Superconducting quantum interference devices SQUIDS

The main hardware types offered by physics are mentioned, namely trapped ions (or trapped atoms), quantum dots, quantum optical cavities, rf superconducting quantum interference devices (SQUIDs) and nitrogen-vacancy (NV) defects on diamond. Some are important simply as a benchmark to evaluate the quality of the implementations offered by chemistry, whereas others might be combined with lanthanide complexes to produce heterogeneous quantum information processors which combine the advantages of different hardware types. 

The superconducting quantum interference device (SQUID) is formed from a superconducting loop containing at least one Josephson junction. Basically, a SQUID amplifier converts an input current to an output voltage with a transresistance of the order of 107 V/A. The input noise is of the order of 10-11 A/(Hz)1/2. The bandwidth of the SQUID amplifier can be up to 80kHz. The dynamic range in 1 Hz bandwidth can be 150dB. 

An application of Josephson junctions is in superconducting quantum interference devices (SQUIDS). Figure 4.61 shows two Josephson junctions passing a current with a magnetic induction B, through the ring of area A. 

Fig. 4.61 Two Josephson junctions comprising a superconducting quantum interference device (SQUID).

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