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 UU05: V: Quantum Optimal Control |
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Sponsoring Units: DQI Chair: Benjamin Lienhard, Massachusetts Institute of Technology Room: Virtual Room 5 |
Wednesday, March 22, 2023 5:00AM - 5:12AM |
UU05.00001: Quantum Algorithms for Quantum Optimal Control Problems with Precise Cost Estimates Xiantao Li Quantum properties are largely responsible for many recent developments in material science and chemical engineering. Such properties are best utilized with external controls. Quantum optimal control (QOC) algorithms, which use first principle-based computer simulations to identify the desired control variables, have been an important route in this direction. |
Wednesday, March 22, 2023 5:12AM - 5:24AM |
UU05.00002: Robust optimal control for a systematic error in the control amplitude Max Cykiert, Eran Ginossar In the NISQ era, physical qubits coherence time and high fidelity gates are essential to the func- |
Wednesday, March 22, 2023 5:24AM - 5:36AM |
UU05.00003: QuantumControl.jl: A modern framework for quantum optimal control Michael H Goerz, Sebastian C Carrasco, Vladimir S Malinovsky We present recent advances in the Julia QuantumControl.jl software framework. The framework contains state-of-the-art implementations of methods for simulating the dynamics of open and closed quantum systems and open loop quantum control, specifically GRAPE and Krotov's method. By exploiting semi-automatic differentiation, it can optimize any computable optimization functional without the memory overhead traditionally associated with automatic differentiation. This includes non-analytic functionals such as entanglement measures. The flexibility of the Julia language allows to easily extend the framework with problem-specific data structures with a runtime performance that rivals traditional compiled languages such as Fortran. We demonstrate the use of the framework for tasks in quantum information and quantum metrology. |
Wednesday, March 22, 2023 5:36AM - 5:48AM |
UU05.00004: Tensor-network optimal control for multi-qubit systems Nguyen H Le, Eran Ginossar Quantum devices in the NISQ era are being built with an increasing number of qubits. Many-body interaction can be purposefully engineered, or in some cases considered a parasitic interaction that cannot be avoided. The many-body Hamiltonian of these devices are also imperfect due to significant uncertainty in multiple parameters. This necessitates the development of a many-body optimal control algorithm capable of realising quantum operations, i.e., a target state or target gate, which is robust against uncertainty. We develop a robust optimal control algorithm based on tensor networks, and demonstrate its effectiveness for implementing multi-qubit entangled states and unitary gates. We show that robustness against variation in the Hamiltonian's parameters can be achieved by optimising only the extreme points of the uncertain region, and an exponential speed up of the optimisation is possible by focusing on the subspaces of the most correlated parameters. The algorithm is used for generating high-fidelity GHZ states and CNOT gates in an interacting multi-qubit system. Implications for near term quantum processors are discussed." |
Wednesday, March 22, 2023 5:48AM - 6:00AM |
UU05.00005: The complex-time picture of Shortcuts to Adiabaticity: interference in the Landau-Zener-Stückelberg-Majorana model Gabriel Cardoso When a Hamiltonian is time-dependent, the instantaneous eigenstates are not exact solutions of the time-dependent Schrödinger equation, except for the limit when the time-dependence is very slow compared to the time-scale set by the gap (the adiabatic theorem). Otherwise, a particle prepared in a given eigenstate will undergo transitions to other eigenstates. In the method of shortcuts to adiabaticity, one completely suppresses such transitions by adding a properly designed correction to the dynamics, the counterdiabatic Hamiltonian. We investigate the physical mechanism by which the counterdiabatic Hamiltonian suppresses transitions in the Landau-Zener-Stückelberg-Majorana model. In the complex-time picture of this model, the probability of transitions is determined by the position of the branch point of the eigenvalues which lies closest to the real-time axis, a fact known as the Dykhne formula. We consider a one-parameter deformation of the Hamiltonian corresponding to ``turning on" the counterdiabatic Hamiltonian and show that this introduces extra relative phases between the different paths in the complex plane. We then derive a new non-perturbative formula for the probability of non-adiabatic transitions in this extended model, and show that in the case of counterdiabatic driving the probability of transitions vanishes due to the exactly destructive interference in the complex plane. This intuition further extends to a whole class of models known as integrable time-dependent quantum Hamiltonians, a fact which we demonstrate by proving that the addition of counterdiabatic Hamiltonians preserves their characteristic integrability condition. |
Wednesday, March 22, 2023 6:00AM - 6:12AM |
UU05.00006: Nonadiabatic Landau-Zener-Stückelberg-Majorana transitions, dynamics, and interference. Oleh Ivakhnenko, Sergey Shevchenko, Franco Nori The quantum two-level system (TLS) is one of the basic models in quantum physics and ubiquitous in nature. On the one hand, this is the “simplest nonsimple quantum problem” [1]; and, on the other hand, this provides the basis for quantum technologies, in which a TLS refers to a qubit. We investigate many different approaches to simplify calculating interesting behavior of such “simple” quantum system. We investigate periodically driven TLSs in different approaches [2] such as adiabatic-impulse model (AIM), rotating-wave approximation (RWA), Floquet method, numerical solving of Schrodinger and Lindblad equations, to describe interferometry and different aspects of each method. Then we compare them to find advantages and disadvantages of each method [2]. |
Wednesday, March 22, 2023 6:12AM - 6:24AM |
UU05.00007: Driving can have no effect, if the phase is chosen appropriately Polina Kofman, Oleh Ivakhnenko, Sergey Shevchenko, Franco Nori For expanding the quantum toolbox, it is important to develop coherent control of individual quantum systems. Our work relates to the possibility of controlling two-level quantum systems under the action of linear excitation. We take into account such factors as the phase difference between the incoming states, finite duration of driving, coupling to the dissipative environment. If starting from the ground state, the transition probability is described by the Landau-Zener-Stuckelberg-Majorana formula [1]. However, in a general superposition initial state, it becomes possible to greatly change the final result by means of quantum interference [2]. We can choose any value between the minimum and maximum values that can be achieved depending on the phase difference, the initial moment of time, at various system parameters. In the superposition state, depending on the tunable parameters, it is possible to obtain a full transition to one of the basis states or to remain in the same superposition state after the transition. Such keeping the occupation population even under driving is analogous to the transitionless driving of Ref. [3]. |
Wednesday, March 22, 2023 6:24AM - 6:36AM |
UU05.00008: Universal Robust Quantum Gates by Geometric Correspondence Yong-Ju Hai, Junning Li, Junkai Zeng, Dapeng Yu, Xiu-Hao Deng Precise and robust quantum control is the key to emerging quantum technologies. We uncover the essential correspondence between driven noisy quantum evolution and geometric curves, and develop a quantum robust control theory with a systematic, explicit, and geometric intuitive framework to construct universal quantum gates that are robust to generic errors. We propose conditions for dynamically correcting errors and quantitative robustness measures for any control pulses, and establish an analytic-numerical hybrid protocol to search for robust control pulses with the simplest waveforms and any given gate time. The resulting universal robust quantum gates are demonstrated with numerical tests for realistic semiconductor spin qubits and superconducting transmon qubits. The theory is ready to assist the future leap of quantum computing. |
Wednesday, March 22, 2023 6:36AM - 6:48AM |
UU05.00009: Non-resonant quantum logic gates Artem Ryzhov, Oleh Ivakhnenko, Sergey Shevchenko, Franco Nori The most common realization of quantum logic gates and control is based on Rabi oscillations, which cause a periodic resonant excitation of the system. It has certain limitations and complications, like counter-rotating terms. We study an alternative approach for implementing quantum logic gates based on Landau-Zener-Stückelberg-Majorana (LZSM) interferometry with non-resonant driving and the alternation of adiabatic evolution and non-adiabatic transitions. Compared to the Rabi oscillations method, the main differences are a non-resonant excitation frequency and a small number of periods in the external excitation. One of the goals is to achieve a higher speed of qubit operations without losing fidelity. Both of these characteristics have major importance for experimental realizations of quantum computers. We study different aspects of non-resonant excitations: qubit dynamics, relaxation, coupling with the environment, and optimizing the speed of gates by increasing the number of periods in the external excitation. We explore related mechanisms and dynamics for single and two-qubit gates. The parameters of the external excitation required for implementing some specific gate are defined using the adiabatic-impulse model approach. This mechanism can be applied for a large variety of multi-level quantum systems and external excitations, providing a method for implementing qubit logic gates on them. |
Wednesday, March 22, 2023 6:48AM - 7:00AM |
UU05.00010: Quantum control of spin qubits using magnetic skyrmions Md Fahim F Chowdhury, Md Mahadi Rajib Quantum control of individual qubits in a dense chip without cross-talk is a fundamental challenge in implementing scalable high-fidelity universal quantum gates [1-2]. Previously, we have shown the feasibility of scalable, small footprint, high-fidelity, and energy-efficient single-qubit quantum gates by tuning the frequency and phase of the nanomagnet’s electric field drive to the Larmor frequency of the spins confined to a nanoscale volume [3]. While the nanoscale magnets allow for energy-efficient and highly localized control field with minimal effect on neighboring qubits, the operating frequency is limited to few GHz. In this work, we show a technique of energy-efficient quantum control of spin qubits with topologically protected nanoscale magnetic skyrmions allowing high frequency control of spin qubits (nominally five times that with nanomagnets) which can potentially lead to high-speed, scalable, and high fidelities quantum computing [4]. |
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