Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V17: Superconducting Transmons and Circuit QED |
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Sponsoring Units: GQI Chair: Ben Palmer, Laboratory for Physical Sciences, University of Maryland Room: 318 |
Thursday, March 19, 2009 8:00AM - 8:12AM |
V17.00001: Experimental study of transmon type qubits coupled to a fast tunable transmission line resonator. Martin Sandberg, Chris Wilson, Fredrik Persson, Io-Chun Hoi, Per Delsing We experimental study a high quality factor (Q-value) transmission line resonator terminated in a superconducting quantum interference device (SQUID). Using an on-chip fast flux bias line we show that we can tune the frequency of such a resonator by hundreds of line widths on a time scale faster the photon lifetime of the resonator. Such a resonator could then be used for dynamic coupling of superconducting quantum bits (qubits). We present preliminary data of two transmon type of qubits coupled to a fast tunable resonator. We show spectroscopy and Rabi oscillations of the qubits far detuned from the resonator. Data showing a relaxation time of 1$\mu $s and a Rabi time of 200 ns have so far been obtained. [Preview Abstract] |
Thursday, March 19, 2009 8:12AM - 8:24AM |
V17.00002: Superconducting qubits can be coupled and addressed as trapped ions Y.X. Liu, L.F. Wei, J.R. Johansson, J.S. Tsai, F. Nori Exploiting the intrinsic nonlinearity of superconducting Josephson junctions, we propose a scalable circuit with superconducting qubits (SCQs) which is very similar to the successful one now being used for trapped ions. The SCQs are coupled to the ``vibrational'' mode provided by a superconducting LC circuit or its equivalent (e.g., a superconducting quantum interference device). Both single-qubit rotations and qubit-LC-circuit couplings and/or decouplings can be controlled by the frequencies of the time-dependent magnetic fluxes. The circuit is scalable since the qubit-qubit interactions, mediated by the LC circuit, can be selectively performed, and the information transfer can be realized in a controllable way. \\[4pt] Y.X. Liu, L.F. Wei, J.R. Johansson, J.S. Tsai, F. Nori, Superconducting qubits can be coupled and addressed as trapped ions, Phys. Rev. B 76, 144518 (2007). URL: http://link.aps.org/abstract/PRB/v76/e144518 [Preview Abstract] |
Thursday, March 19, 2009 8:24AM - 8:36AM |
V17.00003: Second order dispersive regime of circuit QED with a transmon qubit Maxime Boissonneault, J. M. Gambetta, Alexandre Blais In many recent circuit QED experiments [1,2], a transmon-type [3] qubit is fabricated inside a high-Q transmission line resonator. Compared to the Cooper-pair box (CPB), the transmon has both a stronger coupling to the resonator and a significantly longer dephasing time [4]. By going to the dispersive regime, where the qubit-resonator detuning is much larger than the coupling strength, the qubit can be controlled and measured through the resonator. In previous work [5], we have shown that one must include non-linear corrections to the dispersive approximation in strong measurements of a CPB qubit. These corrections cause a saturation of the signal-to-noise ratio and photon-dependant qubit decay and dephasing rates. In this talk, we will show how these non-linear corrections come into play with the transmon, and how they could be used to improve the measurement. [1] Houck et al, Nature, 2007, 449, 328 [2] Majer et al, Nature, 2007, 449, 443 [3] Koch et al, PRA, 2007, 76, 042319, [4] Schreier et al, PRB 77, 180502 (2008), [5] Boissonneault et al, PRA, 2008, 77, 060305(R). [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 8:48AM |
V17.00004: Two Cavity Circuit QED Blake Johnson, Andrew Houck, Jay Gambetta, Alexandre Blais, Steven Girvin, Michel Devoret, Robert Schoelkopf The circuit QED architecture has proven useful for dispersive manipulation and measurement of superconducting qubits. Previous experiments have shown how to use the AC-Stark shift to spectroscopically extract information about the photon number in the cavity[1]. Here we will show how to extend this toward building a photon statistics analyzer by adding a second cavity to the circuit QED architecture. The second cavity allows for decoupling of the preparation and readout of the cavity field state, opening the way for a measurement of the full photon statistics and reconstruction of the Wigner distribution. \newline \newline [1] Resolving photon number states in a superconducting circuit. D. I. Schuster, et. al. Nature (London) 445 515 (2007). [Preview Abstract] |
Thursday, March 19, 2009 8:48AM - 9:00AM |
V17.00005: Multi-Transmon circuit QED using local and fast flux biasing Leonardo DiCarlo, Jerry Chow, Johannes Majer, Luigi Frunzio, Jay Gambetta, Alexandre Blais, Steven Girvin, Robert Schoelkopf We report local and fast flux tuning of Transmon qubits in circuit QED by means of proximal short-circuited coplanar waveguides. We characterize the effect of these additional microwave channels on qubit lifetime. We demonstrate one-qubit $Z$-gates and time-domain control of two-qubit interaction via virtual photon exchange. Gate performance is characterized by process tomography and compared to gating by AC Stark shift as previously investigated by the Yale cQED team [1]. Research supported by NSF, NSA and ARO. [1] Majer \textit{et al.,} \textit{Nature} \textbf{449}, 443 (2007). [Preview Abstract] |
Thursday, March 19, 2009 9:00AM - 9:12AM |
V17.00006: Inline Cavity Qubit with Bifuraction Readout Markus Brink, Nicholas A. Masluk, Kurtis L. Geerlings, Michael Metcalfe, Vladimir Manucharyan, Luigi Frunzio, Steven M. Girvin, Robert J. Schoelkopf, Michel H. Devoret We present the design and data from a new, strongly coupled superconducting qubit based on Josephson junctions and a strictly 1-dimensional distributed element geometry that operates in the Transmon regime. A cavity bifurcation amplifier is used to read the state of the qubit. The same circuit also supports a linear dispersive readout, which enables direct comparison between the latching and dispersive scheme. Most recent results will be discussed. [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:24AM |
V17.00007: Generation of entangled states in circuit QED using sideband transitions P.J. Leek, S. Filipp, P. Maurer, A. Blais, A. Wallraff The deterministic generation of entanglement between pairs of distant qubits is an important goal in the development of a quantum information processor. A promising and potentially scalable method of achieving this is through the use of sideband transitions between qubits and a globally coupled harmonic oscillator. Here we present an experimental demonstration of such a scheme implemented in an electrical circuit. We generate entanglement between a superconducting transmon qubit and a microwave coplanar waveguide resonator, and transfer this entanglement to a second qubit. We show generation of the four Bell states by this method, extracting the full two-qubit density matrix using a joint dispersive two-qubit readout and quantum state tomography. [Preview Abstract] |
Thursday, March 19, 2009 9:24AM - 9:36AM |
V17.00008: Generating entanglement by measurement in circuit QED Jay Gambetta, Chantal Hutchison, Alexandre Blais, Frank Wilhelm In this talk, I will show theoretically how to induce entanglement by measurement in circuit QED. I will use quantum trajectory theory to derive an equation for the conditional state of a two qubit system, conditioned on continuous-in-time measurement of the amplitude and phase of the field leaving the resonator. I will show that with experimental parameters, we can use a decoherence-free subspace to generate an entangled state with a high concurrence and with a success probability of 1/2. Finally I will show that with a simple feedback scheme the same concurrence can be achieved with a success probability of one. [Preview Abstract] |
Thursday, March 19, 2009 9:36AM - 9:48AM |
V17.00009: Towards proving non-classicality with a 3-qubit GHZ state in circuit QED Lev S. Bishop, Jay M. Gambetta, Eran Ginossar, Steven M. Girvin, Andrew A. Houck, Jens Koch, Andreas Nunnenkamp, David J. Price, Robert J. Schoelkopf, Lars Tornberg The demonstration of violation of Bell-type inequalities remains challenging for superconducting qubits, due to short coherence times and limited measurement fidelity. Here, we propose to utilize 3-qubit GHZ states in a circuit QED system to accomplish this key step. In contrast to other schemes where the qubits are measured individually, circuit QED offers the advantage that a single dispersive measurement can directly reveal the parity $\langle\sigma^1_z\otimes\sigma^2_z\otimes\sigma^3_z\rangle$. When combined with appropriate 1-qubit rotations, this provides the necessary ingredients to obtain an effective measurement of Mermin's Bell operator with less stringent requirements on the measurement fidelity. Generation of the GHZ state can proceed via either 1- and 2-qubit gates or preparation by measurement. We present results from quantum trajectory calculations and estimate the resulting violation of the Mermin inequality, based on experimentally feasible parameters. [Preview Abstract] |
Thursday, March 19, 2009 9:48AM - 10:00AM |
V17.00010: Exploration of the Tavis-Cummings Model with Multiple Qubits in Circuit QED J.M. Fink, A. Blais, A. Wallraff Superconducting qubits in coplanar waveguide resonators provide an unprecedentedly large dipole coupling strength to microwave frequency photons confined in an on-chip waveguide resonator [1]. In contrast to atoms in traditional cavity QED a controlled number of qubits remain at fixed positions with constant coupling to the cavity field at all times. Utilizing these properties we have performed measurements with up to three independently flux-tunable qubits to study cavity mediated multi-qubit interactions. By tuning the qubits in resonance with the cavity field individually, we demonstrate the square root of $N$ scaling of the collective dipole coupling strength with the number of resonant atoms $N$ as described by the Tavis-Cummings model. To our knowledge this is the first observation of this nonlinearity in a system in which the atom number can be changed one by one in a discrete fashion. In addition, the energies of both bright and dark coupled multi-qubit / photon states are well explained by the Tavis-Cummings model over a wide range of detunings. On resonance we obtain an equal superposition of a photon and a Dicke state with an excitation equally shared among the $N$ qubits.\\ $[1]$ J.~M.~Fink et al.~\textit{Nature} 454, 315 (2008). [Preview Abstract] |
Thursday, March 19, 2009 10:00AM - 10:12AM |
V17.00011: Two-photon probe of the Jaynes-Cummings model and controlled symmetry breaking in circuit QED Frank Deppe, Matteo Mariantoni, E. P. Menzel, A. Marx, R. Gross, S. Saito, K. Kakuyanagi, H. Tanaka, K. Semba, T. Meno, H. Takayanagi, E. Solano Superconducting qubits behave as artificial two-level atoms. Coupling them to on-chip microwave resonators has given rise to the field of circuit quantum electrodynamics (QED). In this work, we report on the observation of key signatures of a two-photon driven Jaynes-Cummings model, which unveils the upconversion dynamics of a superconducting flux qubit coupled to an on-chip resonator. Our experiment and theoretical analysis show clear evidence for the coexistence of one- and two-photon driven level anticrossings of the qubit-resonator system. This results from the controlled symmetry breaking of the system Hamiltonian, causing parity to become a not well-defined property. Our study provides deep insight into the interplay of multiphoton processes and symmetries in a qubit-resonator system. We acknowledge support from SFB631, NIM, CREST-JST, JSPS-KAKENHI (18201018), MEXT-KAKENHI (18001002), EuroSQUIP, and the Ikerbasque Foundation. [Preview Abstract] |
Thursday, March 19, 2009 10:12AM - 10:24AM |
V17.00012: Dynamics of dispersive single qubit read-out in circuit QED R. Bianchetti, S. Filipp, A. Blais, A. Wallraff In a circuit quantum electrodynamics setup the qubit state is inferred from the response of the coupled qubit-cavity system to a microwave signal applied close to the cavity resonance. We experimentally investigate the frequency dependence of the response for both weak continuous and pulsed measurement signals. We find excellent agreement with theoretical predictions from a generalized Jaynes-Cummings model which includes dissipation and dephasing. The quantitative understanding of the system response is used to optimize the measurement frequency maximizing the signal-to-noise ratio. This allows for an accurate determination of the qubit excited state population from the measured field response. [Preview Abstract] |
Thursday, March 19, 2009 10:24AM - 10:36AM |
V17.00013: Two-qubit tomography with joint dispersive read-out in circuit QED S. Filipp, P. Maurer, P. J. Leek, A. Blais, A. Wallraff Quantum state tomography is an important tool in quantum information science for complete characterization of multi-qubit states and their correlations. We demonstrate that for two superconducting qubits coupled to a common resonator mode a reconstruction of the full density matrix can be achieved by measuring the transmission through the resonator -- without the need for single-shot measurement of individual qubits. Since the resonator transmission depends non-linearly on the dispersive cavity pull of different qubit states, information about qubit-qubit correlations is intrinsically present in the averaged measurement signal. It is shown that this simultaneous two-qubit read-out can be used for quantum state tomography of both separable and entangled states. [Preview Abstract] |
Thursday, March 19, 2009 10:36AM - 10:48AM |
V17.00014: Measurement of Autler-Townes and Mollow transitions in a strongly driven superconducting qubit M. Baur, S. Filipp, A. Blais, A. Wallraff The spectrum of a multilevel atom can be significantly modified when interacting with electromagnetic fields. In the simplest case where a two-level atom is driven on resonance, two sidebands offset from the main atomic line by the Rabi frequency $\Omega$ appear in the fluorescence spectrum, referred to as the Mollow triplet. Similarly, when probing transitions into a third atomic level, the absorption spectrum shows two spectral lines separated by $\Omega$, called the Autler-Townes doublet. Here we present a measurement of the Autler-Townes doublet and the sidebands of the Mollow triplet in a strongly driven superconducting qubit. The corresponding transitions are detected using dispersive read-out of the qubit coupled off-resonantly to a microwave transmission line resonator. The observed frequencies of the Autler-Townes and Mollow spectral lines are in excellent agreement with a generalized dispersive Jaynes-Cummings model. [Preview Abstract] |
Thursday, March 19, 2009 10:48AM - 11:00AM |
V17.00015: Microwave Photon Detector in Circuit QED Juan Jose Garcia-Ripoll, Guillermo Romero, Enrique Solano In this work we propose a design for a microwave photodetector based on elements from circuit QED such as the ones used in qubit designs. Our proposal consists on a microwave guide in which we embed circuital elements that can absorb photons and irreversibly change state. These incoherent absorption processes constitute the measurement itself. We first model this design using a general master equation for the propagating photons and the absorbing elements. We find that the detection efficiency for a single absorber is limited to 50\%, and that this efficiency can be quickly increased by adding more elements with a moderate separation, obtaining 80\% and 90\% for two and three absorbers. Our abstract design has at least one possible implementation in which the absorbers are current biased Josephson junction. We demonstrate that the coupling between the guide and the junctions is strong enough, irrespectively of the microwave guide size, and derivate realistic parameters for high fidelity operation with current experiments. Patent pending No. 200802933, Oficina Espanola de Patentes y Marcas, 17/10/2008. [Preview Abstract] |
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