Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session X30: Circuit Theory, Hamiltonian Analysis and Design Tools IIFocus Live
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Sponsoring Units: DQI Chair: Peter Groszkowski, University of Chicago |
Friday, March 19, 2021 8:00AM - 8:12AM Live |
X30.00001: Measurements of Quantum Hamiltonians with Locally-Biased Classical Shadows Charles Hadfield, Sergey Bravyi, Rudy Raymond, Antonio Mezzacapo Obtaining precise estimates of quantum observables is a crucial step of variational quantum algorithms. We consider the problem of estimating expectation values of Hamiltonians, obtained on states prepared on a quantum computer. Locally-Biased Classical Shadows is a novel estimator for this task, which is locally optimized with knowledge of the Hamiltonian and a classical approximation to the underlying quantum state. It is based on the concept of classical shadows of a quantum state, and has the important property of not adding to the circuit depth for the state preparation. The performance has been tested numerically for molecular Hamiltonians of increasing size, finding a sizable reduction in variance with respect to current measurement protocols that do not increase circuit depths. It has also shown its versatility when techniques to reduce circuit sizes of variational quantum eigensolvers are also implemented. |
Friday, March 19, 2021 8:12AM - 8:24AM Live |
X30.00002: Tight binding as a numerical tool for diagonalizing superconducting-circuit Hamiltonians Daniel Weiss, Wade DeGottardi, Jens Koch, David Ferguson We adopt solid-state tight-binding techniques for the spectral analysis of superconducting circuits with more than four degrees of freedom. Such circuits are typically beyond the reach of standard exact diagonalization techniques, owing to the exponential increase in Hilbert space dimension. We demonstrate that for many circuits of interest (including flux qubit, zero-pi circuit and current-mirror circuit) tight-binding states are better suited for approximating the low-energy excitations than charge-basis states. Their use can dramatically lower the Hilbert space dimension required for convergence to the true spectrum which opens up the way for studying circuits with more than 20 nodes. |
Friday, March 19, 2021 8:24AM - 8:36AM Live |
X30.00003: Floquet theory for effective gate Hamiltonian and crosstalk in a tunable coupling superconducting circuit Camille Le Calonnec, Alexandru Petrescu, Agustin Di Paolo, Catherine Leroux, Pranav Mundada, Andrei Vrajitoarea, Alexander Place, Andrew Houck, Alexandre Blais The realization of high-fidelity 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. Numerically, this can be a resource intensive process as it implies simulating the gate dynamics for each set of device parameters. Here, we present a method to extract the interaction rates directly from Floquet spectrum generated by the drive without having to run dynamical simulations. We apply this technique to a two-qubit entangling parametric gate to optimize the device parameters in order to cancel the static ZZ interaction and minimize the gate time. We show that our method agrees with unitary dynamics simulations and perturbation theory. |
Friday, March 19, 2021 8:36AM - 9:12AM Live |
X30.00004: Superconducting Qubits: Circuit Theory, Hamiltonian Analysis and Design Tools Invited Speaker: Zlatko Minev Superconducting microwave circuits incorporating nonlinear devices, such as Josephson junctions, are a leading platform for emerging quantum technologies. There is a growing need in the community to address challenges from rising circuit complexity to the development of novel qubits. To meet these needs, we require efficient methods for the calculation and optimization of the spectrum, nonlinear interactions, and dissipation in multi-mode distributed quantum circuits. Here, we overview the process of quantum circuit design and present recent results to this end. We introduce the energy-participation ratio (EPR) quantization of Josephson circuits, suitable for a diverse class of general superconducting circuits. Finally, we also introduce an open-source framework to unify superconducting qubit design tools – project Qiskit Metal – which aims to bring together experimentalists and theorists alike seeking to push the boundaries of quantum circuit theory and Hamiltonian analysis. |
Friday, March 19, 2021 9:12AM - 9:24AM Live |
X30.00005: Hardware-Encoding Grid States in a Non-Reciprocal Superconducting Circuit Martin Rymarz, Stefano Bosco, Alessandro Ciani, David Peter DiVincenzo By taking advantage of the gyrator [1] as a source of non-reciprocity in electrical networks, we propose a superconducting circuit [2], whose effective low-energy dynamics is engineered to approximate the GKP stabilizer Hamiltonian [3]. Thus, the doubly degenerate ground space of this system coincides with the code space of the continuous variable GKP code, which constitutes grid states as codewords. |
Friday, March 19, 2021 9:24AM - 9:36AM Live |
X30.00006: Driven-dissipative dynamics in superconducting circuit lattices coupled to quantum baths Botao Du, Ruichao Ma Superconducting circuits have emerged as one of the most powerful platforms for quantum computing and simulation. The long coherence, strong interactions, and high tunability e.g. of the coupling to engineered baths, make circuits an ideal platform for exploring novel quantum many-body states. Recently, a dissipatively stabilized Mott insulator in superconducting circuits was realized [1] by coupling a narrowband incoherent bath with a Bose-Hubbard lattice. Here, we propose experiments to explore the dynamics of quantum correlations in strongly correlated lattices in the presence of broadband baths. We discuss schemes for realizing the dynamically tunable baths. By creating two baths to serve as source and drain we can implement an effective chemical potential for photons to prepare driven-dissipative many-body states, and perform quantum transport measurements across the lattice. We will discuss results from numerical simulations and our experimental progress. |
Friday, March 19, 2021 9:36AM - 9:48AM Live |
X30.00007: Engineering Dynamical Sweet Spots to Protect Qubits from 1/f Noise Ziwen Huang, Pranav Mundada, Andras Gyenis, David I Schuster, Andrew Houck, Jens Koch Protecting superconducting qubits from low-frequency noise is essential for advancing superconducting quantum computation. Based on the application of a periodic drive field, we develop a protocol for engineering dynamical sweet spots which reduce the susceptibility of a qubit to low-frequency noise. Using the framework of Floquet theory, we prove rigorously that there are manifolds of dynamical sweet spots marked by extrema in the quasi-energy differences of the driven qubit. In particular, for the example of fluxonium biased slightly away from half a flux quantum, we predict an enhancement of pure-dephasing by three orders of magnitude. Employing the Floquet eigenstates as the computational basis, we show that high-fidelity single- and two-qubit gates can be implemented while maintaining dynamical sweet-spot operation. We further confirm that qubit readout can be performed by adiabatically mapping the Floquet states back to the static qubit states, and subsequently applying standard measurement techniques. Our work provides an intuitive tool to encode quantum information in robust, time-dependent states, and may be extended to alternative architectures for quantum information processing. |
Friday, March 19, 2021 9:48AM - 10:00AM Live |
X30.00008: Simulations of Charge Noise in Quantum Dot Qubits Due to Temperature Fluctuations Dan Mickelsen, Herve M. Carruzzo, Ruqian Wu, Clare Yu, Sue Nan Coppersmith Silicon quantum dot qubits show great promise but suffer from charge noise. It has recently been proposed that 1/f-like noise spectra can emerge from very small numbers of thermally activated two-level fluctuators in the presence of significant temperature fluctuations [1]. We present the results of Monte Carlo simulations of the noise of a two-level system modeled as a Heisenberg spin with a barrier to spin re-orientations in a bath with a fluctuating temperature. |
Friday, March 19, 2021 10:00AM - 10:12AM Live |
X30.00009: Superconducting qubit gates via analytically-derived accelerated adiabatic pulses. Fnu Setiawan, Peter Groszkowski, Hugo Ribeiro, Aashish Clerk Qubit gates based on adiabatic evolution are appealing as they are robust against small imperfections in the control pulses. Unfortunately, due to their long evolution times, these gates are especially susceptible to dissipation. Recent work [1] has shown how shortcuts to adiabaticity (STA) can be used to design accelerated versions of such gates that completely cancel non-adiabatic errors. However, like almost all STA methods, this approach assumes an idealized rotating-wave approximation (RWA) Hamiltonian that ignores spurious leakage levels. Here, we discuss an analytic approach that allows one to go beyond these limitations. Our approach results in analytically-derived pulse shapes that correct both non-adiabatic errors as well as non-RWA and leakage effects. We show in detail how our approach can be used to analytically design high-fidelity gates in a realistic superconducting fluxonium qubit. |
Friday, March 19, 2021 10:12AM - 10:24AM Live |
X30.00010: Engineering Purely Nonlinear Coupling with the Quarton Yufeng Ye, Kaidong Peng, Mahdi Naghiloo, Gregory Cunningham, Kevin O'Brien We propose using a quarton to facilitate purely nonlinear coupling between two linearly decoupled transmon qubits [1]. The quarton's zero φ2 potential leads to a strong linear scaling of nonlinear coupling strength with Josephson energy; and the quarton's positive φ4 potential can cancel the negative self-Kerr of modes, causing atomic modes to behave more photonic. We show a >1 GHz nonlinear coupling, in the bare mode basis, between two linearized modes with zero self-Kerr; the resulting giant cross-Kerr between photons is promising for applications such as microwave photon detection and bosonic qubit control. |
Friday, March 19, 2021 10:24AM - 10:36AM Live |
X30.00011: The quantum sine-Gordon model with quantum circuits Ananda Roy, Dirk Schuricht, Johannes Hauschild, Frank Pollmann, Hubert Saleur Analog quantum simulation has the potential to be an indispensable technique in the investigation of complex quantum systems. In this work, we numerically investigate a one-dimensional, faithful, analog, quantum electronic circuit simulator built out of Josephson junctions for one of the paradigmatic models of an integrable quantum field theory: the quantum sine-Gordon (qSG) model in 1+1 space-time dimensions. We analyze the lattice model using the density matrix renormalization group technique and benchmark our numerical results with existing Bethe ansatz computations. Furthermore, we perform analytical form-factor calculations for the two-point correlation function of vertex operators, which closely agree with our numerical computations. Finally, we compute the entanglement spectrum of the qSG model and show that the quantum circuit model is less susceptible to corrections to scaling compared to the XYZ chain. We provide numerical evidence that the parameters required to realize the qSG model are accessible with modern-day superconducting circuit technology, thus providing additional credence towards the viability of the latter platform for simulating strongly interacting quantum field theories. |
Friday, March 19, 2021 10:36AM - 10:48AM Live |
X30.00012: Engineering Qubit-Qubit Interactions in Circuit QED Lattices Alicia Kollar The inherent strong coupling between microwave resonators and superconducting qubits available in the circuit QED architecture makes it possible to use the spectrum of multimode photonic environments to engineer qubit-qubit interactions. Previously, one-dimensional cavity arrays and modulated waveguides have been used to induce exponentially-localized interactions [1,2]. |
Friday, March 19, 2021 10:48AM - 11:00AM Live |
X30.00013: Fast crosstalk-free perfect entangler in a tunable coupling superconducting circuit Pranav Mundada, Andrei Vrajitoarea, Alexander Place, Agustin Di Paolo, Camille Le Calonnec, Alexandru Petrescu, Catherine Leroux, Alexandre Blais, Andrew Houck On-demand strong qubit-qubit interactions are crucial for the realization of a scalable quantum computer. Currently, the performance of high coherence transmons is limited by unwanted cross-Kerr or "ZZ" crosstalk. Using interference between two couplers has been previously shown to mitigate ZZ crosstalk. Here, we provide a novel tunable coupler design that harnesses interference due to the higher energy levels to achieve zero static ZZ coupling between the two qubits. Biasing to zero ZZ interaction, we realize a fast perfect entangler with parametric flux modulation and investigate the gate fidelity using randomized benchmarking. |
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