Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session X38: Superconducting Qubits: Circuit Theory, Hamiltonian Analysis and Design Tools |
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Sponsoring Units: DQI Chair: Arne Grimsmo, Univ of Sydney Room: 607 |
Friday, March 6, 2020 11:15AM - 11:27AM |
X38.00001: QuCAT: superconducting quantum circuit analyzer tool in Python Mario Gely, Gary Steele Quantum circuits constructed from Josephson junctions and superconducting electronics are key to many quantum computing and quantum optics applications. Designing these circuits involves calculating the Hamiltonian describing their quantum behavior. In this talk, we present QuCAT, or "Quantum Circuit Analyzer Tool", an open-source framework to help in this task. This open-source Python library features an intuitive graphical or programmatical interface to create circuits, the ability to compute their Hamiltonian, and a set of complimentary functionalities such as calculating dissipation rates or visualizing current flow in the circuit. |
Friday, March 6, 2020 11:27AM - 11:39AM |
X38.00002: Quantization of Large Superconducting Circuits with Tensor Networks Matthew Weippert, Kristina Colladay, David Ferguson, Ryan J Epstein We report on efficient quantum simulation of large superconducting circuits using matrix product states (MPS) and the density matrix renormalization group (DMRG) technique. We analyze a circuit containing a chain of Josephson junctions, forming a superinductor, with a flux-tunable compound center junction. Kuzmin et al. explored similar circuits experimentally, achieving super strong coupling in circuit electrodynamics [1]. We obtain the lowest-lying eigenstates and energies for a chain length of 40 Josephson junctions with derived error bounds. Using these tensor network techniques we investigate the offset charge sensitivity of the circuit as a function of compound junction flux, which is not amenable to classical analysis and is intractable via exact diagonalization. |
Friday, March 6, 2020 11:39AM - 11:51AM |
X38.00003: Tensor-network diagonalization of many-body superconducting qubits Agustin Di Paolo, Thomas Baker, Alexandre Foley, David Senechal, Alexandre Blais We introduce a tensor-network method tailored to the simulation of large-scale superconducting quantum circuits. We leverage information unavailable to other state-of-the-art numerical techniques to produce first-principles coherence-time estimates for the fluxonium qubit. In particular, we study the charge dispersion of this qubit due to coherent quantum phase slip processes. Taking advantage of this novel approach, we present direct numerical evidence of the validity of the effective theory introduced in [V. E. Manucharyan et. al, PRB 85, 024521 (2012)]. |
Friday, March 6, 2020 11:51AM - 12:03PM |
X38.00004: Flux Dual Description of Noise-Insensitive Superconducting Qubits David Ferguson, David J. Clarke, Ryan J Epstein, Moe S Khalil, Daniel Weiss, Jens Koch Many superconducting qubits, such as transmons, are naturally described in terms of Cooper-pair charges hopping on and off of the nodes of the superconducting circuit. Others, such as flux qubits, are naturally described via superconducting vortices hopping in and out of the loops of the superconducting circuit. This talk describes a method to transform the Hamiltonian of a superconducting circuit from the Cooper-pair number basis to the dual vortex-number basis. In contrast to other methods that also accomplish this transformation, our method is non-perturbative and isospectral. It provides a useful framework to compare and evaluate the novel properties of qubits of the flux-qubit type such as nonstoquasticity and decreased sensitivity to environmental noise. |
Friday, March 6, 2020 12:03PM - 12:15PM |
X38.00005: Designing Better Superconducting Qubits using First-Principles Calculations and Theory Sinead Griffin Superconducting qubits have emerged as one of the leading candidates for scalable quantum computing, despite suboptimal coherence times and resonantor quality factors. In this work, we combine first-principles calculations and effective models to describe key performance losses in niobium-based superconducting qubits. We find that defects play a decisive role in their operational efficiency, and that careful control of stoichiometry can significantly improve their performance. We compare our theoretical predictions with recent experiments confirming the importance for defects for understanding decoherence pathways in qubits and quantum materials. |
Friday, March 6, 2020 12:15PM - 12:27PM |
X38.00006: Design and Analysis of Multi-Qubit Superconducting Chips for Extensible Surface Coding Nadia Haider, Alessandro Bruno, Marc Beekman, Piotr Kaminski, Leonardo DiCarlo We present an effective numerical method to analyze qubit-qubit avoided crossings and two-qubit gate times in a superconducting multi-qubit chip. Our hybrid simulation approach, combining finite element and circuit simulation, is a convenient tool to investigate complex chip layouts with limited computational resources. The simulation method has been applied to design and investigate a new multi-qubit chip layout. This new chip design and improved fabrication process have allowed us to also reduce mode hybridization between qubits and resonators and to increase qubit coherence time. |
Friday, March 6, 2020 12:27PM - 12:39PM |
X38.00007: Design and quantization of superconducting circuits Zlatko Minev, Thomas G McConkey, Firat Solgun, Jerry M. Chow, Jay M Gambetta, David McKay Quantum information processing using superconducting circuits has steadily developed into a large and diverse field. The success of building larger devices emphasizes the need to more efficiently and accurately design and quantize the distributed microwave structures, including non-linear elements, such as Josephson tunnel junctions, which comprise these devices. In this talk, we review some recent results on the comparison between several of the commonly used quantization and design approaches. |
Friday, March 6, 2020 12:39PM - 12:51PM |
X38.00008: Derivation of the Hamiltonian of a flux qubit-LC oscillator circuit using the circuit variables Fumiki Yoshihara, Sahel Ashhab, Tomoko Fuse, Kouichi Semba We derive the Hamiltonian of a single-Josephson-junction flux qubit-LC oscillator circuit using the standard quantization procedure [1]. The derived Hamiltonian consists of terms related to the LC oscillator, the flux qubit (and its higher energy levels), and the product of the two flux variables. This Hamiltonian is similar to that of the quantum Rabi model, where a two-level atom and a harmonic oscillator are coupled by a dipole-dipole interaction. Therefore, it is not surprising that the observed transmission spectra of a flux qubit-LC oscillator circuits can be well fitted by the quantum Rabi Hamiltonian [2]. We also find that the simple picture that models the coupling using a common inductor shared by the LC oscillator and the flux qubit needs only a minor modification. We thank Michel Devoret and Motoaki Bamba for stimulating discussions. |
Friday, March 6, 2020 12:51PM - 1:03PM |
X38.00009: Efficient Hamiltonian Parameter Estimation with Sequential Monte Carlo Technique Jérémy Béjanin, Carolyn Earnest, Matteo Mariantoni, Yuval R Sanders As quantum computers grow in size the task of calibrating them becomes more complex. There are many parameters to optimize for and the resulting performance of the qubits depends strongly on how well various quantities are measured. For example, knowledge of the coupling to neighboring qubits or resonators is necessary for two-qubit gates. In addition, it is preferable if qubits are located far away in frequency from harmful systems like Two-Level State defects. |
Friday, March 6, 2020 1:03PM - 1:15PM |
X38.00010: Universal Formalism and Software for Obtaining and Analyzing Hamiltonians of an Arbitrary Superconducting Circuits and Qubits. Andrey Klots, Lev B Ioffe, Robert F McDermott We propose a mathematical formalism and software that allow to express Hamiltonian of any superconducting circuit in a standardized way. The process allows for efficient/quick diagonalization of Hamiltonians of complex circuits. With vastly increasing number of various complicated qubit designs (0-pi qubits, gmons,...) it becomes necessary to be able to describe various LCJ circuits analytically and model them numerically. Normally, this requires thorough study of different degrees of freedom in the circuit in order to decide which variables are essential to understanding the properties of a circuit and which are secondary. Proposed formalism automatically classifies different degrees of freedom of a circuit based on their essential properties (charge quantization, mode frequencies) and role in the circuit. Hamiltonian of any qubit circuit can be automatically obtained and the generalized coordinates can be quantized in a most natural way: through charge number operators for charge islands and photon number operators for oscillatory circuit modes. This, in turn allows us to automatically and efficiently find eigenstates of various quantum qubit circuits. We show how the formalism is used for advancing practical qubit applications. |
Friday, March 6, 2020 1:15PM - 1:27PM |
X38.00011: Quantum landscape engineering of superconducting circuit ground states for higher-order coupler design Tim Menke, Cyrus F. Hirjibehedin, Steven Weber, Jochen Braumüller, Antti Vepsalainen, Roni Winik, Gabriel Orr Samach, David K Kim, Alexander Melville, Bethany Niedzielski, Danna Rosenberg, Mollie Schwartz, Jonilyn Yoder, Alan Aspuru-Guzik, Simon Gustavsson, Andrew James Kerman, William Oliver The response of the ground state energy of a superconducting circuit to external magnetic flux can be shaped by design to engineer quantum devices including artificial spin couplers. We propose a methodology for adding higher-order polynomial terms into the ground state energy versus flux by strongly coupling a series of rf SQUIDs. The fundamental instance of two rf SQUIDs generating a ground state with 4th-order terms is implemented experimentally. Probing this circuit with a sensor flux qubit, the qubit’s transition frequency maps the derivative of the quartic ground state in accordance with simulation. Modest levels of qubit coherence are maintained despite the relatively strong inductive coupling. These results demonstrate the viability of this design for use as a 4-local coupler and show promise for extending to higher polynomial order. |
Friday, March 6, 2020 1:27PM - 1:39PM |
X38.00012: Quantized Hodgkin-Huxley Model for Quantum Neurons Tasio Gonzalez Raya, Mikel Sanz, Enrique Solano The Hodgkin-Huxley model describes the conduction of the nervous impulse through the axon, whose membrane's electric response can be described by multiple connected electric circuits containing capacitors, voltage sources, and conductances. These conductances depend on previous depolarizing membrane voltages, which can be identified with a memory resistive element called memristor. Inspired by the recent quantization of the memristor, the Hodgkin-Huxley model has been studied in the quantum regime. The circuit obtained in this model is proposed as the building block for the construction of quantum neurons networks which can process quantum information. Hence, we study two such circuits connected in series, coupled to a quantized source. Since the main quantum contribution on these systems comes from the second moment of the voltage, we study correlations such as degree of coherence, between voltage and conductance in both circuits, proving they are quantum variables. This study paves the way for advances in hardware-based neuromorphic quantum computing, as well as quantum machine learning, which might be more efficient resource-wise. |
Friday, March 6, 2020 1:39PM - 1:51PM |
X38.00013: Floquet theory for driven-dissipative dynamics of superconducting circuits Camille Le Calonnec, Alexandru Petrescu, Alexandre Blais The manipulation and the measurement of any system made of superconducting qubits rely on the use of often strong microwave drives. Current experiments show that the standard Lindblad Master Equation commonly used to describe these driven systems breaks down even for moderate drive strength. We developed a corrected numerical implementation of the Floquet-Markov Master Equation that exactly takes into account the effects of drives and apply it to study more accurately the dissipative dynamics of superconducting qubits. |
Friday, March 6, 2020 1:51PM - 2:03PM |
X38.00014: Lifetime renormalization of driven transmon qubits and the classification of mechanisms for drive-induced energy relaxation Hakan Tureci, Alexandru Petrescu, Mohammad Moein Malekakhlagh Recent experiments in superconducting qubit systems have shown an unexpectedly strong dependence of the qubit relaxation rate on the readout drive power. This phenomenon limits the maximum measurement strength and thus the achievable readout speed and fidelity. In two recent papers [1,2] we have shown that the leading mechanism responsible for the enhancement of energy relaxation times of weakly anharmonic qubits is the presence of number non-conserving terms in the Josephson potential, which activate additional multi-photon and qubit-cavity correlated relaxation channels in the presence of drives. We address here a realistic experimental setup and account for the joint effects of radiative (Purcell) decay at finite temperature and dephasing. |
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