Non-separated states from squeezed dark-state polaritons in electromagnetically-induced-transparency media

Within the frame of quantized dark-state polaritons in electromagnetically-induced-transparency media, noise fluctuations in the quadrature components are studied. Squeezed state transfer, quantum correlation, and noise entanglement between probe field and atomic polarization are demonstrated in single- and double-$\Lambda$ configurations, respectively. Even though a larger degree of squeezing parameter in the continuous variable helps to establish stronger quantum correlations, inseparability criterion is satisfied only within a finite range of squeezing parameter. The results obtained in the present study may be useful for guiding experimental realization of quantum memory devices for possible applications in quantum information and computation.Comment: 12 pages, 7 figure

Change of polarization degree of light beams on propagation in curved space

Even in free space, which is commonly considered of as a flat space-time in most settings, the degree of polarization of a partially spatially coherent light beam changes as it travels. Similarly, the polarization degree would change when a partially spatially coherent light beam propagates in a curved space-time. The difference of the polarization degree between the curved space and flat space can reveal the essential structure of the curved space. In this work, we consider a simplest case of curved space known as Schwarzschild spacetime. We can simulate the Schwarzschild space-time as an optical material with an effective refractive index. The difference of the polarization degree of a light beam propagating in curved space and flat space can be achieved up to $5\%$, which is detectable in practical measurement. In addition, we have found that the partially spatially coherent light source is necessary for obtaining significant changes in polarization degree. Our results provide an alternative method to estimate the Schwarzschild radius of a massive object with the optical polarization degree measurement.Comment: 14 pages, 4 figure

Gain-assisted quantum heat engine based on electromagnetically induced transparency

We present a scheme to realize a gain-assisted quantum heat engine (QHE) based on electromagnetically induced transparency (EIT). We consider a three-level { \Lambda}-type atomic system that interacts with two thermal reservoirs and a coupling field. The gain without inversion is induced in the system via spontaneously generated coherence (SGC) between two lower levels. To generate SGC, some rigorous conditions must be maintained, but its effect on the system's dynamics are significant, resulting in an enhancement of the emission cross-section and spectral brightness of the QHE