Quantized conductance in quasi-one-dimensional systems not only provides a hallmark of ballistic transport, but also serves as a gateway for exploring quantum phenomena. Recently, a unique hidden Rashba effect, which arises from the compensation of opposite spin polarizations of a Rashba bilayer in inversion symmetric crystals with dipole fields, such as bismuth oxyselenide (${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$), has attracted tremendous attention. However, investigating this effect utilizing conductance quantization remains challenging. Here we report the conductance quantization observed in a chemical vapor deposition (CVD)-grown high-mobility ${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$ nanoribbon, where quantized conductance plateaus up to $44\times 2e^2/h$ ($e$ is the elementary charge, $h$ is the Planck’s constant, and the factor 2 results from spin degeneracy) are achieved at zero magnetic field. Because of the hidden Rashba effect, the quantized conductance remains in multiples of $2e^2/h$ without Zeeman splitting even under magnetic field up to 12 T. Moreover, within a specific range of magnetic field, the plateau sequence follows the Pascal triangle series, namely, $(1,3,6,10,15\dots )\times 2e^2/h$, reflecting the interplay of size quantization in the two transverse directions. These observations are well captured by an effective hidden Rashba bilayer model. Our results demonstrate ${\mathrm{Bi}}_2{\mathrm{O}}_2\mathrm{Se}$ as a compelling platform for spintronics and the investigation of emergent phenomena.

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• Ballistic transport
• Spin-orbit coupling
• Nanoribbon
• Chemical vapor deposition