Thermal resonance-enhanced transparency in room temperature Rydberg gases

Abstract

We report the enhanced optical transmission in the coherent, off-resonant excitation of Rydberg atom gases at room temperature via a two-photon process. Here thermal resonance-enhanced transparency (TRET) is induced when the detuning of the two lasers is adjusted to compensate the atomic thermal-motion-induced energy shifts, i.e. single and two-photon Doppler shifts. We show that the atomic velocity is mapped into the transmission of the probe fields, which can be altered by independently and selectively exciting different velocity groups through sweeping the detuning. The maximal transmission in TRET is about 8 times higher than that under the electromagnetically induced transparency (EIT). Utilizing the TRET effect, we enhance the sensitivity of a Rydberg microwave receiver to be 28.7~nVcm$^{-1}$Hz$^{-1/2}$, ultimately reaching a factor of 2.1 of the EIT case. When atoms of separate velocity groups are excited simultaneously by multiple sets of detuned lasers, the receiver sensitivity further increases, which is linearly proportional to the number of the velocity groups. Our study paves a way to exploit light-matter interaction via the TRET, and contributes to current efforts in developing quantum sensing, primary gas thermometry, and wireless communication with room-temperature atomic gases.

Figures (4)

• Figure 1: TRET in thermal Rydberg gases. (a) Sketch of the experimental setup and (b) relevant energy-level diagram. An 852 nm laser is split into two identical beams, labeled as the reference beam and the probe beam. The 509 nm coupling laser counter-propagates through the vapor cell, and overlaps with the probe laser but not the reference beam. The probe laser (Rabi frequency $\Omega_p$) and the coupling laser ($\Omega_c$) drive the ground atoms $|g\rangle$ to the Rydberg state $|r\rangle$ via an intermediate state $|e\rangle$ with detuning $\Delta_p$. (c) The thermal motion of atoms in the cell follows the Maxwell–Boltzmann distribution $N(v)\sim v^2f(v)$. (d) and (e) Transmission when $\Delta_p/2\pi =0$ MHz and $\Delta_p=225$ MHz. At these detunings the lasers selectively excite velocity groups such that the peak transmission appears at velocity $v_c \simeq 0$ m/s and $v_c \approx v_T = 193$ m/s, correspondingly.
• Figure 2: Transmission of the probe field. (a) Theory simulation and (b) experimental data of the transmission by varying detuning $\Delta_c$ and $\Delta_p$. The solid envelope indicates the position of thermal resonance. The transmission peak under EIT is marked. (c) The dependence of TRET peaks on the laser detuning $\Delta_p + \Delta_c$ for experimental data (red hollow circles) and simulation (blue curve). The dashed line marks the maximum transmission enhanced by the thermal resonance. The data are normalized to the maximum EIT peak.
• Figure 3: Measured sensitivity for $\Delta_p /2\pi$ = 0 MHz with $v_c \approx$ 0 m/s (blue squares) and 220 MHz with $v_c \approx$ 187 m/s (red triangles). The blue and red dashed lines indicate the detectable minimum electric fields. Inset shows the oscillation signal for $\Delta_p /2\pi$ = 0 (blue solid line) and 220 MHz (red dashed line) at a signal field $E_{Sig}=$ 60 $\mu$V/cm. The green circles show the EIT-AT splitting in a strong field region and the black solid line shows the calibrated electric field.
• Figure 4: MW measurement with multiple sets of detuned lasers. (a) Measurement of the transmission signal of 35$D_{5/2}$ as a function of $\Delta_c$ at indicated detuning of $\Delta_p$. (b) Transmission spectra of the $35D_{5/2}$ state as a function of $\Delta_c - \Delta_{\rm offset}$ with different number of laser sets. (c) Sensitivities for $35D_{5/2}$ and $40D_{5/2}$ with different sets of excitation lasers. The sensitivity shows a nearly linear enhancement with the number of laser sets.