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The observer-based feedback control for the two-level bilinear open stochastic quantum system is proposed in this paper. The state of open stochastic quantum system (OSQS) is described in the Cartesian coordinate system. The proposed state observer is designed by using state-dependent differential Riccati equation (SDDRE) and constructed for optimally estimating the state of OSQS from measurement output of the system. The state of observer is continuously updated by the output data of continuous weak measurement (CWM). A Lyapunov Feedback control is designed based on estimated state of the observer for the state transfer of OSQS. An exponential Lyapunov function is chosen to ensure the stability of the system. The observer-based Lyapunov feedback control (OLFC) strategy is developed according to the stochastic Lyapunov stability theorem. The numerical simulation results verify the achievability of the proposed OLFC strategy in terms of state estimation and state transfer of OSQS. Numerical simulations demonstrate that the observer tracks the state of system asymptotically with minimum error of ± 3%. The proposed OLFC has the ability to move the state of OSQS from arbitrary initial state to the final target eigenstate with high fidelity ≥ 90%.

Electromagnetically induced holographic imaging using strongly interacting Rydberg atoms is investigated via electromagnetically induced grating (EIG). We consider two schemes, i.e., by direct detection of holographic imaging pattern, known as electromagnetically induced classical holographic imaging (EICHI), and by employing entangled photon pairs for imaging which is called as electromagnetically induced quantum holographic imaging (EIQHI). Both schemes are employed to obtain 1D and 2D holographic imaging. In EICHI and EIQHI, amplitude and phase information of EIG can be imaged with controllable image variation in size. It is noticed that holographic imaging is influenced by van der Waals (vdW) effect present in Rydberg atoms.

This paper proposes a new Maximum Power Point Tracking (MPPT) technique for photovoltaic (PV) systems especially under Partial Shading (PS). This technique is based on Generalized Pattern Search (GPS) optimization algorithm. The proposed technique adopts the GPS algorithm owing to the reason that its major features like simple implementation, derivative free nature, fast convergence and high accuracy are ideally suited to deal with PS conditions. Furthermore, these features of GPS can well resolve the limitations and drawbacks of previous MPPT techniques, such as fluctuation, low efficiency, high complexity and slow convergence. For comparison, our proposed MPPT algorithm, the Particle Swarm Optimization (PSO) algorithm and the Perturb and Observe (P&O) algorithm have been implemented in MATLAB/Simulink. The comparison results demonstrate that the proposed MPPT technique can efficiently detect the global maximum (GM) in a fewer number of voltage samples, which is nearly 4 times less than the number of voltage samples required by PSO. Moreover, the steady state efficiency of the proposed MPPT is 99.8%, which is higher than the other MPPT techniques. Therefore, the proposed technique distinguishes itself from other MPPT techniques due to its superior quality in terms of convergence speed, dynamic and steady state efficiencies and low complexity.

We consider the resonant interaction of an ultracold two-level atom with an electromagnetic field inside a high- Q micromaser cavity. In particular, we study the tunneling and traversal of ultracold atoms through vacuum-induced potentials for secant hyperbolic square and sinusoidal cavity mode functions. The phase time which may be considered as an appropriate measure of the time required for the atoms to cross the cavity, significantly modifies with the change of cavity mode profile. For example, switching between the sub and superclassical behaviors in phase time can occur due to the mode function. Similarly, negative phase time appears for the transmission of the two-level atoms in both excited and ground states for secant hyperbolic square mode function which is in contrast to the mesa mode case.

In this paper, we study the atomic grating produced by a three-level ladder type system which interacts with a strong standing microwave drive field of finite bandwidth. The upper levels of the atoms are coupled by the drive field while the probe field is applied on the lower two levels. We find that in the presence of phase fluctuations associated with the microwave drive field, the diffraction intensities are significantly affected. Our results show that if the probe and microwave drive are on resonance with their respective atomic transitions, then the diffraction intensities can be improved by properly adjusting the strength of the drive field. However, if the probe field is detuned from the resonance, then the diffraction intensities can be improved by appropriately selecting the strength of the drive field, probe detuning and interaction length of the medium. Interestingly, our results also show that the effects of phase grating can also be enhanced by a pertinent choice of various parameters even in the presence of phase diffusion. This results in the suppression of the zeroth order intensity while the first order intensity is increased.

In this paper, we discuss the effects of detuning on the velocity selection for ultracold three-level atoms in Λ configuration using mazer action. We find sharp resonances in the transmission probability with respect to the detuning. Our results show that the velocity selection of ultracold atoms can easily be tuned and enhanced using off-resonant field in a bimodal cavity.

In this paper, we propose a scheme for the teleportation of general two-partite entangled state of zero and one photon state from one bimodal cavity to another. The scheme can be realized by using cavity quantum electrodynamics (QED).

This proposal investigates the influence of the phase fluctuations on the time evolution of entanglement generation in a three-level correlated emission laser (CEL) with injected coherence. The atoms are injected in the cavity with an initial partial coherent superposition of the upper and lower levels. The corresponding phase φ is considered to be randomly distributed around some fixed phase φ 0 . The fluctuations in phase φ modifies the coherence between the two corresponding atomic levels. Therefore, we observe strong influence of phase fluctuations on the entanglement generation using the injected coherence CEL system.

In this paper, we discuss the velocity selection of ultracold three-level atoms in Λ configuration using a mazer. Our model is the same as discussed by Arun et al. [R. Arun, G.S. Agarwal, M.O. Scully, H. Walther, Phys. Rev. A 62 (2000) 023809] for mazer action in a bimodal cavity. We show that the initial Maxwellian velocity distribution of ultracold atoms can be narrowed due to the presence of resonances in the transmission through dressed-state potential. When the atoms are initially prepared in one of the two lower atomic states then significantly better velocity selectivity is obtained due to the presence of dark states.

In this paper, we study the quantum phase properties of the field in a two-photon micromaser, including the effects of the finite detuning of the intermediate level. For initial coherent state of the cavity field and atoms initially in their excited state multipeak phase structure appears which eventually leads to the randomization of the cavity field phase. However, the approach towards the randomization depends upon the detuning. If the atoms are injected in a coherent superposition of their upper and lower atomic states then the phase distribution evolves into two-peak structure. For initial thermal state and atoms in polarized state, cavity field acquires some phase. We also consider the effect of finite Q of the cavity, random injection of the atoms and fluctuations in the interaction time.

In this paper, we discuss the effects of spatial mode function in an one-photon micromaser in the presence of two-atom events. It is shown that two-atom events allow us a possibility to study the effects of different cavity eigenmodes in a micromaser. We find that squeezing properties of the radiation field depend upon the parity (odd or even) and order (lower or higher) of cavity eigenmodes. For example, squeezing can be obtained for odd-order cavity eigenmodes which completely vanishes for even-order modes. Our results also show that effects similar to self-induced transparency are never obtained in the presence of two-atom events. Finally, we consider the effect of pump fluctuations and cavity losses in our system.

In this paper, we study the effect of cooperative atomic interactions, cavity losses, and pump fluctuations on quantum phase properties of the field in a one-photon micromaser. We consider, initial coherent state of the radiation field and atoms initially in the excited and coherent superposition of their atomic states, respectively. We find that quantum phase properties of the field in a micromaser are highly sensitive to two-atom events and cavity losses. Both contribute to the randomization of the well-defined phase structure associated with the initial coherent state. However, the approach towards the randomization is quite different in the two cases. We also find that the fluctuations, associated with the random injection of the atoms, affect the phase structure of the coherent state.

We present a scheme to reconstruct an arbitrary multimode entangled state of the cavity field using phase sensitive amplification in a driven three level atomic system. Under the parametric limit, when noise in both the qudartures approach to zero, we measure the amplified field quadarture. The complete quadrature distribution is obtained by measuring the amplified noise-free quadartures for different values of the driving field phases. The Wigner function of the initial field is then obtained by employing quantum state tomography. The scheme is insensitive to the noise associated with the finite efficiency of the detectors in the homodyne detection measurement.

We show that a coherent superposition of coherent states remains highly nonclassical when it is amplified through a linear phase-sensitive or phase-insensitive amplifier. The nonclassicality persists for arbitrarily large gain. We also propose a scheme for the observation of quantum interference via phase-sensitive amplification. The basic idea is to amplify a Schrodinger-cat state through a phase-sensitive two-photon CEL amplifier such that there is no added noise in the quadrature of interest and all the noise is fed into the conjugate quadrature. This scheme allows us to avoid the problem of detector efficiency in balanced homodyne detection.

The theory of a two-photon phase-sensitive amplifier is presented when the coherence is produced between the atomic levels by two driving fields in a Raman configuration. It is shown that, under appropriate conditions, there is equal gain but unequal added noise in the two quadratures.

Erratum to ‘‘Velocity selection for ultracold atoms using mazer action in a bimodal cavity” [Opt. Commun. 283 (2010) 54–59] Afshan Irshad , Sajid Qamar , Shahid Qamar a,c,* Department of Physics and Applied Mathematics, Pakistan Institute of Engineering and Applied Sciences, Nilore, Islamabad 45650, Pakistan Centre for Quantum Physics, COMSATS Institute of Information Technology, Islamabad, Pakistan c The Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, 34151 Trieste, Italy