Power spectra and correlations of intensity fluctuations in electromagnetically induced transparency

Abstract

The quantum fluctuations of optical beams are highly correlated in electromagnetically induced transparency (EIT). The intensity fluctuations are enhanced by conversion of phase noise to intensity noise in atomic vapour. We have studied spectra of intensity fluctuations in dense rubidium vapour for different laser beam powers. Observed excess noise spectrum is broader than EIT window at the same optical power. Both spectral widths are proportional to the laser beam intensity. By using signal subtraction scheme we can reduce amplitude of the fluctuations to close the photonic short noise level. This result confirms the high degrees of intensity correlations and can be used to improve quality of optical atomic clocks.

Atomic noise spectra in nonlinear magneto-optical rotation in a rubidium vapor

“…The noise is larger in the low frequency region. The noise level approaches the shot-noise level [20] at higher frequencies. For comparison, traces (a1) and (b1) are recorded with only one laser beam sent to the BPD.…”

“…A simple summation or subtraction of these two signals can suppress the noise. Experiments have shown the ability of reducing the noise to the shotnoise level by taking the difference of two laser beams in an EIT configuration [20]. In NMOR experiments, the recent observation of the intensity correlation [21], along with the power spectra study of the noise at 2.5 MHz [22], indicate the possibility of using the intensity correlation to reduce or eliminate the atomic excess noise.…”

Dynamic control of EIT by changing optical phase

“…In atomic vapor without buffer gas the ground state relaxation time 1/ bc is defined by the time-of-flight. Nonlinear and linear power dependences of the EIT width have been observed [30][31][32][33][34]. In our experiment, the slopes of the experimental curves are several times less than calculated slopes for the de-coherence rates.…”

Intensity correlations in resonance nonlinear magneto-optical rotation

“…The strong coupling of optical fields in Λ-type atoms provides a way of controlling amplitude fluctuations. The amplitude correlations have been studied in EIT [33,34,35,36,37] and NMOE [38] experiments. Observation of sub-Poisson statistics of the amplitude noise is reported in [34].…”

“…Amplitude correlations and anti-correlations are observed in two orthogonally circularly polarized optical beams from the same laser [36] and in orthogonally linearly polarized optical beams from two independent lasers [35]. Power spectra of intensity fluctuations was studied in [37]. Noise spectroscopy of nonlinear magneto-optical resonances in Rb vapor at a detection frequency 2.5 MHz with bandwidth 30 kHz is performed in [38], where the photon noise limit has been reached.…”