Quantum storage of optical signals and coherent manipulation of quantum states based on electromagnetically induced transparency

Abstract

Electromagnetically induced transparency (EIT) techniques are important tools for the storage of the quantum states of light fields in atomic ensembles and for enhancement of the interaction between photons. In this paper, we briefly summarize the recent experimental studies conducted by our group on enhanced cross-phase modulation based on double EIT effects, the quantum interference of stored dual-channel spin-wave excitations and the coherent manipulation of the spin wave vector for the polarization of photons in a single tripod atomic system. The work presented here has potential application in the developing field of quantum information processing. Photons travel fast and are insensitive to the surrounding environment, thus they are often used as carriers of information. However, photons are difficult to trap and store, and the interactions between them are quite weak, which prevent their use in some applications in quantum information processing (QIP). In recent years, electromagnetically induced transparency (EIT) and its related effects have been studied in depth both theoretically and experimentally [1,2]. These studies have shown that EIT effects in three-level or multi-level atomic systems can be applied to significantly reduce the group velocity of light, to trap and store photons using an atomic ensemble and to greatly enhance the optical cross-Kerr nonlinearity. The typical EIT effects can be demonstrated using a three-level -type atomic system, as shown in Figure 1, in which a strong coupling laser beam couples to the atomic transition from the s state to the e state and a weak probe beam couples to the atomic transition from the g state to the e state. Under these conditions, the coherent superposition states s and g are produced and a transparency window for the probe beam appears at a two-photon resonance (Figure 2). This effect is called electromagnetically induced transparency (EIT) or dark resonance [2].Based on the EIT dynamic process, the quantum states of light have been stored successfully in atomic ensembles [3,4]. Recent studies show that EIT and its related effects are important tools in QIP [5][6][7][8][9]. Also, EIT effects can be

Generation of polarization-entangled photon pairs in a cold atomic ensemble

“…The single spin-wave excitation can be mapped into a single anti-Stokes photon via dynamic electromagnetic-inducedtransparency (EIT) reading process. The generated Stokes and anti-Stokes photons are narrow-bandwidth entangled photon pairs which can be effectively stored in atomic ensemble via electromagnetically induced transparency (EIT) [13,14].…”

“…We collected the Stokes photons along z-axis. The spin-wave excitation is then converted into an anti-Stokes photon via an EIT reading process [13] and is collected at the direction opposite to that of the Stokes photons. For verifying photon-photon entanglement, we perform the correlation measurements between the Stokes and anti-Stokes photons at two orthogonal polarization bases (right/left circular polarizations).…”