Quantum Systems Oscillate with Control Fields Exceeding Normal Frequency Limits

Researchers are increasingly focused on developing novel methods for coherent control of quantum systems, and a new study details a mechanism for inducing complete Rabi oscillations in two-level quantum systems even when the driving frequency significantly exceeds the system’s natural frequency. Baksa Kolok and András Pályi, both from the Department of Theoretical Physics, Institute of Physics, Budapest University of Technology and Economics, demonstrate this effect, termed Rabi oscillations induced by nonresonant geometric drive (RING) , which relies on elliptical control fields.

This research is significant because it establishes a pathway to coherent oscillations without the need for resonant energy exchange, potentially enabling high-pass noise filtering and access to non-Abelian phases in finite magnetic fields, and offering a means to amplify Rabi frequencies using existing gate voltages. The findings broaden the scope of quantum control techniques by showcasing a viable approach for off-resonant driving conditions. This enables complete Rabi oscillations, the fundamental building blocks of qubit operations, even when the driving frequency far exceeds the natural frequency of the quantum system. The research details how an elliptically polarized control field, rather than a conventionally tuned resonant frequency, can induce these oscillations, expanding the toolkit for quantum control and offering inherent noise filtering capabilities. The study demonstrates that RING facilitates coherent oscillations by exploiting off-resonant dynamics, a departure from standard qubit control protocols. Numerical simulations and analytical modelling, utilising Floquet theory and perturbation theory, confirm the effect and reveal a unique relationship between the drive frequency and the Larmor frequency, the rate at which a qubit precesses in a magnetic field. Complete Rabi oscillations can be achieved when the drive frequency is significantly higher than the Larmor frequency, following an inverse proportionality, contrasting with conventional resonant control where frequencies must be closely matched. Researchers detail a practical realization of the RING mechanism within electrically driven spin-orbit qubits, a type of quantum bit leveraging the interaction between an electron’s spin and its motion. This implementation allows for amplification of the Rabi frequency using the same gate voltage amplitudes at higher drive frequencies, potentially leading to faster and more efficient quantum computations. Furthermore, the RING mechanism provides access to non-Abelian phases, complex quantum states with unique properties, even in the presence of finite magnetic fields, crucial for advanced quantum computation schemes like holonomic quantum computation. By operating under far-detuned driving conditions, the RING mechanism naturally incorporates high-pass filtering, suppressing low-frequency noise that can disrupt qubit coherence. This inherent noise resilience is a significant advantage for building stable and reliable quantum devices, broadening the landscape of quantum control techniques and paving the way for more robust and versatile quantum technologies. Numerical simulations demonstrate complete Rabi oscillations occurring at a drive frequency of approximately 3GHz, despite a Larmor frequency of only 25MHz. This substantial detuning is central to the observed effect. The excited-state occupation probability, pe, exhibits a chevron-like pattern analogous to resonant driving scenarios, yet deviates in key aspects, lacking mirror symmetry across any drive frequency value and exhibiting a frequency maximising oscillations that does not align with the lowest oscillation frequency. Analysis of the maximum excited-state probability, pe(t), reveals a distinct ‘effective resonance’ condition where full population inversion occurs for drive frequencies considerably higher than the Larmor frequency. This secondary resonance follows an inverse proportionality between drive frequency and Larmor frequency. The simulations were performed with equal driving amplitudes (Ωxz = Ωy) and specific initial phases (φxz = 0, φy = −π/2), starting from the ground state of the static Hamiltonian. The Hamiltonian governing the two-level system incorporates an elliptical drive, described by terms proportional to the cosine of the drive frequency and phase, crucial for inducing the observed Rabi oscillations. A tight-binding discretization underpinned the full numerical simulation of the real-space Hamiltonian, forming the basis for detailed analysis of quantum dynamics. Complementing this, a hybrid numerical, analytical solution was developed, leveraging the effective Floquet matrix derived from Floquet theory and perturbation theory, combining computational efficiency with analytical insight. Further analytical solutions of the effective Floquet dynamics were obtained, validating the numerical results and providing deeper understanding of the underlying physics. The research team analysed the dynamics using these three complementary methods to map chevron-like patterns, identifying complete Rabi oscillations at drive frequencies differing from those observed with resonant drive. The drive frequency for full Rabi oscillations, termed the RING frequency, was expressed as ωRING = ħ2ω4 0 2e2E2 0 α2 cos θ ωL, linking it directly to material properties and applied fields. The study detailed a realization of this control mechanism in electrically driven spin-orbit systems, motivated by the ability to generate strong driving fields relative to the Larmor frequency, a key requirement for the RING mechanism. The amplitude of the Bloch, Siegert oscillation, a potential source of error, was found to be independent of the drive frequency at the effective resonance, simplifying parameter tuning and improving control fidelity.

Scientists have long sought methods to manipulate quantum states with precision, a cornerstone of quantum technologies. This work introduces RING, which sidesteps a fundamental limitation of traditional quantum control by operating effectively even when the driving frequency is far removed from resonance, offering a potentially more robust and versatile pathway to qubit manipulation. The significance lies in its implications for scalability and practical implementation, as existing quantum systems are notoriously sensitive to environmental disturbances and maintaining resonance across multiple qubits becomes increasingly challenging. By decoupling control from precise frequency matching, RING offers a degree of freedom that could simplify the architecture of future quantum processors. Furthermore, the inherent high-pass noise filtering capability is a welcome addition to the toolkit for preserving delicate quantum coherence. However, the current demonstration relies on numerical simulations and a specific physical realisation in electrically driven spin systems. Extending this principle to other qubit modalities will require careful consideration of material properties and device design, and realising the potential for amplifying Rabi frequency using the same gate voltages may present significant engineering hurdles. Future research will likely focus on exploring the limits of this technique, investigating its resilience to different noise sources, and developing strategies for integrating RING into larger, more complex quantum circuits. 👉 More information 🗞 RING: Rabi oscillations induced by nonresonant geometric drive 🧠 ArXiv: https://arxiv.org/abs/2602.11979 Tags: