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Implications of Amplitude Error for Rabi Oscillations

Kiyan Ghaffari

Published Jan 1, 2026• 0 citations
Publisher

Abstract

Rabi oscillations describe the coherent evolution of a two-level quantum system under the influence of a resonant driving field. They are central to quantum computing and determine the utility of qubits. Reliable control of these oscillations requires precise calibration of the driving field; however, experimental implementations are subject to imperfections that stray from what is ideal. One source of error is amplitude miscalibration, where the strength of the applied control pulse fluctuates around its intended value.In this study, the effects of amplitude error on Rabi oscillations were investigated using a formulaic simulation of a single-qubit system. The system was modeled using the Cirq quantum circuit framework, where Rabi oscillations were represented as rotations on the Bloch sphere. Amplitude divergence was incorporated by modifying the Rabi drive strength with Gaussian-distributed noise. The resulting state evolution was compared with the ideal theoretical oscillation in order to visualize the impact of stochastic amplitude variations on qubit dynamics.This model provides a simplified framework for examining how imperfect calibration influences coherent quantum state evolution in two-level systems.

DOI
10.6084/m9.figshare.31743526

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Rabi oscillations describe the coherent evolution of a two-level quantum system under the influence of a resonant driving field. They are central to quantum computing and determine the utility of qubits. Reliable control of these oscillations requires precise calibration of the driving field; however, experimental implementations are subject to imperfections that stray from what is ideal. One source of error is amplitude miscalibration, where the strength of the applied control pulse fluctuates around its intended value.In this study, the effects of amplitude error on Rabi oscillations were investigated using a formulaic simulation of a single-qubit system. The system was modeled using the Cirq quantum circuit framework, where Rabi oscillations were represented as rotations on the Bloch sphere. Amplitude divergence was incorporated by modifying the Rabi drive strength with Gaussian-distributed noise. The resulting state evolution was compared with the ideal theoretical oscillation in order to visualize the impact of stochastic amplitude variations on qubit dynamics.This model provides a simplified framework for examining how imperfect calibration influences coherent quantum state evolution in two-level systems.
The rotation of a quantum bit (qubit) is an important step in quantum computation. The rotation is generally performed using a Rabi oscillation. In a direct two-level qubit system, if the Rabi frequency is comparable to its resonance frequency, the rotating wave approximation is not valid, and the Rabi oscillation is accompanied by the so-called Bloch–Siegert oscillation (BSO) that occurs at twice the frequency of the driving field. One implication of the BSO is that for a given interaction time and Rabi frequency, the degree of rotation experienced by the qubit depends explicitly on the initial phase of the driving field. If this effect is not controlled, it leads to an apparent fluctuation in the rotation of the qubit. Here we show that when an off-resonant lambda system is used to realize a two-level qubit, the BSO is inherently negligible, thus eliminating this source of potential error.
Precise quantum control relies on a deep understanding of the dynamics of quantum systems under external drives. This study investigates the impact of anharmonicity on qubit dynamics under conditions typical for two-qubit entangling gates activated by weak near-resonant microwave drives. We measure the Rabi oscillation frequency as a function of drive amplitude and detuning. Our results reveal a linear dependence of the squared Rabi frequency on the squared drive amplitude, which relates to the ratio of detuning to anharmonicity, demonstrating strong agreement between experimental data and analytical predictions. Additionally, we analyze the leakage and phase errors arising from inaccurate Rabi frequency adjustments in the CZ gate implementation on fluxonium qubits driven by a microwave signal applied to the coupler [Simakov et al., PRX Quantum 4, 040321 (2023)].
We present and analyze a simple scheme to calibrate single–qubit gates. It determines the amplitude and phase difference between a quadrature pair of drives, as well as their common detuning from the qubit resonance. The method is based on a two–dimensional Rabi oscillation, a sequence of two pulses of varying length sourced from the drive pair. We demonstrate error diagnosis using this scheme on an ensemble of nitrogen-vacancy centers in diamond and point out subtle pitfalls in its implementation.
Coherent control of two-level quantum systems is typically achieved using resonant driving fields, forming the basis for qubit operations. Here, we report a mechanism for inducing complete Rabi oscillations in monochromatically driven two-level quantum systems, when the drive frequency is much larger than the Larmor frequency of the qubit. This effect$\unicode{x2015}$Rabi oscillations induced by nonresonant gyrating drive (RING)$\unicode{x2015}$requires a gyrating control field, i.e., an elliptic drive trajectory that encloses a nonzero area per cycle. We illustrate the effect with numerical simulations, and provide an analytical understanding via a simple effective Hamiltonian obtained from Floquet theory and perturbation theory. We show that RING enables coherent oscillations without relying on resonant energy exchange, allows for high-pass noise filtering, provides access to non-Abelian phases in finite magnetic fields. We detail a realization in electrically driven spin-orbit qubits and argue that the RING mechanism enables amplification of the Rabi frequency using the same gate voltage amplitudes at higher drive frequencies. Our results broaden the landscape of quantum control techniques, by highlighting a pathway to achieving coherent oscillations under off-resonant driving conditions.
Temporal fluctuation in the unitary evolution of a two-level system can affect its performance from the initialization stages at the simplest of single-qubit gate operations. This work numerically explored the impact of temporal parameter distribution of the control pulse rotating a single-photon qubit in the Bloch sphere for an emitter in the free space. Next, we showed a stunning improvement in the outcomes, including fidelity, invoking a guided mode-mediated control pulse in a dielectric metasurface. These numerical results identify a source of error and noise during the initialization and propose a simple yet efficient method to implement in experiments, which could effectively mitigate the noise of this particular fluctuation.
In a direct two-level qubit system, when the Rabi frequency is comparable to the resonance frequency, the rotating wave approximation is not appropriate. In this case, the Rabi oscillation is accompanied by another oscillation at twice the frequency of the driving field, the so called Bloch-Siegert oscillation (BSO), which depends on the initial phase of the driving field. This oscillation may restrict the precise rotation of a qubit made of direct two-level system. Here, we show that in case of an effectively two-level lambda system, the BSO is inherently negligible, implying a greater precision for rotation of a qubit made of such a lambda system when compared to a direct two-level qubit in a strong driving field.