Recorded at the 2018 Applied Superconductivity Conference, this presentation provides a survey of the activities in quantum computing research and development in the United States, inlcuding those carried in academic institutions, industrial research laboratories, as well as government research laboratories.

This plenary session was recorded at the 2018 Applied Superconductivity Conference.

The observations of gravitational waves from the mergers of compact binary sources opens a new way to learn about the universe as well as to test General Relativity in the limit of strong gravitational interactions – the dynamics of massive bodies traveling at relativistic speeds in a highly curved space-time. This lecture describes some of the difficult history of gravitational waves proposed about 100 years ago. The concepts used in the instruments and the methods for data analysis that enable the measurement of gravitational wave strains of 10-21 and smaller are presented. The results derived from the measured waveforms, their relation to the Einstein field equations and the astrophysical implications are discussed. The talk ends with a vision for the future of gravitational wave astronomy.

The universe is believed to be permeated by an unknown substance named Dark Matter because it is not visible, interacting extremely weakly with ordinary matter while revealing its existence only through gravitational effects. One of the leading candidates is the axion particle, a pseudo-scalar, similar to the scalar Higgs particle, but much lighter in mass. Axions were also invented to cure a major theoretical defect in strong interactions, that of time reversal violation. Even though the theory of Quantum Chromo Dynamics (QCD, i.e., the theory describing Strong Interactions) works very well, its prediction on time reversal violation is not followed by ten orders of magnitude, as evidenced by the absence of CP-violation in the neutron particle. Axions oscillate at one, albeit unknown, frequency and softly mix with photons whenever a magnetic field is present creating a very faint oscillatory electric field. A 10T magnetic field would generate an oscillatory electric field of order 1pV/m, which in the presence of a high-quality resonator can be significantly enhanced when its frequency coincides with the resonator frequency. Since we don’t know the axion frequency we need to scan all possible frequencies, effectively having to call all the numbers in a large volume phone-book one number at a time. Each phone call would have to last more than 1 minute to have a chance of finding out whether that number is the right one. The scanning rate goes as the magnetic field strength to the fourth power times the resonator volume squared. The axions have eluted discovery for more than thirty five years since they were conceived to be the dark matter, but recent progress in several technological fronts, one of the most important ones being in superconducting magnet technology, give us renewed hope.

There is a revolution in the super-conducting magnet technology: High Temperature Superconducting (HTS) and Low Temperature Superconducting (LTS) cables based on Nb3Sn are becoming more common. This presentation will describe how researchers at the Center for Axion and Precision Physics Research are planning to use the current technology of HTS and LTS from pioneering institutions around the world to finally pin down and discover the axion frequency. Once the frequency is found, then many institutions around the world will be able to launch an axion dark matter experiment and the era of axion astro-physics will be born. The super-conducting magnet technology is a fundamental aspect of this plan.

Numerous astrophysical measurements indicate that much of our universe is made of an undiscovered type of matter, termed 'Dark Matter'. The axion is a hypothetical particle that is a well-motivated candidate for dark matter inspired by the Peccei-Quinn solution to the Strong-CP problem in Nuclear Physics. After decades of work, the US DOE flagship axion dark matter search, ADMX G2, is the first experiment to be sensitive to plausible DFSZ coupling model of dark matter axions, in part due to the addition of superconducting quantum-limited amplifiers. ADMX G2 has begun to search the theoretically-favored axion mass region 2-40 micro-eV, and could now discover dark matter at any time. This presentation will report the first results from exploring the range around 2.7 micro-eV last year (2018), discuss this year's (2019) operations and review the ADMX G2 plans to continue the search to cover the entire mass range.

Acknowledgments: This work was supported by the US Dept. of Energy, High Energy Physics (Awards DE-SC0011665 & DE-SC0010280 & DE-AC52-07NA27344)

Low temperature superconductors (LTS) require liquid helium, yet can only generate a magnetic field lower than 24 T. For full-fledged commercialization of superconducting equipment, high temperature superconducting (HTS) conductors are preferred as they can be cooled by the more cost-efficient liquid nitrogen and they can generate a much higher magnetic field, such as 30 T at 4.2 K. However, one of the major drawbacks of the HTS conductor is its short maximum length of a single conductor wire, typically <500 m. Thus, many joints need to be installed in the superconducting equipment, resulting in a difficult manufacturing process and a complicated operating procedure. Thus, Japan commenced a 10-year JST-MIRAI Program in 2017, focusing on developing the joint technology for linking HTS conductors. The program has two important research and development directions:
(1) Development of improved superconducting joints for a persistent-mode 1.3 GHz NMR magnet, i.e. the Super-High Field NMR Initiative. As the first stage, superconducting joints (10^(-13) Ω) between HTS conductors, such as REBCO[1] and Bi-2223, and HTS and NbTi [2] are being developed, which will be installed in the world’s highest magnetic field (30.5 T) NMR magnet [3], operated at a 1H NMR frequency of 1.3 GHz in the persistent-mode. Based on NMR spectra achieved with the 1.3 GHz NMR for protein samples such as amyloid-beta, the feasibility and validity of the superconducting joints and the NMR magnet will be evaluated.
(2) Development of ultra-low resistance joints between superconducting DC feeder cables for railway systems [4]. As the first step , ultra-low resistive joints (10^(-9) Ω) between superconducting DC feeder cables, > 100 mm in diameter, for railway systems will be developed; the DC cable is comprised of many HTS tapes and cooled by liquid nitrogen flow. It enables the on-site joining process between superconducting DC feeder cables. It will be evaluated by the operational test of a train fed by the joined superconducting DC cables in the Railway Technical Research Institute.
This presentation will describe, (a) a brief review of the JST-MIRAI Program, (b) initial results of the investigation on superconducting joints, (c) preliminary results for the medium field persistent NMR magnets, and (d) current status of the joints between DC feeder cables for railway systems.

[1] K. Ohki, et al., Supercond. Sci. Technol. 30, 115017, 2017.
[2] R. Matsumoto, et al., Applied Physics Express 10.9, 093102, 2017.
[3] H. Maeda et al., eMagRes 5, 1109-1120, 2016.
[4] M. Tomita et al., Energy 122, 579-587, 2017.

Acknowledgments: This work was supported by JST-MIRAI Program Grant Number JPMJMI17A2, Japan.

Dramatic progress has been made in the last decade and a half towards realizing solid-state systems for quantum information processing with superconducting quantum circuits. Artificial atoms (or qubits) based on Josephson junctions have improved their coherence times more than a million-fold, have been entangled, and used to perform simple quantum algorithms. The next challenge for the field is demonstrating quantum error correction that actually improves the lifetimes, a necessary step for building more complex systems. At Yale Prof. Schoelkopf’s group and colleagues have been pursuing a hardware-efficient approach for error correction that relies on encoding information in a superconducting cavity, the so-called “cat codes.” With this approach, the Yale group has applied real-time measurements and feedback to achieve the first extension of the lifetime of a quantum bit through error correction. For scaling, an attractive approach is the modular architecture, in which small quantum processors are networked together using microwave signals on superconducting transmission lines. This presentation will describe the first implementation of a teleported C-NOT gate, which is a key building block for the modular approach.

The Large Hadron Collider (LHC) represents the last big step in particle accelerators for high energy physics. This machine follows three previous generations at increasing energies of complementary particle accelerators: exploratory proton-proton machines and more precise electron-positron machines. The next big step for particle physics is to build the companion electron-positron collider to the CERN Large Hadron Collider, in order to carry out precision studies of the Higgs Boson and other new physics. The leading candidate machine is the proposed International Linear Collider, which will be based on superconducting RF technologies. In this presentation, the technical features of the ILC and the physics potential are discussed.

The use of HTS in Mobility and in Power Technology is not a goal by itself. This plenary presentation will consider general and fundamental aspects and correlations in the respective field and enlighten the basic relations - not requiring the audience to be deep dive experts in the field, but aiming to provide some new insights for everyone. HTS in general is a quite well known phenomenon to many potential end users; some of them have been in touch with HTS during the bloom of 1G-HTS already. Due to the fact that the HTS materials and wires have made extremely good progress in the last years it is important to educate the engineers active in the field and in conventional business on changed and actual boundary conditions and chances. Depending on the specific application in Mobility and Power Technology, the key success properties of HTS and device will vary a lot, and we will try to provide some take-aways to sharpen the awareness and provide some clues to assess the wisdom of a HTS based device. Despite the progress in HTS performance, there are still white spots needing development efforts. These needs are in even more improved performance and/ or in research for new solutions. The presentation will try to sketch some ideas for future optimized devices.

Because of their complexity on length scales from atomic disorder to macroscopic cables, the development of the high performance superconductors relies on accurate characterization of their micro- and macrostructures. Furthermore, the performance of superconductors is often limited by structural and chemical inhomogeneities, both locally and over long lengths, that provide particular challenges for techniques that often sample only small volumes of material. In this talk, Dr. Lee demonstrates how key developments in our understanding of superconductors were made possible by combining quantitative microscopic and micro-chemical techniques with detailed characterizations of superconducting properties. As the community of researchers and engineers push our current generation of superconductors towards its limits, Dr. Lee looks at the new innovations in microscopy required to understand those limitations and provide us with the information we need to make the next generation of superconductor applications a reality.

Acknowledgments: This work was supported by the U.S. Department of Energy (Award Numbers DE-SC0012083 and SC0010690) and the State of Florida. A portion of this work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement No. DMR-1157490 (-2017) DMR-1644779 (2018-) and the State of Florida.