Squeezing Of Field Research Articles

SQUEEZING OSCILLATIONS OF A QUANTIZED FIELD INTERACTING WITH PAIR OF COLD ATOMS VIA INTENSITY-DEPENDENT COUPLING

We study the interaction between a single-mode electromagnetic field and a pair of indistinguishable two-level atoms via the intensity-dependent coupling. This problem is equivalent to the equidistant three-level atom with equal dipole moment matrix transition elements between the adjacent levels. The exact analytical solution for the atom–field state-vector is obtained assuming that at the initial moment the field is in the Holstein–Primakoff SU (1,1) coherent state. The quantum statistical and squeezing properties of the field are investigated. The results obtained are compared with those for the single two-level atom obtained by Buzek. We observe that the exact periodicity of the field squeezing that takes place in the case of the single two-level atom is violated in the case of the pair of cold atoms. That is, the exact periodicity of the physical quantities can be destroyed only if the radiation field interacts with a system of more than one two-level atom.

Quantum statistical properties of the Jaynes–Cummings model in the presence of a classical homogeneous gravitational field

The temporal evolution of quantum statistical properties of an interacting atom–radiation field system in the presence of a classical homogeneous gravitational field is investigated within the framework of the Jaynes–Cummings model. To analyse the dynamical evolution of the atom–radiation system a quantum treatment of the internal and external dynamics of the atom is presented based on an alternative su(2) dynamical algebraic structure. By solving the Schrödinger equation in the interaction picture, the evolving state of the system is found by which the influence of the gravitational field on the dynamical behaviour of the atom–radiation system is explored. Assuming that initially the radiation field is prepared in a coherent state and the two-level atom is in a coherent superposition of the excited and ground states, the influence of gravity on the collapses and revivals of the atomic population inversion, atomic dipole squeezing, atomic momentum diffusion, photon counting statistics and quadrature squeezing of the radiation field is studied.

Measurement Induced Enhancement of Squeezing inNondegenerate Two-Photon Jaynes–Cummings Model

Squeezing properties in the nondegenerate two-photonJaynes–Cummings model are investigated. The effects of direct selectiveatomic measurement and the application of the classical fieldfollowed by atomic measurement are analyzed. Different values ofthe parameters of the classical field are taken into account.It is found that the field squeezing can be enhanced bymeasurement.

Nonclassical Effects of a Four-Level Excited-DoubletAtom Model

We adopt a dynamical algebraic method to study a four-levelexcited-doublet atom model and obtain the explicit expressions ofthe time-evolution operator and the density operator for thesystem. The nonclassical effects of the system, such as collapsesand revivals of the atomic inversion and squeezing of theradiation field, are also discussed.

Comments on ‘Higher order squeezing of the electromagnetic field in spontaneous and in stimulated Raman processes’

Of late, Giri and Gupta [J. Mod. Opt. 52 1769 (2005)] discussed the possibility of getting higher order (fourth and fifth orders) squeezing of the fundamental mode in spontaneous Raman and in stimulated Raman processes. These investigations are based on the earlier works of Kumar and Gupta [Quantum Semiclass. Opt. 7 835 (1995)]. We reinvestigate the model and we found that the entire calculations and hence the conclusion of Giri and Gupta and Kumar and Gupta are not only baseless but also misleading. There will be no squeezing of the fundamental mode in spontaneous and in Raman processes.

Field and dipole squeezing in a driven degenerate Λ quantum-beat system

Abstract The properties of field squeezing and atomic dipole squeezing in a coherent-microwave field driven degenerate Λ quantum-beat system were theoretically investigated. Numerical calculations indicate that the driving microwave may enhance or suppress both dipole squeezing and cavity-field squeezing, depending on the atomic energy level splitting and the microwave Rabi frequency.

Amplitude-squared squeezing of the photon field in a Kerr-nonlinear blackbody

We find the photon field in a Kerr-nonlinear blackbody is an amplitude-squared squeezed state. The squeezing effect decreases with increasing temperature T. The amount of the amplitude-squared squeezing in a Kerr-nonlinear blackbody is much larger than the corresponding squeezing in normal blackbody, and the degree of amplitude-squared squeezing is much larger than the amplitude squeezing for the same range of parameters in a Kerr-nonlinear blackbody. The frequency ω k and parameter γ also have important influences on the amplitude-squared squeezing in a Kerr-nonlinear blackbody.

Nonclassical properties of a time-varying Jaynes–Cummings model

The interactions between a two-level atom and a field with a time-varying frequency have been investigated. The two typical cases, the frequency of the field varying with time in the forms of sine and rectangle, have been considered. The dynamic behaviour of the field squeezing, photon antibunching and atomic dipole squeezing are investigated numerically as a function of time. A number of novel phenomena are discovered and discussed.

Field autocorrelations in electromagnetically induced transparency: Effects of a squeezed probe field

The interaction of a quantized field with three-level atoms in a {lambda} configuration inside a two mode cavity is analyzed. We calculate the stationary quadrature noise spectrum of the field outside the cavity in the case where the input probe field is in a squeezed state and the atoms show electromagnetically induced transparency. If the Rabi frequencies of both dipole transitions of the atoms are different from zero, we show that the output probe field has four maxima of squeezing absorption. We show that in some cases two of these frequencies can be very close to the transition frequency of the atom, in a region where the mean value of the field entering the cavity is hardly altered. Furthermore, part of the absorbed squeezing of the probe field is transferred to the pump field. For some conditions this transfer of squeezing can be complete.

Quantum-feedback-induced enhancement of continuous-variable entanglement in a self-phase-locked type-II nondegenerate optical parameter oscillator

We investigate the enhancement of the intracavity entanglement of a self-phase-locked type-II nondegenerate optical parameter oscillator (SPL NOPO) via homodyne-mediated quantum feedback. It is found that the feedback can effectively enhance the squeezing, entanglement, and purity of the two-mode field in the SPL NOPO. Especially for an ordinary NOPO, our feedback scheme can simulate a standard two-mode squeezed vacuum environment and a pure steady two-mode squeezed vacuum cavity field can be generated, different from the scheme proposed by Mancini [Phys. Rev. A 73, 010304(R) (2006)] in which only a mixed two-mode entangled state is generated.

NTH-ORDER AMPLITUDE SQUEEZING EFFECTS OF RADIATION IN MULTIPHOTON PROCESSES

Squeezing of the electromagnetic field is a purely quantum mechanical phenomenon and this quantum effect is expected to manifest itself in optical processes in which the nonlinear response of the system to the radiation field plays an important role. It has generated a great deal of interest in view of the possibility of reducing the noise of an optical signal below the vacuum limit i.e. zero-point oscillations. In this paper the concept of nth-order amplitude squeezing is introduced in the fundamental mode in four- and six-wave mixing processes as a generalization of the higher-order squeezing under short-time approximation based on a fully quantum mechanical approach. It established the coupled Heisenberg equations of motion involving real and imaginary parts of the quadrature operators. The condition for occurrence of nth-order squeezing is obtained from which higher-order squeezing upto n=3 are studied. Dependence of squeezing on photon number is also established. The conditions for obtaining maximum and minimum squeezing are obtained. The method of present investigation can be applied to any higher-order non-linear optical processes and the technique can also be extended for studying squeezing in any N-photon process in general. Further, nth-order squeezing of radiation in N-photon process can also be investigated. The results obtained may help in selecting a suitable process to generate optimum squeezing in the radiation field.

Joint estimation of real squeezing and displacement

We study the problem of joint estimation of real squeezing and amplitude of the radiation field, deriving the measurement that maximizes the probability density of detecting the true value of the unknown parameters. More generally, we provide a solution for the problem of estimating the unknown unitary action of a nonunimodular group in the maximum likelihood approach. Remarkably, in this case the optimal measurements do not coincide with the so called square-root measurements. In the case of squeezing and displacement we analyze in detail the sensitivity of estimation for coherent states and displaced squeezed states, deriving the asymptotic relation between the uncertainties in the joint estimation and the corresponding uncertainties in the optimal separate measurements of squeezing and displacement. A two-mode setup is also analyzed, showing how entanglement between optical modes can be used to approximate perfect estimation.

Field Squeeze Operators in Optical Cavities with Atomic Ensembles

We propose a method of generating unitarily single and two-mode field squeezing in an optical cavity with an atomic cloud. Through a suitable laser system, we are able to engineer a squeeze field operator decoupled from the atomic degrees of freedom, yielding a large squeeze parameter that is scaled up by the number of atoms, and realizing degenerate and nondegenerate parametric amplification. By means of the input-output theory we show that ideal squeezed states and perfect squeezing could be approached at the output. The scheme is robust to decoherence processes.

Influence of the interaction between atoms on the squeezing of light field and atomic lasers

The Hamiltonian operator of a system of single-mode light field interacting with Bose-Einstein condensate (BEC) of two-level atoms is discussed in terms of the lattice-liquid model. It is indicated that the contribution of the interaction between atoms to the Hamiltonian was irrationally overestimated in the literature, so the Hamiltonian operator is improved in the present paper. Based on the improved Hamiltonian, the equations of motion of the photon and atomic operators are derived analytically. The relevant parameters in the model are estimated in connection with the BEC experimental conditions. The influence of the interaction between atoms in the BEC on the squeezing of light field and the atomic lasers is studied. The results show that the dependence of squeezing factor with atom number in BEC is different from that given in literature. and the fluctuations of two quadrature components of light evolve periodically with cosine law and the fluctuations of two quadrature components of the atomic laser can be squeezed.

Effect of vibrational heating on the entangled field from an ion trapped in a bimodal cavity

The influence of the vibrational heating of a single cold ion trapped in a bimodal cavity under continuous excitation on the generation of two-mode squeezing and entanglement of the cavity field from the ion is discussed. It is found that the vibrational heating gives a strong limitation for the appearance of the two-mode squeezing, but the two cavity modes can develop into a robust entangled Gaussian state.

Higher-order squeezing of quantum field and higher-order uncertainty relations in non-degenerate four-wave mixing

It is found that the field of the combined mode of the probe wave and the phase conjugate wave in the process of non-degenerate four-wave mixing exhibits higher-order squeezing to all even orders. The higher-order squeezed parameter and squeezed limit due to the modulation frequency are investigated. The smaller the modulation frequency is, the stronger the degree of higher-order squeezing becomes. Furthermore, the higher-order uncertainty relations in the process of non-degenerate four-wave mixing are presented for the first time. The product of higher-order noise moments is related to even order number N and the length L of the medium.

Higher-order squeezing of the electromagnetic field in spontaneous and stimulated Raman processes

The occurrence of fourth and fifth-order squeezing in the fundamental mode of the electromagnetic field in spontaneous and stimulated Raman processes under the short-time approximation is investigated on the basis of a fully quantum-mechanical approach. In an idealized model, the Raman process is looked upon as a two-photon on a one phonon interaction process. The coupled Heisenberg equations of motion involving real and imaginary parts of the quadrature operators are established. The dependence of fourth- and fifth-order squeezing in terms of the signal-to-noise ratio on the number of photons is investigated. We have also established the amplitude squeezing effects in the Stokes and vibrational modes, which is found to be dependent on higher-order difference squeezing showing a difference squeezing that can be converted to normal squeezing.

Influence of atomic motion on squeezing of double-mode field in interaction with a moving V-type three-level atom

The influence of atomic motion on squeezing of the double-mode field in the interaction with a moving V-type three level atom is investigated by means of the quantum theory and the method of numerical analysis. The results show, on the one hand, when the initial photon field is in non-correlative coherent state of double-mode, only the quadrature U1 is squeezed and the squeezed degree of U1 increases with the increasing of the parameter β which describes the atomic motion and structure of the field mode. On the other hand, when the initial field is in the vacuum squeezed state of double-mode, the quadrature U2 is squeezed principally and we can obtain a steady squeezed light by choosing an appropriate parameter β.

Phase-independent spectrum of atomic resonance fluorescence from a driven three-level atom in ladder configuration

We investigate the phase-dependent squeezing of resonance fluorescence emitted from a coherently excited three-level atom with a ladder configuration of energy levels. Quantum fluctuation spectra of the optimum-phase quadratures and atomic populations and coherences are calculated. We find that two-photon absorption greatly modifies the steady-state atomic populations and coherence which can lead to squeezing of the total field of fluorescent light, but is not favourable for frequency-dependent squeezing spectra. Optimized squeezing can be attained and controlled with the phase of quadrature of fluorescent light, intensity and detuning of the driving fields and the decay rate of the controlling transition. Analytical picture is provided in dressed states representation for supporting our numerical results in the strong driving field limit.

Influence of Intrinsic Decoherence on Nonclassical Effects of System of a Three-Level Atom in Ξ Configuration**The project supported by National Natural Science Foundation of China under Grant No. 10174066 and Natural Science Foundation of Zhejiang Province of China

With the help of an SU(3) dynamical algebraic structure, we find an exact solution of the Milburn equation for the system of a three-level atom in the Ξ configuration interacting with one quantized field mode with arbitrary detuning. The exact solution is then used to discuss the influence of the intrinsic decoherence on the nonclassical properties of the system, such as collapes and revivals of the atomic populations, oscillations of the photon number distribution, and squeezing of the radiation field.