Effect of buffer gas on an electromagnetically induced transparency in a ladder system using thermal rubidium vapor

Abstract

We report on the first observation of electromagnetically induced transparency (EIT) in a ladder system in the presence of a buffer gas. In particular we study the 5S 1/2 -5P 3/2 -5D 5/2 transition in thermal rubidium vapor with a neon buffer gas at a pressure of 6 Torr. In contrast to the line narrowing effect of buffer gas on Λ-systems we show that the presence of the buffer gas leads to an additional broadening of (32 ± 5) MHz, which suggests a cross section for Rb(5D 5/2 )-Ne of σ−19 m 2 . However, in the limit where the coupling Rabi frequency is larger than the collisional dephasing a strong transparency feature can still be observed.The effect of electromagnetically induced transparency (EIT) arises due to coherence in three-level systems as first described in [1,2], and experimentally demonstrated in [3]. Typically, the three-level system consists of two long-lived states (|1 and |3 ), which are coupled by two lasers, labelled probe and coupling with Rabi frequencies Ω p and Ω c (> Ω p ), to a radiative state |2 with a lifetime, 1/Γ 2 . If the two lasers are resonant, i.e., the detunings δ 12 = δ 23 = 0, the imaginary part of the onephoton coherence Im(ρ 12 ) and the absorption coefficient α ∝ Im(ρ 12 ) are zero, rendering the medium fully transparent [4]. For Ω p < Γ 2 the transparency is caused by a destructive interference of the excitation amplitudes into the intermediate state |2 , which results in the occupation of a dark state |∅ |1 with no contribution from the radiative state. The width of the transparency window is determined by the dephasing rate between states |1 and |3 , Γ 13 , and can be much narrower than the natural linewidth, Γ 13 < Γ 2 . For photon storage applications one is interested in reducing the dephasing rate as the narrow resonance results in a large group index [5] and enables long photon storage times [6]. For thermal atoms, the dephasing rate can be reduced by using the hyperfine ground states as the long lived states forming a Λ-system, and a buffer gas to increase the interaction time with the laser beams [7][8][9].Another topic of interest is the ladder or cascade system where |3 is a higher energy excited state [10][11][12]. For example, if state |3 is a Rydberg state [13], this opens interesting possibilities for quantum information [14][15][16] and electrometry [17,18]. In the ladder system the dephasing rate is typically larger than for Λ-systems due to the spontaneous decay of level |3 . Otherwise, EIT in Λ and ladder systems show generally similar properties. However, the addition of a buffer gas changes this behavior dramatically. In Λ-systems the dephasing of * Electronic address: u.m.krohn@durham.ac.uk the ground state coherences due to the collisions with the buffer gas is negligible and, instead the increased transient time due to collisional diffusion allows an extremely narrow linewidth to be observed [7]. In contrast, for cascade systems the collisional dephasing due to the buffer gas becomes the dominant line broadening mechanism and it is predicted that th...

Two-photon microwave transitions and strong-field effects in a room-temperature Rydberg-atom gas

“…This EIT resonance has a linewidth of 2π × (3.4 ± 0.3) MHz, which is larger than the ≈2π × 1 MHz single-atom EIT linewidth given by γ EIT = 2 c /γ [18], where c is the Rabi frequency of the coupling field and γ is the 5P 3/2 state linewidth. The observed EIT linewidth is likely increased by laser linewidths and transit-time broadening [18,19], however in our experiment the broadening is mostly due to the drift of the probe laser frequency over the course of one data-averaging sequence.…”

Optimized acousto-optic modulation for the V-type electromagnetically induced transparency in rubidium-87 D1 line

“…However, this value can be further improved whenever the techniques related to resonance-width reduction are implemented. Examples of these techniques include a use of paraffin-coated cell [21] and a buffer gas added to the interaction cell [20,21] (except for the effect observed in the Ξ-type interaction, where the buffer gas has been reported to increase the resonance width [24]). Note that the earlier studies have reported the resonance width of up to 20 times smaller than the natural width for D 2 in 87 Rb, using a Laguerre−Gaussian coupling beam [25] and an appropriate beam intensity [24,25].…”

“…Examples of these techniques include a use of paraffin-coated cell [21] and a buffer gas added to the interaction cell [20,21] (except for the effect observed in the Ξ-type interaction, where the buffer gas has been reported to increase the resonance width [24]). Note that the earlier studies have reported the resonance width of up to 20 times smaller than the natural width for D 2 in 87 Rb, using a Laguerre−Gaussian coupling beam [25] and an appropriate beam intensity [24,25]. When all of our 'narrowing' techniques are implemented, the experimental method of ours can be used to build a robust and stable magnetometer using Zeeman sub-levels [26][27][28].…”

Amplified spontaneous emission at 523 μm in two-photon excited rubidium vapor

“…This is largely because of the difficulty of detecting the mid-IR radiation, which is strongly absorbed in conventional Rb cells. We note that similar energy level configurations in Rb atoms have been used extensively for studying ladder-type electromagnetically induced transparency [15,16], nonlinear properties of four-wave mixing and new field generation [17,18], atomic coherence effects [19,20] and transfer of orbital angular momentum [3,21], as well as for imaging of ultracold atoms [22].…”