Josephson junctions Superconducting quantum

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. 

In 1962 a postgraduate student, Brian Josephson, working in the University of Cambridge, and later to win a Nobel Prize, predicted that Cooper pairs should be able to tunnel through a thin (approximately 1 nm) insulating barrier from one superconductor to another with no electrical resistance [46]. This quantum tunnelling was confirmed by experiment and is known as the Josephson effect . The superconducting electronic devices exploit Josephson junctions. 

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).

The simplest superconducting flux qubit is a superconducting loop interrupted by one Josephson junction (radiofrequency rf-SQUID - SQUID is an acronym for superconducting quantum interference device). The potential energy of such a devices is described by the equation ... 

A Josephson junction consists of two closely spaced superconductors separated by a weak connection (Figure 4.6.1). This connection may be provided by an insulator, a normal metal, a semiconductor, a weakened superconductor, or some other material that weakly couples the two superconductors. The two superconducting regions may be characterized by quantum mechanical wave functions and 2 respectively. Normally a much more complicated description would be necessary because... 

The next step in the development of high thin-film devices after the optimization of single layer films is the introduction of defects in precisely defined positions in order locally to alter the properties of the superconductor. The use of grain boundaries as Josephson junctions in SQUlDs (Superconducting Quantum Interference Devices) is an example of how defects can be utilized. 

V. Bouchiat, M. Faucher, C. Thirion, W. Wernsdorfer, T. Fournier, and B. Pannetier, Josephson junctions and superconducting quantum interference devices made by local oxidation of niobium ultrathin films, Appl. Phys. Lett, 79,123-125 [2001],... 

A superconducting quantum interference detector formed by two parallel Josephson junctions. 

We have considered here the influence of dispersion asymmetry and Zee-man splitting on the Josephson current through a superconductor/quantum wire/superconductor junction. We showed that the violation of chiral symmetry in a quantum wire results in qualitatively new effects in a weak superconductivity. In particularly, the interplay of Zeeman and Rashba interactions induces a Josephson current through the hybrid ID structure even in the absence of any phase difference between the superconductors. At low temperatures (T critical Josephson current. For a transparent junction with small or moderate dispersion asymmetry (characterized by the dimensionless parameter Aa = (vif — v2f)/(vif + V2f)) it appears, as a function of the Zeeman splitting Az, abruptly at Az hvp/L. In a low transparency (D Josephson current at special (resonance) conditions is of the order of yfD. In zero magnetic field the anomalous supercurrent disappears (as it should) since the spin-orbit interaction itself respects T-symmetry. However, the influence of the spin-orbit interaction on the critical Josephson current through a quasi-ID structure is still anomalous. Contrary to what holds... 

If a conventional superconductor (S) described by a s-wave order parameter symmetry (OPS) is put together with a non conventional superconductor (D), described by a pure d-wave OPS, to form two junctions in a superconducting loop, as indicated in Fig. 4, a self 7r — frustrated loop is achieved [van Harlingen 1995], Indeed, one of the two SD junctions behaves as a conventional "0" junction, since the Josephson coupling is between the positive lobe of the d-wave superconductor (white color in Fig. 4) and the S electrode on the contrary, the other junction is a V junction, because the coupling is now between the S electrode and the negative lobe. As a consequence, a shift of 7r along the loop is achieved and the device is self-frustrated by a half flux quantum. 

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