Abstract
Quantum entanglement is an essential ingredient for the absolute security of quantum communication. Generation of continuous-variable entanglement or two-mode squeezing between light fields based on the effect of electromagnetically induced transparency (EIT) has been systematically investigated in this work. Here, we propose a new scheme to enhance the degree of entanglement between probe and coupling fields of coherent-state light by introducing a two-photon detuning in the EIT system. This proposed scheme is more efficient than the conventional one, utilizing the ground-state relaxation (population decay or dephasing) rate to produce entanglement or two-mode squeezing which adds far more excess fluctuation or noise to the system. In addition, maximum degree of entanglement at a given optical depth can be achieved with a wide range of the coupling Rabi frequency and the two-photon detuning, showing our scheme is robust and flexible. It is also interesting to note that while EIT is the effect in the perturbation limit, i.e. the probe field being much weaker than the coupling field and treated as a perturbation, there exists an optimum ratio of the probe to coupling intensities to achieve the maximum entanglement. Our proposed scheme can advance the continuous-variable-based quantum technology and may lead to applications in quantum communication utilizing squeezed light.
Highlights
Continuous-variable (CV) quantum entanglement is an important resource which has been paid great attention in modern quantum optics and quantum information sciences, possessing many potential applications in quantum teleportation [1], quantum key distribution [2], quantum communication [3, 4], quantum information processing [5], etc
CV quantum entanglement can be realized in other degree of freedom of optical fields, for instance, the polarization state of light has been extensively studied in CV regime by transforming the quadrature entanglement onto polarization basis [6,7,8,9], and the quadrature entanglement using quantum orbital angular momentum with spatial Laguerre-Gauss mode has been discussed in experiment [10]
We will compare the two entanglement generation processes: one is by decoherence rate, and the other one is by two-photon detuning
Summary
Continuous-variable (CV) quantum entanglement is an important resource which has been paid great attention in modern quantum optics and quantum information sciences, possessing many potential applications in quantum teleportation [1], quantum key distribution [2], quantum communication [3, 4], quantum information processing [5], etc. On the other hand, mixing two independent squeezed lights which are generated from optical parametric amplifiers individually provides a practical method to generate quadrature entanglement [17] These studies above clearly indicate that there is a connection between nonlinear optical processes and CV entanglement generation, so that the integration of all optical elements on chip has been proposed in order to further approach the goal of implementation of quantum computer in future [18]. Research reported on entangled light generation by four-wave mixing (FWM) has been intensely studied in hot atomic vapors [19,20,21,22,23,24,25] It has some potential applications, including the production of multiple quantum correlated beams [26], enhancement of the degree of entanglement [27], quantum metrology [28], etc.
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