arXiv subjects

Ali Motazedifard

Publications and source records attributed to Ali Motazedifard.

27 records · Page 2Linked to original sources

arXiv2019

Force sensing in hybrid Bose-Einstein condensate optomechanics based on parametric amplification

In this paper, the scheme of a force sensor is proposed which has been composed of a hybrid optomechanical cavity containing an interacting cigar-shaped Bose-Einstein condensate (BEC) where the \textit{s}-wave scattering frequency of the BEC atoms as well as the spring coefficient of the cavity moving end-mirror (the mechanical oscillator) are parametrically modulated. It is shown that in the red-detuned regime and under the so-called impedance-matching condition, the mechanical response of the system to the input signal is enhanced substantially, which leads to the amplification of the weak input signal while the added noises of measurement (backaction noises) can be suppressed and lowered much below the standard quantum limit (SQL). In this way, such a hybrid system operates as an ultra-sensitive force sensor which can amplify the input signal and simultaneously suppress the added noises by controlling the amplitudes of modulation and the system cooperativities. The advantage of the presented nonlinear hybrid system accompanied with the mechanical and atomic modulations in comparison to the bare optomechanical cavities is the enhancement of signal amplification as well as the extension of amplification bandwidth.

quant-ph↗

arXiv2018

Strong quadrature squeezing and quantum amplification in a coupled Bose-Einstein condensate- optomechanical cavity via coherent modulation

We consider an optomechanical cavity with a movable end-mirror as a quantum mechanical oscillator (MO) containing an interacting cigar-shaped Bose-Eisenstein condensate (BEC). It is assumed that both the MO and the BEC interact with the radiation pressure of the cavity field in the red-detuned and weak coupling regimes while the two-body atomic collisions frequency of the BEC and the mechanical spring coefficient of the MO are coherently modulated. By analyzing the scattering matrix we find that a frequency-dependent squeezing is induced to the three subsystems only due to the coherent modulations. In the largely different cooperativities regime together with strong modulations, the mechanical mode of the MO and the Bogoliubov mode of the BEC exhibit quadrature squeezing which can surpass the so-called 3dB limit (up to 75 dB) with high robustness to the thermal noises. Surprisingly, in this regime by controlling the system and modulation parameters, a very high degree of squeezing (up to 16 dB) together with high purity of quantum state for the output cavity field is achievable. Furthermore, one can attain simultaneous strong quantum amplification, added-noise suppression, and controllable gain-bandwidth for the complementary quadratures of squeezed ones in the subsystems.

quant-ph↗

arXiv2018

Measurement of thickness of thin film by fitting to the intensity profile of Fresnel diffraction from a nano phase step

Diffraction of light beams from the phase steps due to the abrupt changes in the boundary of step leads to Fresnel fringes that their visibility and intensity profile depend on the change of the step height or light incident angle. The visibility has been utilized in measurements of different physical quantities. In this paper, for the first time to our knowledge, by introducing the fitting method as a fast method we show that by fitting the theoretical intensity distributions on the experimental intensity profiles of the light diffracted from a step at different incident angles, one can specify the step height with few nano meters precision. In addition, we show that this approach provides accurate film thickness in a broad range of thicknesses using modest instrumentation. Furthermore, based on Fresnel diffraction an optical device is manufactured to measurement of thickness of thin films.

physics.ins-det↗

arXiv2018

Effects of quadratic coupling and squeezed vacuum injection in an optomechanical cavity assisted with a Bose-Einstein condensate

We investigate theoretically a hybrid system consisting of a Bose-Einstein condensate (BEC) trapped inside a laser driven membrane-in-the-middle optomechanical cavity assisted with squeezed vacuum injection whose moving membrane interacts both linearly and quadratically with the radiation pressure of the cavity. It is shown that such a hybrid system is very suitable for generating strong quadrature squeezing in the mechanical mode of the membrane and the Bogoliubov mode of the BEC in the unresolved sideband regime. More interestingly, by choosing a suitable sign for the quadratic optomechanical coupling (QOC) one can achieve a very high degree of squeezing in the mechanical mode and a strong entanglement between the mechanical and atomic modes without the necessity of using squeezed light injection. Furthermore, the QOC changes the effective oscillation frequencies of both the mechanical and the atomic modes and affects their relaxation times. It can also make the system switch form optical bistability to tristability

quant-ph↗

arXiv2017

Controllable generation of photons and phonons in a coupled BEC-optomechanical-cavity via the parametric dynamical Casimir effect

We theoretically propose and investigate a feasible experimental scheme for the realization of the dynamical Casimir effect (DCE) in a hybrid optomechanical cavity with a moving end mirror containing an interacting cigar-shaped Bose-Einstein condensate (BEC). We show that in the red-detuned regime of cavity optomechanics together with the weak optomechanical coupling limit by \textit{coherent} modulation of the \textit{s}-wave scattering frequency of the BEC and the mechanical spring coefficient of the mechanical oscillator (MO), the mechanical and atomic quantum vacuum fluctuations are parametrically amplified, which consequently lead to the generation of the mechanical/Bogoliubov-type Casimir phonons. Interestingly, in the coherent regime corresponding to the case of largely different optomechanical coupling strengths of the cavity field to the BEC and the MO, or equivalently largely different cooperativities, one can generate a large number of Casimir photons due to the amplification of the intracavity vacuum fluctuations \textit{induced} by the time modulations of the BEC and the MO. The number of generated Casimir particles are externally controllable by the cooperativities, and the modulation amplitudes of the atomic collisions rate and the mechanical spring coefficient.

quant-ph↗

arXiv2017

Synchronization dynamics of two nanomechanical membranes within a Fabry-Perot cavity

Spontaneous synchronization is a significant collective behavior of weakly coupled systems. Due to their inherent nonlinear nature, optomechanical systems can exhibit self-sustained oscillations which can be exploited for synchronizing different mechanical resonators. In this paper, we explore the synchronization dynamics of two membranes coupled to a common optical field within a cavity, and pumped with a strong blue-detuned laser drive. We focus on the system quantum dynamics in the parameter regime corresponding to synchronization of the classical motion of the two membranes. With an appropriate definition of the phase difference operator for the resonators, we study synchronization in the quantum case through the covariance matrix formalism. We find that for sufficiently large driving, quantum synchronization is robust with respect to quantum fluctuations and to thermal noise up to not too large temperatures. Under synchronization, the two membranes are never entangled, while quantum discord behaves similarly to quantum synchronization, that is, it is larger when the variance of the phase difference is smaller.

quant-ph↗

arXiv2017

Dynamical Casimir effect of phonon excitation in the dispersive regime of cavity optomechanics

In this paper, we theoretically propose and investigate a feasible experimental scheme for realizing the dynamical Casimir effect (DCE) of phonons in an optomechanical setup formed by a ground-state precooled mechanical oscillator (MO) inside a Fabry-P{é}rot cavity, which is driven by an amplitude-modulated classical laser field in the dispersive (far-detuned) regime. The time modulation of the driving field leads to the parametric amplification of the mechanical vacuum fluctuations of the MO, which results in the generation of Casimir phonons over time scales longer than the cavity lifetime. We show that the generated phonons exhibit quadrature squeezing, bunching effect, and super-Poissonian statistics which are controllable by the externally modulated laser pump. In particular, we find that the scheme allows for a perfect squeezing transfer from one mechanical quadrature to another when the laser frequency is varied from red detuning to blue detuning. Moreover, by analyzing the effect of the thermal noise of the MO environment, we find that there exists a critical temperature above which there is no phonon quadrature squeezing to occur. We also show that in the presence of time modulation of the driving laser the linewidth narrowing of the displacement spectrum of the MO can be considered as a signature of the generation of Casimir phonons.

quant-ph↗

arXiv2016

Force sensing based on coherent quantum noise cancellation in a hybrid optomechanical cavity with squeezed-vacuum injection

We propose and analyse a feasible experimental scheme for a quantum force sensor based on the elimination of back-action noise through coherent quantum noise cancellation (CQNC) in a hybrid atom-cavity optomechanical setup assisted with squeezed vacuum injection. The force detector, which allows for a continuous, broad-band detection of weak forces well below the standard quantum limit (SQL), is formed by a single optical cavity simultaneously coupled to a mechanical oscillator and to an ensemble of ultracold atoms. The latter acts as a negative-mass oscillator so that atomic noise cancels exactly the back-action noise from the mechanical oscillator due to destructive quantum interference. Squeezed vacuum injection enforces this cancellation and allows to reach sub-SQL sensitivity in a very wide frequency band, and at much lower input laser powers.

quant-ph↗

arXiv2015

An analogue model for controllable Casimir radiation in a nonlinear cavity with amplitude-modulated pumping: Generation and quantum statistical properties

We present and investigate an analogue model for a controllable photon geberation via the dynamical Casimir effect (DCE) in a cavity containing a degenerate optical amplifier (OPA) which is pumed by an amplitude-modulated field. The time modulation of the pump field in the model OPA system is equivalent to a periodic modulation of the cavity length, which is responsible for the generation of the Casimir radiation. By taking into account the rapidly oscillating terms of the modulation frequency, the effects of the corresponding counter-rotating terms (CRTs) on the analogue Casimir radiation emerge clearly. We find that the mean number of generated photons and their quantum statistical properties exhibit oscillatory behaviors, which are controllable through the modulation frequency as an external control parameter.We also recognize a new phenomenon, the so-called "Anti-DCE," in which pair photons can be coherently annihilated due to the time-modulated pumping. We show that the Casimir radiation exhibits quadrature squeezing, photon bunching and super-Poissonian statistics which are controllable by modulation frequency. We also calculate the power spectrum of the intracavity light field. We find that the appearance of the side bands in the spectrum is due to the presence of the CRTs.

quant-ph↗