We investigate the time evolution of entanglement of various entangled states of a two-qubit system exposed to either thermal or squeezed reservoirs. We show that, except for the vacuum reservoir, the sudden-death of entanglement always exists in the thermal and squeezed reservoirs. We present explicit expression for the sudden-death time of entanglement for various entangled states. We find that the sudden-death of entanglement results from the portion of the double excitation component in the initial entangled state. In this sense, the maximally entangled states of a two-qubit system that do not have the double excitation component is more robust against the quantum fluctuations of the vacuum reservoir.

We present a proposal to manipulate the Goos-Hänchen shift of a light beam via a coherent control field, which is injected into a cavity configuration containing the two-level atomic medium. It is found that the lateral shifts of the reflected and transmitted probe beams can be easily controlled by adjusting the intensity and detuning of the control field. Using this scheme, the lateral shift at the fixed incident angle can be enhanced (positive or negative) under the suitable conditions on the control field, without changing the structure of the cavity.PACS number(s): 42. 50. Md, 42.25.Gy, 42.25.Bs

No abstract

We study an experimental scheme to generate Gaussian two-mode entangled states via beam splitter. Specifically, we consider a nonclassical Gaussian state ͑squeezed state͒ and a thermal state as two input modes, and evaluate the degree of entanglement at the output. Experimental conditions to generate entangled outputs are completely identified and the critical thermal noise to destroy entanglement is analytically obtained. By doing so, we discuss the possibility to link the resistance to noise in entanglement generation with the degree of single-mode nonclassicality.

We propose a scheme for the measurement of joint photon statistics and Wigner function of the entangled field states between two separate cavities. The scheme utilizes the momentum state of the two-level atoms in Bragg's regime. The probability of finding the atom in any one of the momentum states is the product of joint photon statistics and an oscillatory function. The argument of the function contains the information of the joint photon numbers in two cavities. We use the method of state reduction to a single set of joint photon numbers, which is a consequence of the measuring sequence. The repeated measurement of the set of photon numbers gives the joint photon statistics of the entangled field state. The complete entangled state can be reconstructed as a Wigner function from the knowledge of photon statistics of the coherently displaced entangled state.

5-aminolevulanic acid (ALA), belonging among the promising second generation of sensitizers, was evaluated as an inducer of photodamage on HeLa (human cervical adenocarcinoma) cell line. A diode laser (635 nm) was used as a source for initiation of the photodynamic effect. We studied the influence of different incubation times, various concentrations of sensitizer, different irradiation doses and various combinations of sensitizer and light doses on the photodamage of HeLa cells. Viability of cells was determined by means of neutral red assay. The quantitative cellular uptake of ALA sensitizer was done by spectrophotometric measurements. No prominent cytotoxic or phototoxic effects on HeLa were observed due to sensitizer or light doses when studied independently of each other. However phototoxicity evoked by laser irradiated sensitizer was detected in HeLa cell line.

The aim of this study was to investigate the mechanism of cell death by photodynamic therapy (PDT) in the Rhabdomyosarcoma (RD) cell line. The present study evaluates the effects of photodynamic therapy (PDT) with 5-ALA as photosensitizer using human muscle cancer cells as experimental model. We study the photosensitizer uptake, cytotoxicity, phototoxicity, and cellular viability of the RD cells which was estimated by means of neutral-red spectrophotometric assay. The given experiment was consisted of two steps. For the first one, RD cells were exposed to 5-ALA at concentrations of 0 up to 1000 μg of ALA/ml in minimum essential medium (MEM). The optimal uptake of photosensitizer (5-ALA) in RD cells was investigated by means of spectrometric measurements. Cells viability was determined by means of neutral red assay (NRA). In the second step, 5-ALA exposed RD cells were irradiated with red light (a diode laser, λ = 635 nm) at total light dose of 80 J/cm 2 . The influence of different incubation times and concentrations of 5-ALA, different irradiation doses and various combinations of photosensitizer and light doses on the viability of RD cells were investigated. It was observed that sensitizer concentration or light doses have no significant effect on cells viability when studied independently. The maximal cellular uptake occurred after 47 hours in vitro incubation. The phototoxic assay showed that ALA-PDT induced killing of 76% of the cells at 250 μg/ml drug dose and 80 J/cm 2 light dose.

We investigate the phenomenon of sudden death of entanglement in a bipartite system subjected to dissipative environments with arbitrary initial pure entangled state between two atoms. We find that in a vacuum reservoir the presence of the state where both atoms are in excited states is a necessary condition for the sudden death of entanglement. Otherwise entanglement remains for an infinite time and decays asymptotically with the decay of individual qubits. For pure 2-qubit entangled states in a thermal environment, we observe that the sudden death of entanglement always happens. The sudden death time of the entangled states is related to the temperature of the reservoir and the initial preparation of the entangled states.