Enhanced third-order and fifth-order Kerr nonlinearities in a cold atomic system via Rydberg-Rydberg interaction

Real-imaginary spectrum decomposition of the transparency spectra in microwave dressed Rydberg systems

To distinguish the contributions of electromagnetically induced transparency (EIT) and Autler-Townes splitting (ATS) in their applications in precision laser spectroscopy, we propose a real-imaginary spectrum decomposition method to investigate the transparency spectra in a four-level microwave (MW) dressed Rydberg system. We show that the opening transparency windows in the absorption spectra of probe field is a prominent character by EIT, EIT-ATS crossover, and ATS when the MW field is turned off and the intensity of the control field is adjusted. When the MW field is turned on and gradually increased, the EIT is destroyed and disappears. In addition, the most prominent characters that open a transparency window are the EIT-ATS crossover and the ATS. Then, if we further increase the intensity of the MW field, we find that the transparency windows open mainly due to the ATS. Compared to the previous considerations of this issue, which were limited to three-level systems, our four-level scheme reported here is useful for understanding the features of quantum interference in multilevel atomic systems, and has potential applications to study enhanced sensitivity, measurement spectroscopic, quantum processing, quantum communication, and transmission.

Biphoton generation enhanced by nonlocal nonlinearity via Rydberg interactions

Strongly correlated Stokes and anti-Stokes photon pairs (biphotons) exhibiting very large generation rates and spectral brightnesses could be attained at extremely low pump powers and optical depths. This is realized via spontaneous four-wave mixing in cold atoms with enhanced nonlocal (Rydberg) optical nonlinearities and prepared into a dark state with a large population imbalance. The scheme works with all light fields on resonance yet with negligible linear absorption and Raman gain.

Giant nonlocal Kerr nonlinearity and polaritonic solitons in a Rydberg-dressed Bose-Einstein condensate

We present a scheme to generate nonlocal optical Kerr nonlinearity and polaritonic solitons via matter-wave superradiance in a Rydberg-dressed Bose-Einstein condensate (BEC). We show that the polariton spectrum of the scattered field generated by the superradiance is changed significantly due to the existence of the long-range Rydberg-Rydberg interaction between atoms, i.e. it has a roton-maxon form; moreover, the BEC structure factor displays a strong dependence on the Rydberg-dressing, which can be tuned in a controllable way. We also show that such a Rydberg-dressed BEC system can support a giant nonlocal optical Kerr nonlinearity, and hence allow the formation and stable propagation of polaritonic solitons, which have ultraslow propagation velocity and ultralow generation power. The results reported here are useful to understand the unique properties of Rydberg-dressing in BECs and have potential applications in optical information processing and transmission.

Optimal optical Ferris wheel solitons in a nonlocal Rydberg medium

We propose a scheme for the creation of stable optical Ferris wheel (OFW) solitons in a nonlocal Rydberg electromagnetically induced transparency (EIT) medium. Depending on a careful optimization of both the atomic density and the one-photon detuning, we obtain an appropriate nonlocal potential provided by the strong interatomic interaction in Rydberg states that can perfectly compensate for the diffraction of the probe OFW field. Numerical results show that the fidelity remains larger than 0.96, while the propagation distance has exceeded 160 diffraction lengths. Higher-order OFW solitons with arbitrary winding numbers are also discussed. Our study provides a straightforward route to generate spatial optical solitons in the nonlocal response region of cold Rydberg gases.

Dephasing of ultracold cesium 80D5/2-Rydberg electromagnetically induced transparency

We study Rydberg electromagnetically induced transparency (EIT) of a cascade three-level atom involving 80D_5/2 state in a strong interaction regime employing a cesium ultracold cloud. In our experiment, a strong coupling laser couples 6P_3/2 to 80D_5/2 transition, while a weak probe, driving 6S_1/2 to 6P_3/2 transition, probes the coupling induced EIT signal. At the two-photon resonance, we observe that the EIT transmission decreases slowly with time, which is a signature of interaction induced metastability. The dephasing rate γ_OD is extracted with optical depth OD = γ_ODt. We find that the optical depth linearly increases with time at onset for a fixed probe incident photon number R_in before saturation. The dephasing rate shows a nonlinear dependence on R_in. The dephasing mechanism is mainly attributed to the strong dipole-dipole interactions, which leads to state transfer from nD_5/2 to other Rydberg states. We demonstrate that the typical transfer time τ_0(80D) obtained by the state selective field ionization technique is comparable with the decay time of EIT transmission τ_0(EIT). The presented experiment provides a useful tool for investigating the strong nonlinear optical effects and metastable state in Rydberg many-body systems.

Fifth-order optical nonlinear response of semiconducting 2D LTMD MoS2

The effective fifth-order susceptibility, ${\chi}_{\rm eff}^{(5)}$, of two-dimensional (2D) semiconducting layered transition metal dichalcogenide (LTMD) molybdenum disulfide (${\rm MoS}_2$) is reported here for the first time, to the best of our knowledge. Using the $ Z $-scan technique with a laser operating at 800 nm, 1 kHz, 100 fs, we investigated the nonlinear behavior of ${\rm MoS}_2$ suspended in acetonitrile (concentration, 70 µg/ml). The effective nonlinear refractive index ${{n}_{4,{eff}}} = - ({7.6 \pm 0.5}) \times {10^{- 26}}\; {{\rm cm}^4}/{{\rm W}^2}$, proportional to ${\rm Re}{\chi}_{\rm eff}^{(5)}$, was measured for monolayer ${\rm MoS}_2$ nanoflakes, prepared by a modified redox exfoliation method. We also determined the value of the nonlinear refractive index ${{n}_2} = + ({4.8 \pm 0.5}) \times {10^{- 16}}\;{{\rm cm}^2}/{\rm W}$, which is related to the material's effective third-order optical susceptibility real part, ${Re\chi}_{\rm eff}^{(3)}$. For comparison, we also investigated the nonlinear response of tungsten disulfide (${\rm WS}_2$) monolayers, prepared by the same method and suspended in acetonitrile (concentration, 40 µg/ml), which only exhibited the third-order nonlinear effect in the same intensity range, up to ${120}\;{{{\rm GW}/{\rm cm}}^2}$. Nonlinear absorption was not observed in either ${\rm MoS}_2$ or ${\rm WS}_2$.

Self-Induced Transparency in Warm and Strongly Interacting Rydberg Gases

We study dispersive optical nonlinearities of short pulses propagating in high number density, warm atomic vapors where the laser resonantly excites atoms to Rydberg P states via a single-photon transition. Three different regimes of the light-atom interaction, dominated by either Doppler broadening, Rydberg atom interactions, or decay due to thermal collisions between ground state and Rydberg atoms, are found. We show that using fast Rabi flopping and strong Rydberg atom interactions, both in the order of gigahertz, can overcome the Doppler effect as well as collisional decay, leading to a sizable dispersive optical nonlinearity on nanosecond timescales. In this regime, self-induced transparency (SIT) emerges when areas of the nanosecond pulse are determined primarily by the Rydberg atom interaction, rather than the area theorem of interaction-free SIT. We identify, both numerically and analytically, the condition to realize Rydberg SIT. Our study contributes to efforts in achieving quantum information processing using glass cell technologies.

Polarization dependence of 133Cs 6S1/2-6P3/2-11S1/2 electromagnetically induced transparency at room temperature

The effect of polarization on the ladder-type electromagnetically induced transparency (EIT) spectra of ¹³³Cs atoms at room temperature for the transitions 6²P_1/2-6²P_3/2-11²S_1/2 is experimentally studied. The entire spectra with additional peaks arising from the Doppler effect are observed. As the relative angle between the probe's and coupling's plane of polarization arranges at 0^°, 45^°, and 90^°, the peak height ratio of 44'3" to 44'4" increases by more than 7 times with corresponding values of 0.19, 0.69, and 1.4. Meanwhile, that of 45'4" to 44'4" are found to be 0.61, 0.87, and 1.23 (doubled), respectively. A theoretical model built to explain the experimental results with the considerations of optical pumping effect, two-photon transition probability, dephasing rate, and integration all over the velocity distribution. The simulation and experimental results are well-agreed.

Electromagnetically Induced Transparency in Media with Rydberg Excitons 2: Cross-Kerr Modulation

By mapping photons into the sample of cuprous oxide with Rydberg excitons, it is possible to obtain a significant optical phase shift due to third-order cross-Kerr nonlinearities realized under the conditions of electromagnetically induced transparency. The optimum conditions for observation of the phase shift over π in Rydberg excitons media are examined. A discussion of the application of the cross-phase modulations in the field of all-optical quantum information processing in solid-state systems is presented.

Enhancing Third- and Fifth-Order Nonlinearity via Tunneling in Multiple Quantum Dots

The nonlinearity of semiconductor quantum dots under the condition of low light levels has many important applications. In this study, linear absorption, self-Kerr nonlinearity, fifth-order nonlinearity and cross-Kerr nonlinearity of multiple quantum dots, which are coupled by multiple tunneling, are investigated by using the probability amplitude method. It is found that the linear and nonlinear properties of multiple quantum dots can be modified by the tunneling intensity and energy splitting of the system. Most importantly, it is possible to realize enhanced self-Kerr nonlinearity, fifth-order nonlinearity and cross-Kerr nonlinearity with low linear absorption by choosing suitable parameters for the multiple quantum dots. These results have many potential applications in nonlinear optics and quantum information devices using semiconductor quantum dots.

Enhancement of Goos-Hänchen shift due to a Rydberg state

This paper hints at the Goos-Hänchen shift properties of a cavity containing an ensemble of atoms using a four-level atomic system involving a Rydberg state. By means of the stationary phase theory and density matrix formalism in quantum optics, we study theoretically the Goos-Hänchen shifts in both reflected and transmitted light beams. It is realized that as a result of the interaction between Rydberg and excited states in such a four-level atom-light coupling scheme the maximum positive and negative Goos-Hänchen shifts can be obtained in reflected and transmitted light beams owning to the effect of the Rydberg electromagnetically induced transparency (EIT) or Rydberg electromagnetically induced absorption. In particular, when the switching field is absent and the Rydberg EIT is dominant in the medium, a giant Goos-Hänchen shift can be achieved for both reflected and transmitted light beams.

Dynamics of vortex-antivortex pairs and rarefaction pulses in liquid light

We present a numerical study of the cubic-quintic nonlinear Schrödinger equation in two transverse dimensions, relevant for the propagation of light in certain exotic media. A well-known feature of the model is the existence of flat-top bright solitons of fixed intensity, whose dynamics resembles the physics of a liquid. They support traveling wave solutions, consisting of rarefaction pulses and vortex-antivortex pairs. In this work, we demonstrate how the vortex-antivortex pairs can be generated in bright soliton collisions displaying destructive interference followed by a snake instability. We then discuss the collisional dynamics of the dark excitations for different initial conditions. We describe a number of distinct phenomena including vortex exchange modes, quasielastic flyby scattering, solitonlike crossing, fully inelastic collisions, and rarefaction pulse merging.