Mohammad Mahmoudi - Academia.edu (original) (raw)

Papers by Mohammad Mahmoudi

Laser Physics Letters, 2019

Generation and detection of structured light have recently been the subject of intense study, aim... more Generation and detection of structured light have recently been the subject of intense study, aiming to realize high-capacity optical storage and continuous-variable quantum technologies. Here, we present a scheme to extract the orbital angular momentum content of Laguerre-Gaussian light beams in a double-Λ four level system of GaAs/AlGaAs multiple quantum wells. Arising from a quantum interference term, absorption of a non-vortex probe field depends upon the azimuthal phase of vortex fields so that both magnitude and sign of the azimuthal index/indices can be mapped into the absorption profile.

The atom-photon entanglement is studied in a three-level lambda-type closed-loop atomic system in... more The atom-photon entanglement is studied in a three-level lambda-type closed-loop atomic system in multi-photon resonance condition and beyond it. It is shown that the von Neumann entropy in such a system is phase dependent, and it can be controlled by either intensity or relative phase of applied fields. It is demonstrated that for the special case of Rabi frequency of applied fields, the system is disentangled.

The light propagation of a probe field pulse in a four-level double-lambda type system driven by ... more The light propagation of a probe field pulse in a four-level double-lambda type system driven by laser fields that form a closed interaction loop is studied. Due to the finite frequency width of the probe pulse, a time-independent analysis relying on the multiphoton resonance assumption is insufficient. Thus we apply a Floquet decomposition of the equations of motion to solve the time-dependent problem beyond the multiphoton resonance condition. We find that the various Floquet components can be interpreted in terms of different scattering processes, and that the medium response oscillating in phase with the probe field in general is not phase-dependent. The phase dependence arises from a scattering of the coupling fields into the probe field mode at a frequency which in general differs from the probe field frequency. We thus conclude that in particular for short pulses with a large frequency width, inducing a closed loop interaction contour may not be advantageous, since otherwise ...

We study the propagation of a Laguerre-Gaussian (LG) beam through a dispersive atomic medium. We ... more We study the propagation of a Laguerre-Gaussian (LG) beam through a dispersive atomic medium. We restrict ourselves to applying a weak probe field and three strong coupling fields to the medium, which leads to developing a four-level double V-type atomic system. We first regard all the three strong coupling fields as the plane-waves and calculate an analytical expression for the group velocity of the probe LG field on the optical axis at the waist of the field. It appears that the resulting formula in a dispersive medium is in good agreement with that of the free space. We also find a more general analytical expression for the group velocity of the probe LG field out of the optical axis and compare with its projection onto the propagation axis. It is turned out that these two quantities are equal on the optical axis, at the waist of the beam and the Rayleigh range. Finally, we assume one of the strong coupling fields to be an LG field and explore how its orbital angular momentum (OA...

arXiv: Quantum Physics, 2018

Atom-photon entanglement provides an essential resource for quantum communication and quantum com... more Atom-photon entanglement provides an essential resource for quantum communication and quantum computation. How to conveniently and efficiently achieve a maximal entanglement between atomic system and spontaneous emission field has been a challenging task. Here, we present a simple, yet we believe a powerful, method to generate entangled states between photons and an N-type atomic system. Beside the achievement of a nearly perfect entanglement, we also examine evidence for a link between entanglement and populations in dressed and bare states; It is found that a maximal entanglement can be established when populations in both dressed and bare states are spread over states. Moreover, the system would be disentangled in the absence of evenly distributed populations, another reason for further strengthen our claim that the physical origin of such entanglement is quantum correlation produced by distribution of the populations. We then discuss the dependence of the entanglement on Rabi fr...

Optics and Photonics Society of Iran, 2017

In this paper, optical effects of a hybrid complex system consisting of a semiconductor quantum d... more In this paper, optical effects of a hybrid complex system consisting of a semiconductor quantum dot and a metal nanoparticle interacting with a weak field is investigated. Nonlinear density matrix equations are used in order to describe optical properties of the quantum dot, the nanoparticle, and the entire system. Then, dependency of the susceptibilities of these component on the interparticle distance between the quantum dot and the nanoparticle is studied. It is demonstrated that for a wide range of frequencies, susceptibility of the quantum dot leads to gain without inversion and is calculated that the susceptibility is severely dependent on presence of the metal nanoparticle.

Laguerre-Gaussian (LG) beams contain a helical phase front with a doughnut-like intensity profile... more Laguerre-Gaussian (LG) beams contain a helical phase front with a doughnut-like intensity profile. We use the LG beam to introduce a rather simple method for generation of a vector beam (VB), a beam with spatially-dependent polarization in the beam cross section, via the nonlinear magneto-optical rotation (NMOR). We consider the NMOR of the polarization of a linearly polarized probe field passing through an inverted Y-type four-level quantum system interacting with a LG control field and a static magnetic field. It is shown that the polarization of the transmitted field is spatially distributed by the orbital angular momentum (OAM) of the LG control field, leading to generation of the VB with azimuthally symmetric polarization distribution. We show that the polarization and intensity distributions of the VB spatially vary by changing the OAMs of the LG control field. Moreover, the radial index of the LG control field has a major role in more spatially polarization distributing of th...

Scientific Reports

We present a convenient way to obtain an optical power limiting behavior in a quantum dot molecul... more We present a convenient way to obtain an optical power limiting behavior in a quantum dot molecule system, induced by an interdot tunneling. Also, the effect of system parameters on the limiting performance is investigated; interestingly, the tunneling rate can affect the limiting performance of the system so that the threshold of the limiting behavior can be a function of the input voltage, allowing the optimization of the limiting action. Furthermore, by investigating the absorption of the probe field, it is demonstrated that the optical limiting is due to a reverse saturable absorption mechanism; indeed, analytical results show that this mechanism is based on a cross-Kerr optical nonlinearity induced by the tunneling. Additionally, the limiting properties of the system are studied by using a Z-scan technique.

Physical Review B

We study the propagation of probe pulses carrying orbital angular momentum (OAM) in a crystal of ... more We study the propagation of probe pulses carrying orbital angular momentum (OAM) in a crystal of molecular magnets characterized by a double-light-matter coupling scheme. The model is based on the four-wave mixing (FWM) of applied fields interacting with the magnetic dipole moment of the molecular magnets. We consider the light-matter interaction under the situation where a weak probe field carries an optical vortex and investigate the exchange of optical vortices between different frequencies via the FWM in the microwave region. The propagation of OAM beams with nonzero radial indices is then explored. It is found that the conservation of both azimuthal and radial indices is satisfied over the swapping of OAM states of light. Superimposing two initially weak OAM modes with different topological charges creates specific vortex beams with a very characteristic form. The resulting beam contains a central vortex as well as several singly charged peripheral vortices distributed at the same radial distance from the center of the light beam. This complex pattern of vortices arises because the intensity radius of two interfering OAM modes is different. It is shown that the boundary region of intensity dominance of two OAM modes can be controlled by the molecular magnets parameters and strong cw electromagnetic fields. Our proposed scheme may provide a route to study the solid systems suitable for quantum technologies as well as for OAM exchange devices for quantum information processing.

Optics Express

We study the propagation of a Laguerre-Gaussian (LG) beam through a dispersive atomic medium. We ... more We study the propagation of a Laguerre-Gaussian (LG) beam through a dispersive atomic medium. We restrict ourselves to applying a weak probe field and three strong coupling fields to the medium, which leads to developing a four-level double V-type atomic system. We first regard all the three strong coupling fields as the plane-waves and calculate an analytical expression for the group velocity of the probe LG field on the optical axis at the waist of the field. It appears that the resulting formula in a dispersive medium is in good agreement with that of the free space. We also find a more general analytical expression for the group velocity of the probe LG field out

Journal of the Optical Society of America B

We study the orbital angular momentum (OAM) transfer from a weak Laguerre-Gaussian (LG) field to ... more We study the orbital angular momentum (OAM) transfer from a weak Laguerre-Gaussian (LG) field to a weak plane-wave in two closed-loop three-level V-type atomic systems. In the first scheme, the atomic system has two non-degenerate upper levels which the corresponding transition is excited by a microwave plane-wave. It is analytically shown that the microwave field induces an OAM transfer from an LG field to a generated third field. In the second scheme, we consider a three-level V-type atomic system with two near-degenerate excited states and study the effect of the quantum interference due to the spontaneous emission on the OAM transfer. It is found that the spontaneously generated coherence (SGC) induces the OAM transfer from the LG field to the weak planar field, while the OAM transfer does not occur in the absence of the SGC. The suggested models prepare a rather simple method for the OAM transfer which can be used in quantum information processing and data storage.

Scientific Reports

The atom-photon entanglement using the Laguerre-Gaussian (LG) beams is studied in the closedloop ... more The atom-photon entanglement using the Laguerre-Gaussian (LG) beams is studied in the closedloop three-level V-type quantum systems. We consider two schemes with near-degenerate and nondegenerate upper levels: in the first, the effect of the quantum interference due to the spontaneous emission is taken into account and in the second, a microwave plane wave is applied to the upper levels transition. It is shown that the atom-photon entanglement in both schemes depends on the intensity profile as well as the orbital angular momentum (OAM) of the applied fields so that the various spatially dependent entanglement patterns can be generated by Laguerre-Gaussian beams with different OAMs. However, due to the zero intensity,no entanglement appears in the center of the optical vortex beams. As a result, the entanglement between dressed atom and its spontaneous emissions in different points of the atomic vapor cell can be controlled by the OAM of the applied fields. Moreover, our numerical results show that the number of the local maximum degree of entanglement (DEM) peaks depends on the OAM of the applied fields. The degrees of freedom for OAM play a crucial role in spatially dependent atom-photon entanglement in such a way that it may possess broad applications in high-dimensional quantum information processing and data storage.

Journal of Optics

We present a convenient and effective way to generate a novel phenomenon of trapping, named trap ... more We present a convenient and effective way to generate a novel phenomenon of trapping, named trap split, in a conventional four-level double-Λ atomic system driven by four femtosecond Laguerre-Gaussian laser pulses. We find that trap split can be always achieved when atoms are trapped by such laser pulses, as compared to Gaussian ones. This feature is enabled by interaction of the atomic system and the Laguerre-Gaussian laser pulses with zero intensity in the center. A further advantage of using Laguerre-Gaussian laser pulses is the insensitivity to fluctuation in intensity of the lasers in such a way that the separation between traps remains constant. Moreover, it is demonstrated the suggested scheme with Laguerre-Gaussian laser pulses can form optical traps with spatial sizes that are not limited by the wavelength of the laser and can, in principle, become smaller than the wavelength of light. This work would greatly facilitate the trapping and manipulating the particles and generation of trap split. It may also suggest the possibility of extension into new research fields, such as micro-machining and biophysics.

Journal of the Optical Society of America B

The optical trap potential is studied in a four-level double-Λ closed-loop atomic system in the m... more The optical trap potential is studied in a four-level double-Λ closed-loop atomic system in the multiphoton resonance condition. We apply four femtosecond Gaussian laser beams to generate a closed-loop configuration. It is shown that the induced optical dipole force on the system dramatically depends on the relative phase of applied fields, and it switches from focusing to defocusing in the transverse direction, simply by properly changing the relative phase. Through special switching of the relative phase, the trapping potential splits into two positions, which has novel applications in trapping and manipulating the particles. Moreover, it is further demonstrated that trap depth can be manipulated by the relative phase. Finally, a maximum coherent population transfer is achieved for a special value of the relative phase of applied fields.

Laser Physics, 2016

The propagation of an electromagnetic pulse through a dielectric slab doped with a triple quantum... more The propagation of an electromagnetic pulse through a dielectric slab doped with a triple quantum dot (QD) nanostructure has been discussed in the presence of electron tunneling. We include the effect of an incoherent pump field in the transmission and reflection of a pulse in a triple QD. It is shown that the reflected and transmitted pulses can be switched from subluminal to superluminal light propagation by changing either the rate of the incoherent pump field or the inter-dot tunneling between QD1, QD2 and QD3 in a slab. Furthermore, it is demonstrated that the inter-dot tunnel coupling can significantly affect the behavior of optical bistability (OB) and optical multi-stability (OM) in a dielectric slab. The obtained results can be used for the development of new types of nanoelectronic devices for realizing the switching process.

Quantum Information Processing, 2015

The density matrix equations of motion in near-degenerate three-level V-type closedloop atomic sy... more The density matrix equations of motion in near-degenerate three-level V-type closedloop atomic system are calculated numerically in Floquet frame. The dynamical behavior of atom-photon entanglement between the dressed atom and its spontaneous emission is studied in semi classical approach beyond the two-photon resonance condition in such a system. The quantum entropy of these two subsystems is investigated by using the von Neumann entropy. It is shown that, the degree of entanglement measure (DEM) can be controlled via the intensity and the detuning of coupling optical field and quantum interference induced by spontaneous emission. Moreover in the absence of quantum interference the steady state behavior of DEM can be achieved even in beyond the two-photon resonance condition. Furthermore in the absence of quantum interference for special parameters of Rabi frequency and detuning of driving laser field disentanglement can be occurred. Also the electromagnetically induced transparency condition can be obtained when the system is disentangled.

Journal of the Optical Society of America B, 2015

The interaction of two orthogonally polarized beams and a four-level GaAs quantum well (QW) waveg... more The interaction of two orthogonally polarized beams and a four-level GaAs quantum well (QW) waveguide is investigated. It is shown that, by applying a static magnetic field normal to the propagation direction of the driving beams, the birefringence can be induced in the QW waveguide. Moreover, it is demonstrated that the dephasing rate between two ground states of the QW waveguide makes it a dichromatic medium and can also diminish the induced birefringence. Our results show how a large and complete magneto-optical rotation in the QW waveguide can be obtained via adjusting the intensity of the magnetic field and also the length of the QW waveguide.

Laser Physics, 2015

ABSTRACT The optical bistability (OB) behavior of a dielectric slab doped with quantum dot (QD) m... more ABSTRACT The optical bistability (OB) behavior of a dielectric slab doped with quantum dot (QD) molecules is investigated in the presence of the inter-dot tunneling effect. It is shown that the threshold point of OB reduces by increasing inter-dot tunneling as well as by reducing the slab thickness. It is worth noting that the threshold of OB in a slab doped with QD molecules is smaller, by at least one order of magnitude, in respect to free QD molecules. We find that the inter-dot tunneling induces a negative group delay to the reflected pulse and it propagates in the superluminal region. Such simple control can be used in all optical switching.

The European Physical Journal D, 2010

We analyze the behavior of optical bistability in a four-level mercury atomic system driven by a ... more We analyze the behavior of optical bistability in a four-level mercury atomic system driven by a cavity and two external coherent fields by means of a unidirectional ring cavity. We find that without interacting dark resonances and for large intensity of coupling field, the optical bistability disappears. So, the double dark resonances could significantly establish the optical bistability. Moreover, we demonstrate that the double dark resonances can dramatically reduce the threshold of optical bistability.

Journal of Modern Optics

We propose a laser cooling mechanism that leads to a temperature significantly lower than the sin... more We propose a laser cooling mechanism that leads to a temperature significantly lower than the single-photon recoil limit, about 4 × 10 −4 E r. This mechanism benefits from sharp and high-contrast spectra which are induced by interacting dark-state resonances. It is theoretically demonstrated that four-level atoms illuminated by two counter-propagating probe beams and two additional beams directed perpendicularly to other two, exhibit new cooling effects; For red detuned probe lasers, atoms can be subject to a strong viscous force with an extremely small diffusion, characteristic of heating caused by the stochastic nature of spontaneous emission processes. By quantum mechanical simulations, we then find that the lowest temperature approaches 0.3 nK for the case of mercury, significantly lower than the recoil energy limit. A further advantage of our proposed scheme is that there is no need for an external magnetic field or a strong external confining potential.

Laser Physics Letters, 2019

Generation and detection of structured light have recently been the subject of intense study, aim... more Generation and detection of structured light have recently been the subject of intense study, aiming to realize high-capacity optical storage and continuous-variable quantum technologies. Here, we present a scheme to extract the orbital angular momentum content of Laguerre-Gaussian light beams in a double-Λ four level system of GaAs/AlGaAs multiple quantum wells. Arising from a quantum interference term, absorption of a non-vortex probe field depends upon the azimuthal phase of vortex fields so that both magnitude and sign of the azimuthal index/indices can be mapped into the absorption profile.

The atom-photon entanglement is studied in a three-level lambda-type closed-loop atomic system in... more The atom-photon entanglement is studied in a three-level lambda-type closed-loop atomic system in multi-photon resonance condition and beyond it. It is shown that the von Neumann entropy in such a system is phase dependent, and it can be controlled by either intensity or relative phase of applied fields. It is demonstrated that for the special case of Rabi frequency of applied fields, the system is disentangled.

The light propagation of a probe field pulse in a four-level double-lambda type system driven by ... more The light propagation of a probe field pulse in a four-level double-lambda type system driven by laser fields that form a closed interaction loop is studied. Due to the finite frequency width of the probe pulse, a time-independent analysis relying on the multiphoton resonance assumption is insufficient. Thus we apply a Floquet decomposition of the equations of motion to solve the time-dependent problem beyond the multiphoton resonance condition. We find that the various Floquet components can be interpreted in terms of different scattering processes, and that the medium response oscillating in phase with the probe field in general is not phase-dependent. The phase dependence arises from a scattering of the coupling fields into the probe field mode at a frequency which in general differs from the probe field frequency. We thus conclude that in particular for short pulses with a large frequency width, inducing a closed loop interaction contour may not be advantageous, since otherwise ...

We study the propagation of a Laguerre-Gaussian (LG) beam through a dispersive atomic medium. We ... more We study the propagation of a Laguerre-Gaussian (LG) beam through a dispersive atomic medium. We restrict ourselves to applying a weak probe field and three strong coupling fields to the medium, which leads to developing a four-level double V-type atomic system. We first regard all the three strong coupling fields as the plane-waves and calculate an analytical expression for the group velocity of the probe LG field on the optical axis at the waist of the field. It appears that the resulting formula in a dispersive medium is in good agreement with that of the free space. We also find a more general analytical expression for the group velocity of the probe LG field out of the optical axis and compare with its projection onto the propagation axis. It is turned out that these two quantities are equal on the optical axis, at the waist of the beam and the Rayleigh range. Finally, we assume one of the strong coupling fields to be an LG field and explore how its orbital angular momentum (OA...

arXiv: Quantum Physics, 2018

Atom-photon entanglement provides an essential resource for quantum communication and quantum com... more Atom-photon entanglement provides an essential resource for quantum communication and quantum computation. How to conveniently and efficiently achieve a maximal entanglement between atomic system and spontaneous emission field has been a challenging task. Here, we present a simple, yet we believe a powerful, method to generate entangled states between photons and an N-type atomic system. Beside the achievement of a nearly perfect entanglement, we also examine evidence for a link between entanglement and populations in dressed and bare states; It is found that a maximal entanglement can be established when populations in both dressed and bare states are spread over states. Moreover, the system would be disentangled in the absence of evenly distributed populations, another reason for further strengthen our claim that the physical origin of such entanglement is quantum correlation produced by distribution of the populations. We then discuss the dependence of the entanglement on Rabi fr...

Optics and Photonics Society of Iran, 2017

In this paper, optical effects of a hybrid complex system consisting of a semiconductor quantum d... more In this paper, optical effects of a hybrid complex system consisting of a semiconductor quantum dot and a metal nanoparticle interacting with a weak field is investigated. Nonlinear density matrix equations are used in order to describe optical properties of the quantum dot, the nanoparticle, and the entire system. Then, dependency of the susceptibilities of these component on the interparticle distance between the quantum dot and the nanoparticle is studied. It is demonstrated that for a wide range of frequencies, susceptibility of the quantum dot leads to gain without inversion and is calculated that the susceptibility is severely dependent on presence of the metal nanoparticle.

Laguerre-Gaussian (LG) beams contain a helical phase front with a doughnut-like intensity profile... more Laguerre-Gaussian (LG) beams contain a helical phase front with a doughnut-like intensity profile. We use the LG beam to introduce a rather simple method for generation of a vector beam (VB), a beam with spatially-dependent polarization in the beam cross section, via the nonlinear magneto-optical rotation (NMOR). We consider the NMOR of the polarization of a linearly polarized probe field passing through an inverted Y-type four-level quantum system interacting with a LG control field and a static magnetic field. It is shown that the polarization of the transmitted field is spatially distributed by the orbital angular momentum (OAM) of the LG control field, leading to generation of the VB with azimuthally symmetric polarization distribution. We show that the polarization and intensity distributions of the VB spatially vary by changing the OAMs of the LG control field. Moreover, the radial index of the LG control field has a major role in more spatially polarization distributing of th...

Scientific Reports

We present a convenient way to obtain an optical power limiting behavior in a quantum dot molecul... more We present a convenient way to obtain an optical power limiting behavior in a quantum dot molecule system, induced by an interdot tunneling. Also, the effect of system parameters on the limiting performance is investigated; interestingly, the tunneling rate can affect the limiting performance of the system so that the threshold of the limiting behavior can be a function of the input voltage, allowing the optimization of the limiting action. Furthermore, by investigating the absorption of the probe field, it is demonstrated that the optical limiting is due to a reverse saturable absorption mechanism; indeed, analytical results show that this mechanism is based on a cross-Kerr optical nonlinearity induced by the tunneling. Additionally, the limiting properties of the system are studied by using a Z-scan technique.

Physical Review B

We study the propagation of probe pulses carrying orbital angular momentum (OAM) in a crystal of ... more We study the propagation of probe pulses carrying orbital angular momentum (OAM) in a crystal of molecular magnets characterized by a double-light-matter coupling scheme. The model is based on the four-wave mixing (FWM) of applied fields interacting with the magnetic dipole moment of the molecular magnets. We consider the light-matter interaction under the situation where a weak probe field carries an optical vortex and investigate the exchange of optical vortices between different frequencies via the FWM in the microwave region. The propagation of OAM beams with nonzero radial indices is then explored. It is found that the conservation of both azimuthal and radial indices is satisfied over the swapping of OAM states of light. Superimposing two initially weak OAM modes with different topological charges creates specific vortex beams with a very characteristic form. The resulting beam contains a central vortex as well as several singly charged peripheral vortices distributed at the same radial distance from the center of the light beam. This complex pattern of vortices arises because the intensity radius of two interfering OAM modes is different. It is shown that the boundary region of intensity dominance of two OAM modes can be controlled by the molecular magnets parameters and strong cw electromagnetic fields. Our proposed scheme may provide a route to study the solid systems suitable for quantum technologies as well as for OAM exchange devices for quantum information processing.

Optics Express

We study the propagation of a Laguerre-Gaussian (LG) beam through a dispersive atomic medium. We ... more We study the propagation of a Laguerre-Gaussian (LG) beam through a dispersive atomic medium. We restrict ourselves to applying a weak probe field and three strong coupling fields to the medium, which leads to developing a four-level double V-type atomic system. We first regard all the three strong coupling fields as the plane-waves and calculate an analytical expression for the group velocity of the probe LG field on the optical axis at the waist of the field. It appears that the resulting formula in a dispersive medium is in good agreement with that of the free space. We also find a more general analytical expression for the group velocity of the probe LG field out

Journal of the Optical Society of America B

We study the orbital angular momentum (OAM) transfer from a weak Laguerre-Gaussian (LG) field to ... more We study the orbital angular momentum (OAM) transfer from a weak Laguerre-Gaussian (LG) field to a weak plane-wave in two closed-loop three-level V-type atomic systems. In the first scheme, the atomic system has two non-degenerate upper levels which the corresponding transition is excited by a microwave plane-wave. It is analytically shown that the microwave field induces an OAM transfer from an LG field to a generated third field. In the second scheme, we consider a three-level V-type atomic system with two near-degenerate excited states and study the effect of the quantum interference due to the spontaneous emission on the OAM transfer. It is found that the spontaneously generated coherence (SGC) induces the OAM transfer from the LG field to the weak planar field, while the OAM transfer does not occur in the absence of the SGC. The suggested models prepare a rather simple method for the OAM transfer which can be used in quantum information processing and data storage.

Scientific Reports

The atom-photon entanglement using the Laguerre-Gaussian (LG) beams is studied in the closedloop ... more The atom-photon entanglement using the Laguerre-Gaussian (LG) beams is studied in the closedloop three-level V-type quantum systems. We consider two schemes with near-degenerate and nondegenerate upper levels: in the first, the effect of the quantum interference due to the spontaneous emission is taken into account and in the second, a microwave plane wave is applied to the upper levels transition. It is shown that the atom-photon entanglement in both schemes depends on the intensity profile as well as the orbital angular momentum (OAM) of the applied fields so that the various spatially dependent entanglement patterns can be generated by Laguerre-Gaussian beams with different OAMs. However, due to the zero intensity,no entanglement appears in the center of the optical vortex beams. As a result, the entanglement between dressed atom and its spontaneous emissions in different points of the atomic vapor cell can be controlled by the OAM of the applied fields. Moreover, our numerical results show that the number of the local maximum degree of entanglement (DEM) peaks depends on the OAM of the applied fields. The degrees of freedom for OAM play a crucial role in spatially dependent atom-photon entanglement in such a way that it may possess broad applications in high-dimensional quantum information processing and data storage.

Journal of Optics

We present a convenient and effective way to generate a novel phenomenon of trapping, named trap ... more We present a convenient and effective way to generate a novel phenomenon of trapping, named trap split, in a conventional four-level double-Λ atomic system driven by four femtosecond Laguerre-Gaussian laser pulses. We find that trap split can be always achieved when atoms are trapped by such laser pulses, as compared to Gaussian ones. This feature is enabled by interaction of the atomic system and the Laguerre-Gaussian laser pulses with zero intensity in the center. A further advantage of using Laguerre-Gaussian laser pulses is the insensitivity to fluctuation in intensity of the lasers in such a way that the separation between traps remains constant. Moreover, it is demonstrated the suggested scheme with Laguerre-Gaussian laser pulses can form optical traps with spatial sizes that are not limited by the wavelength of the laser and can, in principle, become smaller than the wavelength of light. This work would greatly facilitate the trapping and manipulating the particles and generation of trap split. It may also suggest the possibility of extension into new research fields, such as micro-machining and biophysics.

Journal of the Optical Society of America B

The optical trap potential is studied in a four-level double-Λ closed-loop atomic system in the m... more The optical trap potential is studied in a four-level double-Λ closed-loop atomic system in the multiphoton resonance condition. We apply four femtosecond Gaussian laser beams to generate a closed-loop configuration. It is shown that the induced optical dipole force on the system dramatically depends on the relative phase of applied fields, and it switches from focusing to defocusing in the transverse direction, simply by properly changing the relative phase. Through special switching of the relative phase, the trapping potential splits into two positions, which has novel applications in trapping and manipulating the particles. Moreover, it is further demonstrated that trap depth can be manipulated by the relative phase. Finally, a maximum coherent population transfer is achieved for a special value of the relative phase of applied fields.

Laser Physics, 2016

The propagation of an electromagnetic pulse through a dielectric slab doped with a triple quantum... more The propagation of an electromagnetic pulse through a dielectric slab doped with a triple quantum dot (QD) nanostructure has been discussed in the presence of electron tunneling. We include the effect of an incoherent pump field in the transmission and reflection of a pulse in a triple QD. It is shown that the reflected and transmitted pulses can be switched from subluminal to superluminal light propagation by changing either the rate of the incoherent pump field or the inter-dot tunneling between QD1, QD2 and QD3 in a slab. Furthermore, it is demonstrated that the inter-dot tunnel coupling can significantly affect the behavior of optical bistability (OB) and optical multi-stability (OM) in a dielectric slab. The obtained results can be used for the development of new types of nanoelectronic devices for realizing the switching process.

Quantum Information Processing, 2015

The density matrix equations of motion in near-degenerate three-level V-type closedloop atomic sy... more The density matrix equations of motion in near-degenerate three-level V-type closedloop atomic system are calculated numerically in Floquet frame. The dynamical behavior of atom-photon entanglement between the dressed atom and its spontaneous emission is studied in semi classical approach beyond the two-photon resonance condition in such a system. The quantum entropy of these two subsystems is investigated by using the von Neumann entropy. It is shown that, the degree of entanglement measure (DEM) can be controlled via the intensity and the detuning of coupling optical field and quantum interference induced by spontaneous emission. Moreover in the absence of quantum interference the steady state behavior of DEM can be achieved even in beyond the two-photon resonance condition. Furthermore in the absence of quantum interference for special parameters of Rabi frequency and detuning of driving laser field disentanglement can be occurred. Also the electromagnetically induced transparency condition can be obtained when the system is disentangled.

Journal of the Optical Society of America B, 2015

The interaction of two orthogonally polarized beams and a four-level GaAs quantum well (QW) waveg... more The interaction of two orthogonally polarized beams and a four-level GaAs quantum well (QW) waveguide is investigated. It is shown that, by applying a static magnetic field normal to the propagation direction of the driving beams, the birefringence can be induced in the QW waveguide. Moreover, it is demonstrated that the dephasing rate between two ground states of the QW waveguide makes it a dichromatic medium and can also diminish the induced birefringence. Our results show how a large and complete magneto-optical rotation in the QW waveguide can be obtained via adjusting the intensity of the magnetic field and also the length of the QW waveguide.

Laser Physics, 2015

ABSTRACT The optical bistability (OB) behavior of a dielectric slab doped with quantum dot (QD) m... more ABSTRACT The optical bistability (OB) behavior of a dielectric slab doped with quantum dot (QD) molecules is investigated in the presence of the inter-dot tunneling effect. It is shown that the threshold point of OB reduces by increasing inter-dot tunneling as well as by reducing the slab thickness. It is worth noting that the threshold of OB in a slab doped with QD molecules is smaller, by at least one order of magnitude, in respect to free QD molecules. We find that the inter-dot tunneling induces a negative group delay to the reflected pulse and it propagates in the superluminal region. Such simple control can be used in all optical switching.

The European Physical Journal D, 2010

We analyze the behavior of optical bistability in a four-level mercury atomic system driven by a ... more We analyze the behavior of optical bistability in a four-level mercury atomic system driven by a cavity and two external coherent fields by means of a unidirectional ring cavity. We find that without interacting dark resonances and for large intensity of coupling field, the optical bistability disappears. So, the double dark resonances could significantly establish the optical bistability. Moreover, we demonstrate that the double dark resonances can dramatically reduce the threshold of optical bistability.

Journal of Modern Optics

We propose a laser cooling mechanism that leads to a temperature significantly lower than the sin... more We propose a laser cooling mechanism that leads to a temperature significantly lower than the single-photon recoil limit, about 4 × 10 −4 E r. This mechanism benefits from sharp and high-contrast spectra which are induced by interacting dark-state resonances. It is theoretically demonstrated that four-level atoms illuminated by two counter-propagating probe beams and two additional beams directed perpendicularly to other two, exhibit new cooling effects; For red detuned probe lasers, atoms can be subject to a strong viscous force with an extremely small diffusion, characteristic of heating caused by the stochastic nature of spontaneous emission processes. By quantum mechanical simulations, we then find that the lowest temperature approaches 0.3 nK for the case of mercury, significantly lower than the recoil energy limit. A further advantage of our proposed scheme is that there is no need for an external magnetic field or a strong external confining potential.