Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session W41: Engineered Superconducting Qubit InteractionsFocus Recordings Available

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Sponsoring Units: DQI Chair: Mollie Schwartz, MIT Lincoln Laboratory Room: McCormick Place W196C 
Thursday, March 17, 2022 3:00PM  3:12PM 
W41.00001: Dynamics of coupled superconducting oscillators at high drive power: a timecoarse graining approach Wentao Fan, Hakan E Tureci, Kanupriya Sinha We present a computationally efficient theoretical approach to accurately capture the dynamics of coupled quantum nonlinear oscillators at high drive power embedded in an environment with a given spectral function. We take the point of view that the most resourceefficient approach should both require and provide no more and no less information than what can be measured in a particular experiment. We posit that one possible approach to do that is through timecoarse graining starting with the full Hamiltonian of the system and the environment with a wellcharacterized spectral function. A systematic derivation of effective (low frequency) quantum models is presented for basic models of interest in superconducting quantum systems. Specifically, we present the drivedependent renormalized Hamiltonian and dissipative super operators of a driven Josephson nonlinear oscillator coupled to a 50ohm transmission line through a linear resonator. 
Thursday, March 17, 2022 3:12PM  3:24PM 
W41.00002: Optimization of twoqubit gate rates and crosstalk in a tunable coupling superconducting device Camille Le Calonnec, Alexandru Petrescu, Catherine Leroux, Agustin Di Paolo, Sara F Sussman, Charles Guinn, Pranav S Mundada, Andrei Vrajitoarea, Alexander P Place, Andrew A Houck, Alexandre Blais The implementation of fast and highfidelity quantum gates involves a multitude of parameters governing important properties of the system, such as the gate rate, leakage and the extent of spurious interactions. One therefore needs to carefully choose these parameters to optimize the gate fidelity and speed. We study the case of two far detuned fixed frequency transmons coupled through a fluxtunable coupler. Here, we present the results of a parameter search run to maximize gate rates while minimizing unwanted crossKerr interaction using a method based on Floquet theory. We also estimate variations on the quantities of interest due to imprecision in device fabrication. Finally, we study spectator effects in a multiqubit chip. 
Thursday, March 17, 2022 3:24PM  3:36PM 
W41.00003: Fast parametrically driven entangling gates in superconducting circuits using a tunable coupler Charles Guinn, Sara F Sussman, Pranav S Mundada, Andrei Vrajitoarea, Catherine Leroux, Alexander P Place, Camille Le Calonnec, Agustin Di Paolo, Alexandru Petrescu, Alexandre Blais, Andrew A Houck A major challenge in realizing scalable quantum computers is the optimization of twoqubit entangling gates. In current superconducting architectures, ZZ crosstalk introduces unwanted entanglement while slow gates push fidelities down due to decoherence. It is thus desirable to make entangling gates as fast as possible while maintaining control over multiqubit interactions. In this work we demonstrate a tunable coupler that can be flux biased to mitigate ZZ crosstalk while allowing fast parametrically driven twoqubit entangling gates between fardetuned fixedfrequency transmons. 
Thursday, March 17, 2022 3:36PM  4:12PM 
W41.00004: PIQUE: a new framework for quantum systems engineering Invited Speaker: Archana Kamal Highfidelity quantum state preparation, manipulation, and measurement are the three cornerstones of any quantum information processing platform. In this talk I will describe a new paradigm called PIQUE (for ParametricallyInduced QUantum Engineering), which tackles all three challenges in a unified framework employing Josephson junctionbased parametric circuits. I will first discuss some novel functionalities for quantum state stabilization and readout afforded by strong parametric interactions, which build upon and advance stateoftheart capabilities of circuitQED architectures. Next, I will discuss some new opportunities enabled by parametric systems for the exploration of fundamental open quantum system physics. 
Thursday, March 17, 2022 4:12PM  4:24PM 
W41.00005: "Minimal" topological quantum circuit Tobias Herrig, RomanPascal Riwar The outlook of protected quantum computing spurred enormous progress in the search for topological materials, sustaining a continued race to find the most experimentally feasible platform. Here, we show that one of the simplest quantum circuits, the Cooperpair transistor, exhibits a nontrivial Chern number which has not yet been discussed, in spite of the exhaustive existing literature. Surprisingly, the resulting quantized current response is robust with respect to a large number of external perturbations, most notably lowfrequency charge noise and quasiparticle poisoning. Moreover, the fact that the higher bands experience crossings with higher topological charges leads to all the bands having the same Chern number, such that there is no restriction to stay close to the ground state. Remaining small perturbations are investigated based on a generic Master equation approach. Finally, we discuss a feasible protocol to measure the quantized current. 
Thursday, March 17, 2022 4:24PM  4:36PM 
W41.00006: Single Shot iToffoli Gate in Dispersively Coupled Superconducting Qubits Aneirin J Baker, Michael J Hartman, Ivan Tsitsilin, Federico Roy, Gehard Huber, Niklas Glaser, Stefan Filipp Quantum algorithms often benefit from the ability to execute multiqubit (>2) gates. To date such multiqubit gates are typically decomposed into single and twoqubit gates, particularly in superconducting qubit architectures. The ability to perform multiqubit operations in a single step could vastly improve the fidelity and execution time of many algorithms. 
Thursday, March 17, 2022 4:36PM  4:48PM 
W41.00007: Automating Quantization and Diagonalization of Superconducting Circuits Sai Pavan Chitta, Jens Koch The analysis of superconducting circuits currently consists of a multistep process combining analytical and numerical elements that together enable the transition from a lumpedelement circuit diagram to a quantum Hamiltonian ready to be diagonalized. Important aspects include the choice of appropriate circuit variables, incorporation of constraints imposed by Kirchhoff's laws, the elimination of cyclic variables, and the distinction of degrees of freedom subject to periodic versus confining boundary conditions upon quantization. We present work that systematizes these steps in a manner amenable to algorithmic implementation, thus opening the pathway for streamlined and efficient analysis of unexplored superconducting circuits to serve as qubits, tunable couplers, and similar parts of quantum processors. A concrete implementation of this circuit quantization tool is made available as an extension to the opensource scqubits package. 
Thursday, March 17, 2022 4:48PM  5:00PM 
W41.00008: Liberating Quantum Processors from Parasitic Interactions Mohammad H Ansari I explain two methods for zeroing parasitic interaction between a pair of qubits. A year ago, for the first time we showed that magnetic modulation helps to set the interaction to zero in a hybrid circuit containing a transmon coupled to a flux qubits. Most recently we developed the theory and showed the possibility of zeroing parasitic interaction in nonmodulable fixed parameter qubits. For this we need to use microwave driving, and we named this technique "dynamic cancellation." This owes to a fundamental symmetry in the Hamiltonian of superconducting processors. Using our understanding of parasitic interactions and how to eliminate them, one can aim for perfect two qubit gate. One example I show is PF gate. 
Thursday, March 17, 2022 5:00PM  5:12PM 
W41.00009: ThreeQubit Parasitic Interactions in Superconducting Circuits Xuexin Xu, Mohammad H Ansari Superconducting qubits have proven to be an excellent candidate for quantum computing. But because of the imperfections in the gate fidelity of these qubits, making a giant network with many coupled qubits is still a far fetched dream. A much needed indepth study is required to understand the nature of qubitqubit couplings, especially the socalled parasitic interactions in order to minimize the leakage and have a muchimproved gate fidelity. We study the Hamiltonian of a circuit containing multiple superconducting qubits coupled via shared resonators. We derive, both analytically and numerically, the parasitic multiZ interactions for such a system. We also provide possible parameter regimes to minimize the parasitic interactions in order to achieve higher fidelity gate implementations for larger circuits. 
Thursday, March 17, 2022 5:12PM  5:24PM 
W41.00010: Ultrastrong capacitive and inductive couplings of flux qubits María HitaPérez, Gabriel Jaumà, Manuel Pino Garcia, Juan Jose GarciaRipoll

Thursday, March 17, 2022 5:24PM  5:36PM 
W41.00011: Generating families of threequbit gates from simultaneous twoqubit gates, part 1: theory Anton Frisk Kockum, Xiu Gu, Jorge FernándezPendás, Pontus Vikstål, Tahereh Abad, Christopher W Warren, Andreas Bengtsson, Giovanna Tancredi, Vitaly Shumeiko, Jonas Bylander, Göran Johansson Decoherence of qubits limits nearterm quantum computers to only run lowdepth quantum circuits with acceptable fidelity. This severely restricts what quantum algorithms can be compiled and implemented on such devices. One way to overcome these limitations is to expand the available gate set from single and twoqubit gates to multiqubit gates, which entangle three or more qubits in a single step. Here, we show that such multiqubit gates can be realized by the simultaneous application of multiple twoqubit gates to a group of qubits where at least one qubit is involved in two or more of the twoqubit gates. Multiqubit gates implemented in this way are as fast as, and often even faster than, the constituent twoqubit gate operations. Importantly, these multiqubit gates are ready to be used in current quantumcomputing platforms without any modification of the quantum processor. We demonstrate this idea for two specific cases: simultaneous controlledZ gates and simultaneous iSWAP gates. We show how the resulting multiqubit gates relate to other wellknown multiqubit gates and simulate gate fidelities well above 99%. 
Thursday, March 17, 2022 5:36PM  5:48PM 
W41.00012: Generating families of threequbit gates from simultaneous twoqubit gates, part 2: experiment Christopher W Warren, Anton Frisk Kockum, Jorge Fernández Pendás, Shahnawaz Ahmed, Giovanna Tancredi, Amr Osman, Janka Biznárová, Xiu Gu, Göran Johansson, Jonas Bylander Whether one is working on noisy intermediatescale quantum (NISQ) algorithms or towards error correction, the coherence of a quantum processor sets bounds on the depth which can be achieved for any sequence of operations. Each of these cases requires the generation of large, entangled states. This is typically achieved by implementing a universal gate set formed of single and twoqubit operations. While generating these states is achievable, as devices grow larger in terms of the number of qubits, the depth needed to entangle all qubits increases. 
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