Ultra low noise YBCO nanoSQUIDs implementing nanowires

We present results on ultra low noise YBa${}_2$Cu${}_3$O${}_{7-\delta }$ nano Superconducting QUantum Interference Devices (nanoSQUIDs). To realize such devices, we implemented high quality YBCO nanowires, working as weak links between two electrodes. We observe critical current modulation as a function of an externally applied magnetic field in the full temperature range below the transition temperature $T_C$. The white flux noise below 1 $\mu \Phi_0/\sqrt{$\mathrm{H}\mathrm{z}$}$ at T = 8 K makes our nanoSQUIDs very attractive for the detection of small spin systems.