Nature - USA (2020-05-14)

0 20 40 60 80 100

−0.15

−0.1

−0.05

0

0.05

0.1

0.15

0.2

Time[ms]

RF response [A.U.]

X

Y

R

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

0

500

1000

1500

2000

2500

f−fLar [kHz]

RF response [A.U.]

Experiment

Fit

ab

52 S1/2

52 P1/2

52 P3/2

F=1

F=2

F’=1

F’=2

F’=1

F’=2

F’=0

F’=3

Repump

Pump

Probe

-∆

Extended Data Fig. 1 | Magneto-optical resonance signal. a, Spin response to
an RF pulse. X and Y are the outputs of the lock-in amplifier, with a π/2 phase
difference between them. RX=+^22 Y is the demodulated amplitude. b, The
associated Fourier transformation of the spin response signal. fLar is the centre
frequency for demodulation, with the subscript ‘Lar’ representing ‘Larmor
frequency’. f is the actual frequency of the signal before demodulation.

f − fLar represents the frequency of the signal after demodulation, that is, at the

lock-in amplifier output. Inset, energy levels of^87 Rb. All the atoms are pumped

into the F = 2 , mF = −2 state, so that they are oriented along x. The magnetic field

leads to a splitting of the magnetic sublevels by the Larmor frequency ΩL. A.U.,

arbitrary units.