Measuring the current-phase relation of a Josephson junction

The current through a Josephson junction is governed by the current-phase relation (CPR) that depends on the phase difference between the electrodes. Notable applications are qubits, Josephson diodes and microscopic imaging techniques. This thesis presents a method to measure the CPR based on [1]. The junction under study is incorporated into a superconducting loop that is inductively coupled to a dc-SQUID magnetometer. The measured flux is proportional to the junction’s phase and by controlling the current through the junction’s loop it is possible to directly measure the CPR. This thesis outlines several important considerations and constraints of this method. Furthermore we provide CPR measurements of a superconductor-normal- superconductor (SNS) junction made from Nb and Cu. It shows a clear temperature dependence with a qualitative change in shape as well as a quantitative change in amplitude of the current-phase relation. These results are in agreement with theory. In the...Show moreThe current through a Josephson junction is governed by the current-phase relation (CPR) that depends on the phase difference between the electrodes. Notable applications are qubits, Josephson diodes and microscopic imaging techniques. This thesis presents a method to measure the CPR based on [1]. The junction under study is incorporated into a superconducting loop that is inductively coupled to a dc-SQUID magnetometer. The measured flux is proportional to the junction’s phase and by controlling the current through the junction’s loop it is possible to directly measure the CPR. This thesis outlines several important considerations and constraints of this method. Furthermore we provide CPR measurements of a superconductor-normal- superconductor (SNS) junction made from Nb and Cu. It shows a clear temperature dependence with a qualitative change in shape as well as a quantitative change in amplitude of the current-phase relation. These results are in agreement with theory. In the future a flux-locked loop can be used to further improve the measurements.Show less

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Measuring the current-phase relation of a Josephson junction