Quantum-enhanced rubidium atomic magnetometer based on Faraday rotation via 795 nm stokes operator squeezed light

Abstract

With the help of Stokes operator Ŝ2 squeezed state (also called polarization squeezed state (PSS)) of 795 nm light, rubidium-87 (87Rb) atomic magnetometer based on Faraday rotation (FR) has been implemented and characterized. The PSS of Stokes operator Ŝ2 of 795 nm light has been prepared by means of coherently combining the polarization coherent state (PCS) of a linearly p-polarized bright 795 nm light beam and a linearly s-polarized squeezed vacuum state (SVS) generated by a 397.5 nm ultraviolet laser pumped sub-threshold optical parametric oscillator (OPO) with a PPKTP bulk crystal inside the OPO cavity. PSS with a squeezing level of −3.7 ± 0.3 dB has been achieved around the analysis frequency of 10 kHz. At different transitions of D1 line, various frequency detuning, and reasonable atomic vapor cell’s temperature, FR has been measured and compared. To decrease absorption (scattering) losses and the back-action from atomic spin noise to the probe beam’s polarization noise for maintaining the quantum properties of PSS of Stokes operator Ŝ2 of 795 nm light, we had to run our magnetometer with 87Rb vapor cell’s temperature below 60 °C, at which the PSS was almost destroyed. The sensitivities of magnetic field measurement were characterized via measuring signal-to-noise ratio of the alternating current calibrated magnetic field signal with a balanced polarimeter. Under the conditions of the atomic number density of ∼5.8 × 1010 cm−3 (T ∼ 40 °C) and the probe beam with a detuning of ∼−400 MHz relative to the 5S1/2 (F g = 2) − 5P1/2 (F e = 1) transition of 87Rb D1 line, a typical sensitivity of ∼19.5 pT (Hz1/2)−1 has been achieved employing PSS of Stokes operator Ŝ2 as the probe, compared with a sensitivity of ∼28.3pT (Hz1/2)−1 using PCS as the probe. We preliminarily demonstrated that the quantum-enhanced sensitivity in a Faraday-rotation-based 87Rb atomic magnetometer with the help of PSS of 795 nm light.

A Multi-Pass Optically Pumped Rubidium Atomic Magnetometer with Free Induction Decay

“…The PSN can be suppressed by introducing the squeezed light. In previous work, our group demonstrated the improvement of sensitivity by introducing a Stokes operator polarization-squeezed light in the rubidium atomic magnetometer based on the Faraday rotation [ 32 ], and we also systematically analyzed the effect of frequency detuning on the squeezed level; we found that there was an obvious loss in the squeezed level when the probe light is resonant with rubidium atomic atoms. This indicated that the probe light with large frequency detuning was a better choice for compatibility with the polarization-squeezed light.…”

“…Additionally, the dual-beam FID rubidium atomic magnetometer with large detuning of the probe beam frequency avoided atomic resonance absorption at the detection phase, which was caused by a measurement deviation [ 42 ]. This result laid a foundation for subsequent employing Stokes operator polarization-squeezed light [ 32 ] to improve SNR, and further improve the sensitivity of the magnetometer. Compared to previous works [ 32 , 41 ], FID type rubidium atomic magnetometer more broadly and accurately measured magnetic fields, and was not limited to tracking magnetic field in real-time.…”

“…In 2021, this research group further introduced polarization-squeezed light into the Bell–Bloom all-optical atomic magnetometer, and they also analyzed the main noise in different frequency segments [ 31 ]. Our group demonstrated a rubidium atomic magnetometer based on the Faraday rotation and introduced Stokes operator polarization-squeezed light instead of coherent light; the quantum enhancement effect of the squeezed light was demonstrated at the analysis frequency of 10 kHz by using polarization-squeezed light with a squeezed level of −3.7 dB [ 32 ].…”

Quantum Polarimetry

“…where we denote operator variances by Var 𝑋 = 𝑋 2 − 𝑋 2 , have led to the fruitful discovery and implementation of "polarization squeezing," which may ultimately have applications in quantum-enhanced polarimetry and other communication tasks (Abdel-Aty et al, 2002;Agarwal and Puri, 1994;Alodjants et al, 1998;Alodzhants et al, 1995;Andersen and Buchhave, 2003;Bai et al, 2021;Barreiro et al, 2011;Beduini and Mitchell, 2013;Birrittella et al, 2021;Bowen et al, 2002;Brif and Mann, 1996;Chaudhury et al, 2007;Chirkin, 2015;Chirkin et al, 1993;Civitarese et al, 2013;Corney et al, 2008;Dong et al, 2008;Gühne and Tóth, 2009;Golubev et al, 2004;Gross, 2012;Hald et al, 1999;Han et al, 2018;He et al, 2011;Heersink et al, 2003Heersink et al, , 2005Hillery and Mlodinow, 1993;Hsu et al, 2009;Iskhakov et al, 2009;Josse et al, 2003;Karassiov, 1994;Kitagawa and Ueda, 1993;Klimov and Muñoz, 2013;Klyshko, 1997;Korolkova et al, 2002;Korolkova and Loudon, 2005;Lassen et al, 2007;Luis and Korolkova, 2006;Ma et al, 2011;Mahler et al, 2010;…”

Improving Sensitivity of an Amplitude-Modulated Magneto-Optical Atomic Magnetometer using Squeezed Light

“…Previous experiments utilized a linearly polarized optical probe field in which the coherent vacuum in the orthogonal polarization was replaced by the squeezed vacuum. They demonstrated the improved magnetometer sensitivity for ac magnetic field in the spectral range in which squeezing was observable [21][22][23][24]. Technical 1/f noise has prevented detection of slowly varying dc magnetic fields.…”