Quantum Computing with Superconducting Flux Qubits S. Han, University of Kansas , DMR-0325551

1. Quantum Computing with Superconducting Flux QubitsS. Han, University of Kansas, DMR-0325551 We have designed, fabricated, and characterized SQUID flux qubits aiming for scalable quantum computation. Energy relaxation time (T1)between the “0” and “1” states of the qubit has been measured using a high-precision time-domain technique. The result of T1~7 ms is very encouraging. Temperature dependence of relaxation time agrees very well with the spin-boson model. Qubit Detector Supercurrent ‘0’ ‘1’ Bias control SEM micrograph of a SQUID flux qubit. The qubit has a second order gradiometer configuration which makes it immune to fluctuations of homogeneous magnetic field. Experiments show the qubit has a relaxation time of ~7 ms, corresponding to a maximum decoherence time of ~14 ms, a figure that is very promising for realization of quantum computing..

2. Epitaxial Barrier NbN/AlN/NbN Tunnel Junctionsfor Quantum Information ApplicationsZ. Wang, Kobe Advanced ICT Research Center, NICT, JAPAN, DMR-0325551 We fabricated high-qualityNbNtunnel junctions with epitaxial AlN barrier by reactive dc-magnetron sputtering. The junctions show excellent propertiesin a wide range of Jc, from 100 A/cm2 to 20 kA/cm2, suitable for quantum information applications. TEM and electron diffraction show atomically smooth and sharp interfaces between the superconducting NbN electrodes and the insulating AlN tunnel barrier The epitaxial tunnel barrier greatly reduce the number of defects (microscopic two-level fluctuators) which have been identified as the dominant decoherence mechanism in all types of solid-state Josephson superconducting qubits. TEM micrograph of the junction cross section (center and left) and electron diffraction patterns (right) for an NbN/AlN/NbN junction with a Jc of 400 A/cm2. ASC2006-1EG01

3. Epitaxial Barrier NbN/AlN/NbN Tunnel Junctionsfor Quantum Information ApplicationsZ. Wang, Kobe Advanced ICT Research Center, NICT, JAPAN, DMR-0325551 Mission of KARC Is acting as a base for basic research that plays an important role in the National Institute of Information and Communications Technology, Incorporated Administrative Agency. We are conducting a variety of bio, brain, nanotechnology, superconductor, quantum and laser, etc. research, aiming at the creation of knowledge and technological breakthroughs, and dream of contributing to future, affluent info-communications. The Superconducting Electronics Group web site http://www-karc.nict.go.jp/102/E_index.html contains our research subjects, activities, and recent research presentations. Equipments and facilities We have a 600 m2 area clean room (class 100 and class 1,000) for fabrication of superconducting junctions and circuits. Various equipments are available both for device fabrication and analysis in the clean room. We have rf and dc reactive sputtering systems, RIE, ECR, laser ablation, ion-beam deposition, i-line stepper, e-beam writer, x-ray diffraction, SEM, AFM, etc.

4. Superconducting Qubit Stony Brook Superconducting DevicesDesign and FabricationVijay Patel & Wei Chen   JJs– 1mmx1mm • 1/f fluctuations in Ic lead todecoherence. • Stony Brook Nb junctions are 100 times quieter than typical—the best available. Data from Shawn Pottorf Quantum Computer: Need to Reduce Decoherence  Great Josephson Junctions Required J. E. Lukens, Stony Brook University, DMR-0325551