Bijita Sarma

Controllable optical bistability in a hybrid optomechanical system

We investigate, theoretically, the effect of optical feedback from a cavity containing an ultracold two-level atomic ensemble, on the bistable behavior shown by a mean intracavity optical field in an optomechanical cavity resonator. It turns out that the optical bistability can be controlled by tuning the frequency and power of the driving laser and is largely affected by the presence of the atomic ensemble in the feedback cavity. In essence, our work emphasizes the possibility of realization of a controllable optical switch depending on the hybrid interaction, commanding lower threshold power than a single optomechanical cavity.

Ground state cooling of micromechanical oscillators in the unresolved sideband regime induced by a quantum well

We theoretically demonstrate the ground-state cooling of a mechanical oscillator in an optomechanical cavity in the presence of a quantum well, in the unresolved-sideband regime. Due to the presence of the quantum well, the cavity response gets modified and leads to asymmetric heating and cooling processes. The cooling rate of the mechanical resonator can potentially be enhanced by tuning the cavity-field detuning. It is demonstrated that, even when the cavity is in the unresolved-sideband regime, the effective interaction of the exciton and mechanical modes can bring the system back to an effective resolved-sideband regime. The time evolution of the mean phonon number in the mechanical resonator is studied using the quantum master equation. The average phonon occupancy in the mechanical resonator tends to 0 with time, exhibiting dynamic controllability of cavity dissipation.

Tunable phonon blockade in weakly nonlinear coupled mechanical resonators via Coulomb interaction

Realizing quantum mechanical behavior in micro- and nanomechanical resonators has attracted continuous research effort. One of the ways for observing quantum nature of mechanical objects is via the mechanism of phonon blockade. Here, we show that phonon blockade could be achieved in a system of two weakly nonlinear mechanical resonators coupled by a Coulomb interaction. The optimal blockade arises as a result of the destructive quantum interference between paths leading to two-phonon excitation. It is observed that, in comparison to a single drive applied on one mechanical resonator, driving both the resonators can be beneficial in many aspects; such as, in terms of the temperature sensitivity of phonon blockade and also with regard to the tunability, by controlling the amplitude and the phase of the second drive externally. We also show that via a radiation pressure induced coupling in an optomechanical cavity, phonon correlations can be measured indirectly in terms of photon correlations of the cavity mode.

Atom assisted cavity cooling of a micromechanical oscillator in the unresolved sideband regime

The ground state cooling of a mechanical oscillator in an optomechanical cavity containing an ensemble of identical two-level ground-state atoms is studied in the highly unresolved-sideband regime. The system exhibits electromagnetically-induced transparency-like quantum interference effect. The mutual interaction with the cavity optical field gives rise to an indirect coupling between the atomic and mechanical modes. In presence of this interaction, the noise spectrum gets modified and leads to asymmetric cooling and heating rates. Using the quantum master equation, time evolution of the average phonon number is studied and it is observed that the average phonon occupancy in the mechanical resonator exhibits ground-state cooling.