Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session W6: Superconducting Qubits |
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Sponsoring Units: GQI Chair: Irfan Siddiqi, University of California, Berkeley Room: Portland Ballroom 253 |
Thursday, March 18, 2010 11:15AM - 11:51AM |
W6.00001: Superconducting Phase Qubits: Two-Qubit Tomography and Adjustable Coupling Invited Speaker: Proof of principle quantum gates and algorithms have now been implemented using superconducting qubits. ~Some of the next goals for superconducting qubits include the development of scalable coupling schemes between qubits and the implementation of benchmarking methods that will allow for the direct comparison of superconducting qubit gate and algorithm performance to that of other quantum computing architectures. We first present work on benchmarking a universal quantum gate implemented using fixed, capacitive coupling.~We use standard quantum process tomography as the benchmarking tool to obtain the fidelity of the universal gate. Additionally, we show how the chi matrix obtained from quantum process tomography can be analyzed to extract useful information about correlations of the noise acting on our system.~The drawbacks of using fixed coupling and its effects on gate performance will also be discussed. Motivated by these drawbacks, we describe the need for tunable coupling and show how it can be implemented using a modular, drop-in coupler that is built from simple circuit components. We show how this element can be used to vary the two-qubit interaction strength between 0 and $\sim $100 MHz, allowing us to potentially remove problems inherent with fixed coupling. Finally, we present experimental data demonstrating dynamic control of the coupling strength using vacuum Rabi oscillation experiments. [Preview Abstract] |
Thursday, March 18, 2010 11:51AM - 12:27PM |
W6.00002: Atomic physics and quantum optics using circuits: An overview of recent results on superconducting qubits Invited Speaker: Superconducting (SC) circuits can behave like atoms making transitions between a few energy levels. Such circuits can test quantum mechanics at macroscopic scales and be used to conduct atomic-physics experiments on a silicon chip. This presentation overviews a few of our theoretical studies on SC circuits and quantum information processing including: SC qubits for photon generation and for lasing; 2-1 photon coexistence; cooling qubits and their environment; using SC qubits to probe nearby defects; hybrid circuits involving both charge and flux qubits; quantum tomography in SC circuits; preparation of macroscopic quantum superposition states of a cavity field via coupling to a SC qubit; generation of nonclassical photon states using a SC qubit in a microcavity; cluster states; using these circuits as quantum analog emulators of Kitaev lattices; controllable scattering of photons inside a one-dimensional resonator waveguide; and controllable couplings among qubits. [Preview Abstract] |
Thursday, March 18, 2010 12:27PM - 1:03PM |
W6.00003: Realization of Simple Quantum Algorithms with Circuit Quantum Electrodynamics Invited Speaker: Superconducting circuits have made considerable progress in the requirements of quantum coherence, universal gate operations and qubit readout necessary to realize a quantum computer. However, simultaneously meeting these requirements makes the solid-state realization of few-qubit processors, as previously implemented in nuclear magnetic resonance, ion-trap and optical systems, an exciting challenge. We present the realization of a two-qubit superconducting processor based on circuit quantum electrodynamics (cQED), and report progress by the Yale cQED team towards a four-qubit upgrade. The architecture employs a microwave transmission-line cavity as a quantum bus coupling multiple transmon qubits. Unitary control is achieved by concatenation of high-fidelity single-qubit rotations induced via resonant microwave tones, and multi-qubit adiabatic phase gates realized by local flux control of qubit frequencies. Qubit readout uses the cavity as a quadratic detector, such that a single, calibrated measurement channel gives direct access to multi-qubit correlations. We present generation of Bell states; entanglement quantification by strong violation of Clauser-Horne-Shimony-Holt inequalities; and implementations of the Grover search and Deutsch-Jozsa algorithms. We report experimental progress in extending adiabatic phase gates and joint readout to four qubits, and improving qubit coherence on the road to realizing more complex quantum algorithms. Research done in collaboration with J. M. Chow, J. M. Gambetta, Lev S. Bishop, B. R. Johnson, D. I. Schuster, A. Nunnenkamp, J. Majer, A. Blais, L. Frunzio, M. H. Devoret, S. M. Girvin, and R. J. Schoelkopf. [Preview Abstract] |
Thursday, March 18, 2010 1:03PM - 1:39PM |
W6.00004: Quantum measurement in superconducting qubits Invited Speaker: Recent research on superconducting qubits has been accompanied by innovative ideas and technological advances in measurement techniques. For example, some experiments have demonstrated measurements of qubit states where the back-action was limited by the Heisenberg uncertainty principle. I will briefly mention some of the measurement ideas employed in recent experiments. I will then present some of our recent results on the information about the state of a qubit gained by a weakly coupled detector. In particular, we analyze the case where the measurement is concurrent with coherent dynamics or decoherence. In this case, extracting meaningful measurement results from the observed signal can become a complicated task. However, with proper analysis several pieces of information are accessible. Our approach complements the stochastic master equation approach, which describes the evolution of the qubit's state but does not keep track of the acquired measurement information. [Preview Abstract] |
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