Invited Session: Robust Quantum Control
Paper ID: 59
Authors: Emily Wright, Leo Van Damme, Niklas J. Glaser, Amit Devra, Federico A. Roy, Julian Englhardt, Niklas Bruckmoser, Leon Koch, Achim Marx, Johannes Schirk, Christian M. F. Schneider, Lasse Södergren, Ivan Tsitsilin, Florian Wallner, Steffen J. Glaser, Max Werninghaus and Stefan Filipp
Title: Superconducting Qubit Gates Robust to Parameter Fluctuations
Abstract: State-of-the-art single-qubit gates on superconducting transmon qubits can achieve the fidelities required for error-corrected computations. However, parameter fluctuations due to qubit instabilities, environmental changes, and control inaccuracies make it difficult to maintain this performance. To mitigate the effects of these parameter variations, we numerically derive gates robust to amplitude and frequency errors using gradient ascent pulse engineering (GRAPE). We analyze how fluctuations in qubit frequency, drive amplitude, and coherence affect gate performance over time. The robust pulses suppress coherent errors from drive amplitude drifts over 15 times more than a Gaussian pulse with derivative removal by adiabatic gate (DRAG) corrections. Furthermore, the robust gates, originally designed to compensate for quasi-static errors, also demonstrate resilience to stochastic, time-dependent noise, which is reflected in the dephasing time. They suppress added errors during increases in dephasing by up to 1.7 times more than DRAG.
Paper ID: 66
Authors: Paul Eastham
Title: Quantum control and the environment in open quantum systems
Abstract: Designing robust, reliable controls for quantum systems requires us to account for the interactions with their environment, which produce noise, decoherence, and dissipation. This is typically done using approximations, such as Born-Markov, which treat the environment as fixed and neglect system-environment correlations. Even where these approximations appear reasonable they introduce errors which can be larger than the accuracies sought in quantum devices. I will discuss how exact tensor-network methods can be used to design optimal control protocols which steer the full many-body state of an open quantum system, and how these methods can be accessed in the open-source OQuPy code. Using them, and other approaches, I will present and analyze optimal controls for qubit reset in the spin-boson model of a transmon. These controls overcome the limitations on speed and fidelity that otherwise arise from the formation of polarons by manipulating the environment state through a control of either the system-environment coupling, or the qubit splitting.
Paper ID: 67
Authors: Dominique Sugny
Title: The Pontryagin Maximum Principle for universally robust optimal control of two-level quantum systems
Abstract: We show how to apply the Pontryagin Maximum Principle (PMP) in Quantum Optimal control to design robust controls against experimental imprecision. We consider two-level quantum systems, for which optimal solutions can be derived analytically or designed using numerical optimization algorithms. A pedagogical introduction to the PMP with robustness constraints will be followed by a description of different examples. Our main focus will be on universal robustness, where the perturbation operator is unknown.
Paper ID: 73
Authors: Carrie Weidner, Sophie Schirmer, Sean O'Neil, Edmond Jonckheere and Frank Langbein
Title: Robust and optimal control of ultracold atoms in optical lattices, and why you should care
Abstract: Over the past few years, substantial work has been done on both the design of robust controllers for quantum systems, as well as determining the robustness of existing optimized controllers. There is also particular interest in determining optimal controls that are experimentally viable, which often requires one to be careful about how one optimizes and/or post-processes their controllers. In this talk, I will discuss my collaborators' and my work on determining controller robustness for optimal controls applied to two problems with atoms in one-dimensional optical lattices: optimized spin transfer in deep, singly-occupied lattices and atom optics in shallow lattice systems, the latter with applications in quantum-enabled inertial sensing. Finally, I'll discuss the wider applicability (and potential pitfalls) of our methods to other systems, particularly with regards to experimental viability.
Paper ID: 101
Authors: Pablo Poggi
Title: Universally Robust Quantum Control
Abstract: In this talk I will present a framework to prepare quantum states and gates which are insensitive to any kind of weak perturbation by using optimal control. To this end, I will show that the fidelity susceptibility, which quantifies the perturbative error to leading order and corresponds to the quantum Fisher Information of the dynamical process, can be expressed in superoperator form. This allows us to numerically search for control pulses which are robust to any class of systematic unknown errors by minimizing the norm of a suitably-defined dynamical robustness superoperator. We show that the proposed optimal control protocol is equivalent to searching for a sequence of unitaries that mimics the first-order moments of the Haar distribution, i.e. it constitutes a 1-design. This connection, in turn, demonstrates the existence of universally robust quantum control protocols for any Hilbert space dimension. I will illustrate the power of this framework by showing its application to the generation of robust one- and twoqubit gates, and discussing how generalized robustness requirements can be built into the formalism.
Paper ID: 102
Authors: Guido Pupillo
Title: Towards fault-tolerant quantum computing with neutral atoms
Abstract: Neutral atoms have emerged as a leading platform for digital quantum simulations and quantum computing, with present-day systems surpassing a thousand qubits and achieving gate fidelities at the 99.9% level. As the field transitions toward scalable, fault-tolerant quantum computing, robust quantum error correction becomes increasingly important. In this talk, I will describe recent work developing architectures for efficient quantum error correction tailored to Rydberg-atom arrays. I will present new ideas and codes for performing error correction, highlighting conditions under which the latter offer advantages over conventional schemes. One example is low-density parity-check codes that can encode more information and protect better from physical errors with respect to conventional surface codes. Both challenges and new ideas for performing error-corrected logical quantum computation within this framework are discussed.