Fig. 1: Energy level diagram and experimental setup for time crystal measurement.

a Energy level diagram based on three-photon Rydberg electromagnetically induced transparency (EIT) scheme. γ₁, γ₂, and γ correspond to the decay rates of states \(\left\vert e\right\rangle\), \(\left\vert m\right\rangle\), and \(\left\vert R\right\rangle\), respectively. The Rydberg state \(\left\vert R\right\rangle\) is divided into Floquet sidebands when atoms are driven by an RF field; three sideband energy levels, \(\left\vert R\right\rangle\), \(\left\vert {R}_{1}\right\rangle\), and \(\left\vert {R}_{2}\right\rangle\) with energy interval ω, are illustrated. b Simplified experimental setup. An RF field is applied to the atoms by two electrodes with a loading frequency ranging from 0 MHz ~ 2π × 30 MHz. c and d Triggered probe transmission within 0.7 ms time interval caused by switching on the RF field [U = 3.8 V], which oscillates with distinct frequencies [f = 2π × 18.1 kHz (c) and f = 2π × 8.3 kHz (d)] obtained by setting Δ_c = −2π × 24.1 MHz for (c) and Δ_c = −2π × 32.4 MHz for (d), thus revealing the distinct time crystals. The different colored lines in c and d are from different experimental trials. The dips and peaks of oscillations correspond to the low and high density of excited Rydberg atoms [marked by different numbers of circles in (d)]. e, f Distributions of the Fourier amplitudes with the dominant frequency on the complex plane. In this process, we recorded the probe transmission within the time intervals Δt = 0.7 ms with 300 data points after the RF-field is turned on for e 0.8 ms and f 2.8 ms. The signal in f appears to be noisier than in e because the signal has more low-frequency noise.