We control and monitor the state of the single superconducting vortex. Using our fastest thermometer in the nanoworld, we measured the thermal transient due to the vortex expulsion from the superconductor. An energy dissipated due to this expulsion is equivalent to the absorption of a single photon of the visible light. The magnetic field enters the type II superconductor in a mixed state in the form of thin flux filaments. In a very small core, in the center of the vortex, the material loses its superconducting properties, and a superconducting current circulates around the core to compensate for the external flux filaments field. The magnetic field flux of a vortex is equal to the quantum of the field flux h/2e, so the number of vortices depends on the intensity of the applied field, which the superconductor must compensate for in its volume. While the penetration of the magnetic field itself, as long as it does not create vortices in a large part of the superconductor, does not significantly affect its properties, the motion of the vortices can deteriorate or even prevent the operation of superconducting devices. In fact, the moving vortex is a non-superconducting current flowing in a volume of material that generates Joule heat. The reasons for the motion of the vortices are their electromagnetic interactions and interactions with electric current, which are the source of forces that detach the vortices from their pinning sites, for example, on the dislocation, in the volume of the material. Therefore, in order to design and realize superconducting devices using type II superconductors, such as high-temperature superconductors, some alloys of exotic metals, or sufficiently thin type I superconductors, it is very important to have a thorough understanding of the thermodynamics of the vortex network or the associated energy flow processes that occur with their participation. Even at low magnetic fields in a typical type II superconductor, many vortices can appear and interact with each other, making it often difficult to determine how much potential a single vortex has to weaken superconductivity. This is particularly important for nanostructures, where the influence of individual vortices can be significant. To better understand these phenomena, we constructed a nano-trap for a single vortex connected to a superconducting thermometer. The heat flow associated with vortex motion is so fast that no existing method of temperature measurement has been able to monitor and measure it. We used a cryogenic thermometer previously developed at the Instutute, which can respond to temperature changes on the order of a single nanosecond.

In our experiment, we set the vortex in motion using current pulses and then studied how this motion affected the temperature of the nanostructure. This allowed us to find out how much energy is released when a single vortex is expelled from the nanostructure. It turned out that the heat measured was equivalent to the energy of about 2 electron volts, or the energy of a single photon of visible light. This research is of considerable importance in the technology of superconducting quantum computers, where the moving vortices can be a serious problem for the operation of quantum bits. Our experiments also lay the foundation for the development of electronics based on superconducting vortices, where the carrier of information would be a single vortex instead of an electron.