Hydrogen 1S–2S

Plate 43 speaks for itself: “Fourteen sure digits from one hydrogen jump.”

The Physics

The 1S–2S transition in hydrogen is driven by two photons of 243 nm and has a very narrow line. Its frequency is among the most precisely measured in physics and tests QED and the proton radius.

λ = 2c / f = 243.13 nm

• λ: wavelength of each of the two exciting photons, m
• c: speed of light, m s⁻¹
• f: 1S–2S frequency 2 466 061 413 187 035(10) Hz, Hz

Fractional uncertainty 4.2×10⁻¹⁵. Parthey et al., PRL 107, 203001 (2011).

Honest caveat: A 2013 re-measurement gave 2 466 061 413 187 018(11) Hz, agreeing within errors.

Sources

• C. G. Parthey et al., Phys. Rev. Lett. 107, 203001 (2011).
• A. Matveev et al., Phys. Rev. Lett. 110, 230801 (2013).

On the poster

Plate 043, “Hydrogen 1S–2S”: the pixel-art plate with its slogan “Fourteen sure digits from one hydrogen jump.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.