Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session C46: Superconducting Qubits: Control and Crosstalk |
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Sponsoring Units: GQI Chair: Benjamin Palmer, Laboratory for Physical Sciences Room: 393 |
Monday, March 13, 2017 2:30PM - 2:42PM |
C46.00001: Josephson Junction Double-Balanced Modulator for Qubit Control Ofer Naaman, Joshua Strong, David Ferguson, Jonathan Egan, Robert Hinkey, Nancyjane Bailey We report on a double-balanced modulator built with a Josephson junction bridge embedded in a band-pass network. The device was engineered to operate in the 6-10 GHz range, dissipate no power on chip, exhibit saturation powers in excess of 1 nW, and actuate using flux signals with IF bandwidth from DC to 850 MHz. We discuss the characterization of the device performance using S-parameter and saturation power measurements, and demonstrate its balanced operation in a carrier-suppressed modulation experiment. The device can be integrated with passive components to implement an on-chip vector modulator functioning as a drop-in replacement for the ubiquitous I/Q mixer. [Preview Abstract] |
Monday, March 13, 2017 2:42PM - 2:54PM |
C46.00002: A Josephson Junction based SPDT switch Helin Zhang, Nathan Earnest, Yao Lu, Ruichao Ma, Srivatsan Chakram, David Schuster RF microwave switches are useful tools in cryogenic experiments, allowing for multiple experiments to be connected to a single cryogenic measurement chain. However, these switches dissipate a substantial amount of heat, preventing fast switching. Josephson junction (JJ) are a promising avenue for realizing millikelvin microwave switching[1,2]. We present a JJ based single-pole-double throw (SPDT) switch that has fast switching time, no heat dissipation, large on/off contrast, and works over a wide bandwidth. The switch can be used for real-time switching between experiments, routing single photons, or even generating entanglement. We will describe the design of the switch and present experimental characterization of its performance. \newline [1]. Benjamin J. Chapman, Bradley A. Moores, Eric I. Rosenthal, Joseph Kerckhoff, K. W. Lehnert \emph{General purpose multiplexing device for cryogenic microwave systems}, Appl. Phys. Lett. 108, 222602 (2016) \newline [2]. O. Naaman, J. A. Strong, D. G. Ferguson, J. Egan, N. Bailey, R. T. Hinkey \emph{Josephson junction microwave modulators for qubit control}, arXiv:1610.07987v1 [Preview Abstract] |
Monday, March 13, 2017 2:54PM - 3:06PM |
C46.00003: Direct Synthesis of Microwave Waveforms for Quantum Computing James Raftery, Andrei Vrajitoarea, Gengyan Zhang, Zhaoqi Leng, Srikanth Srinivasan, Andrew Houck Current state of the art quantum computing experiments in the microwave regime use control pulses generated by modulating microwave tones with baseband signals generated by an arbitrary waveform generator (AWG). Recent advances in digital analog conversion technology have made it possible to directly synthesize arbitrary microwave pulses with sampling rates of 65 gigasamples per second (GSa/s) or higher. These new ultra-wide bandwidth AWG's could dramatically simplify the classical control chain for quantum computing experiments, presenting potential cost savings and reducing the number of components that need to be carefully calibrated. Here we use a Keysight M8195A AWG to study the viability of such a simplified scheme, demonstrating randomized benchmarking of a superconducting qubit with high fidelity. [Preview Abstract] |
Monday, March 13, 2017 3:06PM - 3:18PM |
C46.00004: Superconducting Qubit with Integrated Single Flux Quantum Controller Part I: Theory and Fabrication Matthew Beck, Edward Leonard Jr., Ted Thorbeck, Shaojiang Zhu, Caleb Howington, JJ Nelson, Britton Plourde, Robert McDermott As the size of quantum processors grow, so do the classical control requirements. The single flux quantum (SFQ) Josephson digital logic family offers an attractive route to proximal classical control of multi-qubit processors. Here we describe coherent control of qubits via trains of SFQ pulses. We discuss the fabrication of an SFQ-based pulse generator and a superconducting transmon qubit on a single chip. Sources of excess microwave loss stemming from the complex multilayer fabrication of the SFQ circuit are discussed. We show how to mitigate this loss through judicious choice of process workflow and appropriate use of sacrificial protection layers. [Preview Abstract] |
Monday, March 13, 2017 3:18PM - 3:30PM |
C46.00005: Superconducting Qubit with Integrated Single Flux Quantum Controller Part II: Experimental Characterization Edward Leonard Jr., Matthew Beck, Ted Thorbeck, Shaojiang Zhu, Caleb Howington, JJ Nelson, Britton Plourde, Robert McDermott We describe the characterization of a single flux quantum (SFQ) pulse generator cofabricated with a superconducting quantum circuit on a single chip. Resonant trains of SFQ pulses are used to induce coherent qubit rotations on the Bloch sphere. We describe the SFQ drive characteristics of the qubit at the fundamental transition frequency and at subharmonics ($\omega_{01}/n, n=2,3,4,\dots$). We address the issue of quasiparticle poisoning due to the proximal SFQ pulse generator, and we characterize the fidelity of SFQ-based rotations using randomized benchmarking. [Preview Abstract] |
Monday, March 13, 2017 3:30PM - 3:42PM |
C46.00006: Autonomous Reversible Fluxon Logic Gates Waltraut Wustmann, Kevin D. Osborn The low-dissipative motion of fluxons in long Josephson junctions (LJJ) may be exploited in future computational settings such as reversible digital computing and flux qubit readout. The former aims to minimize energy cost per logical operation and in the latter a fluxon delay dependent on the state of the flux qubit is detected. We study the scattering of fluxons between LJJs which are connected by a special interface containing only a few ordinary JJs. The structure exhibits intriguing phenomena, where the fluxon is forward-scattered as either fluxon or antifluxon, depending on the interface parameters. These processes are moreover reversible, involving almost no energy loss. We identify the phenomena with the Identity and NOT gate, respectively, by noting that the fluxon and antifluxon can represent the two bit states. Unlike existing reversible digital logic which rely on adiabatic external drives, these reversible gates are autonomous. The gate dynamics are quantitatively captured by a collective coordinate approach using only two variables, where each one represents a LJJ field using a fluxon and mirror antifluxon. We then show that a reversible 2-bit gate can be made which is related to the dynamics of the 1-bit gates. [Preview Abstract] |
Monday, March 13, 2017 3:42PM - 3:54PM |
C46.00007: On-chip control signal measurements for superconducting qubits Brooks Foxen, Zijun Chen, Ben Chiaro, Andrew Dunsworth, Charles Neill, Chris Quintana, Jim Wenner, John M. Martinis As superconducting quantum computing circuits grow in complexity, efficiently tuning up high-fidelity gate operations will become increasingly important. Chip mounts, wire bonds, and even commercial microwave connectors cause signal path irregularities that distort control waveforms in complex ways. I will present measurements of the system transfer function, from room temperature DAC to superconducting chip, with the goal of parameterizing gate distortion. Additionally we can use this model to improve the signal path and our gate performance. [Preview Abstract] |
Monday, March 13, 2017 3:54PM - 4:06PM |
C46.00008: Crosstalk in superconducting quantum circuits Christian Kraglund Andersen, Yves Salathe, Johannes Heinsoo, Sebastian Krinner, Andrian Beckert, Alexandre Blais, Andreas Wallraff Quantum information protocols beyond the simplest tests requires a large number of qubits to be implemented in a scalable way with a design that allows for high fidelity one- and two-qubit gates and single-shot readout. However, practical designs typically suffer from unwanted crosstalk between the qubits. In this talk we analyze the crosstalk from a theoretical point of view. We divide the crosstalk into three main contributions: a constant qubit-qubit interaction, cross-driving leading to AC-stark shifts and cross-flux dependence leading to unwanted phase changes of the qubits. We address how the crosstalk influences the performance of the chip and, in particular, how the crosstalk can be mitigated when scaling up the system to multiple qubits to achieve a set of gates with minimal-crosstalk. Finally, we apply the analysis to an experimentally implemented qubit design. [Preview Abstract] |
Monday, March 13, 2017 4:06PM - 4:18PM |
C46.00009: High Fidelity, Numerical Investigation of Cross Talk in a Multi-Qubit Xmon Processor Alireza Najafi-Yazdi, Julian Kelly, John Martinis Unwanted electromagnetic interference between qubits, transmission lines, flux lines and other elements of a superconducting quantum processor poses a challenge in engineering such devices. This problem is exacerbated with scaling up the number of qubits. High fidelity, massively parallel computational toolkits, which can simulate the 3D electromagnetic environment and all features of the device, are instrumental in addressing this challenge. In this work, we numerically investigated the crosstalk between various elements of a multi-qubit quantum processor designed and tested by the Google team. The processor consists of 6 superconducting Xmon qubits with flux lines and gatelines. The device also consists of a Purcell filter for readout. The simulations are carried out with a high fidelity, massively parallel EM solver. We will present our findings regarding the sources of crosstalk in the device, as well as numerical model setup, and a comparison with available experimental data. [Preview Abstract] |
Monday, March 13, 2017 4:18PM - 4:30PM |
C46.00010: Design and characterization of a multi-qubit circuit for quantum simulations Vinay Ramasesh, Kevin O'Brien, Allison Dove, John Mark Kreikebaum, James Colless, Irfan Siddiqi Superconducting qubits, due to remarkable progress in coherence times, have recently realized a variety of quantum simulation experiments. These simulations, which promise to shed light on open questions in fields ranging from quantum chemistry to quantum chromodynamics, have largely been performed with either a single qubit or a few coupled qubits. Implementing more sophisticated simulations requires scaling up the number of qubits on a single chip.~ Additionally, the recent development of a broadband near-quantum-limited amplifier offers the possibility to simultaneously read out the state of multiple qubits on a single device. We present initial progress on the design, fabrication, and characterization of such a multi-qubit cQED circuit, with a focus towards near-term quantum simulation applications. This work was supported by the Army Research Office [Preview Abstract] |
Monday, March 13, 2017 4:30PM - 4:42PM |
C46.00011: Engineering Signal Integrity in Multi-qubit Devices: Part I William O'Brien, Andrew Bestwick, Mehrnoosh Vahidpour, Jon Tyler Whyland, Joel Angeles, Diego Scarabelli, Marius Villiers, Michael Curtis, Anthony Polloreno, Michael Selvanayagam, Alexander Papageorge, Nickolas Rubin, Chad Rigetti Cross-talk between qubits can lead to coherence errors, which are particularly difficult to correct in a quantum algorithm. To mitigate noise channels, we have developed a superconducting circuit architecture that partitions devices into shielded compartments with well-defined boundaries. These structures are designed to isolate each component of the circuit. We describe the design and process flow for fabricating robust superconducting boundaries. We present preliminary results on our success in attenuating unwanted cross-talk, while enabling the desired coupling among components. [Preview Abstract] |
Monday, March 13, 2017 4:42PM - 4:54PM |
C46.00012: Engineering Signal Integrity in Multi-qubit Devices: Part II Mehrnoosh Vahidpour, William O'Brien, Andrew Bestwick, Joel Angeles, Jon Tyler Whyland, Diego Scarabelli, Marius Villiers, Michael Curtis, Anthony Polloreno, Michael Selvanayagam, Alexander Papageorge, Nicholas Rubin, Chad Rigetti Rapidly increasing complexity of quantum hardware presents novel engineering challenges in cryogenics and microwave design. The issue of signal integrity comes to the forefront when designing a collection of individually-addressable qubits that share an electromagnetic environment. Engineering that environment properly is imperative to reducing cross-talk and loss, and ensuring that gate operations can be performed with high fidelity. Recent progress in novel fabrication techniques and practice is presented, showcasing a set of advancements that significantly improve signal isolation and reduce loss. [Preview Abstract] |
Monday, March 13, 2017 4:54PM - 5:06PM |
C46.00013: Hardware for dynamic quantum computing experiments: Part I Blake Johnson, Colm Ryan, Diego Riste, Brian Donovan, Thomas Ohki Static, pre-defined control sequences routinely achieve high-fidelity operation on superconducting quantum processors. Efforts toward dynamic experiments depending on real-time information have mostly proceeded through hardware duplication and triggers, requiring a combinatorial explosion in the number of channels. We provide a hardware efficient solution to dynamic control with a complete platform of specialized FPGA-based control and readout electronics; these components enable arbitrary control flow, low-latency feedback and/or feedforward, and scale far beyond single-qubit control and measurement. We will introduce the BBN Arbitrary Pulse Sequencer 2 (APS2) control system and the X6 QDSP readout platform. The BBN APS2 features: a sequencer built around implementing short quantum gates, a sequence cache to allow long sequences with branching structures, subroutines for code re-use, and a trigger distribution module to capture and distribute steering information. The X6 QDSP features a single-stage DSP pipeline that combines demodulation with arbitrary integration kernels, and multiple taps to inspect data flow for debugging and calibration. We will show system performance when putting it all together, including a latency budget for feedforward operations. [Preview Abstract] |
Monday, March 13, 2017 5:06PM - 5:18PM |
C46.00014: Hardware for dynamic quantum computing experiments: Part II Diego Rist\`e, Colm Ryan, Marcus da Silva, Brian Donovan, Thomas Ohki, Blake Johnson In fault-tolerant quantum computing, non-transversal gates will require ancillary qubits to interact with the logical register. Measurements of these ancillas must then determine subsequent logical operations in real time. Here we use the in-house developed BBN APS2 control system and X6 QDSP readout platform to test efficient feedback and feed-forward protocols on small registers of physical transmon qubits. By comparing closed- and (postselected) open-loop experiments, we observe no significant error added by feedback other than decoherence during its latency ($<0.02\,T_2^\star$). Demonstrations include the simultaneous reset of a three-qubit register, deterministic entanglement by measurement, and teleportation. [Preview Abstract] |
Monday, March 13, 2017 5:18PM - 5:30PM |
C46.00015: Using a Superconducting Qubit as a Millikelvin Vector Network Analyzer Markus Jerger, Z\'enon Eric Vasselin, Arkady Fedorov In experiments that require fast electrical control pulses, it is often crucial that the signal reaching the sample is a faithful reproduction of the intended signal. For highest precision, the frequency-dependent transmission coefficient of the control line has to be taken into account. When both ends of the line are accessible, the transmission coefficient is readily measured with a network analyzer, but when one end is inside a cryostat or signal transmission on the sample is to be taken into account that can be challenging. We have developed a method for the in-situ characterization of the response of a cryogenic microwave input line with the aid of a superconducting qubit. By periodically modulating the energy level splitting of the qubit, we determine the amplitude and phase of transmission of the line controlling the level splitting from DC to 100s of megahertz at millikelvin temperatures. This can be directly applied to improve the fidelity of a number of protocols, most notably controlled phase gates between two superconducting quantum bits using magnetic flux frequency control. These gates are the most common way to generate two-qubit operations in superconducting quantum processors and their fidelities rely on frequency control on a nanosecond time scale. [Preview Abstract] |
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