Current Developments in Atomic, Molecular, Optical and Nano Physics
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Research Activities of the Group
  01. Research Group on Bose-Einstein Condensation, Cold Atoms & Quantum Optics  

Professor Man Mohan (Group Leader), Dr.Aranya B Bhattacherjee (Asso. Professor in Physics), Dr. Tarun Kumar ( Asst. Professor in Physics), Dr. Priyanka Verma (Asst. Professor in Physics), Sonam Mahajan ( Doctoral Student), Neha Aggarwal ( Doctoral Student)

Our group at University of Delhi is looking at various theoretical aspects of the physics of dilute trapped Bose Einstein Condensates, which includes exotic quantum phases of light coupled to an atom in a cavity through multiphoton transitions, Novel quantum optical effects in periodically modulated BEC interacting with light field, nonlinear excitations in BEC, interaction of two component BEC in 1D, 2D and 3D, localization properties of BEC and Dynamics of BEC in time dependent optical lattices.

The research on BEC’s in optical lattice is a part of a more extensive investigation of the properties of BEC’s, in which we are involved. Because the wave mechanical properties of the atoms are amplified to levels at which they can be observed and manipulated directly, BEC atomic assemblies are particularly interesting and useful for the study of macroscopic quantum effects, which is one of the main aim of our research. We have studied a hybrid optomechanical quantum device formed by a Bose Einstein Condensate (BEC) confined in a high quality factor optical cavity with an oscillatory end mirror for the detection of weak forces. We show using the stochastic cooling technique that the atomic two-body interaction can be utilized to cool the mirror and achieve position squeezing essential for making sensitive measurements of weak forces. We further show that the atomic two-body interaction can also increase the signal to noise ratio (SNR) and decrease the noise of the off-resonant stationary spectral measurements. We investigated the possibility of approaching the quantum ground-state of a hybrid optomechanical quantum device formed by a Bose-Einstein condensate (BEC) confined inside a high-finesse optical cavity with an oscillatory end mirror. Cooling is achieved using two experimentally realizable schemes: back-action cooling and cold damping quantum feedback cooling. In both the schemes, we found that increasing the two body atom-atom interaction brings the mechanical oscillator to its quantum ground state. It has been observed that back-action cooling is more effective in the good cavity limit while the cold damping cooling scheme is more relevant in the bad cavity limit. It is also shown that in the cold damping scheme, the device is more efficient in the presence of BEC than in the absence of BEC.We have also developed a new tool for controlling the superfluid properties of a condensate loaded in an optical lattice inside a cavity. The optomechanical system we have studied is given in the Fig. below. We have observed that motion of a cavity mirror gives a powerful insight into the way superfluid fraction of the condensate can be enhanced or diminished. We have studied the optomechanical effects (effects of moving one of the cavity mirror) on the Bloch energy, effective mass, Bogoliubov excitation spectrum, superfluid fraction and the Mott-superfluid phase diagram of a Bose-Einstein condensate confined in an optical cavity.

  02.  Group on Collisional and Radiative Processes in Plasma  

Professor Man Mohan (Group Leader), Dr. Avninder Kumar Singh (Asso. Professor in Physics), Dr. Nupar Verma (Asso. Professor in Physics), Dr. Narendra Kumar (Asst. professor in Physics ), Dr. Alok Kumar Singh Jha (Asst. professor in Physics), Dr. Jagjit Singh (Asst. professor in Physics), Sunny Aggarwal (Doctoral Student), Arun Goyal (Doctoral Student), Indu (Doctoral Student)

In recent years, the high quality observational data returned by space missions such as International Ultraviolet Explorer (EUVE), the Advanced Satellite for cosmology and Astrophysics (ASCA), the Hopkins Ultraviolet telescope (HUT), the Hubble Space Telescope (HST), and Solar and Heliospheric Observatory (SOHO), has highlighted the need for highly accurate atomic data. There is no doubt that this situation will be further emphasized by the launch of future space missions such as FUSE. The accuracy of atomic data is crucial for the interpretation of the spectra from these missions in terms of the physical conditions in the astrophysical sources. The need for accurate atomic and molecular data is immense, with applications in such diverse field as astronomy, fusion research, and lasers. The type of data depends upon the region or the object being studied. As very few of the ions of interest can be studied experimentally in the laboratory, the user must depend primarily on theoretical data.

In this direction our group is involved in the calculations of accurate collision strengths, radiative and autoionisation transition probability, photoionisation cross-sections, oscillator strengths and wavelengths for allowed and forbidden transitions which are urgently needed for the interpretation of observational data & for modeling astrophysical objects. In our calculations we are including important physical effects mainly configuration interaction, autoionizing resonances, exchange, coupling and relativistic effects, which are incorporated by using Configuration Interaction Technique for the atomic structure and accurate R-matrix method for the collisions. we have done atomic structure and photoionization coss section calculations for complex ions. We have used configuration interaction (CI) method CIV3 of Hibbert for the calculations of level energies, oscillator strengths and transition probabilities for Sulphur like Fe XI and Ti VII. We have also presented level energies, oscillator strengths, radiative rates, lifetimes and line strength for W XL and Kr XXXV using the multiconfigurational Dirac-Fock (MCDF) method as implemented in GRASP code, while the close-coupling R-matrix method is used to study the photoionization cross section of Fe X and Si II. We have predicted many few spectral lines, which are yet to be observed, and which will form the basis for the future experimental work.

  03.  Our Group on Atoms & Molecules in Strong Radiation Fields & Chemical Physics  

Professor Man Mohan (Group Leader), Dr. Rachna Kundliya (Asst. Prof.), Dr. Sidharth Lahon (Asst. professor in Physics), Manoj Malik (Doctoral Student)

We are studying numbers of striking non-linear phenomenon in atoms and molecules, which occur when they are exposed to intense short femto-second laser pulses. Some of these are Above threshold ionization (ATI ) i.e the absorption of more photons then necessary for ionization and High harmonic generation (HHG), which has become potential method to produce coherent radiation with wavelength reaching into soft X-ray region. In super-intense field we found that the real atom can be stabilized against ionization due to drastic change of atomic structure using two laser pulses differing in phase. For studying such processes we have developed number of non-perturbative methods like Floquet and Quasi Energy approaches . For real laser pulses with non-periodic Hamiltonian we have developed numerical computational methods, such as Split Operator Technique (SOT), Fast-Fourier Technique (FFT) and Runge-Kutta (RK) method etc. for solving dynamical coupled equations. We have also developed an efficient pseudo-spectral L2 technique for calculating accurate multi-photon ionization cross-sections of atoms, which give results in agreement with experimental results. Our group is also involved in the calculation of simultaneous electron-photon excitation (SEPE) processes aiming for explaining the projected experiment using electron and high frequency synchrotron photon beams such as ELECTRA at Trieste and ALS at Berkeley. During this peroid, we had studied the effect of electric field and magnetic fields on the Quantum Dot with spin orbit coupling therotically, for this I have studied several books and research paper. The theoretical approach followed is non-perturbative and is based on the Floquet theory and quasienergy technique. . Floquet theory is employed to solve the equation of motion for laser driven intraband transitions between the states of the conduction band of quantum dot with spin effect.Floquet theory relates the solution of Schrodinger equation involving a periodic Hamiltonian to the solution of another equation with a time independent Hamiltonian represented by an infinite matrix (called the Floquet matrix). Spin fliping with rashba spin orbit couplig in presence of laser fields for the quantum dot is also studied.

  04.  Research on Molecular Dynamics & Inter Molecular Energy Transfer Processes  

Knowledge of the chemical, energetic and spectral properties of polyatomic molecules is important for studies of chemical reactivity, isotope separation, combustion processes, chemical lasers and other technologies as well as being a splendid stimulus to the ever-expanding predictive abilities of chemical theorists.

In the field of Molecular dynamics we are investigating the nature of multiphoton excitation of several triatomic molecules in its ground electronic state coupled to different vibrational modes under strong laser field using non-perturbative techniques. The quantum theory of chemical reactions and theory of intermolecular energy transfer is the basis of chemical dynamics and molecular modeling. Our group is using different approaches to study energy transfer in various processes like rotational-rotational (R-R), rotational-vibrational (R-V), vibrational-vibrational (V-V) for explaining the flow of energy in Chemical dynamics i.e where does it go, how long does it take to get there which has direct practical applications.

  05.  Our Group on Nano-Technology & Photonics  

Professor Man Mohan (Group Leader), Dr. Pradeep Jha (Assoc. Professor), Rinku Sharma (Assot. Prof.) , Dr. Sanjay Tayagi ( Asst. Prof.), Dr. Monica Gambhir (Asst. professor in Physics), Mr. Sidharth Lahon (Asst. professor in Physics), Mr. Manoj Malik (Doctoral Student), Sukirti Gumber (Doctoral Student)

Photonics refers to the science and technology relating to the transportation of information by light, and underpins the information revolution in which light is used to transmit, store and sort information. Nanoscience is directed at discovering and understanding the way matter behaves at the nanoscale, and underpins the technology of creating materials, devices and systems through the control of matter at the atomic level. The nanostructure exhibit strongly size dependent chemical & physical properties which represent limiting behaviours for different types of matter (atomic to bulk) The variations with size are enormous ,and represents a new opportunity to optimize material properties by varying their size & shape rather than by changing their chemical composition. Thus the primary advantage of any nanostructure material lies in the extensive tunability of its properties. For example, the fundamental characteristics of a material , such as it melting temperature , color ,saturation magnetization and coercivity , charging energy ,chemical reactivity ,etc., are all functions of size and shape. For instance, the color of semiconductor quantum dots can be varied continuously from the near infrared to the ultraviolet. Such colors changes correlate to electron and hole energy levels, which in turn affect the catalytic and chemical behavior of the particles. Thus, nanoscale building blocks lend major new experimentally controllable variables for fabricating desired materials. Atom manipulations, and matter diffraction from light waves are important new tools emerging from atomic and optical physics, which may lead to new ways of fabricating nanostructures.

Our group is focusing on the recent developments in nanoscience using new theoretical computational tools. For example the interaction of shaped pulses sequences could contribute to the “assembly “ of nanostructured materials, or to the manipulation of electronic coherence in quantum dot molecules and solids .The interaction of intense optical fields with nanostructures is of interest. Mutiphoton ionization, and the measurement of nonlinear susceptibilities as a function of the size are currently important fields. In strong e.m field, collisions of atoms or molecules with the nanostructures will allow electron transfer from quantum dot to the colliding atom or tunnel directly to vacuum states. Such enhanced electron emission processes will find applications in, for example, electron induced catalysis, air pollution abatement, etc. Using UV or even low energy x-rays from synchotron light sources, 3-dimensional nanostructures or layers can be produced.

To improve and develop microelectronics devices, the basic understanding of the various dynamical processes in the nanostructures has to be studied in detail. We are also looking in to the excitation of nanostructures out of their equilibrium and the subsequent relaxation processes with various rates, which has now become a key area of nanostructure research.

  Some Important Research Publications of the Group  
  National International Collaboration of our Group  

(1) Atomic Structure and Collision Physic and Astrophysical Applications
Prof. Anil Pradhan
Prof. Sultana Nahar

Ohio-University, U.S.A

(2) In the field of Atomic Structure & Collision Physics
Prof. A. Hibbert
Department of Applied Mathematics & Theoretical Physics
Queen’s University of Belfast
Northern Ireland

Prof. Yoshiro Azuma
Sophia Unversity
Faculty of Science and Technology
Tokyo, Japan

(3) In the Field of Chemical Physics
Prof. Robert E Wyatt
Department of Chemistry
University of Texas
Texas, U.S.A.

  Interactions of Strong Laser Field with Matter  

Prof. A. D Bandrauk
Universite de Sherbrooke

Prof. T. Tung Nguyen-Dang
University Of Laval ,Quebec

Prof. N.Rahman
Univ. of Trieste

  In the fields of Quantum Optics, Bose Einstein Condensation & Cold Atoms  

Prof. Nick P. Bigelow
University, U.S.A

Prof. Peter Littlewood
FRS, Fellow of Royal Society
Cavendish Laboratory

Prof. E. Arimondo
INFM, University of Pisa , ITALY

Prof. K. Hakuta
Chofu, Tokyo, Japan

International Centre for theoretical Physics
Research Collaboration with Scientists in ICTP, Trieste, ITALY

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