Biswajit Sen

Higher-order nonclassicalities in a codirectional nonlinear optical coupler: Quantum entanglement, squeezing, and antibunching

Higher-order nonclassical properties of fields propagating through a codirectional asymmetric nonlinear optical coupler which is prepared by combining a linear waveguide and a nonlinear (quadratic) waveguide operated by second harmonic generation are studied. A completely quantum mechanical description is used here to describe the system. Closed form analytic solutions of Heisenbergs equations of motion for various modes are used to show the existence of higher-order antibunching, higher-order squeezing, and higher-order two-mode and multimode entanglement in the asymmetric nonlinear optical coupler. It is also shown that nonclassical properties of light can transfer from a nonlinear waveguide to a linear waveguide.

Single-mode and intermodal higher-order nonclassicalities in two-mode Bose-Einstein condensates

Biswajit Sen , Sandip Kumar Giri, Swapan Mandal, C. H. Raymond Ooi, Anirban Pathak Department of Physics, Vidyasagar Teachers’ Training College, Midnapore-721101, India Department of Physics, Panskura Banamali College, Panskura-721152, India Department of Physics, Visva-Bharati, Santiniketan, India Department of Physics, University of Malaya, 50603 Kuala Lumpur, Malaysia Jaypee Institute of Information Technology, A-10, Sector-62, Noida, UP-201307, India RCPTM, Joint Laboratory of Optics of Palacky University and Institute of Physics of Academy of Science of the Czech Republic, Faculty of Science, Palacky University, 17. listopadu 12, 771 46 Olomouc, Czech RepublicSandip Kumar Giri, Biswajit Sen, C H Raymond Ooi4† and Anirban Pathak Department of Physics, Panskura Banamali College, Panskura-721152, India Department of Physics, Vidyasagar University, Midnapore 721102, India Department of Physics, Vidyasagar Teachers’ Training College, Midnapore-721101, India Department of Physics, University of Malaya, 50603 Kuala Lumpur, Malaysia Jaypee Institute of Information Technology, A-10, Sector-62, Noida, UP-201307, India RCPTM, Joint Laboratory of Optics of Palacky University and Institute of Physics of Academy of Science of the Czech Republic, Faculty of Science, Palacky University, 17. listopadu 12, 771 46 Olomouc, Czech Republic

Squeezed states in spontaneous Raman and in stimulated Raman processes

The Hamiltonian and the equations of motion for various modes involving spontaneous and stimulated Raman processes are derived. The coupled differential equations involving these modes are solved analytically by using an intuitive approach (IA). The solution of the present paper does not require any short time approximation. As a matter of fact, the present solution for field operators and hence the squeezing for various modes are valid for all interaction time t. In this way, the present paper is more general compared to the earlier investigations where short-time approximations were found a must. By exploiting the solutions for the field operators, we obtain the squeezing effects of input coherent light for pure and for mixed field modes. The IA employs the perturbation theory and hence we came across the secular terms in the solution. Of course, for small coupling constants these secular terms could be summed for all orders. To establish our claim, we remove the secular terms at least for one occasion.

Nonclassical properties of a contradirectional nonlinear optical coupler

Abstract We investigate the nonclassical properties of output fields propagated through a contradirectional asymmetric nonlinear optical coupler consisting of a linear waveguide and a nonlinear (quadratic) waveguide operated by second harmonic generation. In contrast to the earlier results, all the initial fields are considered weak and a completely quantum-mechanical model is used here to describe the system. Perturbative solutions of Heisenbergs equations of motion for various field modes are obtained using Sen–Mandal technique. Obtained solutions are subsequently used to show the existence of single-mode and intermodal squeezing, single-mode and intermodal antibunching, two-mode and multi-mode entanglement in the output of contradirectional asymmetric nonlinear optical coupler. Further, existence of higher order nonclassicality is also established by showing the existence of higher order antibunching, higher order squeezing and higher order entanglement. Variation of observed nonclassical characters with different coupling constants and phase mismatch is discussed.

Amplitude-squared and amplitude-cubed squeezing in stimulated Raman and in spontaneous Raman scattering

Coherent light coupled to a third-order nonlinear medium is responsible for spontaneous and for stimulated Raman processes. The analytical solutions up to second order in coupling constants of various field modes for spontaneous Raman and for stimulated Raman processes are utilized to obtain the amplitude-squared and amplitude-cubed squeezing of the input coherent light. The amplitude-squared and amplitude-cubed squeezing are completely ruled out for all modes for spontaneous Raman processes. For stimulated Raman processes, we observe that the squeezing for amplitude-squared and amplitude-cubed are possible for pump and for vibrational phonon modes. It is found that the percentage of higher ordered amplitude squeezing decreases with the increase of the orders. The squeezing in Stokes and in anti-Stokes modes are ruled out even for stimulated Raman processes.

Squeezing, photon bunching, photon antibunching and nonclassical photon statistics in degenerate hyper Raman processes

An initially prepared coherent state coupled to a second-order nonlinear medium is responsible for stimulated and spontaneous hyper Raman processes. By using an intuitive approach based on perturbation theory, the Hamiltonian corresponding to the hyper Raman processes is analytically solved to obtain the temporal development of the field operators. It is true that these analytical solutions are valid for small coupling constants. However, the interesting part is that these solutions are valid for reasonably large time. Hence, the present analytical solutions are quite general and are fresh compared to those solutions under short-time approximations. By exploiting the analytical solutions of field operators for various modes, we investigate the squeezing, photon antibunching and nonclassical photon statistics for pure modes of the input coherent light responsible for hyper Raman processes. At least in one instance (stimulated hyper Raman processes for vibration phonon mode), we report the simultaneous appearance of classical (photon bunching) and nonclassical (squeezing) effects of the radiation field responsible for hyper Raman processes.

Comments on ‘Higher order squeezing of the electromagnetic field in spontaneous and in stimulated Raman processes’

Of late, Giri and Gupta [J. Mod. Opt. 52 1769 (2005)] discussed the possibility of getting higher order (fourth and fifth orders) squeezing of the fundamental mode in spontaneous Raman and in stimulated Raman processes. These investigations are based on the earlier works of Kumar and Gupta [Quantum Semiclass. Opt. 7 835 (1995)]. We reinvestigate the model and we found that the entire calculations and hence the conclusion of Giri and Gupta and Kumar and Gupta are not only baseless but also misleading. There will be no squeezing of the fundamental mode in spontaneous and in Raman processes.

Higher-order two-mode and multimode entanglement in Raman processes

The existence of higher order entanglement in the stimulated and spontaneous Raman processes is established using the perturbative solutions of the Heisenberg equations of motion for various field modes that are obtained using the Sen-Mandal technique and a fully quantum mechanical Hamiltonian that describes the stimulated and spontaneous Raman processes. Specifically, the perturbative Sen-Mandal solutions are exploited here to show the signature of the higher order two-mode and multi-mode entanglement. In some special cases, we have also observed higher order entanglement in the partially spontaneous Raman processes. Further, it is shown that the depth of the nonclassicality indicators (parameters) can be manipulated by the specific choice of coupling constants, and it is observed that the depth of nonclassicality parameters increases with the order.

Sub-shot noise photon-number correlation in stimulated and spontaneous Raman processes

The light initially prepared in a coherent state runs the stimulated and spontaneous Raman processes in a second-order nonlinear medium. Using analytical expressions of field operators for the light modes, we determine the quantum statistical properties of the modes in the stimulated and spontaneous Raman processes. By a choice of phase, we obtain a boson-pair property correlating the pump and vibration modes and such a property correlating the pump and anti-Stokes modes. The Stokes and vibration modes exhibit the boson-pair property for all initial phase differences between the pump mode and the other ones. In the spontaneous Raman process only the Stokes and vibration modes show such a property.

Lower Order and Higher Order Entanglement in Four-Wave Mixing Process

Possibilities of generation of lower order and higher order intermodal entanglement in 87Rb 5S − 5P−5D hyperfine manifoldare rigorously investigated using the Sen-Mandal perturba ive technique by showing the equivalence of the system with the four-wave mix ing (FWM) process. The investigation has revealed that for a set of experimentally realizable par ameters we can observe lower order and higher order intermodal entanglement between pump and sign al modes and signal and idler modes in a FWM process associated with the 87Rb 5S − 5P − 5D hyperfine manifold. In addition, trimodal entanglement involving pump, signal and idler modes is also rep rted.