http://absimage.aps.org/image/MAR05/MWS_MAR05-2004-005765.pdf

Superconducting quantum bits

We summarize progress in the development and application of metamaterial structures utilizing superconducting elements. After a brief review of the salient features of superconductivity, the advantages of superconducting metamaterials over their normal metal counterparts are discussed. We then present the unique electromagnetic properties of superconductors and discuss their use in both proposed and demonstrated metamaterial structures. Finally we discuss novel applications enabled by superconducting metamaterials, and then mention a few possible directions for future research.

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The physics and applications of superconducting metamaterials

The exploration of the Jaynes–Cummings Hamiltonian in a circuit-QED system—where an ‘artificial atom’ made of a superconducting circuit is strongly coupled to a microwave field—provides direct evidence for nonlinearities due to quantum mechanics on the level of single atoms and photons. On the level of single atoms and photons, the coupling between atoms and the electromagnetic field is typically very weak. By using a cavity to confine the field, the strength of this interaction can be increased by many orders of magnitude, to a point where it dominates over any dissipative process. This strong-coupling regime of cavity quantum electrodynamics1,2 has been reached for real atoms in optical cavities3, and for artificial atoms in circuit quantum electrodynamics4 and quantum dot systems5,6. A signature of strong coupling is the splitting of the cavity transmission peak into a pair of resolvable peaks when a single resonant atom is placed inside the cavity, an effect known as vacuum Rabi splitting. The circuit quantum electrodynamics architecture is ideally suited for going beyond this linear-response effect. Here, we show that increasing the drive power results in two unique nonlinear features in the transmitted heterodyne signal: the supersplitting of each vacuum Rabi peak into a doublet and the appearance of extra peaks with the characteristic spacing of the Jaynes–Cummings ladder. These findings constitute direct evidence for the coupling between the quantized microwave field and the anharmonic spectrum of a superconducting qubit acting as an artificial atom.

http://absimage.aps.org/image/MAR09/MWS_MAR09-2008-000290.pdf

Nonlinear response of the vacuum Rabi resonance

Phase-slip lines can be viewed as dynamically created Josephson junctions in a homogeneous superconducting film. In contrast to phase-slip centers, phase-slip lines occur in wide superconducting strips, where the order parameter may vary in two dimensions. We investigated phase-slip lines in two different materials using several methods. We observed Shapiro steps under microwave radiation, which shows that the frequency of the order parameter oscillation is equal to Josephson frequency. A periodic oscillation of a critical current versus the applied magnetic field was found in strips with a hole in the middle. The latter effect provides a clear evidence of macroscopic quantum interference across a phase-slip line. We have used low temperature scanning laser microscopy to visualize the phase-slip lines and to distinguish them from possible local inhomogeneities in the films.

Josephson behavior of phase-slip lines in wide superconducting strips.

Magnonics addresses the physical properties of spin waves and utilizes them for data processing. Scalability down to atomic dimensions, operation in the GHz-to-THz frequency range, utilization of nonlinear and nonreciprocal phenomena, and compatibility with CMOS are just a few of many advantages offered by magnons. Although magnonics is still primarily positioned in the academic domain, the scientific and technological challenges of the field are being extensively investigated, and many proof-of-concept prototypes have already been realized in laboratories. This roadmap is a product of the collective work of many authors, which covers versatile spin-wave computing approaches, conceptual building blocks, and underlying physical phenomena. In particular, the roadmap discusses the computation operations with the Boolean digital data, unconventional approaches, such as neuromorphic computing, and the progress toward magnon-based quantum computing. This article is organized as a collection of sub-sections grouped into seven large thematic sections. Each sub-section is prepared by one or a group of authors and concludes with a brief description of current challenges and the outlook of further development for each research direction. 

Advances in Magnetics Roadmap on Spin-Wave Computing

The capabilities of laser scanning microscopy (LSM) as a spatially-resolved method of testing high-Tc superconductivity (HTS) materials and devices are described. The earlier results obtained by the authors are briefly reviewed. Some novel applications of LSM are illustrated, including imaging the HTS responses in rf mode, probing the superconducting properties of HTS single crystals, and development of two-beam laser scanning microscopy. The existence of the phase slip lines mechanism of resistivity in HTS materials is proven by LSM imaging.

Laser scanning microscopy of HTS films and devices (Review Article)

The work describes the capabilities of Laser Scanning Microscopy (LSM) as a spatially resolved method of testing high_Tc materials and devices. The earlier results obtained by the authors are briefly reviewed. Some novel applications of the LSM are illustrated, including imaging the HTS responses in rf mode, probing the superconducting properties of HTS single crystals, development of twobeam laser scanning microscopy. The existence of the phase slip lines mechanism of resistivity in HTS materials is proven by LSM imaging.

Laser Scanning Microscopy of HTS Films and Devices

Spatially resolved characterization of superconducting films and cryoelectronic devices by means of low temperature scanning laser microscope

Superconducting quantum coherent circuits have opened up a novel area of fundamental low-temperature science since they could potentially be the element base for future quantum computers. Here we report a quasi-three-level coherent system, the so-called superconducting qutrit, which has some advantages over a two-level information cell (qubit) and is based on the qutrit readout circuit intended to measure individually the states of each qubit in a quantum computer. The designed and implemented radio-frequency superconducting qutrit detector (rf SQUTRID) with atomic-size ScS-type contact utilizes the coherent-state superposition in the three-well potential with energy splitting $\ensuremath{\Delta}{E}_{01}/{k}_{B}\ensuremath{\approx}1.5\phantom{\rule{0.16em}{0ex}}$K at the 30th quantized energy level with good isolation from the electromagnetic environment. The reason why large values of $\ensuremath{\Delta}{E}_{01}$ (and thus using atomic-size Nb-Nb contact) are required is to ensure an adiabatic limit for the quantum dynamics of magnetic flux in the rf SQUTRID.

Quantum superposition of three macroscopic states and superconducting qutrit detector

The low temperature scanning laser microscopy is used to study spatial characteristics of current-induced resistive states in wide superconducting Sn films. The irregularities of edge potential barrier and the current distribution in a film cross section are visualized. The results are in good qualitative agreement with Aslamazov-Lempitsky theory.

O. G. Turutanov

Papers

Laser scanning microscopy of HTS films and devices (Review Article)

Laser Scanning Microscopy of HTS Films and Devices

Spatially resolved characterization of superconducting films and cryoelectronic devices by means of low temperature scanning laser microscope

Quantum superposition of three macroscopic states and superconducting qutrit detector

Laser scanning visualization of evolution of vortex instability in current-carrying superconducting strips