Andal Narayanan

Two-dimensional imaging through turbid media using a continuous wave light source

We introduce here a scheme for two-dimensional imaging of an object hidden in a turbid medium using a low power continuous wave source and report its practical implementation. As already known, periodic polarisation modulation of an input continuous wave and subsequent polarisation discrimination enables the separation of the ballistic signal from the diffuse light. In the present work, this is achieved by modulating the input polarisation, recording a sequence of spatially filtered images using a CCD camera, and Fourier transforming the time sequence to extract the periodic ballistic signal. With this technique we have achieved sub-millimeter resolution imaging in scattering media that are more than 30 transport mean free paths thick.

Phase-sensitive microwave optical double resonance in an N system

An experimental investigation of a Microwave Optical Double Resonance (MODR) phenomenon is carried out in a four level N system of 85Rb atoms, at room temperature. This N system consists of a closed three level Λ subsystem irradiated with two optical fields and one microwave field. The MODR response is investigated in a separate probe field which drives a resonant transition from one of the ground states of the Λ system to a fourth level. We find that, under two-photon resonance condition for the optical fields, the MODR becomes a function of the relative phase between the beat frequency envelop of the optical fields and the microwave field. The variation in MODR is shown to be correlated with the phase-sensitive variation of the EIT phenomenon seen in such microwave-connected closed Λ systems. We envisage that this phase-sensitive variation in the MODR, can be utilized for a phase-sensitive manipulation of non-linear optical phenomena in N systems.

Observation of narrow fluorescence from doubly driven four-level atoms at room temperature

Unusually narrow spectral features are seen in fluorescence peaks from 85Rb atoms under the action of two driving laser fields that are in a three-dimensional molasses configuration. One of the lasers, L1, is held at a fixed detuning from the cooling transition, while the other, L2, is scanned across the repumping transitions. The fluorescence peaks are split into symmetric pairs, with the separation within a pair increasing with the detuning of the L1 laser. For large detunings, additional small peaks are seen. A simple model is proposed to explain these experimental observations.

Effects of temperature and ground-state coherence decay on enhancement and amplification in aΔatomic system

We study phase-sensitive amplification of electromagnetically induced transparency in a warm

Mechanical switch for state transfer in dual-cavity optomechanical systems

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Density-matrix approach to a strongly coupled two-component Bose-Einstein condensate

Rb vapor wherein a microwave driving field couples the two lower-energy states of a {\Lambda} energy-level system thereby transforming into a {\Delta} system. Our theoretical description includes effects of ground-state coherence decay and temperature effects. In particular, we demonstrate that driving-field-enhanced electromagnetically induced transparency is robust against significant loss of coherence between ground states. We also show that for specific field intensities, a threshold rate of ground-state coherence decay exists at every temperature. This threshold separates the probe-transmittance behavior into two regimes: probe amplification vs probe attenuation. Thus, electromagnetically induced transparency plus amplification is possible at any temperature in a {\Delta} system.

Microwave controlled Electromagnetically Induced Transparency inside an RF cavity

Dual cavity opto-electromechanical systems (OEMS) are those where two electromagnetic cavities are connected by a common mechanical spring. These systems have been shown to facilitate high fidelity quantum state transfer from one cavity to another. In this paper, we explicitly calculate the effect on the fidelity of state transfer, when an additional spring is attached to only one of the cavities. Our quantitative estimates of loss of fidelity, highlight the sensitivity of dual cavity OEMS when it couples to additional mechanical modes. We show that this sensitivity can be used to design an effective mechanical switch, for inhibition or high fidelity transmission of quantum states between the cavities.

Directional optical switch using interacting dark states

The time evolution equations for average values of population and relative phase of a strongly coupled two-component Bose-Einstein condensate (BEC) are derived analytically. The two components are two hyperfine states, which are coupled by an external laser that drives fast Rabi oscillations between these states. Specifically, this derivation incorporates the two-mode model proposed in J. Williams et al., e-print cond-mat 9904399 for the strongly coupled hyperfine states

Threshold nonlinear absorption in Zeeman transitions

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Nobel Prize for physics — 2003

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