Dynamical Sweet and Sour Regions in Bichromatically Driven Floquet Qubits

TL;DR

This paper explores how bichromatic Floquet driving of qubits can create regions with enhanced coherence, called dynamical sweet spots, by analyzing spectral and lifetime properties to improve noise robustness in quantum hardware.

Contribution

It introduces a novel bichromatic Floquet approach that identifies continuous manifolds of dynamical sweet spots, improving qubit coherence and noise resilience over monochromatic methods.

Findings

Identification of high-coherence regions (sweet spots) under bichromatic drives.

Analytical expressions for quasienergy gaps and dephasing rates.

Bichromatic driving alleviates the trade-off between different noise sensitivities.

Abstract

Modern superconducting and semiconducting quantum hardware use external charge and microwave flux drives to both tune and operate devices. However, each external drive is susceptible to low-frequency (e.g., $1/f$) noise that can drastically reduce the decoherence lifetime of the device unless the drive is placed at specific operating points that minimize the sensitivity to fluctuations. We show that operating a qubit in a driven frame using two periodic drives of distinct commensurate frequencies can have advantages over both monochromatically driven frames and static frames with constant offset drives. Employing Floquet theory, we analyze the spectral and lifetime characteristics of a two-level system under weak and strong bichromatic drives, identifying drive-parameter regions with high coherence (sweet spots) and highlighting regions where coherence is limited by additional sensitivity to noise at the drive frequencies (sour spots). We present analytical expressions for quasienergy gaps and dephasing rates, demonstrating that bichromatic driving can alleviate the trade-off between DC and AC noise robustness observed in monochromatic drives. This approach reveals continuous manifolds of doubly dynamical sweet spots, along which drive parameters can be varied without compromising coherence. Our results motivate further study of bichromatic Floquet engineering as a powerful strategy for maintaining tunability in high-coherence quantum systems.