Josephson结开关电流分布的测量方案探讨

Josephson结的开关电流存在着一定的分布.利用开关电流的分布,我们可以推算出Josephson结的逸出率.进一步结合合适的微波辐照,还可以获得结的诸如能级、拉比振荡等许多相关的量子特性.Josephson结的开关电流分布的获得,对于研究超导量子比特,包括相位量子比特、电荷量子比特、磁通量子比特和涡流量子比特以及他们的组合量子比特都有着重要意义.我们提出了三种测量方案,对这三种方案进行了比较,并初步的对自制的NbN/AlNx/NbN Josephson结的开关电流进行了多次(104次)测量,得到一定温度下的开关电流分布的直方图.针对三种方案各自的优缺点及已有的结果,我们提出了需要进一步改进的措施,对于下一步开展在极低温下(mK)Josephson结的开关电流分布的测量有着重要的意义.

MEASUREMENTS ON THE SWITCHING CURRENT DISTRIBUTION OF A JOSEPHSON JUNCTION

Josepshon junction has its switching current distribution, from which one could get not only the escape rate but also other quantum information like the energy level quantization, Rabi oscillation with proper microwave. The measurements on the switching current distribution of a Josephson junction is very helpful to the development of supercondutor qubit including phase qubit, chage qubit, flux qubit and their combinations. We present three measurement techniques and perform a measurement (10+4 times) on the switching current distribution of a homemade NbN/AlN-x/NbN Josephson junction at certain temperature. According to the disadvantages of the presently used technique and the result we get, more advices are given to the next measurements on the switching current distribution at the ultra low temperature (mK).