制。我们将详细阐述NB相位量子位的连贯性，并具有对称潜力和有关约瑟夫森Qubits最佳设计的新想法。我们的最终目标是将SFSπJunctions与Josephson UX和四分之一相位量线进行集成和表征。这两种类型的量楼能够以对称点（魔术）点运行和读数，因此它们可能更容易受到各种逆转因素的影响。这些量子位的相干时间较长，应得出结论π-缝线的可能影响，以确保在这些电路中必要的相位偏差。这些结果将与在这些连接中的噪声模型中获得的结果进行比较，物理参数将在实验中找到。我们希望我们的实验能为在量子信息电路中广泛使用SFSπJunctions开辟道路。