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CRC Press eBooks

High-frequency and Digital Applications of the Josephson Effects

J. C. Gallop

Published Oct 19, 2017• 0 citations

Abstract

We have already seen, in Chapter 2 , that the complex response of a Josephson junction to applied electromagnetic radiation forms a basis for both broad-band and heterodyne detection modes, ranging from low frequencies to the far-infrared. Greater detail of actual working devices of this type will be given in this chapter. The second topic dealt with is digital applications of squid s. This is already a significant, and may in the future become a dominant, use of low-power superconducting technology. At first sight the contents of this chapter may seem to divide into two rather disconnected areas. However, logic devices have two important characteristics in common with radiation detectors: first, both involve very high-frequency operation, since slow digital devices are of little or no practical interest. Second, both applications demand the use of well characterised and reproducible small-area junctions with similar parameters. In what follows, more details of junction fabrication methods will be given than have been discussed earlier in the book. This reflects the fact that well defined junction properties are of the utmost importance in achieving high performance in these areas. It seems paradoxical that squid s, for all their unparalleled sensitivity, will operate very satisfactorily with far from ideal Josephson junctions. This is mainly because squid s have only been used in rather low-frequency applications, for which the low resistive and reactive impedances associated with poor-quality junctions do not limit performance.

DOI: 10.1201/9780203738887-6

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In Chapter 2 we made use of a hypothetical arrangement of a strongly coupled superconducting ring, interrupted by a region of weak superconductivity, to derive the essential features of the Josephson effects. In practice this same arrangement is actually employed as the basis of one of the most useful superconducting devices developed so far, the single-junction, or rf, squid . (As mentioned in the Introduction, squid is an acronym for Superconducting QUantum Interference Device.) Here the essential physics behind the operation of these important devices will be described, and in the following section the practical realisation of an rf squid with its associated readout electronics will be explained. Chapter 4 will treat in a similar way dc squid s, which are related devices possessing two weak links in a single ring, whose mode of operation is rather different.

In the realm of physics, a pivotal moment occurred six decades ago when Brian Josephson made a groundbreaking prediction, setting in motion a series of events that would eventually earn him the prestigious Nobel Prize eleven years later. This prediction centered around what is now known as the Josephson effect, a phenomenon with far-reaching implications. At the heart of this effect lies the Josephson junction (JJ), a device that has become a linchpin in various scientific applications. This chapter delves into the foundational principles of the Josephson effect and the remarkable properties of JJs. From their role in metrology to their application in radiation detectors, these junctions have ushered in a new era of electronics. Exploiting the unique features of superconductive devices, such as high speed, low dissipation, and dispersion, JJs find today practical implementation in the development of superconductive qubits and nanotechnology applications.

Barrier tunnelling devices based on the Josephson effect include superconducting quantum interference detectors (SQUID) in conventional and scanning forms. The use of a scanning SQUID detector to detect a half-flux quantum in a ring of Josephson junctions identifies d-wave superconductivity. The shunted Josephson junction is the basis for the rapid single flux quantum RSFQ class of superconducting logic circuits. The use of RSFQ to form fast analogue to digital ADC converter devices is reported. Various types of radiation detectors are described including SIS detectors, Josephson-effect detectors, and optical point-contact antenna devices.

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CSIRO is the Australian national science agency and has had a long-history in research and development of superconducting electronic devices and systems for various practical applications. In this paper, I will give a brief introduction about the Josephson junction technology and describe CSIRO’s research progress in developing various novel high-Tcsuperconducting (HTS) Josephson junction devices and their applied systems. Recently, CSIRO has led the frontier research and development of high-frequency HTS Josephson detectors and heterodyne mixers ranging from microwave, millimeter, to terahertz (THz) frequency bands. These high-frequency superconducting quantum sensors/devices have demonstrated superior performance and applied in sensing and communication systems.