Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session M28: Superconducting Qubits: Measurement & Photodetection |
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Sponsoring Units: GQI Chair: Konrad Lenhert, National Institute of Standards and Technology Room: 601 |
Wednesday, March 5, 2014 11:15AM - 11:27AM |
M28.00001: Efficient Measurement of Superconducting Resonators Steven Sendelbach, Micah Stoutimore, Josh Strong, Ofer Naaman, Brooks Campbell, John Martinis S-parameter measurements of high-Q superconducting resonators at single-photon drive powers often require significant averaging with associated long acquisition time. We have developed a procedure for optimizing the frequency sweep-plan of the measurement, and found that an appropriate choice of frequencies has a significant impact on its efficiency. An optimized sweep-plan design offers up to a factor of two reduction in the variance of extracted parameters, in comparison to a linear sweep-plan having the same total acquisition time. We experimentally compare the performance of the optimized and linear sweeps in measurements of high-Q aluminum CPW resonators. [Preview Abstract] |
Wednesday, March 5, 2014 11:27AM - 11:39AM |
M28.00002: Fast Multiplexed Readout of Xmon Qubits Part I: Design Daniel Sank, E. Jeffrey, J.Y. Mutus, T.C. White, R. Barends, J. Kelly, Y. Chen, P. Roushan, B. Campbell, Z. Chen, B. Chiaro, A. Dunsworth, A. Megrant, C. Neill, P. O'Malley, C. Quintana, A. Vainsencher, J. Wenner, A.N. Cleland, J.M. Martinis Realization of a surface code quantum computer requires fast scalable qubit readout. Previous systems have shown accurate readout in continuous wave mode. This neglects the transient response time which is crucial for the operation of the surface code and for measurement accuracy in the presence of finite qubit T1. We have designed a readout system, based on an integrated band pass filter, which achieves very fast transient response while maintaining long qubit T1. Our design uses separate readout resonators for each qubit. This allows individual qubit readout with frequency multiplexing while preventing correlated measurement errors. By connecting each resonator to a single filter the device requires zero additional on chip area and no extra control lines. We present design considerations, theory of operation, and physical layout of the device. With high fidelity gates this system forms the final element needed for a surface code cell. [Preview Abstract] |
Wednesday, March 5, 2014 11:39AM - 11:51AM |
M28.00003: Fast Multiplexed Readout of Xmon Qubits Part II: Results Evan Jeffrey, Daniel Sank, Josh Mutus, Theodore White, Rami Barends, Brooks Campbell, Zijun Chen, Yu Chen, Ben Chiaro, Andrew Dunsworth, Julian Kelly, Anthony Megrant, Peter O'Malley, Charles Neill, Chris Quintana, Pedram Roushan, Amit Vainsencher, James Wenner, Andrew Cleland, John Martinis Fast and scalable qubit readout is an essential part of building a surface code based quantum computer. Here we show single- and multi-qubit frequency multiplexed readout of Xmon qubits with independent readout resonators coupled to a single readout line. We analyze both the CW behavior and the the transient response, finding that the ring-up time of the resonators is a major contribution to total readout time -- an important criterion for scalability in a fault tolerant system. Our bandpass filter design allows fast ring-up without compromising T1. We show single-qubit readout with an intrinsic fidelity of 99\% in 120~ns. Multiple-qubit readout is limited by amplifier saturation and achieves 99\% fidelity on 4 qubits in 200~ns. Correlated errors are a major problem for surface code quantum computing. We measure very low correlated errors and measurement crosstalk, which we attribute to using independent readout resonators. [Preview Abstract] |
Wednesday, March 5, 2014 11:51AM - 12:03PM |
M28.00004: Optimizing filtering for fast measurements in circuit QED Jay Gambetta, Oliver Dial, Andrew Cross, Douglas Mcclure, Jerry Chow, Matthias Steffen Quantum error correction schemes, for example the popular surface code, involve running interleaved gate operations and measurements on a set of physical qubits. For this reason it is important to have fast measurements. In a fast measurement most of the information will be in the transients of the signal. In this talk we present a filtering technique to extract optimal qubit state information from the transient response of the resonator. I will also discuss techniques for rapidly driving the readout resonator to its ground state independent of the qubit state. We acknowledge support from IARPA under contract W911NF-10-1-0324. [Preview Abstract] |
Wednesday, March 5, 2014 12:03PM - 12:15PM |
M28.00005: Ultrafast quantum nondemolition measurement based on diamond-shaped artificial atom Bruno K\"ung, Etienne Dumur, Igor Diniz, Alexey Feofanov, Thomas Weissl, C\'ecile Naud, Wiebke Guichard, Alexia Auff\`eves, Olivier Buisson We present a theoretical study of a quantum nondemolition readout scheme based on a superconducting artificial atom with two internal degrees of freedom [1]. In comparison with the most widely employed readout scheme for superconducting qubits, the dispersive readout in a circuit quantum electrodynamics architecture, our approach promises a significantly stronger measurement signal. This should allow for a high-fidelity readout in a single shot. Our device consists of two transmons (i.e., small capacitively shunted Josephson junctions) coupled via a large inductance. The resulting circuit exhibits a symmetric and an antisymmetric oscillation which we use as a logical and ancilla qubit, respectively. The Josephson non-linearity leads to a cross-Kerr-like coupling of the two oscillations. This allows us to read out the logical qubit state by measuring the ancilla qubit frequency. To measure the ancilla qubit frequency, we couple it to a superconducting microwave resonator, allowing for a large amplitude and a fast response of the transmitted microwave signal. At the same time, the logical qubit remains weakly coupled and far detuned from the resonator, preventing qubit relaxation due to the Purcell effect. \\[4pt] [1] I. Diniz et al., Phys. Rev. A {\bf 87}, 033837 (2013) [Preview Abstract] |
Wednesday, March 5, 2014 12:15PM - 12:27PM |
M28.00006: High quality superconducting resonators for QND Measurements of Qubits and Sensitive Photon Detections LianFu Wei We proposed an approach to implement the QND measurements of qubits by probing the intensity and phase transmissions of driven signals through a dispersively-coupled cavity. With such a technique we foud that the states of the qubits can be high-effectively reconstructed tomographically and Bell's-, Mermin's- and Svetlichny's inequalities for confirming the existences of quantum nonlocal correlations can be tested numerically. We designed and fabricated the half-wavelength- and quarter-wavelength superconducting transmission line resonators with various coupling configurations by sputtering and photolithographic techniques. The measured quality factors of these resonators are 10$^4$ and 10$^6$, respectively, at low-temperature (20mK). We have experimentally demonstrated that the fabricated resonators could be served as the desired sensitive detectors of single photons. Applications of these resonators for experimental solid state quantum information processing are possible. [Preview Abstract] |
Wednesday, March 5, 2014 12:27PM - 12:39PM |
M28.00007: Tailoring Multiqubit Measurement Operators Through Dynamic Cavity States (Part 1) J. Blumoff, K. Chou, S. Nigg, M. Reed, B. Vlastakis, R. Heeres, L. Frunzio, S. Girvin, M.H. Devoret, R.J. Schoelkopf Recent improvements in resonator coherence times in the field of superconducting qubits have allowed access to a rich new toolbox which takes advantage of their large and long-lived Hilbert space. In this talk, I introduce several techniques utilizing the cavity state and protocols built from these techniques. We condition the evolution of a cavity state via dispersive interactions with multiple qubits, and manipulate the system to implement quantum erasure, selectively reducing the space of the resulting entanglement. This can be tailored to create a spectrum of measurement operators including measurements on a selectable subset of the system. This ability is a prerequisite for most approaches to quantum error correction. The following talk will cover the experimental implementation. [Preview Abstract] |
Wednesday, March 5, 2014 12:39PM - 12:51PM |
M28.00008: Tailoring multi-qubit measurement operators through dynamic cavity states (Part 2) K. Chou, J. Blumoff, S. Nigg, M. Reed, B. Vlastakis, R. Heeres, L. Frunzio, S. Girvin, M.H. Devoret, R.J. Schoelkopf Recent improvements in cavity coherence in cQED have allowed high precision manipulation of photonic cavity states, illustrating a powerful toolbox for manipulating and encoding quantum information in either superconducting qubits or cavity states. In order for this architecture to become a viable system for computation, it will be necessary to have the flexibility to probe both global as well as limited properties of a register of qubits. In particular, the ability to tailor measurement operators is a technology that will be required for error correction. Extending the theoretical framework discussed in the previous talk, we will show experimental work toward realizing this goal. Our design consists of a register of qubits coupled to a high Q storage cavity and ancilla qubit enabled fast readout through a low Q cavity. [Preview Abstract] |
Wednesday, March 5, 2014 12:51PM - 1:03PM |
M28.00009: Photon-number-dependent Purcell relaxation rate Eyob A. Sete, Jay M. Gambetta, Alexander N. Korotkov We analyze the Purcell relaxation rate of a superconducting qubit coupled to a resonator, which is coupled to a transmission line and pumped by an external microwave drive. Considering the typical regime of the qubit measurement, we focus on the case when the qubit frequency is significantly detuned from the resonator frequency. Surprisingly, the Purcell rate decreases when the strength of the microwave drive is increased. This suppression becomes significant in the nonlinear regime. The microwave drive also causes excitation of the qubit; however, the excitation rate is much smaller than the relaxation rate. Our analysis also applies to a more general case of a two-level quantum system coupled to a cavity. [Preview Abstract] |
Wednesday, March 5, 2014 1:03PM - 1:15PM |
M28.00010: Low-Power Dispersive Measurements of High-Coherence Flux Qubits David Hover, A.P. Sears, T. Gudmundsen, A.J. Kerman, P.B. Welander, J.L. Yoder, A. Kamal, S. Gustavsson, X.Y. Jin, J. Birenbaum, J. Clarke, W.D. Oliver We report on progress towards nondestructive dispersive measurements of a high-coherence flux qubit. A~capacitively shunted flux qubit that incorporates high-Q MBE aluminum will have longer relaxation and dephasing times when compared to a conventional flux qubit, while also maintaining the large anharmonicity necessary for complex gate operations. We numerically investigate the expected measurement fidelity of the improved qubit and present measurements that explore the boundary between destructive and nondestructive dispersive readout. This research was funded in part by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA); and by the Assistant Secretary of Defense for Research {\&} Engineering under Air Force Contract number FA8721-05-C-0002.~ All statements of fact, opinion or conclusions contained herein are those of the authors and should not be construed as representing the official views or policies of IARPA, the ODNI, or the U.S. Government [Preview Abstract] |
Wednesday, March 5, 2014 1:15PM - 1:27PM |
M28.00011: Large gain quantum-limited qubit state measurement using a two mode nonlinear cavity Saeed Khan, R. Vijay, Irfan Siddiqi, Aashish Clerk A single nonlinear cavity dispersively coupled to a qubit functions as a large gain detector near a bifurcation, but also has an unavoidable large backaction that prevents quantum-limited measurement at weak couplings [1]. We show theoretically that a modified setup involving two cavities (one linear, one nonlinear) and a dispersively coupled qubit allows for a far more optimal measurement. In particular, operating near a point of bifurcation, one is able to both achieve a large gain as well as a near quantum-limited backaction. The increased system flexibility also enables large measurement rate and smaller nonlinear shot noise dephasing than is possible with single nonlinear cavity setups. We present analytic results for the gain and noise of this detector and a heuristic understanding of the physics, thus presenting a complete description of this new way of performing weak qubit state measurements. The setup we describe can easily be realised in experiments with superconducting circuits involving Josephson junctions [2, 3].\\[4pt] [1] C. LaFlamme, A.A. Clerk, Phys. Rev. A 83, 033803 (2011)\\[0pt] [2] F.R. Ong et al., Phys. Rev. Lett. 106, 167002 (2011)\\[0pt] [3] M. Hatridge et al., Phys. Rev. B 83, 134501 (2011) [Preview Abstract] |
Wednesday, March 5, 2014 1:27PM - 1:39PM |
M28.00012: Catching Classical Shaped Microwave Photons in a Superconducing Resonator with 99.4\% Efficiency James Wenner, Y. Yin, Y. Chen, R. Barends, B. Chiaro, E. Jeffrey, J. Kelly, A. Megrant, J. Mutus, C. Neill, P. O'Malley, P. Roushan, D. Sank, A. Vainsencher, T. White, Alexander N. Korotkov, A.N. Cleland, John M. Martinis Deterministic quantum state transfer requires receivers to transfer quantum states from traveling qubits to fixed logic qubits. Reflections must be minimized to avoid energy loss and phase interference. Here, we classically drive a 6GHz superconducting coplanar resonator with tunable coupling to the drive/readout line while we measure the reflected and captured signals with a HEMT amplifier. Using an exponentially increasing drive pulse, we demonstrate a 99.4\% deterministic single photon absorption efficiency (97.4\% receiver efficiency). We further demonstrate that experimental absorption efficiencies agree with theory within 3\% for various pulse parameters and shapes. With the fidelity now at the error threshold for fault tolerant quantum communication (96\%) and computation (99.4\%) and comparable to fidelities of good logic gates and measurements, new designs may be envisioned for quantum communication and computation systems. [Preview Abstract] |
Wednesday, March 5, 2014 1:39PM - 1:51PM |
M28.00013: Qubit coupling to superconducting whispering gallery mode resonator Z.K. Minev, I.M. Pop, K. Serniak, M.H. Devoret A protected quantum register composed of a high quality mode coupled to a quantum bit and a fast readout mode promise a hardware efficient and technically realizable module-based quantum network [Science 339, 1169 (2013); PRL 111, 120501 (2013)]. Such a module is designed in an integrated manner by embedding a quantum bit inside the clean environment of a superconducting whispering gallery mode resonator. Its two orthogonal modes can have a large asymmetry in coupling to a microwave transmission line, thus realizing a storage and readout mode. [Preview Abstract] |
Wednesday, March 5, 2014 1:51PM - 2:03PM |
M28.00014: Graph theory and nonreciprocity in coupled-mode systems Leonardo Ranzani, Jose Aumentado Coupled-mode systems involving more than 2 interacting modes can break reciprocal symmetry and unidirectional mode conversion can be observed. This is the case, for example, in multiple-pump parametric processes and in superconducting DC-SQUID amplifiers.\footnote{A. Kamal, \textit{et al.} ``Noiseless non-reciprocity in a parametric active device'' \textit{Nature Physics}, 7.4, (2001): 311-315} While reciprocity in dual-mode systems can be broken only in a sequenced coupling scheme, a sequence is not required in systems with more than 2 interacting modes. The analysis of such systems is, however, extremely complex when a high number of coupled modes is involved. In this talk we are going to discuss how graphs can be used to analyse reciprocity in coupled-mode systems and reveal the conditions that need to be satisfied for reciprocity to be broken. In this representation modes are associated to vertices and couplings to edges in an abstract graph. General conditions for reciprocity can be determined from the connectivity of the graph. [Preview Abstract] |
Wednesday, March 5, 2014 2:03PM - 2:15PM |
M28.00015: Probe susceptibility of a strongly driven qubit Matti Silveri, Jani Tuorila, Mika Kemppainen, Erkki Thuneberg The characteristic of a quantum system change upon coupling it to a driving field. In a typical circuit QED setup, driving is implemented with microwaves and the driven superconducting qubit is probed via a coupled LC cavity whose transmission or reflection properties are measurable. However, the entanglement between the qubit and the driving field leads to the formation of quasienergy states and, thus, modifications of the probe response. Even if the non-driven qubit-cavity system lies in the dispersive regime, the response of the driven system may be better described by an absorptive approach[1]. We have shown by using the Floquet formalism and a calculation reminiscent of the Fermi's golden rule that the concept of the probe susceptibility can be extended to strongly driven quantum systems[2,3]. Furthermore, we have applied these results to interpret and explain accurately a measurement where a charge qubit is strongly driven via the Josephson nonlinearity and probed via an LC cavity[3]. [1] J. Tuorila et al., Phys. Rev. Lett. 105, 257003 (2010). [2] M. Silveri et al., Phys. Rev. B 87, 134505 (2013). [3] J. Tuorila et al., Supercond. Sci. Technol. 26, 124001 (2013). [Preview Abstract] |
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