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SQUIDs 50th Anniversary - Special Session at Applied Superconductivity Conference 2014 (ASC 2014)

SQUIDs in Electronics

Presenter: Arnold Silver

The first superconducting circuit employing Josephson junctions was published in 1964 and subsequently named SQUID (Superconducting Quantum Interference Device).  The SQUID has matured over the ensuing 50 years and is the most widely recognized superconductor electronic sensor.  Starting with IBM’s Josephson computer project in the 1970’s, SQUIDs became the basic building block in low temperature superconductor integrated circuits for analog-to-digital conversion, digital computing, cryogenic detector array readout, mixed signal and microwave integrated circuits, and quantum information systems.  This presentation will focus on the role of SQUIDs in these integrated circuit applications.

The Ubiquitous SQUID

Presenter: John Clarke

The Superconducting QUantum Interference Device (SQUID) is 50 years old this year. Since its beginnings as a primitive device confined to a handful of cryogenics laboratories, the SQUID has evolved into a sensor able to detect exquisitely tiny signals generated by sources in a rich variety of disciplines. Today’s SQUIDs are fabricated on a wafer scale with high reproducibility using photolithographic or electron-beam patterning techniques. Although there are many different SQUID designs, the workhorse dc SQUID consists of a thin-film Nb loop interrupted by two Nb-AlOx-Nb tunnel junctions. When the SQUID is biased in the voltage state, a magnetic flux applied to the loop causes the voltage to oscillate with a period of one flux quantum. Suitable electronics enables one to resolve changes in flux corresponding to a millionth of a flux quantum—or even less—in one second. Coupled to an appropriate input circuit, the SQUID can detect tiny changes in, for example, magnetic field, magnetic field gradient, magnetic susceptibility, voltage, position and temperature. SQUID amplifiers operate at frequencies extending into the microwave regime, with quantum limited noise performance. SQUIDs find applications in physics, chemistry, biology, medicine, materials science, nondestructive evaluation, geophysics, cosmology, astrophysics and quantum information.  The Axion Dark Matter eXperiment (ADMX) at the University of Washington, Seattle is designed to search for the axion, a candidate for cold dark matter. The detector consists of a cooled microwave cavity surrounded by a 7-T superconducting magnet. In the presence of a magnetic field the axion is predicted to decay into a photon, which, if its frequency is on resonance with a cavity mode, couples energy into an antenna inserted into the cavity. In the prototype detector, the cavity temperature was about 2 K and the signal was amplified by a cooled semiconductor amplifier. In the version to begin operation in 2014, the cavity will be cooled to 0.1 K and the signal will be amplified by a quantum limited SQUID, increasing the axion search rate by three orders of magnitude.   Ultralow field magnetic resonance imaging (ULFMRI) in magnetic fields of the order of 0.1 mT—four orders of magnitude lower than in conventional MRI systems—is enabled by the combination of prepolarized proton spins and signal detection with a SQUID. A particular advantage of ULFMRI is that the longitudinal relaxation time is more sensitive to different tissue types than high field MRI. Furthermore, this tissue contrast can be enhanced by a careful choice of imaging frequency, typically a few kilohertz. The next generation of ULFMRI systems is expected to reduce the imaging time by an order of magnitude. Potential clinical applications include imaging tumors and traumatic brain injury.

The Commercialization of SQUIDs

Presenter: Robert Fagaly

Within a few years of Josephson’s seminal paper on superconducting tunneling, devices were being fabricated to measure a wide variety of electromagnetic quantities. Before the end of the decade, SQUID devices were being offered for sale. In the 1970’s, SQUIDs began transitioning from laboratory instruments to applications in medicine, geology and materials science. Over the last 40 years of commercial sales, SQUID systems have generated well over a half billion dollars in product revenues. This paper discusses the evolution of the many small businesses that began to offer SQUIDs as commercial products, their product areas and their successes and failures.

Biosensing Using SQUID and Magnetic Markers

Presenter: Keiji Enpuku

In this talk, I will review recent progress in biosensing using SQUID and magnetic markers. Magnetic markers consisting of polymer-coated magnetic nanoparticles have been widely used for biomedical applications. In biomedical diagnosis, a detecting antibody, which is conjugated on the surface of the marker, is bound to a biological target. The binding reaction between them is detected with the magnetic signal from the bound markers. Since the signal from the bound markers becomes very weak at early stage of disease, it is necessary to develop highly sensitive detection system.  Several SQUID systems have so far been developed for this purpose. Measurement methods, including AC susceptibility, harmonic signal, magnetic relaxation and remanence, have also been developed, depending on the properties of the markers. The SQUID systems have been applied to both in vitro and in vivo diagnosis and high sensitivity of the system has been successfully demonstrated by the detection of several disease-related proteins. For in vitro diagnosis, magnetic immunoassay techniques have been developed for liquid-phase detection of biological targets. With this method, we can magnetically distinguish bound and unbound (free) markers by using the Brownian relaxation of the markers.  As a result, we can eliminate time-consuming washing processes for marker separation, unlike the case of the conventional optical method. This method also allows the study of how the binding of targets and markers proceeds in time, i.e., perform a quantitative evaluation of the binding kinetics.    For in vivo diagnosis, the position and quantity of the markers, which have accumulated in the affected area inside an animal or human body, are detected. This method is called magnetic particle imaging (MPI). When we apply MPI to the detection of breast cancer or sentinel lymph node, it is necessary to detect the markers locating at 3 to 5 cm in depth. The small amount of markers, e.g. 1 μg, should be detected with reasonable spatial resolution. Several systems have been developed for this purpose. 

Push the Limits in Exploration - SQUIDs in Geophysics

Presenter: Ronny Stolz

50 years of incessant SQUID research afford a good opportunity to ask for the impact that SQUIDs have made on the general technical progress. This paper highlights the SQUID applications in geophysics and in particular the efficient and eco-friendly exploration of the Earth’s resources, where SQUID technology provides a fundamentally new approach and allows acquiring qualitatively new data sets. After a brief introduction into the history of SQUIDs in geophysics, two applications and according examples will be introduced and discussed which are making impact in mineral exploration today: transient electromagnetics and full tensor gradiometry. A short outlook of the exciting opportunities and perspectives of the use of SQUIDs in other geophysical applications in years to come will be presented. 

SQUIDs and Superconducting Detectors for B-mode Cosmology in the Era of BICEP-2

Presenter: Kent Irwin

SQUIDs and superconducting detectors are now widely deployed in cosmic microwave background (CMB) telescopes, which has led to a dramatic improvement in the sensitivity of CMB measurements. The BICEP-2 experiment at the South Pole recently reported the most sensitive measurement to date of the polarization of the CMB, and the first detection of a curl, or "B-mode" pattern in the polarization of the CMB at degree angular scales. Primordial B-mode polarization is the distinctive signature of gravitational waves from inflation at the energy scale of Grand Unification, but additional non-primordial sources of B-mode polarization also exist, including polarized dust and gravitational lensing. I will describe the role of SQUIDs and superconducting detectors in reaching this important milestone, and their use in efforts to further understand B-mode signals in the CMB. Constraints on both primordial and gravitational-lensing B-mode signals will play an increasingly important role in our understanding of inflation, the properties of neutrinos, and the fundamental physics of the universe.