Abstract

We present in vivo images of the human brain acquired with an ultralow field magnetic resonance imaging (ULF-MRI) system operating at a field B0 ≈ 130 microtesla. The system features pre-polarization of the proton spins at a field Bp ≈ 0.1 T and detection of the nuclear magnetic resonance signals with a SQUID-based, superconducting, second-derivative gradiometer. We report measurements of the longitudinal relaxation time T1 of brain tissue, cerebrospinal fluid (CSF), blood and scalp fat at both B0 and Bp. These measurements enable us to construct inversion recovery sequences that we combine with a Carr-Purcell-Meiboom-Gill (CPMG) echo train to obtain images in which any given tissue can be nulled out and another tissue highlighted. Such techniques greatly enhance the already high intrinsic T1-contrast obtainable at ULF. We illustrate the power of this technique with an image showing only the superior sagittal sinus, with other components eliminated. We further show that, as expected at ULF, the transverse relaxation time T2 approaches T1 in all four brain components. We present T2-weighted images that with our technique can be acquired in about 20% of the time required for T1-weighted images and comparable tissue contrast. With the use of multiple sensors, for example, those in a SQUID-based system for magnetic source imaging, we believe these techniques would enable one to obtain high-contrast imaging of the components of the brain, including the visualization of brain tumors without the need of a contrast agent.

Abstract

Superconducting quantum computing is now at an important crossroad, where “proof of concept” experiments involving small numbers of qubits can be transitioned to more challenging and systematic approaches that could actually lead to building a quantum computer.  Our optimism is based on two recent developments: a new hardware architecture for error detection based on “surface codes”, and recent improvements in the coherence of superconducting qubits.  I will explain how the surface code is a major advance for quantum computing, as it allows one to use qubits with realistic fidelities, and has a connection architecture that is compatible with integrated circuit technology.  We have also recently demonstrated a universal set of logic gates in a superconducting Xmon qubit that achieves single-qubit gate fidelity of 99.92% and a two-qubit gate fidelity up to 99.4%. This places Josephson quantum computing at the fault-tolerant threshold for surface code error correction. Our quantum processor is a first step towards the surface code, using five qubits arranged in a linear array with nearest-neighbor coupling. Using this device we have further demonstrated generation of the five-qubit Greenberger-Horne-Zeilinger (GHZ) state using the complete circuit and full set of gates, giving a state fidelity of 82% and a Bell state (2 qubit) fidelity of 99.5%.  These results demonstrate that Josephson quantum computing is a high-fidelity technology, with a clear path to scaling up to large-scale, fault-tolerant quantum circuits.

Abstract

A number of awards and prizes were presented to outstanding individuals who have made significant contributions to the success of the field of applied superconductivity. The announcement of the recipients of these awards and prizes was made during the ASC 2014 Opening Session.

The following awards are presented in this video:

• The IEEE Award for Continuing and Significant Contributions in the Field of Applied Superconductivity
• The IEEE Dr. James Wong Award for Continuing and Significant Contributions to Applied Superconductor Materials Technology
• The IEEE Max Swerdlow Award for Sustained Service to the Applied Superconductivity Community
• The IEEE Council on Superconductivity Carl H. Rosner Entrepreneurship Award
• The IEEE Council on Superconductivity Van Duzer Prize
• Cryogenic Society of America Roger W. Boom Award

Abstract

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 (ULF-MRI) 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 pre-polarized proton spins and signal detection with a SQUID. A particular advantage of ULF-MRI 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 ULF-MRI systems is expected to reduce the imaging time by an order of magnitude. Potential clinical applications include imaging tumors and traumatic brain injury.

Abstract

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 1970s, 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.

More information provided here.

More information provided here.

Abstract

We have developed compact, fast and easy-to-use dc SQUID-based noise thermometers for the temperature range accessible with dilution refrigerators, i.e., from ca. 1K to 1mK. Two implementations have been realized: Magnetic Field Fluctuation Thermometers and Current Sensing Noise Thermometers. In both thermometers, the thermally induced motion of charge carriers in metallic temperature sensors cause thermal magnetic flux noise. SQUID sensors optimized for the detection of this noise are employed, and the sought temperature is extracted from the thermal noise power spectrum using the Nyquist theorem. For the calibration of the thermometers, one reference measurement at a known temperature suffices. We have developed a procedure for reference measurements with direct traceability to the Provisional Low-Temperature Scale (PLTS)-2000 as well as methods to determine the uncertainty of the temperature estimates. SQUID sensor design, thermal anchoring and electromagnetic shielding of our SQUID noise thermometer configurations will be discussed and validation measurements in comparison with the PLTS-2000 will be presented. The results of the validation measurements attest the high linearity, accuracy and speed of our noise thermometers. The devices exhibit noise temperatures below 0.1mK, and estimates of the sought temperature with relative uncertainties of <1% are obtained within measurement times of a few seconds.

Abstract

We present our LTS SQUID magnetometer system which contains two SQUID triples with different effective areas. The system was developed to measure the signals of the transient electromagnetic method as well as weak natural fluctuations of the Earth magnetic field. The sensors are produced in our recently introduced technology using sub-m Josephson junctions. They provide very high sensitivity which is difficult to be measured directly. Especially, in the low-frequency range, one has to deal with strong external disturbances. In this work, two methods to estimate the noise from measurements in the Earth's magnetic field at a magnetically quiet site are described. The achieved results are compared to measurements in superconducting and magnetic shielding.

Abstract

SQUIDs can be used for a new technology for ultra-sensitive magnetic detection and imaging of tissue cells marked using superparamagnetic nanoparticles. The detection limit of this technique can be as low as 10,000 cells. By comparison, state of the art spiral X-ray CT requires over 1 million cancerous cells for detection. This method consists of targeting cells using antibody labeled nanoparticles, followed by detection and imaging of the targeted area using a high-resolution SQUID-based gradiometer array. Super-paramagnetic relaxometry (SPMR) is used for detection of targeted cells with high specificity: only bound nanoparticles will be detected via Neel relaxation. The binding occurs only with cancer cells because of specific antibodies conjugated to the nanoparticle surface. By combining SPMR with ultra-low field magnetic resonance imaging (ULF MRI), using the same instrument, the targeted area can be imaged to provide anatomical information. The same magnetic particles work as MRI contrast agents. The combination of ULF MRI and SPMR provide both accurate localization and cell count of the targeted tissue. This approach provides a robust diagnostic tool for the detection and localization of cancerous tissue targeted with magnetic markers at a very early disease stage. ULF MRI and SPMR measurements have never been combined before in a single device. We will describe our design of such a combined SQUID-based instrument, and present our first experimental results of combined SPMR and ULF MRI on phantoms.

Abstract

We present in vivo images of the human brain acquired with an ultralow field magnetic resonance imaging (ULF-MRI) system operating at a field B0 130 microtesla. The system features pre-polarization of the proton spins at a field Bp 0.1 T and detection of the nuclear magnetic resonance signals with a SQUID-based, superconducting, second-derivative gradiometer. We report measurements of the longitudinal relaxation time T1 of brain tissue, cerebrospinal fluid (CSF), blood and scalp fat at both B0 and Bp. These measurements enable us to construct inversion recovery sequences that we combine with a Carr-Purcell-Meiboom-Gill (CPMG) echo train to obtain images in which any given tissue can be nulled out and another tissue highlighted. Such techniques greatly enhance the already high intrinsic T1-contrast obtainable at ULF. We illustrate the power of this technique with an image showing only the superior sagittal sinus, with other components eliminated. We further show that, as expected at ULF, the transverse relaxation time T2 approaches T1 in all four brain components. We present T2-weighted images that with our technique can be acquired in about 20% of the time required for T1-weighted images and comparable tissue contrast. With the use of multiple sensors, for example, those in a SQUID-based system for magnetic source imaging, we believe these techniques would enable one to obtain high-contrast imaging of the components of the brain, including the visualization of brain tumors without the need of a contrast agent.

Abstract

Functional and structural information about the human brain can be obtained noninvasively with magnetoencephalography (MEG) and magnetic resonance imaging (MRI), respectively. MEG, which is based on the recording of the extracerebral magnetic fields, gives a direct measure (projection) of neuronal currents. On the other hand, MRI, in which polarized spin populations are manipulated and observed magnetically, provides 3-dimensional images of proton density and relaxation times. It was demonstrated recently (McDermott et al., PNAS 21, 78577861, 2004) that high-quality MRI is possible at magnetic fields as low as 100 microteslas if the sample is first polarized in a higher field and if SQUID sensors are used to detect the spin precession. Subsequently, it was demonstrated (Zotev et al., J. Magn. Reson. 194, 115120, 2008; Vesanen et al., Magn. Reson. Med. 2012, DOI 10.1002/mrm.24413) that MEG and ultra-low-field MRI (ULF MRI) can be performed with same SQUID sensor array; this guarantees that the coordinate systems of MEG and MRI are the same. In addition, the combination of the two techniques improves workflow. Advantages of ULF-MRI include high T1 contrast, the absence of susceptibility artifacts, quiet and safe operation, open structure, and relatively low cost when added to an MEG system. ULF-MRI may also be suitable for performing electrical impedance tomography (EIT) of the head; better knowledge of the conductivity structure, together with the error-free registration, could dramatically improve the accuracy of locating neuronal sources. The challenge in making combined MEG and MRI practical is to improve the data rate sufficiently. We need to improve SQUID sensitivity by a factor of 510 (to about 0.5 fT/sqrt[Hz]) and increase the pre-polarization field strength by a factor of 5 (to 100 mT or more). If we succeed in doing this in an array of several hundred sensors, clinically and scientifically useful MEG-MRI systems may be available within a few years.

Abstract

Gordon Bryce Donaldson was born in Edinburgh, Scotland on August 10, 1941, and died in Glasgow on November 28, 2012, at the age of 71. Gordon was an undergraduate student at Christ's College, Cambridge from 1959 to 1962 when he received his BA. He and Christine were married in 1962, shortly after his graduation. Subsequently, he was a research student at the Royal Society Mond Laboratory, Cambridge from 1962 to 1965, when he received his Ph.D. Under the supervision of John Adkins, Gordon measured the energy gap in Zn-ZnO-Zn tunnel junctions and investigated the subgap quasiparticle resistance of Al-AlOx-Ag tunnel junctions as an ultralow temperature thermometer. Immediately after receiving his Ph.D., Gordon became a Lecturer in the Physics Department at the newly created Lancaster University. He spent 1974 1975 on sabbatical leave at the University of California, Berkeley where, together with Mark Ketchen, Wolf Goubau and John Clarke, he developed the first thin-film, planar gradiometer based on a dc SQUID (Superconducting QUantum Interference Device). In 1975, Gordon returned to Scotland as a Lecturer in the Department of Applied Physics at the University of Strathclyde, Glasgow. In 1985 he became Professor of Applied Physics, a position he occupied until his retirement in 2006. On his arrival in Glasgow Gordon quickly established a new research group to make SQUIDs for useful applications. From modest beginnings with two staff and one tiny laboratory, the group grew steadily until, at its peak, it had approaching thirty members, plus a host of collaborators worldwide. He and colleagues at Glasgow University and the city's Southern General Hospital secured substantial funding from the Wellcome Trust to set up a new biomagnetism facility in 1988 on the hospital campus, using SQUID gradiometers made at Strathclyde for measurements on patients and volunteers. Studies over ten years included fetal, stereopsis and spinal and peripheral nerve measurements. Another of his main research interests was the use of SQUIDs for non-destructive evaluation (NDE), targeted at defects in aluminum and carbon-fiber aircraft components. This started long before the discovery of high-temperature superconductors (HTS), initially with wire-wound gradiometers and niobium SQUIDs, but soon progressed to miniature thin-film niobium integrated SQUID gradiometers, made in the dedicated facility at Strathclyde. This was followed by major programs to develop and demonstrate HTS gradiometers for NDE, supported by a pulsed laser deposition system developed in the Group to grow HTS films and bi-crystal junctions. Notable advances included the development of semi-portable NDE systems for use on curved surfaces and the application of neural nets to the interpretation of defects in carbon fiber composites. Gordon was very active within the superconducting community. He organized the International Superconductivity Conference (ISEC) at the University of Strathclyde in 1991. He was Coordinator for the UK Committee on High-Transition Temperature Superconductivity. In 1991 he founded the Cambridge Winter School in Superconductivity to train junior researchers from the UK and overseas. He was Chair of the Low-Temperature Group of the Institute of Physics, London. He spent productive sabbatical leaves at the University of Virginia in 1982 and at CSIRO in Sydney in 1999. His many achievements were recognized by his election as a Fellow of the Royal Society of Edinburgh in 1991. Gordon is survived by his wife, Christine, by his children, Ian and Anne, and by two grandchildren. We are grateful to Ian and Anne Donaldson for their help in preparing this remembrance.

Abstract

Gordon Bryce Donaldson was born in Edinburgh, Scotland on August 10, 1941, and died in Glasgow on November 28, 2012, at the age of 71. Gordon was an undergraduate student at Christ's College, Cambridge from 1959 to 1962 when he received his BA. He and Christine were married in 1962, shortly after his graduation. Subsequently, he was a research student at the Royal Society Mond Laboratory, Cambridge from 1962 to 1965, when he received his Ph.D. Under the supervision of John Adkins, Gordon measured the energy gap in Zn-ZnO-Zn tunnel junctions and investigated the subgap quasiparticle resistance of Al-AlOx-Ag tunnel junctions as an ultralow temperature thermometer. Immediately after receiving his Ph.D., Gordon became a Lecturer in the Physics Department at the newly created Lancaster University. He spent 1974 1975 on sabbatical leave at the University of California, Berkeley where, together with Mark Ketchen, Wolf Goubau and John Clarke, he developed the first thin-film, planar gradiometer based on a dc SQUID (Superconducting QUantum Interference Device). In 1975, Gordon returned to Scotland as a Lecturer in the Department of Applied Physics at the University of Strathclyde, Glasgow. In 1985 he became Professor of Applied Physics, a position he occupied until his retirement in 2006. On his arrival in Glasgow Gordon quickly established a new research group to make SQUIDs for useful applications. From modest beginnings with two staff and one tiny laboratory, the group grew steadily until, at its peak, it had approaching thirty members, plus a host of collaborators worldwide. He and colleagues at Glasgow University and the city's Southern General Hospital secured substantial funding from the Wellcome Trust to set up a new biomagnetism facility in 1988 on the hospital campus, using SQUID gradiometers made at Strathclyde for measurements on patients and volunteers. Studies over ten years included fetal, stereopsis and spinal and peripheral nerve measurements. Another of his main research interests was the use of SQUIDs for non-destructive evaluation (NDE), targeted at defects in aluminum and carbon-fiber aircraft components. This started long before the discovery of high-temperature superconductors (HTS), initially with wire-wound gradiometers and niobium SQUIDs, but soon progressed to miniature thin-film niobium integrated SQUID gradiometers, made in the dedicated facility at Strathclyde. This was followed by major programs to develop and demonstrate HTS gradiometers for NDE, supported by a pulsed laser deposition system developed in the Group to grow HTS films and bi-crystal junctions. Notable advances included the development of semi-portable NDE systems for use on curved surfaces and the application of neural nets to the interpretation of defects in carbon fiber composites. Gordon was very active within the superconducting community. He organized the International Superconductivity Conference (ISEC) at the University of Strathclyde in 1991. He was Coordinator for the UK Committee on High-Transition Temperature Superconductivity. In 1991 he founded the Cambridge Winter School in Superconductivity to train junior researchers from the UK and overseas. He was Chair of the Low-Temperature Group of the Institute of Physics, London. He spent productive sabbatical leaves at the University of Virginia in 1982 and at CSIRO in Sydney in 1999. His many achievements were recognized by his election as a Fellow of the Royal Society of Edinburgh in 1991. Gordon is survived by his wife, Christine, by his children, Ian and Anne, and by two grandchildren. We are grateful to Ian and Anne Donaldson for their help in preparing this remembrance.

Abstract

Superconducting digital electronics, based on the Josephson effect, in the former Soviet Union - from 1967 to 1991.

The research efforts by several academic and industrial groups included the catch-up work on latching logic and memory, the original design of non-latching Josephson cryotrons, and the conceptual development of single-flux-quantum devices circuits. The latter work has eventually led to the invention of reversible parametric-quantron circuits in 1975, and ultrafast RSFQ logic in 1985.

Abstract

In 1962 Brian Josephson predicted that a superconducting tunnel junction subjected to microwave radiation of frequency f will produce voltages quantized in units of hf/2e, where h is the Planck constant and e is the elementary charge.

This ac Josephson effect was of immediate interest to metrology because it relates voltage (a poorly known quantity) to frequency (known to high accuracy) through two fundamental constants. The basic effect was verified experimentally by Sidney Shapiro, and the predicted quantization was subsequently shown to be of metrological accuracy by Don Langenberg and collaborators, among others.

Thus, in 1972 the ac Josephson effect was adopted internationally as a practical standard of voltage, becoming the first quantum electrical standard. Today, series arrays including as many as 300,000 Josephson junctions produce quantized dc voltages well in excess of 10 V and are used in measurement laboratories around the world. In addition, pulse-driven junction arrays have been used to generate highly accurate ac waveforms. The metrological community now anticipates that the Josephson volt and the quantum Hall resistance will soon lead to a redefinition of the SI units that eliminates the kilogram as a base unit and rids the system of its last remaining artifact standard.

Abstract

In 1964, Jaklevic, Lambe, Silver, and Mercereau demonstrated quantum interference in a superconducting ring containing two Josephson tunnel junctions. The following year saw the appearance of the SLUG (Superconducting Low-inductance Undulatory Galvanometer)_a blob of solder frozen around a length of niobium wire_that was used as a voltmeter with femtovolt resolution. Although primitive by today's standards, the SLUG was used successfully in a number of ultrasensitive experiments, including a comparison of the Josephson voltage-frequency relation in different superconducting materials and the detection of charge imbalance in superconductors.

A full theory of the dc SQUID (Superconducting QUantum Interference Device) appeared in 1977.

Today, the square washer dc SQUID with an integrated input coil finds a wide range of applications. SQUIDs are used in a variety of configurations_for example, magnetometers, gradiometers, low-frequency and microwave amplifiers, and susceptometers_in applications including magnetoencephalography, magnetocardiography, geophysics, nondestructive evaluation, standards, cosmology, reading out superconducting quantum bits, and a myriad of one-of-a-kind experiments in basic science. Experiments are described to hunt for the axion_a candidate for cold dark matter_ and to perform magnetic resonance imaging in microtesla magnetic fields.

Abstract

Arnold H. Silver presents a first-hand account of three pioneering experiments, embedding two Josephson tunnel junctions in thin film multiply connected superconducting circuits, illustrated: Two-junction interference superimposed on single junction Fraunhofer diffraction. The Aharonov-Bohm effect of a vector potential in a magnetic field-free region, Kinetic inductance in thin superconducting films via superconducting pair de-Broglie waves.

The first experiments demonstrating macroscopic quantum interference in superconductors were performed in 1962 and 1963 at the Ford Motor Company Scientific Laboratory as the analog of two-slit interference.

 These experiments followed some unusual microwave observations in superconductors and the demonstrations of flux quantization in superconductors and the Josephson junction. Following these experiments, our efforts shifted to bulk niobium structures using "point-contact" junctions as prototype Josephson junctions, resulting in the invention of the dc (two-junction) and rf (one-junction) Superconducting Quantum Interference Devices, which we named SQUIDs. I will present a first-hand account of the unique sequence of events that led to these discoveries and inventions.

Abstract

Confirmed experimentally in 1963, Brian Josephson's predictions that both direct and alternating supercurrents flow through a tunnel barrier between two superconducting films were a key breakthrough in the development of superconductivity applications. Electron tunneling in such junctions had been reported in 1960 by Giaever and the group at A. D. Little. Using copies of entries in my Bell Labs notebooks, I will show how, in a collaboration with P. W. Anderson, the direct supercurrent and its dependence on small magnetic fields was observed in January 1963. The alternating supercurrent was observed by S. Shapiro a few months later. Early in 1964, following experiments by R. D. Parks and J. M. Mochel, Anderson extended the Josephson Effects from tunnel junctions to weak superconducting links.

Abstract

Brian Josephson Debates John Bardeen. Mathematics versus intuition, the vitality of youth versus prestige and maturity; that was the essence of the spectacle of the debate between the graduate student and the Nobel Laureate when Josephson and Bardeen faced-off in London in 1962. Josephson was fascinated by the reality of the phase in the wavefunction of superconductivity, as demonstrated by magnetic flux quantization; could there be other manifestations of the phase? He was intrigued by a Cohen, Falicov, and Phillips paper on tunneling theory and quickly set about applying it to superconductors. At the time the prevailing view in his laboratory, as expressed by his graduate adviser Brian Pippard, was that a single electron had a low probability of tunneling; thus two electrons tunneling simultaneously would be rare indeed. Surprisingly, Josephson's mathematics told him otherwise. Bardeen argued that the math was wrong. Shortly thereafter, experiments by Philip Anderson and John Rowell decided the issue in favor of Josephson; for tunneling, mathematics beat intuition.