Superconductors can host quantized magnetic flux tubes surrounded by supercurrents, called Abrikosov vortices. Vortex penetration into a superconducting film is usually limited to its edges and triggered by external magnetic fields or local electrical currents. With a view to novel research directions in quantum computation, the possibility to generate and control single flux quanta in situ is thus challenging. We introduce a far-field optical method to sculpt the magnetic flux or generate permanent single vortices at any desired position in a superconductor. It is based on a fast quench following the absorption of a tightly focused laser pulse that locally heats the superconductor above its critical temperature. We achieve ex-nihilo creation of a single vortex pinned at the center of the hotspot, while its counterpart opposite flux is trapped tens of micrometers away at its boundaries. Our method paves the way to optical operation of Josephson transport with single flux quanta.
We propose the use of a laser beam tightly focused on a superconducting strip to create a Josephson junction by photothermal effect. The critical current of this junction can be easily controlled by the laser intensity. We show that a periodic modulation of the intensity substantially changes the dynamic properties of the junction and results in the appearance of Shapiro steps without microwave radiation. The experimental realization of optically driven Josephson junctions may open a way for the ultra-fast creation and switching of complex patterns of superconducting devices with tunable geometry and current-phase relations.A Josephson junction (JJ), consisting of two superconductors separated by a nonsuperconducting material (the so-called weak link) or a solid superconductor with an artificial constriction, is one of the key elements of modern cryogenic electronics, 1 quantum computing systems, 2,3 ultrasensitive electric and magnetic sensors 4 and other types of quantum devices. The non-dissipative electric current flowing through the junction is coupled with the phase difference between the gap potentials inside the superconducting electrodes, and the corresponding current-phase relation (CPR) ( ) determines all main static and dynamic characteristics of a Josephson system. 5,6 For basic JJs with an insulating or a normal metal weak link, the CPR is primary controlled by temperature and/or external magnetic field. Cooling the sample switches the CPR from a sinusoidal function to a linear one, while the magnetic field damps the critical current (the maximal current which can flow through the junction without dissipation) and induces peculiar Fraunhofer oscillations. 5 Even richer physics arise when the superconducting electrodes are separated by a ferromagnetic layer. 7 In contrast to the usual JJ with the zero phase in the ground state, ferromagnets allow to create -junctions with a spontaneous ground state phase = 8,9 or even 0 -junctions with = 0 ≠ 0, . The latter possibility requires a strong spin-orbit coupling 10,11 or a large spin splitting of the electron energy bands due to the exchange field. 12,13 By applying an external magnetic field and changing the exchange field orientation, one can tune 0 , which opens new perspectives for the elements of the rapid single flux-quantum logics. 1,14,15 However, in all existing types of tunable JJs, the weak link needs to be embedded into the system during the fabrication process and can hardly be tuned afterwards. The versatility and performance of Josephson devices would greatly benefit from simple methods to tune in situ the CPR of the built-in JJs and eliminate fabrication inhomogeneities.
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