Josephson qubits are one of the most promising approaches for solid-state quantum information processing. I will discuss recent experiments at UC Santa Barbara that demonstrate our ability to synthesize complex quantum states of microwave photons in superconducting resonators using phase qubits. I will review experiments that generate photon number (Fock) states up to 12 photons, as well as a protocol for arbitrary states and their measurement via Wigner tomography. The violation of Bell’s inequality has also been demonstrated along with a closure of the measurement loophole. I will also discuss a recent experiment that shows complex entanglement of microwave photons in a pair of superconducting resonators. We use as a benchmark the generation of NOON states, with N photons in one resonator and 0 in the other, superposed with the state with the occupation numbers reversed. The resonator states are analyzed using bipartite Wigner tomography, which is required to distinguish entanglement from an ensemble of mixed states. These experiments have led to the development of a new RezQu architecture that utilizes memory resonators for each qubit, a common coupling bus, and the qubit zero state to turn off the coupling between the memory and bus. With experimental demonstration of Bell-state memory, CNOT gates, C-phase gates for the quantum Fourier transform, and Toeffoli gates, we believe it is possible to operate in the immediate future quantum processors with 9 to 17 modes.
John Martinis, H. Wang, Matteo Mariantoni, Radoslaw C. Bialczak, M. Lenander, Erik Lucero, M. Neeley, A. O'Connell, D. Sank, M. Weides, J. Wenner, T. Yamamoto, Y. Yin, J. Zhao, and A. N. Cleland, University of California, Santa Barbara
John M. Martinis attended the University of California at Berkeley from 1976 to 1987, where he received two degrees in Physics: B.S. (1980) and Ph.D. (1987). His thesis research focused on macroscopic quantum tunneling in Josephson Junctions. After completing a post-doctoral position at the Commisiariat Energie Atomic in Saclay, France, he joined the Electromagnetic Technology division at NIST in Boulder. At NIST he was involved in understanding the basic physics of the Coulomb Blockade, and worked to use this phenomenon to make a new fundamental electrical standard based on counting electrons. While at NIST he also invented series-array SQUID amplifiers. In 1993 he started an effort building high-resolution x-ray microcalorimeters based on superconducting sensors and series-array SQUIDs. This effort has grown to include applications in x-ray microanalysis and astrophysics, and optical and infrared astronomy. More recently he started a project to build a new fundamental standard of temperature based on noise thermometry, and in 2001 he helped initiate a project to use a microcalorimeter optical photon counter with high quantum efficiency for quantum communications. Since 2002 his research effort has focused on building a quantum computer using large-area Josephson junctions. Dr. Martinis was a NIST Fellow, and is a Fellow of the American Physical Society. In June of 2004 he moved to the University of California, Santa Barbara where he currently holds the Wooster Chair. At UCSB, he is continuing his work on quantum computation. Along with Andrew Cleland, he was awarded the AAAS science breakthrough of the year for 2010 for work showing quantum behavior of a mechanical oscillator.