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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Creation of Photon States with Negative Wigner Function with Tunable N-Level EIT Processes

Sutapa Ghosh, A. Gorlach, Chen Mechel, Maria V. Chekhova, Ido E. Kaminer, G. Eisenstein

Published Jun 23, 2025• 0 citations
Publisher

Abstract

Strong optical nonlinearities are key to a range of optical technologies, in particular, to the generation of quantum light states. This paper proposes and demonstrates a novel nonlinear mechanism based on an N-level electro-magnetic induced transparency (EIT) in a warm rubidium vapor. Our scheme relies on using an optical frequency comb as a pump and a CW probe signal, which co-propagate and interact in warm rubidium vapor, as shown in Fig. 1(a). Multiple comb lines excite N-level EIT resonances as shown in Fig. 1(b), which modifies the optical response of the medium, creating a giant Kerr nonlinearity [1], which opens the way for different phenomena like slow light propagation or generation of quantum light states. Here, we experimentally create the giant Kerr nonlinearity, with the magnitude ranging from 1.2 x 10–7to 7.7 × 10–7m2V-2.

DOI
10.1109/cleo/europe-eqec65582.2025.11110216

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Strong optical nonlinearities are key to a range of optical technologies, in particular, to the generation of quantum light states. This paper proposes and demonstrates a novel nonlinear mechanism based on an N-level electro-magnetic induced transparency (EIT) in a warm rubidium vapor. Our scheme relies on using an optical frequency comb as a pump and a CW probe signal, which co-propagate and interact in warm rubidium vapor, as shown in Fig. 1(a). Multiple comb lines excite N-level EIT resonances as shown in Fig. 1(b), which modifies the optical response of the medium, creating a giant Kerr nonlinearity [1], which opens the way for different phenomena like slow light propagation or generation of quantum light states. Here, we experimentally create the giant Kerr nonlinearity, with the magnitude ranging from 1.2 x 10–7to 7.7 × 10–7m2V-2.
We present undergraduate-friendly instructions on how to produce light pulses propagating through warm Rubidium vapor with speeds less than 400 m/s, i.e., nearly a million times slower than c. We elucidate the role played by electromagnetically induced transparency (EIT) in producing slow light pulses and discuss how to achieve the required experimental conditions. The optical setup is presented, and details provided for preparation of pump, probe, and reference pulses of the required size, frequency, intensity, temporal width, and polarization purity. EIT-based slow light pulses provide the most widely studied architecture for creating quantum memories. Therefore, the basic concepts presented here are useful for physics and engineering majors who wish to get involved in the development of cutting-edge quantum technologies.
This thesis presents theoretical derivations and experimental demonstrations of Kerr optical nonlinearities and their dynamics. The Kerr nonlinearity studied is based on electromagnetically induced transparency (EIT), and is known for having an unusually large cross-phase modulation (XPM) [1]. Also, quantum nondemolition (QND) measurements of photon number using the EIT Kerr nonlinearity are discussed. We first discuss the EIT line shapes in hot atomic vapors both with and without buffer gasses, and for the specific case of EIT line shapes on the D1 line of rubidium. Using a Bloch-vector formalism to describe EIT, we derive new expressions describing the dynamical evolution of the EIT Kerr nonlinearity and the rise-time of the EIT Kerr effect. The theory of the EIT Kerr dynamics is confirmed by experiments using hot rubidium vapor in a buffer gas. These experimental observations confirm that the rise-time of the EIT Kerr effect is linearly proportional to the optical thickness of the EIT medium and inversely proportional to the width of the EIT transparency resonance.
We consider an active-Raman-gain scheme for realizing giant Kerr nonlinearity and superluminal optical solitons in a four-state atomic system with a gain doublet. We show that this scheme, which is fundamentally different from those based on electromagnetically induced transparency (EIT), is capable of working at room temperature and eliminating nearly all attenuation and distortion.We demonstrate that, due to the appearance of a gain spectrum hole induced by the quantum interference effect induced by a signal field, a significant enhancement of Kerr nonlinearity of probe field can be realized effectively, which can be more than ten times larger than that arrived by the EIT-based scheme with the same energy-level configuration. Based on these important features, we obtain a giant cross-phase modulation effect and hence a stable long-distance propagation of optical solitons, which have superluminal propagating velocity and very low generating power.
A four-level N-type atomic medium is considered to study the effect of spontaneous generated coherence (SGC) and Kerr nonlinearity on light pulse propagation. A light pulse is propagating inside the medium where each atom follows four-level N-type atom-field configuration of rubidium ( 85 Rb) atom. The atom-field interaction leads to electromagnetically induced transparency (EIT) process. The atom-field interaction is accompanied by normal dispersion and in the presence of SGC and Kerr nonlinearity the dispersion property of the proposed atomic medium is modified, which leads to enhancement of positive group index of the medium. The enhancement of positive group index then leads to slow group velocity inside the medium. A more slow group velocity is also investigated by incorporated the collective effect of SGC and Kerr nonlinearity. The control of group velocity inside a four-level N-type atomic medium via collective effect of SGC and Kerr nonlinearity is the major part of this work.
In this work, we present an analytical method to achieve giant Kerr nonlinearity without absorption in a five-level atomic medium. By using iterative perturbation technique on density matrix equations, we have derived the analytical expressions of nonlinear susceptibility and Kerr nonlinear coefficient in the presence of spontaneously generated coherence (SGC) and relative phase between applied laser fields. It shows that, this five-level atomic medium exhibits multiple electromagnetically induced transparency (EIT) at three different frequencies, at the same time, the Kerr nonlinear coefficient is enhanced around three transparent spectral regions; in each such EIT region appears a pair of positive-negative peaks of Kerr nonlinear coefficient. In particular, these nonlinear peaks are moved to the center of the EIT windows via SGC. This means that the Kerr nonlinear coefficient is enhanced with completely suppressed absorption at different transparency frequencies. Furthermore, the magnitude and the sign of the Kerr nonlinear coefficient are easily controlled according to the SGC strength, the coupling laser intensity, and the relative phase between applied laser fields. Such a giant nonlinear medium can be useful for photonic devices working in the resonant frequency region without absorption. As a typical application, this giant Kerr nonlinear material has been applied to an interferometer for the formation of optical bistability, and showed the appearance of OB at the resonant frequency with significantly reduced threshold intensity and OB width.