Session A5: Industrial Physics Forum: Small-Scale Applications

Prospects of superconducting qubits for quantum computation

Superconducting qubits are solid state electrical circuits fabricated using techniques adapted from those of conventional integrated microprocessor fabrication. They are based on the Josephson tunnel junction, the only non-dissipative, strongly non-linear circuit element compatible with low temperature operation. In contrast to microscopic entities such as spins, atoms or ions, superconducting qubits can be well coupled to each other, an appealing feature for 2-qubit gate implementation. Very recently, new circuit architectures have greatly improved the isolation of qubits from unwanted noise, yielding coherence quality factors well in excess of 100,000. Entanglement, the key property that distinguishes a quantum processor from a classical one, has been produced and measured for up to 3 qubits.\footnote{DiCarlo, L. et al. Nature 467, 574-578 (2010);}$^,$\footnote{Neeley, M. et al. Nature 467, 570-573 (2010).} Current experiments are addressing the problem of whether the Preskill criterion of 10,000 coherent 1- and 2-qubit gate operations can be met to enable quantum error correction.   

Superconductor Digital Electronics: -- Current Status, Future Prospects

Two major applications of superconductor electronics: communications and supercomputing will be presented. These areas hold a significant promise of a large impact on electronics state-of-the-art for the defense and commercial markets stemming from the fundamental advantages of superconductivity: simultaneous high speed and low power, lossless interconnect, natural quantization, and high sensitivity. The availability of relatively small cryocoolers lowered the foremost market barrier for cryogenically-cooled superconductor electronic systems. These fundamental advantages enabled a novel Digital-RF architecture - a disruptive technological approach changing wireless communications, radar, and surveillance system architectures dramatically. Practical results were achieved for Digital-RF systems in which wide-band, multi-band radio frequency signals are directly digitized and digital domain is expanded throughout the entire system. Digital-RF systems combine digital and mixed signal integrated circuits based on Rapid Single Flux Quantum (RSFQ) technology, superconductor analog filter circuits, and semiconductor post-processing circuits. The demonstrated cryocooled Digital-RF systems are the world's first and fastest directly digitizing receivers operating with live satellite signals, enabling multi-net data links, and performing signal acquisition from HF to L-band with 30 GHz clock frequencies. In supercomputing, superconductivity leads to the highest energy efficiencies per operation. Superconductor technology based on manipulation and ballistic transfer of magnetic flux quanta provides a superior low-power alternative to CMOS and other charge-transfer based device technologies. The fundamental energy consumption in SFQ circuits defined by flux quanta energy 2x10$^{-19}$ J. Recently, a novel energy-efficient zero-static-power SFQ technology, eSFQ/ERSFQ was invented, which retains all advantages of standard RSFQ circuits: high-speed, dc power, internal memory. The voltage bias regulation, determined by SFQ clock, enables the \textit{zero-power at zero-activity regimes}, indispensable for sensor and quantum bit readout.   

Superconducting Receivers for Millimeter and Submillimeter Astrophysics

Important information about the structure and evolution of the Universe can be obtained from astrophysical measurements at millimeter and submillimeter wavelengths. The noise in receiver systems used for such measurements should approach as closely as possible the fundamental limits such as photon noise and quantum fluctuations. Narrow line emissions are measured by such major projects as the recently launched 1.5B$ Herschel Space telescope and the 1B$ International Alma project, which is now under construction. These projects are enabled by heterodyne receivers with superconducting hot electron bolometer (HEB) mixers and Quasiparticle (SIS) mixers. The temperature and polarization of broad band thermal sources such as the Cosmic Microwave Background and dust emission are being measured from a variety of high altitude telescopes in Chile and at the South Pole using large format arrays of transition edge sensor (TES) bolomters. The status of international efforts in this field will be described with special reference to the rapidly developing technology of very large format arrays of TES bolometers with SQUID-based output multiplexers.   

The Ubiquitous SQUID: From Axions to Cancer

I briefly review the principles, practical implementation and applications of the dc SQUID (Superconducting QUantum Interference Device), an ultrasensitive detector of magnetic flux. Cosmological observations show that a major constituent of the universe is cold dark matter (CDM). A candidate particle for CDM is the axion which, in the presence of a magnetic field, is predicted to decay into a photon with energy given by the axion mass, ranging from 0.001 to 1 meV. The axion detector constructed at LLNL consists of a cooled, tunable cavity surrounded by a 7-T superconducting magnet. Photons from the axion decay would be detected by a cooled semiconductor amplifier. To search for the axion over an octave of frequency, however, would take two centuries. Now at the University of Washington, Seattle the axion detector will be upgraded by cooling it to 50 mK and installing a near-quantum limited SQUID amplifier. The scan time will be reduced by three orders of magnitude to a few months. In medical physics, we use an ultralow-field magnetic resonance imaging (ULFMRI) system with SQUID detection to obtain images in a magnetic field of 0.132 mT, four orders of magnitude lower than in conventional MRI. An advantage of low fields is that different types of tissue exhibit much greater contrast in the relaxation time T1 than in high fields. We have measured T1 in ex vivo specimens of surgically removed healthy and malignant prostate tissue. The percentage of tumor in each specimen is determined with pathology. The MRI contrast between two specimens from a given patient scales with the difference in the percentage of tumor; in healthy tissue T1 is typically 50 percent higher than in a tumor. These results suggest that ULFMRI with T1-weighted contrast may have clinical applications to imaging prostate cancer and potentially other types of cancer.   

Semiconductor Circuit Diagnostics By Magnetic Field Imaging

At the forefront of IC technology development are 3D circuit technologies such as system-in-package (SiP), wafer-level-packaging (WLP), through-silicon-vias (TSV), stacked die approaches, flex packages, etc. They integrate multiple devices, many times stacking them in layers with complex, intricate and very long interconnections in significantly reduced area, in addition to an ever-increasing number of opaque layers.~ We could very well say that the near future looks like the perfect nightmare for the Failure Analysis (FA) engineer with localization of defects becoming a major challenge. Magnetic field imaging (MFI) allows the fields generated by the circuit currents to go through various packaging layers and be imaged. I will describe in this talk Magma, a scanning magnetic field imaging system based on a high temperature superconducting SQUID device based on YBa2Cu3O7-$\delta $. The HTS SQUIDs used have a noise level of $\sim $ 20pT/$\surd $(Hz) and for typical scanning conditions, a field sensitivity of about 0.7 nT. While current shorts are imaged with spatial resolution, up to 3 micron (with peak localization) resistive opens can also be imaged and currently different strategies are being adapted for imaging opens with large working distances of 50-100s of microns. Higher spatial resolution ($\sim $250nm) is obtained by the use of magneto-resistive devices as sensors though the working distance requirement is sever