Sadiq N A W A Z Khan

Ultracold atoms have become one of the most exciting platforms to synthesize novel condensed matter physics. Here we realize a sawtooth superradiance lattice in Bose-Einstein condensates and investigate its chiral edge currents. Based on one-dimensional superradiance lattice (SL) in standing wave-coupled electromagnetically induced transparency, a far-detuned standing-wave field is introduced to synthesize a magnetic field. The relative spatial phase between the two standing-wave coupling fields introduce a magnetic flux in the sawtooth loop transitions of the lattice. This flux determines the moving direction of excitations created in the SL and results in nonsymmetric reflectivities when the SL is probed in two opposite directions. Our work demonstrates an in situ technique to synthesize and detect artificial gauge field in cold atoms. npj Quantum Information (2020) 6:18 ; https://doi.

We study the electromagnetically induced-absorption-like (EIA-like) effect for an n-type system in an 87 Rb Bose-Einstein condensate (BEC) using the absorption imaging technique for coupling and driving lasers operating at the D1 and D2 lines of 87 Rb. The coherent effect is probed by measuring the number of atoms remaining after the BEC is exposed to strong driving fields and a weak probe field. The absorption imaging technique accurately reveals the EIA-like effect of the n-type system. This coherent effect in an n-type system is useful for optical storage, tunable optical switching, and so on. Modifying the absorptive or dispersive properties of a medium using coherent driving fields to study coherent phenomena is a hot topic in atomic and optical physics. These phenomena are not only of fundamental interest for understanding light-matter interaction but also applicable in various light-matter-interaction-based devices. The schemes devised for observation of such effects include n-type, ladder-type, Λ-type, V-type, cascade and tripod. In such systems, electromagnetically induced transparency (EIT), [1,2] coherent population trapping, [3] superluminal, [4] and subluminal [5] light propagation, electromagnetically induced absorption (EIA) due to spontaneously generated coherence, [6−9] storage of light, [10,11] coherent nonlinear optics at low light levels [12−14] and lasing without inversion (LWI) [15] have been studied deeply. For this purpose, hot as well as cold atoms are used. However, a BEC is a useful tool for observing various phenomena that are not possible in hot atoms due to the Doppler shift. BECs also allow the absorption imaging technique in addition to transmission or scattering techniques for the probing of such coherent phenomena inside the medium. Such an absorption imaging technique is not suitable for hot atoms as they are moving at high speeds. The absorption imaging studies of the EIT [16] and EIA [17] in a BEC of 87 Rb have already proved that this technique is capable of precisely revealing the coherent properties of the systems under study in ultracold atoms. In this work, we study the EIA-like effect for an n-type system in a 87 Rb BEC as shown in Fig. 1. A similar n-type system studied here is already discussed, [18−20] where the probe light transmission as a function of frequency detuning is measured. Our system, however, is different from the previous systems [18,19] because in our system the driving and coupling lasers share the same lower ground level in the n-type system while in the system of Ref. [18,19] the driving and probe lasers share the same lower level. Also, we measure the number of remaining atoms in the absorption image after the BEC is exposed to strong driving and coupling lasers and weak probe lasers, while they measure the transmission spectrum of the probe laser directly using a photodetector. In principle, this absorption imaging technique is equivalent to the measurement of the transmission of the weak probe beam. In transmission spectroscopy, absorption of the probe reduces the laser transmission while in absorption imaging, the number of atoms reduces in the BEC due to heating caused by the probe laser. As shown in Fig. 1(b), the coupling laser at frequency c , locked between the lower ground state = 1 and the ′ = 1 state of the 1 line and the weak probe laser at frequency p , is optically phase-loop locked to the coupling laser and its frequency may be scanned from the = 2 to ′ = 1 transition , together forming a Λ-type system. We construct the n-type system by adding a driving laser to couple the transition between the | = 1⟩ to | ′ = 2⟩ transition of the 2 line. Since the BEC is prepared in the | = 2, = 2⟩ state, we lock the driving laser to the | = 1⟩ to | ′ = 2⟩ transition of the 2 line represented by d , as opposed to the study in Ref. [18-20] The Λ-type system results in the standard EIT (Fig. 2(a)) but adding the driving laser transforms the EIT into an EIA-like shape (Fig. 2(c)), and it is quite different from the EIA. This n-type configuration resembles the absorption line-shape of EIA just as Autler-Townes splitting in a three-level system resembles the line-shape of EIT although having different origins. [18,21] *

We study the electromagnetically induced-absorption-like (EIA-like) effect for an n-type system in an 87Rb Bose–
Einstein condensate (BEC) using the absorption imaging technique for coupling and driving lasers operating at
the 𝐷1 and 𝐷2 lines of 87Rb. The coherent effect is probed by measuring the number of atoms remaining after
the BEC is exposed to strong driving fields and a weak probe field. The absorption imaging technique accurately
reveals the EIA-like effect of the n-type system. This coherent effect in an n-type system is useful for optical
storage, tunable optical switching, and so on