Nano Superconducting Quantum Interference Device

Direct current Superconducting QUantum Interference Device (dc SQUID) is the most sensitive magnetic flux and field detector known so far. Due to the low operating temperature and quantum working principle, a SQUID exhibits an equivalent energy sensitivity that approaches the quantum limit. Recently, great efforts have been focused to the development of nanoSQUIDs, making such a nanosensor a powerful tool to study the magnetic properties of nanoparticles at a microscopic level. This chapter focuses on nanoSQUIDs and its applications, after discussing the principles on which the SQUID is based, namely the Josephson effect and flux quantization in a superconducting ring. One of the most important factors of merit of a SQUID device is the magnetic flux noise or more precisely the spectral density of magnetic flux noise. Depending on the quantity to be measured, a suitable SQUID sensor design needs to be employed. The chapter reports on the basic principle of the main SQUID configurations.