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.

使用具有反转电流相位关系的超导体-铁磁体-超导体（SFS）π结，可以为超导微电子和纳米电子电路开辟新的可能性。在该项目的第一阶段，我们已经证明了基于Nb的约瑟夫森π结（ S) 和 CuNi (F) 材料可以自然地与现有的铌技术集成，从而实现数字和量子电路，特别是不会降低相关的量子相干性。至少在几纳秒的时间尺度上观察到了 π 结的存在，这对于传统设计的铌相量子位来说是典型的。受这一成功的启发，在本提案中，我们希望探索基于 SFS 的 π 的退相干极限。 -结移相器，通过测量这些器件在微波频率下引起的能量弛豫和相移，我们将详细阐述对称势的 Nb 量子位相干性的最新改进以及优化设计的新思路。我们的最终目标是将 SFS π 结与约瑟夫森 ux 和四次相量子位进行集成和表征，这两种类型的量子位能够在对称（神奇）点上运行和读出。这些量子位的较长相干时间可能更不受各种退相干因素的影响，应该可以得出 π 结可能产生的影响，确保这些电路中必要的相位偏差。这些结果将与这些结的噪声模型中获得的结果进行比较，我们希望我们的实验将为 SFS π 结在量子信息电路中的广泛使用开辟道路。