Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session P29: Focus Session: Superconducting Qubits |
Hide Abstracts |
Sponsoring Units: GQI Chair: Robert McDermott, University of Wisconsin--Madison Room: C148 |
Wednesday, March 23, 2011 8:00AM - 8:36AM |
P29.00001: LeRoy Apker Award Talk: Parallel State Transfer and Efficient Quantum Routing on Quantum Networks Invited Speaker: We study the routing of quantum information in parallel on multi-dimensional networks of tunable qubits and oscillators. These theoretical models are inspired by recent experiments in superconducting circuits using Josephson junctions and resonators. We show that \emph{perfect parallel state transfer} is possible for certain networks of harmonic oscillator modes. We further extend our model to analyze the distribution of entanglement between every pair of nodes in the network, and find that the routing efficiency of hypercube networks is both optimal and robust in the presence of dissipation and finite bandwidth. [Preview Abstract] |
Wednesday, March 23, 2011 8:36AM - 8:48AM |
P29.00002: Towards long coherence superconducting qubits Matthias Steffen, Antonio Corcoles, Jerry Chow, Chad Rigetti, Mark Ketchen, Mary Beth Rothwell, George Keefe, Jim Rozen, Mark Borstelmann, Jack Rohrs, David DiVincenzo The capacitively shunted flux qubit (CSFQ) has recently been shown to have coherence times of 1-2 microseconds repeatedly over many devices at typical qubit operating frequencies. Experiments in our group strongly suggest that losses associated with the shunting capacitor limit the current coherence times. As a result we propose novel approaches towards decreasing capacitive losses by employing geometric and/or materials developments. We show experimental data and compare these with theoretical predictions [Preview Abstract] |
Wednesday, March 23, 2011 8:48AM - 9:00AM |
P29.00003: Circuit QED without selection rules: the dispersive regime of the fluxonium qubit Guanyu Zhu, Jens Koch Manipulation and readout of superconducting qubits with microwave photons, as realized in circuit QED, commonly employ the dispersive regime. In this regime, the qubit-photon interaction strength is small compared to the relative detuning $\Delta$, and manifests itself only in the dispersive energy shifts $\chi$, crucial for dispersive readout and spectroscopy of the qubit. For Cooper Pair Box and transmon, these shifts are known to scale like $1/\Delta$ and $1/\Delta^2$, respectively, making readout at very large detuning challenging. We show that the relation between $\chi$ and $\Delta$ is mainly dictated by selection rules, and derive general expressions describing the dispersive regime of a multi-level qubit with arbitrary matrix elements. This generalization turns out essential for describing the dispersive regime of the fluxonium qubit, where no simple selection rules exist. We show that this lack of selection rules explains the suprising magnitude of disperse shifts, at detunings as large as $\sim$8GHz, and also causes peculiarities observed in the fluxonium spectroscopy. [Preview Abstract] |
Wednesday, March 23, 2011 9:00AM - 9:12AM |
P29.00004: Tunable coupling in circuit quantum electrodynamics with a superconducting V-system Srikanth Srinivasan, Anthony Hoffman, Devin Underwood, Jay Gambetta, Andrew Houck We demonstrate a new superconducting charge qubit that realizes a V-shaped energy level spectrum, enabling tunable coupling between the qubit and a superconducting cavity while retaining all of the advantages, including charge noise insensitivity, common to other charge qubits such as the transmon. Tunable coupling is achieved with quantum interference between the two excited states of the qubit. We report measurements of the vacuum Rabi splitting, showing that the coupling strength can be tuned from greater than 40 MHz to less than 200 kHz using fast flux bias lines. This dynamically tunable coupling is an intrinsic property of the qubit and requires no additional coupling circuit elements. This new qubit design shows great promise for future quantum information processing and quantum optics experiments. [Preview Abstract] |
Wednesday, March 23, 2011 9:12AM - 9:24AM |
P29.00005: Inductive coupling of superconducting qubits to coplanar waveguide resonators J.D. Strand, M.P. DeFeo, P. Bhupathi, C. Song, M. Ware, B. Xiao, B.L.T. Plourde Superconducting qubits coupled to microwave resonators provide a promising basis for a scalable quantum computing architecture and enable explorations of circuit quantum electrodynamics. One approach for achieving strong coupling between a qubit and resonator involves sharing the kinetic inductance of a narrow superconducting line. We are investigating different designs for inductively coupling qubits, including capacitively shunted flux qubits, to coplanar waveguide resonators. We are working to optimize the coupling while accommodating the space requirements of different qubit types and preserving the performance of the resonator. We present microwave measurements of these structures as well as modeling of the qubit-resonator coupling. [Preview Abstract] |
Wednesday, March 23, 2011 9:24AM - 9:36AM |
P29.00006: Transmon qubits coupled to compact resonators S. Shankar, K. Geerlings, E. Edwards, L. Frunzio, R.J. Schoelkopf, M.H. Devoret Compact resonators comprising of a meander inductor and an interdigitated capacitor are desirable building blocks for a multi-qubit processor due to their small size. We present an experiment on a superconducting transmon qubit coupled capacitively to such a compact resonator. We have fabricated low-loss Nb based compact resonators with an area within 1 mm$^2$ on a sapphire substrate to operate between 5 and 8 GHz. The resonator geometry was optimized to achieve an intrinsic quality factor above 300,000 at single-photon microwave powers and temperatures below 100 mK. Transmon qubits were made using Al/AlOx/Al Josephson junctions shunted by an Al interdigitated capacitor with an identical width and gap as the resonator. We will present our experimental progress towards measuring relaxation times of these qubits. [Preview Abstract] |
Wednesday, March 23, 2011 9:36AM - 9:48AM |
P29.00007: Design of a dc SQUID Phase Qubit with Controlled Coupling to the Microwave Signal R.P. Budoyo, A.J. Przybysz, B.K. Cooper, H. Kwon, Z. Kim, B. Cheng, A.J. Dragt, J.R. Anderson, C.J. Lobb, F.C. Wellstood, M. Khalil, S. Gladchenko, M. Stoutimore, B.S. Palmer, K.D. Osborn We have designed an Al/AlO$_{x}$/Al dc SQUID phase qubit on a sapphire substrate with a qubit junction area of 0.3 $\mu$m$^2$ to minimize loss associated with two-level systems in the junction oxide barrier. The qubit junction is shunted with a 1.5 pF interdigitated capacitor, and is isolated from the bias leads by an LC filter and an inductive isolation network using a larger Josephson junction. A previous device we built with similar parameters had its relaxation time $T_{1}$ limited by coupling to the microwave line. To reduce this coupling, we adopted a transmission line design and verified the coupling strength using microwave simulations. The new design will also allow us to measure the coupling to the SQUID by throughput measurements. We will discuss our design, the microwave simulations, our estimates for the overall coherence time due to losses and noise from various sources, and our progress towards testing the device. [Preview Abstract] |
Wednesday, March 23, 2011 9:48AM - 10:00AM |
P29.00008: Two junction effects in dc SQUID phase qubit B.K. Cooper, H. Kwon, A.J. Przybysz, R. Budoyo, J.R. Anderson, C.J. Lobb, F.C. Wellstood The dc SQUID phase qubit was designed to allow one isolation junction to filter bias current noise from a second junction operating as a single junction phase qubit. As junctions shrink to minimize dielectric loss, the Josephson inductances of each junction approach the coupling loop inductance and this single junction picture appears inadequate. We consider a two-junction model of the dc SQUID phase qubit, where the qubit now corresponds to one of the normal oscillatory modes of the full SQUID. We discuss applications of this model to sweet spots in various control parameters and unusual behavior in the tunneling state measurement. [Preview Abstract] |
Wednesday, March 23, 2011 10:00AM - 10:12AM |
P29.00009: Two-Dimensional quantum dynamic in a dc SQUID Florent Lecocq, I.M. Pop, Z. Peng, I. Matei, C. Naud, F.W. Hekking, W. Guichard, O. Buisson, R. Dolata, A.B. Zorin The dynamics of a dc SQUID presents a large variety of quantum effects at very low temperature such as 2D MQT signature, multilevel and phase qubit dynamics. We have shown that along the zero current bias line, the quantum dynamics is protected from current fluctuations. Along this line, the potential is quadratic-quartic and enhanced phase qubit properties have been demonstrated\footnote{E. Hoskinson et al, Phys. Rev. Lett. 102, 097004 (2009)} When the dc SQUID loop inductance is of the order of the Josephson inductance the dynamic becomes two dimensional. As a consequence, in addition to the oscillation mode producing the phase qubit, a second oscillation mode exists, called transverse mode. Here we report spectroscopic evidence and coherence properties of both oscillators as well as coherent oscillations between the quantum states of these two coupled oscillators. [Preview Abstract] |
Wednesday, March 23, 2011 10:12AM - 10:24AM |
P29.00010: Stark effect and generalized Bloch-Siegert shift in a strongly driven two-level system Matti Silveri, Jani Tuorila, Mika Sillanp\"a\"a, Yuriy Makhlin, Erkki Thuneberg, Pertti Hakonen A superconducting qubit was driven in an ultrastrong fashion by an oscillatory microwave field, which was created by coupling via the nonlinear Josephson energy. The observed Stark shifts of the ``atomic'' levels are so pronounced that one has to go beyond the rotating wave approximation to properly explain the measurements. The difference between the prediction of the rotating wave approximation and the full calculation including all higher orders constitutes the generalized Bloch-Siegert shift which was verified in the measurement. Based on the Floquet approach for the driven two-level system, we calculate the landscape of the quasienergy splitting and the matrix elements of the probe transition, which were probed by resonant absorption via a cavity. The calculation taking into account both the resonance condition and the magnitude of the probe absorption agrees well with the measurement results. [Preview Abstract] |
Wednesday, March 23, 2011 10:24AM - 10:36AM |
P29.00011: Time-Reversal Symmetry and Temporal Coherent Back-Scattering in a Driven Two-Level System Simon Gustavsson, Mark Rudner, Jonas Bylander, Leonid Levitov, Will Oliver Coherent backscattering, resulting from quantum interference of the paths related by time-reversal symmetry, is a phenomenon fundamental for quantum-chaotic dynamics. It manifests itself in diverse transport phenomena which were predicted and studied in mesoscopic electron systems in 1980's and 1990's: universal conductance fluctuations (UCF), weak localization and anti-localization, etc. Here we present first experimental realization of the essential physics of coherent backscattering in a driven quantum system, a two-level system repeatedly driven through an avoided level crossing. Our experiment is performed with a superconducting qubit driven through level crossing by a sequence of RF pulses. Each passage through the level crossing serves a Landau-Zener-type ``scattering event,'' with the wave function splitting between the up and down qubit states in a coherent fashion and recombining at a subsequent passage through the level crossing. Time-reversal symmetry can be enforced in our system by the driving protocol, resulting in constructive interference in the up-down transition rates. We observe an enhancement of the speckle-like fringe contrast analogous to UCF, which is suppressed in the absence of time reversal symmetry. [Preview Abstract] |
Wednesday, March 23, 2011 10:36AM - 10:48AM |
P29.00012: Dark states of cavity-coupled qubits S. Filipp, A.F. van Loo, A. Wallraff In circuit quantum electrodynamics (QED) the cavity-mediated dispersive interaction is the dominant inter-qubit coupling mechanism when the qubits are detuned from the resonator. This mechanism can be used to realize two-qubit gates. Here, we investigate the strength of this interaction explicitly considering the Fabry-Perot like multi-mode structure of the microwave frequency transmission line resonator. We observe the formation of dark states when the qubits are driven jointly by the same resonator microwave field and tuned into resonance with each other [1]. These dark states arise from the symmetry properties of the coupled quantum system at the avoided level crossing. Furthermore, we study the suppression of spontaneous emission of the coupled-qubit system by driving it into its dark state using microwave fields local to the individual qubits.\\[4pt] [1] S. Filipp \emph{et al.}, arXiv:1011.3732 (2010). [Preview Abstract] |
Wednesday, March 23, 2011 10:48AM - 11:00AM |
P29.00013: Entanglement between the charge and phase degrees of freedom in a superconducting qubit Mun Dae Kim The charge and phase are conjugate variables with each other in superconducting qubits which are characterized by either the charge or the phase degree of freedom. In this study we propose a qubit scheme where the charge and phase degrees of freedom are entangled in the qubit. In our qubit the qubit states consists of the phase states of the qubit, while the qubit states can be measured through the charge state detection. The qubit operation can be performed at the optimal point with respect to both the external magnetic flux and gate voltage. We discuss the fidelity of the Rabi oscillation and the possible way of enhancement of fidelity. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700