Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session U25: Superconducting Qubits: Qubit-Field Interactions and Qubit Theory |
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Sponsoring Units: GQI Chair: Jay Gambetta, IBM Room: 327 |
Thursday, March 21, 2013 11:15AM - 11:27AM |
U25.00001: Cavity-Mediated Landau-Zener Interferometry Between Two Superconducting Qubits C.M. Quintana, K.D. Petersson, L.W. McFaul, S.J. Srinivasan, A.A. Houck, J.R. Petta Avoided crossings between two energy levels as a function of some external parameter are common to many quantum mechanical systems. In the field of circuit quantum electrodynamics (cQED), the energies of superconducting qubits can be tuned via applied magnetic flux, and a microwave cavity-mediated coupling between two qubits placed in the same resonator leads to an avoided crossing in the system's energy spectrum when the two singly-excited qubit states become degenerate. We utilize such an avoided crossing between two transmon qubits to explore Landau-Zener transition physics, using nanosecond timescale flux bias pulses to non-adiabatically traverse the avoided crossing. We explore the dynamics of single- and double-passage through the resulting ``beam splitter'' of two-qubit states. In particular, we test the general asymptotic Landau-Zener formula for non-adiabatic transition probabilities and demonstrate the creation of two-transmon entanglement via a single passage through the beam splitter. We also study interference phenomena associated with double passage through the avoided crossing (analogous to an optical interferometer), and explore the dependence of the interference fringes on the level velocity with which the passages are made. [Preview Abstract] |
Thursday, March 21, 2013 11:27AM - 11:39AM |
U25.00002: First-order sideband transitions with flux-driven asymmetric transmons J.D. Strand, M.E. Ware, Felix Beaudoin, Alexandre Blais, T. Ohki, B. Johnson, B.L.T. Plourde We present data demonstrating first-order sideband transitions between a qubit and a resonator performed with a digitally synthesized waveform coupled to the qubit loop as a magnetic flux. The resulting first-order sideband transitions are much faster (up to 85 MHz in our measurements) than second-order processes and have the potential to create fast quantum gates. The frequency of the red sideband can also be made quite low, typically a few hundred MHz in our experiment, and at these low frequencies expensive microwave generators are not required, simplifying the control electronics and making the process more scalable. We chose to test this process with asymmetric transmons in which one junction is several times larger than the other. This asymmetry creates a shallow flux modulation curve that is optimum for this flux-driven sideband process. [Preview Abstract] |
Thursday, March 21, 2013 11:39AM - 11:51AM |
U25.00003: Manipulating Kerr effects in a superconducting cavity via a superconducting qubit Victor V. Albert, Gerhard Kirchmair, Brian Vlastakis, Zaki Leghtas, Mazyar Mirrahimi, S.M. Girvin, R.J. Schoelkopf, Liang Jiang Typically, models of qubit-cavity interactions in superconducting circuits have included terms strictly linear in amplitude of the cavity modes. Due to ever-increasing experimental ability to realize larger coupling strengths, induced nonlinearities in the cavity contribute significantly to the dynamics and thus need to be accounted for. Such nonlinearities include interactions between the photon numbers of two cavity modes (cross-Kerr) and between a mode and itself (self-Kerr). Motivated by the recent experimental demonstration of self-Kerr in superconducting cavities, we investigate quantum control of Kerr effects via a dispersively coupled superconducting qubit, which not only enables us to enhance or suppress the Kerr coupling, but also opens the possibility to investigate higher order Kerr effects. [Preview Abstract] |
Thursday, March 21, 2013 11:51AM - 12:03PM |
U25.00004: Giant Cross Kerr Effect via a Superconducting Artificial Atom I.-C. Hoi, C.M. Wilson, G. Johansson, T. Palomaki, T.M. Stace, B. Fan, A. Frisk Kockum, L. Tornberg, P. Delsing We investigate the effective interaction between two microwave fields, mediated by a superconducting artificial atom (transmon qubit) which is strongly coupled to a coplanar transmission line. The interaction between the fields and atom realizes an effective cross Kerr coupling. Using this, we demonstrate average Kerr phase shifts of up to 25 degrees per photon with both coherent microwave fields at the single-photon level. Our results provide an important step towards quantum gates with propagating photons in the microwave regime. [Preview Abstract] |
Thursday, March 21, 2013 12:03PM - 12:15PM |
U25.00005: Requirements for Electromagnetically Induced Transparency in a Transmon J.E. Robinson, S. Novikov, Z.K. Keane, B. Suri, F.C. Wellstood, B.S. Palmer In the dressed atom picture, a three-level system can interact with two photons via the Autler-Townes (AT) effect, where the system exhibits two peaks separated by the generalized Rabi frequency of the coupling photon. The system can also exhibit electromagnetically induced transparency (EIT), where the first excited state is made transparent to the probe photon by a strong coupling drive. We examine the results from a multi-tone measurement in a transmon qubit coupled to a 3D cavity, which exhibits an AT splitting, as expected from the dressed atom picture, similar to previous results.\footnote{M. Baur, et al. {\it Phys. Rev. Lett.} {\bf 102}, 243602 (2009).}$^,$\footnote{Mika A. Sillanp\"{a}\"{a}, et al. {\it Phys. Rev. Lett.} {\bf 103}, 193601 (2009).} We will discuss the requirements for a crossover from an AT doublet to an EIT signal, as they relate to the limitations of our device. We will also examine the quantum information implications of realizing EIT in superconducting system. [Preview Abstract] |
Thursday, March 21, 2013 12:15PM - 12:27PM |
U25.00006: Probing Electromagnetically Induced Transparency in a Transmon Sergey Novikov, J.E. Robinson, Z.K. Keane, B. Suri, F.C. Wellstood, B.S. Palmer We have designed, fabricated, and measured a transmon made from a single Al/AlOx/Al Josephson-Junction on a sapphire substrate with $f_{01} \sim $ 5 GHz. The transmon was mounted in a 3D microwave cavity (OFHC copper, $f_c \sim $ 7.5GHz), similar to other recent experiments\footnote{Paik, H. \textit{et al.} Phys. Rev. Lett. 107, 240501.}$^,$\footnote{Rigetti, C. \textit{et al.} Phys. Rev. B 86, 100506.}. The observed coherence times were $T_1, T_2^* \sim $ 10$\mu$s allowing us to investigate the possibility of electromagnetically induced transparency (EIT) and other population trapping effects, such as the Autler-Townes (AT) splitting. We will discuss the experiments to look for and distinguish between AT and EIT given the constraints placed by the transmon and the readout limitations imposed by the cavity. [Preview Abstract] |
Thursday, March 21, 2013 12:27PM - 12:39PM |
U25.00007: cQED Susceptibility of Superconducting Transmons coupled to a Microstrip Resonator Cavity David Pappas, Martin Sandberg, Jiansong Gao, Michael Vissers, Anton Kockum, Goran Johansson The light-matter interaction of multi-level transmons strongly coupled to a cavity and the external drive field are measured over a wide frequency and power range. The transmons are fabricated from TiN capacitor plates with small Al/AlOx/Al shadow evaporated junctions. The long T1's of these devices, approximately 10 us, allow for a rich spectrum of doubly dressed states to be observed and modeled. Both single- and two-photon absorption features are identified as the drive power is increased. Quantitative agreement of the absorption spectra in both the weak and strong drive limits is obtained using the measured junction properties and the temperature. [Preview Abstract] |
Thursday, March 21, 2013 12:39PM - 12:51PM |
U25.00008: Tunable Coupling between Two Resonators Controlled by a Flux Qubit: the Quantum Switch E. Hoffmann, M. Haeberlein, A. Baust, M.J. Schwarz, E.P. Menzel, H. Huebl, F. Deppe, A. Marx, R. Gross, D. Zueco, J.-J. Garcia Ripoll, E. Solano In the field of quantum information processing, superconducting circuits have become a well-established platform. In particular, systems consisting of a few qubits and/or harmonic oscillator circuits have been investigated. When scaling up these systems, it seems practical to aim for active guidance elements allowing for a directed transmission of quantum signals. One way to achieve this is by implementing switchable coupling between two microwave resonators. We show experimental progress on two superconducting transmission line resonators, where a superconducting flux qubit mediates a controllable coupling - the Quantum Switch. We show an experimental characterization of such a device and discuss spectroscopic evidence for the switching behavior.\\[4pt] We acknowledge support from the DFG via SFB~631, the German excellence initiative via NIM, and EU projects CCQED, SOLID and PROMISCE, the Basque Foundation for Science, Basque Government IT472-10, and Spanish MICINN FIS2009-12773-C02-01, DZ granted by ARAID [Preview Abstract] |
Thursday, March 21, 2013 12:51PM - 1:03PM |
U25.00009: Catch-Disperse-Release Readout for Superconducting Qubits Eyob A. Sete, Eric Mlinar, Alexander N. Korotkov, Andrei Galiautdinov, John M. Martinis We analyze a qubit readout scheme for superconducting qubits via controlled capture, dispersion, and release of a microwave field. A tunable coupler is used to decouple the microwave resonator from a transmission line during dispersive interaction with the qubit, thus circumventing the Purcell effect. We show that fast and high-fidelity qubit readout can be achieved for nonlinear dispersive qubit-resonator interaction and for sufficiently adiabatic tuning of the qubit frequency. Interestingly, the Jaynes-Cummings nonlinearity results in quadrature squeezing of the microwave field which leads to a significant decrease in measurement error. The effects of qubit anharmonicity and imperfect quantum efficiency of the microwave amplification on the measurement error are also discussed. [Preview Abstract] |
Thursday, March 21, 2013 1:03PM - 1:15PM |
U25.00010: Realizing a Deterministic Teleportation Protocol in Superconducting Circuits Lars Steffen, Markus Oppliger, Matthias Baur, Arkady Fedorov, Andreas Wallraff Teleportation of a quantum state may be used for distributing entanglement between distant qubits in quantum communication and for realizing universal and fault-tolerant quantum computation. Previously, we have demonstrated the implementation of a teleportation protocol, up to the single-shot measurement step, with superconducting qubits coupled to a microwave resonator [1]. Using full quantum state tomography and calculating the projection of the measured density matrix onto the basis states of two qubits has allowed us to reconstruct the teleported state with an average output state fidelity of 86\%. In ongoing experiments we attempt to implement single shot read-out and feed-back to perform full deterministic quantum teleportation.\newline [1] M.~Baur, A.~Fedorov, L.~Steffen, S.~Filipp, M.P.~da~Silva, and A.~Wallraff, Phys. Rev. Lett. \textbf{108}, 040502 (2012) [Preview Abstract] |
Thursday, March 21, 2013 1:15PM - 1:27PM |
U25.00011: Methods for entanglement in circuit QED Felix Motzoi, Mohan Sarovar, Michael Goerz, Christiane Koch, Birgitta Whaley We discuss some progress in methods of generating entanglement in superconducting qubit architectures. We focus on the minimal time required to generate a perfect entangler in a given system, specifically by combining simultaneously multiple given forms of coupling. Typically the different terms will generate different dynamics and when multiple coupling terms exist one will have a choice about which local equivalence class to use to generate entanglement. Here, we consider the case where we want to simultaneously include the different forms of coupling that will be present in the circuit QED system, such as direct coupling, cavity mediated coupling, or virtual transitions in the multi-qubit space, with similar interaction strengths. No specific gate is targeted, but rather entanglement generation is optimized. Incoherent effects such as measurement/feedback based control can also be included to generate entanglement, even when the qubits are spatially separated (i.e. in different cavities) and no interaction exists. [Preview Abstract] |
Thursday, March 21, 2013 1:27PM - 1:39PM |
U25.00012: Tuning from coherent interaction to super- and subradiance with artificial atoms in a 1D waveguide Kevin Lalumi\`ere, Alexandre Blais, Barry C. Sanders, Arjan F. Van Loo, Arkady Fedorov, Andreas Wallraff Taking advantage of the near ideal spatial mode-matching, strong interaction between light and artificial atoms fabricated in a 1D waveguide has been demonstrated experimentally [1]. Here, we study the situation where multiple and possibly un-identical atoms are fabricated in the same waveguide. We find that atom relaxation and Lamb-shift are modified, leading to collective effects. Depending on the distance between the artificial atoms, or equivalently the phase shift accumulated by light traveling from one atom to another, we find that it is possible to tune between a strong modification of individual atomic relaxation with the formation of sub- and superradiant states, and a strong modification of the Lamb-shift leading to a coherent exchange-type interaction between the atoms. These predictions are based on a master equation derived for an inhomogeneous set of atoms coupled to a transmission line. Comparison with experimental results will be discussed.\\[4pt] [1] O. Astafiev et al., Science 327, 840 (2010) [Preview Abstract] |
Thursday, March 21, 2013 1:39PM - 1:51PM |
U25.00013: Quantum dynamics of triplet superconducting circuits David G. Ferguson, Jens Koch, James Sauls We generalize the formalism of ``circuit quantization''~[1] to circuits comprised of spin-triplet superconducting elements. This introduces the dynamics associated with the spin of the Cooper pairs in addition to the phase and charge dynamics. The dynamics of the order parameter for spin-triplet superconductors is encoded in the vector $\vec{d}$ for the spin-projections of the Cooper pairs, which is coupled to the dynamics of the electronic spin polarization, $\vec{S}$. At frequencies below the superconducting gap, $\hbar\omega\ll\Delta$, the classical spin dynamics is described by Leggett's equations for $\vec{d}$ and $\vec{S}$~[2]. Weak spin-orbit coupling ($E_{\mbox{s-o}}\ll\Delta$) leads to frequency shifts of the normal-state spin resonance. Quantization of a spin-triplet superconducting circuit is achieved by including the Hamiltonian that generates Leggett's equations. Analytical and numerical results for the spectra of the quantized Hamiltonians of varrious circuits are reported. As a case study, we highlight the low energy excitation frequencies of two triplet superconductor islands coupled by a Josephson junction.\\[4pt] [1]~M. H. Devoret, Quantum fluctuations in electrical circuits, (Les Houches Session LXIII, 1995).\\[0pt] [2]~A. J. Leggett, Rev. Mod. Phys. 47, 331 (1975) [Preview Abstract] |
Thursday, March 21, 2013 1:51PM - 2:03PM |
U25.00014: A Vector Potential for Flux Qbits Eliot Kapit, Erich Mueller We design a superconducting circuit, based on three junction flux qbits, in which the motion of magnetic flux mimics the behavior of charged lattice bosons hopping in a magnetic field. For realistic device parameters one can reach the strongly interacting bosonic quantum Hall limit where one will find anyonic excitations. We explore the design principles for using these circuits to study many-body physics, for example explaining how the magnitude and phase of the effective hopping matrix elements can be controlled by tuning offset voltages. The circuits could be used for topological quantum computation. [Preview Abstract] |
Thursday, March 21, 2013 2:03PM - 2:15PM |
U25.00015: ABSTRACT WITHDRAWN |
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