Optical switching by controlling the double-dark resonances in a N-tripod five-level atom

We have investigated the optical switching in a five-level atom in a novel configuration of electromagnetically induced transparency. This N-tripod type level scheme combines the attractive features of cross-phase modulation appearing in N-type atoms with the ability to slow light pulses associated with tripod atoms. The addition of a new driving field to the usual tripod configuration allows to control the double-dark resonances which appear in the four-level tripod system and thus enables to manipulate the probe absorption and dispersion properties. We have studied the temporal dynamics of two pulses, a probe pulse and a switch propagating pulse through the sample. In the presence of the switching field, a deep in the absorption at resonance due to one-photon electromagnetically induced transparency appears and the atomic system is transparent to the probe field, which propagates at a very small group velocity. By tuning the fields, one of the usual double-dark resonances appearing in tripod system can be controlled (Stark-shifted) and the medium, which is transparent in the absence of the control field, will become highly absorptive. The linear and cross-phase modulation susceptibilities have been calculated and we predict the possibility to realize two-photon switching and giant cross-phase modulation. Finally we address the question about the generation of an entangled coherent state and we show that the giant cross-phase modulation provided by this N-tripod atomic system can be used for realizing polarization quantum phase gates.     

Effective generation of polarization-entangled photon pairs in a cavity-QED system

We propose a cavity-QED scheme to effectively generate Einstein-Podolsky-Rosen polarization-entangled photon pairs. Assisted by a classical π-polarized pump field, a tripod four-level atom successively couples to two high-Q optical cavities possessing polarization degeneracy. Through stimulated Raman adiabatic passage process the polarization-entangled photon pairs can be produced.     

Ultraslow optical solitons in a four-level tripod atomic system

We investigate possible formation and propagation of localized, shape-preserving nonlinear optical pulse in a resonant, lifetime-broadened four-level tripod atomic system via electromagnetically induced transparency (EIT). We prove both analytically and numerically that although in anomalous dispersion regimes near resonance a superluminal optical soliton may appear, such soliton suffers serious absorption. However, by choosing appropriate parameters to make the system work in normal dispersion regimes and within an EIT transparency window, ultraslow optical solitons with very low light intensity can form and propagate stably in the system.     

Parametric conversion and maximally entangled photon pair via collective excitations in a cycle atomic ensemble

We study the propagation of two quantized optical fields via considering the collective effects of photonic emissions and excitations of a three-level cyclic-type system (such as atomic ensemble with symmetry broken, or the chiral molecular gases, or manual “atomic” array with symmetry broken), where the quantum transitions is driven by two quantized fields and a classical one. The results show that the parametric conversion and maximally entangled photon pair generation can be achieved by means of the collective excitation of the two upper energy levels induced by the classic optical field. This investigation may be used for the generated coherent short-wavelength quantum radiation and quantum information processing.     

Generation of pair coherent state using weak cross-Kerr media

We firstly give a nonlocal method for generating pair coherent state with two traveling wave fields in distinct districts. The experimental scheme proposed is based on a two-mode photon number matching process, which employs weak cross-Kerr media and on/off detection. Then we discuss the details for implementing this scheme, showing that it is robust against the low quantum efficiency of photon detectors and offers nearly perfect pair coherent states. Finally, we show how a two-mode Schrödinger cat state and a generalized two-mode correlated photon number state can be prepared via this matching process.     

Phase-dependent gain and absorption properties of mid- to far-infrared lights in three-coupled-quantum-wells

We investigate the phase-dependent gain and absorption behaviors of mid- to far-infrared lights under a cascade configuration in an asymmetric semiconductor three-coupled-quantum-well (TCQW) structure based on intersubband transitions (ISBTs). In the proposed TCQW scheme, the amplification of the probe and signal fields, i.e., the far- and mid-infrared waves, can be realized with realistic experimental parameters. The gain-absorption spectra are strongly dependent on the relative phase of the applied laser fields. The influences of the probe detuning and the two pump Rabi energies on the gain-absorption responses of two weak far- and mid-infrared light fields are also discussed in details. The results show that amplifications of the far- and mid- infrared waves can be achieved by adjusting the relative phase, the probe detuning, and the two pump Rabi energies appropriately. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the wide adjustable parameters. For practical applications, this investigation may provide a new possibility for realizing the efficient gain of far- and mid-infrared waves in the solid-state materials.     

Microwave solitons in molecular magnets via electromagnetically induced transparency

Using the Schrödinger-Maxwell equations, we investigate the formation of microwave solitons in a crystal of molecular magnets. This system is subjected to one dc magnetic field and two (probe and coupling) ac resonant magnetic fields. The results show that the probe magnetic field can freely propagate in a crystal of molecular magnets due to quantum interference. Furthermore, within certain parameter range, both bright and dark microwave solitons can occur in such a highly resonant medium. We also obtain the analytical expressions for the phase shift and absorption coefficient of the probe magnetic field.     

Observing Zitterbewegung with ultracold atoms

We propose an optical lattice scheme which would permit the experimental observation of Zitterbewegung (ZB) with ultracold, neutral atoms. A four-level tripod variant of the setup for stimulated Raman adiabatic passage (STIRAP) has previously been proposed for generating non-Abelian gauge fields. Dirac-like Hamiltonians, which exhibit ZB, are simple examples of such non-Abelian gauge fields; we show how a variety of them can arise, and how ZB can be observed, in a tripod system. We predict that the ZB should occur at experimentally accessible frequencies and amplitudes.     

Quantum states transfer between coupled fields

We study the exchange of states in coupled fields along their time evolution. The coupling is described by a quadratic form in terms of annihilation and creation operator in the field Hamiltonian. An analytical approach is employed to describe the time evolution of the field state in Fock's space and the conditions for an arbitrary initial states to be transferred with 100% fidelity is determined. We show that only for initial states C₀|0>+C_N|N>, this situation can occurs. The important |1〉↔|0〉 qubits transfer is a particular case of this transference of number state. The relation between the coupling constant and characteristic field frequencies for complete state transference is also determined.     

Tunneling-induced enhancement of self-Kerr nonlinearity in asymmetric quantum wells

We propose an asymmetric AlGaAs/GaAs double quantum wells (QWs) structure for realizing the enhancement of self-Kerr nonlinearity. It is found, with resonant tunneling, that the self-Kerr nonlinearity can be clearly enhanced, while the absorption of probe field is very small and can be safely neglected. We attribute the enhancement of self-Kerr nonlinearity mainly to the constructive interference induced by resonant tunneling.     

Coherent Phase Control of Ultrafast Polarization Beats in Reverse V-Type Three-Level System

We investigate the third-order nonlinear absorption and dispersion of femto- and atto-second polarization beats between the one-photon degenerate four-wave mixing process and the two-photon nondegenerate four-wave mixing process in the pure homogeneously-broadened reverse V-three-level using twin noisy fields. The third-order nonlinear response can be controlled and modified by the colour-locked correlation of twin noisy fields. Most importantly, the coherent phase control in optical heterodyne detection for studying the phase dispersion of the third-order susceptibility is demonstrated. The radiation-matter detuning oscillation is also considered in the freauencv domain.     

Quantum theory of super-resolution for optical systems with circular apertures

We present the two-dimensional quantum theory of super-resolution, applicable for a large variety of optical systems with circular pupils. Our theory is formulated in terms of circular prolate spheroidal functions which form the eigen basis of two-dimensional imaging system with circular pupils. We provide, in particular, analytical and numerical results for the point-spread function characterizing reconstruction of optical objects with super-resolution from diffraction-limited images. We evaluate the super-resolution factor as a function of the signal-to-noise ratio in the input object for coherent light and multimode squeezed light.     

Mid-infrared efficient generation by resonant four-wave mixing in a three-coupled-quantum-well nanostructure

We present a cascade configuration for the realization of highly efficient four-wave mixing (FWM) process in an asymmetric semiconductor three-coupled-quantum-well (TCQW) structure based on intersubband transitions (ISBTs). In the proposed TCQW scheme, the efficiency of the generated FWM mid-infrared (MIR) signal is significantly enhanced and the obtained maximum efficiency is greater than 50%. The corresponding explicit analytical expressions for the input probe and generated FWM pulsed fields are derived by use of the coupled Schrödinger-Maxwell approach and the FWM efficiency versus several variables is also discussed in details. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the wide adjustable parameters. This nonlinear optical process in the TCQW solid-state material can be used for efficiently generating coherent short-wavelength radiation.     

Bright entangled light from two-mode cascade laser

We show that a two-mode three-level cascade laser driven by external coherent fields generate intense entangled light. It turns out that external driving fields which are at resonance with the cavity modes substantially improve the intensity of the two-mode light in the cavity in a region where the squeezing and entanglement is significant making the system under consideration a viable source of bright squeezed as well as entangled light.     

Quantum nondemolition measurement of transverse atomic position in Kapitza-Dirac atomic beam scattering

It is demonstrated that one can measure the distribution of the transverse position of an atom crossing one or more optical cavities by monitoring the phase of the standing wave fields in the cavities. For the atom-field interaction the Kapitza-Dirac regime is assumed; it is shown that in this regime the method represents a quantum nondemolition measurement of the atomic position. On the other hand it can be applied to prepare narrow distributions of the transverse atomic position. In order to show this, a numerical simulation is performed, which illustrates the collapse of a broad initial Gaussian wavepacket, which can be coherent or incoherent, to a distribution with narrow peaks. Preparing the cavity fields in a squeezed state, one can greatly enhance the impact of the cavity field measurements on the atomic density matrix.     

Interaction of Triply-Dressing Electromagnetically Induced Transparency in Five-level Folding Atomic System

We consider a five-level atomic folding system, which involve two kinds of dressing mechanisms （the nested- cascade and the sequential-cascade） in interaction of three-dressing fields, the numerical results show that three- dressing fields are interchangeable under certain conditions, which can be considered as two four-level sub-system configurations （a nested-cascade N configuration and a sequential-cascade inverted-Y configuration）.     

Optical bistability via amplitude and phase control of a microwave field

We investigate the steady-state optical bistability behavior in a three-level Λ-type atomic system closed by a microwave field under the condition that the applied fields are in resonance with corresponding atomic transitions. It is shown that the bistable hysteresis cycles can be controlled by both the amplitude and the phase of the microwave field.     

Preparation of Cluster States of Atomic Qubits in Cavity QED

We propose an optical scheme to generate cluster states of atomic qubits, with each trapped in separate optical cavity, via atom-cavity-laser interaction. The quantum information of each qubit is encoded on the degenerate ground states of the atom, hence the entanglement between them is relatively stable against spontaneous emission. A single-photon source and two classical fields are employed in the present scheme. By controlling the sequence and time of atom-cavity-laser interaction, we show that the atomic cluster states can be produced deterministically.     

Three-qubit phase gate on three modes of a cavity

We show that a three-qubit phase gate on three modes of a cavity can be realized via resonant atom–cavity interaction. By introducing two strong classical fields and modulating the amplitudes, we obtain the effective form of nonlinear interaction between photons in the three-mode cavity. The availability is testified via numerical analysis. We also consider both the situations with and without effect of decoherence.