Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D75: Superconducting Qubit Optimal Control IFocus
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Sponsoring Units: DQI Chair: Fnu Setiawan, University of Chicago Room: Room 401/402 |
Monday, March 6, 2023 3:00PM - 3:36PM |
D75.00001: Flux-pulse optimization for entangling gates on a tunable-coupler architecture Invited Speaker: Nicolas Didier Improving the performance of entangling gates at scale is important to achieve quantum advantage and perform quantum error correction. The implementation of tunable couplers made of flux-tunable transmons has led to substantial progress in this direction. In this talk, we present optimal flux control techniques for superconducting qubits, focusing on the engineering of dynamical sweet spots. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D75.00002: Demonstrating two-qubit gates at the quantum speed limit using superconducting qubits. Bora Basyildiz, Joel Howard, Alexander Lidiak, Casey W Jameson, Kyle Clark, Tongyu Zhao, Mustafa Bal, Junling Long, David Pappas, Meenakshi Singh, Zhexuan Gong The speed of elementary quantum gates, particularly two-qubit gates, ultimately sets the limit on the speed at which quantum circuits can operate. In this work, we experimentally demonstrate commonly used two-qubit gates at nearly the fastest possible speed allowed by the physical interaction strength between two superconducting transmon qubits. We achieve this quantum speed limit by implementing experimental gates designed using a machine learning-inspired optimal control method. The machine learning-based algorithm can achieve the speed limit of various two-qubit gates in an N-qubit system through the optimization of single-qubit pulses, and this algorithm significantly outperforms standard optimal control algorithms such as GRAPE. Importantly, our method only requires the single-qubit drive strength to be moderately larger than the interaction strength to achieve an arbitrary two-qubit gate close to its analytical speed limit with high fidelity. Thus, the method is applicable to a variety of platforms including those with comparable single-qubit and two-qubit gate speeds, or those with always-on interactions. |
Monday, March 6, 2023 3:48PM - 4:00PM |
D75.00003: Demonstration of high-fidelity parametric-resonance gates at scale Eyob A Sete, Angela Q Chen, Riccardo Manenti, Shobhan Kulshreshtha, Stefano Poletto We demonstrate high-fidelity parametric-resonance entangling gates in multi-qubit floating tunable coupler architectures. We considered two configurations of the tunable coupler pads where the zero-coupling coupling can be achieved when the coupler frequency is either above (asymmetric configuration) or below (symmetric configuration) the qubits frequencies. We realized iSWAP and CZ two-qubit gates on both configurations and obtained high-fidelity values with interleaved randomized benchmarking. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D75.00004: Novel Superconducting Qubit Discovery via an Enumeration Based Approach Eli J Weissler, Zhenxing Liu, Joshua L Combes, Mohit Bhat Long term, noise protected qubits have the potential to be more error resistant than the qubits used today. We will report progress on a circuit enumeration-based procedure to discover new noise protected superconducting qubits. We will discuss tradeoffs in designing the procedure and efforts to streamline the approach by reducing the number of duplicate circuits considered. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D75.00005: Error suppression in the cross-resonance gate via recursive DRAG. Boxi Li, Tommaso Calarco, Felix Motzoi The cross-resonance gate is one of the widely used two-qubit gates for superconducting qubits. The state-of-the-art experiments have demonstrated high-fidelity gate operations and it is also the default two-qubit gate on the IBM NISQ devices. The cross-resonance gate is known to be subjected to several coherent errors such as non-adiabatic transitions on the control qubit and ZZ phase error. They are often suppressed through long pulse ramping time and echoed gate design, which inevitably increases the gate time. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D75.00006: Numerically modeling the Hamiltonian of a microwave-driven superconducting circuit Yao Lu, Kevin C Smith, Daniel K Weiss, Xinyuan You, Yaxing Zhang, Suhas S Ganjam, Aniket Maiti, John W Garmon, Ian M Shem, Jens Koch, Steven M Girvin, Robert J Schoelkopf Modeling the time-dependent Hamiltonian of a driven Josephson circuit is imperative to superconducting quantum computation. So far, static circuit Hamiltonians have been modeled by numerical schemes such as BBQ or EPR. In contrast, numerical modeling of the driven Hamiltonian in the presence of external voltage or flux modulation, without relying on a lumped-element circuit model, has been largely unexplored. Here, we present a numerical method that leverages finite-element simulation to obtain the low-energy time-dependent Hamiltonian of a multimode and multi-junction Josephson device with complex geometry in the presence of external drives. Our scheme serves as a promising toolbox for characterizing the driven properties of realistic circuit devices in complicated electromagnetic environments - a task not typically amenable to standard lumped-element circuit analysis. Consequently, our technique should have wide application to the optimization of various circuit designs. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D75.00007: Quantum state transfer between two superconducting resonators by parametric voltage modulation on gated Josephson junctions Yinqi Chen, Javad Shabani, Hugh O Churchill, Vladimir E Manucharyan, Maxim G Vavilov Quantum state transfer between elements of superconducting circuits is crucial for quantum information applications, such as initialization, control, and readout of qubit systems. In this talk, we analyze the exchange of excitations between microwave cavities based on parametric resonance. We consider two coupled superconducting coplanar waveguide resonators connected to gated superconductor-semiconductor Josephson junctions on one of their terminals. Periodical modulation of the gate voltage of one of the junctions causes the photon excitations to transfer from one resonator to another. We evaluate the role of non-linearity and dissipation introduced by the super-semi junctions on the accuracy of state transfer. In particular, as the resonators acquire the signatures of the gatemon energy spectrum at strong anharmonicity, such parametric resonance can be used to generate fast, high-fidelity two qubit gates. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D75.00008: A strongly coupled two-qubit system with weak quantum crosstalk Konstantin Nesterov, Denis Chevallier, Chiara Pelletti, Larry Chen, Bingcheng Qing, Ravi K Naik, David I Santiago, Irfan Siddiqi, Alexei Marchenkov In microwave-activated two-qubit gate schemes, a strong static exchange interaction between superconducting qubits leads to a strong hybridization between their eigenstates and thus enables fast operations. However, a larger exchange-interaction strength generally increases spurious quantum (ZZ) crosstalk, diminishing addressability for single-qubit gates. In this talk, we discuss the design of a system of transmons with multiple coupling paths between qubits, which provides a high entangling-gate rate with reduced static quantum crosstalk. We optimize the layout configuration of such a system by means of a finite-element analysis combined with the energy-participation-ratio technique [1]. This approach allows us to find the quantum Hamiltonian for a given physical layout and therefore accurately estimate the ZZ coupling magnitude as well as the rates of two-qubit gates. |
Monday, March 6, 2023 5:00PM - 5:12PM |
D75.00009: Analysis of underlying mechanisms and alleviation of static ZZ coupling Simon Pettersson Fors, Jorge Fernández-Pendás, Anton Frisk Kockum Gate fidelities and gate times are continuously being improved in the ongoing attempts to create a superconducting quantum computer. However, the ZZ coupling remains as a fundamental obstacle to further improve the performance of current superconducting qubit systems. Here, we present a theoretical analysis of the underlying mechanisms which cause the static ZZ coupling, with the aim of both alleviating and utilizing the effect in single- and two-qubit gates. This analysis uses perturbation theory to study a simplified model and validates the results via a more detailed model and numerical investigations. We expect that these insights into the static ZZ coupling will contribute to improving gate fidelities in two-qubit entangling gates. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D75.00010: Planar multi-mode superconducting circuit design for high-dimensional computation Murat C Sarihan, Kangdi Yu, Madeline K Taylor, Ananyo Banerjee, Jin Ho Kang, Cody S Fan, Kai-Chi chang, Chee Wei Wong Transmon qubits have recently been advanced as the building blocks of noisy intermediate-scale quantum processors. In these quantum processors and building blocks, multi-qubit gate fidelity and interqubit connectivity becomes crucial, wherein transmons create a bottleneck due to weak transverse coupling among nearest-neighbor qubits. Multi-mode superconducting qubits, or multimons, are demonstrated as an alternative, where fully-connected qubits with strong longitudinal coupling form hybridized modes to achieve high-fidelity multi-qubit gates over a larger Hilbert space. With this approach, a three-qubit system is demonstrated with a complete gate set using 3D superconducting cavities, the latter of which can be less susceptible for large-scale integration [1,2,3]. For this purpose, we propose planar coupling strategies for multimons inspired by state-of-the-art planar topologies of Josephson ring modulator-based devices [4, 5]. In this work, we successfully coupled two pairs of coplanar waveguide resonators to a trimon with equal strength in a differential configuration to effectively control and readout a three-qubit system through the two hybridized longitudinal modes. We also proposed a coupling scheme between multiple trimons for scalable quantum processors. |
Monday, March 6, 2023 5:24PM - 5:36PM |
D75.00011: Efficient Machine Learning Systems for High-Fidelity Qubit Readout Satvik Maurya, Chaithanya N Mude, William D Oliver, Benjamin Lienhard, Swamit Tannu Multi-qubit readout is among the most error-prone operations in superconducting quantum computing systems. These errors occur for various reasons, including but not limited to: crosstalk between the readout tones in a frequency-multiplexed readout scheme, spontaneous state transitions during the measurement, excitations caused by the readout pulse, and thermal noise added to the readout signal as it travels from the refrigerator to the room-temperature electronics. Prior works on reducing readout errors include machine learning-assisted readout, where a neural network is used for more robust discrimination by compensating for crosstalk errors. However, the neural network size can limit systems' scalability, especially if fast hardware discrimination is required. This work presents a scalable approach for mitigating single-shot readout errors by using a matched filter in conjunction with a significantly smaller and scalable neural network for qubit-state discrimination. In addition, we optimize the training of the matched filter and neural network by using a pre-classifier that filters incorrectly labeled training data. Fast and accurate discrimination of qubit states is essential for deploying quantum error correction codes. To that end, we investigate computationally efficient and scalable machine learning algorithms for enabling high-fidelity multi-quit readout that are readily implementable on FPGAs. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D75.00012: High-fidelity qutrit entangling gates with superconducting circuits based on parametric coupling Mahadevan Subramanian, Adrian Lupascu Recently, significant progress has been made in the demonstration of single qutrit and coupled qutrit gates with superconducting circuits. Coupled qutrit gates have significantly lower fidelity than single qutrit gates, owing to long implementation times. We present a protocol to implement CZ gates using two fixed frequency transmons capacitively coupled to a tunable transmon. We make use of fundamental gates that are iSWAP-like exchanges between the two qutrit states |01> to |10> and the states |12> to |21>. Parametric coupling is used to conduct these exchanges by driving an AC flux in the tunable coupler of an appropriate frequency which is different for the two kinds of exchanges. We show that these gates have high expressibility when combined with single qutrit rotations. We show that a high-fidelity CZ gate can be obtained by combining these entangling gates with single qutrit rotations. |
Monday, March 6, 2023 5:48PM - 6:00PM |
D75.00013: Multi-Qubit coupler for superconducting circuits with controllable inductive interactions Klaus Liegener, Stefan Filipp Multi-qubit couplers are envisioned to provide fast gates between next-to-nearest neighbor qubits as well as between multiple qubits in one step. Common proposals, such as a capacitively coupled squid loop acting as a tunable element which however suffer from residual qubit-qubit interactions. Instead, this talk focuses on an architecture where all qubits connect inductively via squid loops to an intermediate node. In the limit of negligible capacitive coupling between the qubits and the coupler node, said intermediate node becomes frozen and enforces the appearance of interaction terms between all qubits connected to the coupler. We find a suitable configuration in parameter space, where by controlling the coupler with two external flux bias lines, pairwise interactions can be activated while other qubits remain decoupled. We present a derivation of the relevant circuit QED Hamiltonian and simulate parameter regimes that are experimentally accessible. We further explore its potential for creating multi-qubit gates. |
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