Squeezed Vacuum Field Research Articles

Response of a two-level atom to a narrow-bandwidth squeezed-vacuum excitation

Using the coupled-system approach we calculate the optical spectra of the fluorescence and transmitted fields of a two-level atom driven by a squeezed vacuum of bandwidths smaller than the natural atomic linewidth. We find that in this regime of squeezing bandwidths the spectra exhibit unique features, such as a hole burning and a three-peak structure, which do not appear for a broadband excitation. We show that the features are unique to the quantum nature of the driving squeezed vacuum field and do not appear when the atom is driven by a classically squeezed field. We find that a quantum squeezed-vacuum field produces squeezing in the emitted fluorescence field which appears only in the squeezing spectrum while there is no squeezing in the total field. We also discuss a nonresonant excitation and find that depending on the squeezing bandwidth there is a peak or a hole in the spectrum at a frequency corresponding to a three-wave-mixing process. The hole appears only for a broadband excitation and results from the strong correlations between squeezed-vacuum photons.

Bistable behaviour in squeezed vacua: I. Stationary analysis

A time-independent theoretical and numerical analysis of an optical bistable model of two-level atoms in a ring cavity, driven by a coherent field and in contact with a squeezed vacuum field is presented in the two cases of absorptive and dispersive optical bistability (OB). In the former case, a suitable choice of the phase of the squeezed vacuum field reduces the threshold for OB to occur compared with the normal vacuum case. In the latter case, regions of OB are identified as one or two disconnected simple closed curves depending on the cooperation parameter C ≷ C crit max : C crit max is the maximum possible value of the critical value of C at fixed values of the squeezed vacuum field parameters. Phase switching effects between different (output) states of the system is investigated in detail. In the absorptive case, one- or two-way optical switching is possible depending on C ≷ C crit max . We also present results which demonstrate more complicated switching behaviour in the dispersive case.

INFLUENCE OF THE VIRTUAL PHOTON FIELD ON THE ATOMIC QUANTUM CHARACTER IN TWO-MODE SQUEEZING VACUUM FIELD

We have investigated in the time-evolution and the squeezing character of atomic operators in a system of two-mode squeezed vacuum field interacting with a two-level atom without the rotating-wave approximation by means of quantum theory.The results obtained using the numerical method indicate that the influence of the virtual-photon field on the atomic quantum character is mainly the cause for quantum chaos which is related to the quantum character of the system itself.

Optical bistability in V medium by squeezed vacuum input

We discuss the optical bistable behavior of a system of N V-type three-level atoms pumped by a coherent input field and coupled to a squeezed vacuum field by treating the optical bistability of such a system as an input-output problem. It is shown that bistability can be realized due to the squeezed vacuum input.

Absorption spectrum of a strongly driven atom in a detuned squeezed vacuum

We present numerical and analytical results for the Mollow probe absorption spectrum of a coherently driven two-level system in a narrow bandwidth squeezed vacuum field. The spectra are calculated for the case where the Rabi frequency of the driving field is much larger than the natural linewidth and the squeezed vacuum carrier frequency is detuned from the driving laser frequency. The driving laser is on resonance. We show that in a detuned squeezed vacuum the standard Mollow features are each split into triplets. The central components of each triplet are weakly dependent on the squeezing phase but the sidebands strongly depend on the phase and can have dispersive or absorptive/emissive profiles. We also derive approximate analytical expressions for the spectral features and find that the multi-peak structure of the spectrum can be interpreted either via the eigenfrequencies of a generalized Floquet Hamiltonian or in terms of three-photon transitions between dressed states involving a probe field photon and a correlated photon pair from the squeezed vacuum field.

Optical bistability via squeezed vacuum input

We discuss the optical bistable behavior of a system of N Λ-type three-level atoms pumped by a coherent input field and coupled to a squeezed vacuum field by treating the optical bistability of such a system as an input-out problem. It is shown that bistability can be realized due to the squeezed vacuum input.

ATOMIC DIPOLE SQUEEZING AND COHERENT POPULATION TRAPPING IN THE SYSTEM OF TWO-MODE SQUEEZED VACUUM FIELD INTERACTING WITH A TWO-LEVEL ATOM

The atomic quantum behaviors in the system of two-mode squeezed vacuum field interacting with a two-level atom via two-photon process are studied by means of quantum theory.The condition for the occurrence of coherent trapping and the influence of the squeezing parameters on the atomic dipole squeezing are discussed.

Quantum trajectory theory for a two-level atom in a squeezed vacuum field with non-radiative dephasing

The quantum trajectory theory is employed to study the decay of a two-level atom in a partial as well as a pure squeezed vacuum with non-radiative dephasing. We show that ensemble averages taken over a large number of trajectories are in perfect agreement with theoretical results. We find that single trajectories, however, reveal interesting features, which are not accessible by the theoretical approach. Specifically, single trajectories for one of the polarization quadratures of the atom damped by classical (|M| = N) and quantum (|M| = N(N + 1)) squeezed vacua reveal mostly coherent evolution in the latter. Resulting from this, the decay rate of the polarization quadrature for the quantum squeezed vacuum is slower than that for the classical squeezed vacuum.

Quantum trajectory theory for a two-level atom in a squeezed vacuum field with non-radiative dephasing

Quantum trajectory theory for a two-level atom in a squeezed vacuum field with non-radiative dephasing

Interference pattern with a dark center in resonance fluorescence from two atoms driven by a squeezed vacuum field

We study the resonance fluorescence from two interacting atoms driven by a squeezed vacuum field and show that this system produces an interference pattern with a dark center. We discuss the role of the interatomic interactions in this process and find that the interference pattern results from an unequal population of the symmetric and antisymmetric states of the two-atom system. We also identify intrinsically nonclassical effects versus classical squeezed field effects.

Resonance fluorescence spectrum in a weak squeezed field with an arbitrary bandwidth

We analyze the linewidth narrowing in the fluorescence spectrum of a two-level atom driven by a squeezed vacuum field of a finite bandwidth. It is found that the fluorescence spectrum in a low-intensity squeezed field can exhibit a (omega - omega(0))(-6) frequency dependence in the wings. We show that this fast fall-off behavior is intimately related to the properties of a narrow-bandwidth squeezed field and does not extend into the region of broadband excitation. We apply the Linear response model and find that the narrowing results from a convolution of the atom response with the spectrum of the incident field. On the experimental side, we emphasize that the linewidth narrowing is not sensitive to the solid angle of the squeezed modes coupled to the atom. We also compare the fluorescence spectrum with the quadrature-noise spectrum and find that the fluorescence spectrum for an off-resonance excitation does not reveal the noise spectrum. We show that this difference arises from the competing three-photon scattering processes. [S1050-2947(98)04308-X].

Aharonov-Bohm-Type Electron Interference in a Two-Mode Squeezed Vacuum Field

Electron interference related to Aharonov-Bohm effect in the presence of the two-mode quantized radiation field is investigated. Characteristics of the temporal behavior of electron interference are discussed. It is shown that for the two-mode squeezed vacuum field the time evolution of the intensity of electron interference can exhibit very interesting periodic spontaneous collapse and revival (CR). In addition, the relation between CR and the quantum fluctuation in electron interference is also discussed.

The Partial Revival of the Quadrature Variance Product in the Dynamics of the Squeezed Vacuum Field in the Jaynes-Cummings Model

We consider the time evolution of a squeezed vacuum cavity field interacting with an initially excited two-level atom via the Jaynes-Cummings model in the Rotating Wave approximation. For large enough initial squeezing, we recognize a new partial revival phenomenon in terms of the quadrature variance product. We show the time evolution of the field quasiprobability Q-function, which provides a quadrature space picture of the partial revival phenomenon. An interpretation of the phenomenon in terms of a certain kind of first momentum of the photon distribution function is given.

Analytical solution for the Mollow and Autler-Townes probe absorption spectra of a three-level atom in a squeezed vacuum

The Mollow and Autler-Townes probe absorption spectra of a three-level atom in a cascade configuration with the lower transition coherently driven and also coupled to a narrow bandwidth squeezed-vacuum field are studied. Analytical studies of the modifications caused by the finite squeezed-vacuum bandwidth to the spectra are made for the case when the Rabi frequency of the driving field is much larger than the natural linewidth. The squeezed vacuum center frequency and the driving laser frequency are assumed equal. We show that the spectral features depend on the bandwidth of a squeezed vacuum field and whether the sources of the squeezing field are degenerate (DPA) or nondegenerate (NDPA) parametric amplifiers. In a broadband or narrow bandwidth squeezed vacuum generated by a NDPA, the central component of the Mollow spectrum can be significantly narrower than that in the normal vacuum. When the source of the squeezed vacuum is a DPA, the central feature is insensitive to squeezing. The Rabi sidebands, however, can be significantly narrowed only in the squeezed vacuum produced by the DPA. The two lines of the Autler-Townes absorption spectrum can be narrowed only in a narrow bandwidth squeezed vacuum, whereas they are independent of the phase and are always broadened in a broadband squeezed vacuum.

Index of refraction of a two-level atom in a squeezed vacuum field

We study the index of refraction of a two-level atom replacing the usually applied coherent driving fields by a squeezed vacuum field. This system can produce a large index of refraction accompanied by vanishing absorption when the carrier frequency of the squeezed vacuum is detuned from the atomic resonance.

Resonance fluorescence spectra of three-level atoms in a squeezed vacuum.

The fluorescence field from one of the two allowed transitions in a three level atom can sense squeezed fluctuations of a vacuum field coupled to the other transition. A study is made of fluorescence spectra of three-level atoms in lambda, vee and cascade configurations, strongly driven by two laser fields, both tuned to one photon resonance. Only one of the two one-photon transitions is coupled to a narrow-band squeezed vacuum field, the bandwidth being much smaller than the difference in the atomic transition frequencies, though much larger than atomic decay rates and Rabi frequencies of the driving fields. It is found that in all configurations the spectra consist of five lines, one central and two pairs of sidebands, with intensities and widths which are strongly influenced by the squeezed vacuum. However, only the central component and the outer sidebands exhibit a dependence on the squeezing phase. The spectral features are explained in terms of the dressed-atom model for the system. It is shown that the coherent mixing of the atomic states by the strong driving fields modifies transition rates between the dressed states resulting in the phase dependence of the spectral features.

Anomalous resonance fluorescence from an atom in a cavity with injected squeezed vacuum.

As a realistic system for observing the distinctive features of the interaction of squeezed light with atoms, we consider a single, coherently driven, two-level atom in a resonant optical cavity coupled to a broadband squeezed vacuum field. In the bad cavity limit we derive equations of motion for the atomic operators that are identical to those for the free-space situation, except for having modified parameters. We focus our attention on the resonance fluorescence from this system and show that, in the above limit, many of the unusual spectral features previously reported for the free atom situation persist. We also confirm the link between these anomalous spectra and the collapse of an atom into a pure state. The cavity parameter values needed to verify some of these interesting effects appear to be within the range of present day technology. \textcopyright{} 1996 The American Physical Society.

Two-photon excitation of three-level atoms in a squeezed vacuum

We have investigated the two-photon transition (6S 1/2→6P 3/2→6D 5/2) of trapped atomic Cesium for excitation by squeezed vacuum generated via non-degenerate (two-color) parametric clown conversion. The excitation rate exhibits a, non-quadratic dependence of aI 2 + bI on the incident photon flux ( I), reflecting the nonclassical correlations of the squeezed vacuum field.

Detailed balance and entropy for atoms in squeezed vacuum

It is shown that the principle of detailed balance is not obeyed in both systems of a single 2-level atom and the two-atom Dicke model interacting with a broad band squeezed vacuum field. Examination of the Boltzmann-Gibbs entropy shows that the stability of either system depends on the initial conditions. In particular, the two-atom system is unstable even for initially ground state condition, unlike the thermal field driven case.

Squeezed vacuum as an accelerator of revivals in the Dicke model

A two-level atom interacting with a single-mode squeezed vacuum cavity field does not manifest collapses and revivals of the oscillations [Milburn, Opt. Acta 31, 671 (1984)]. Here we show that the dynamic response of the inversion of an assemblage of A two-level atoms to such a field (Dicke model) may be qualitatively different. The dynamic properties of the model with an initial squeezed vacuum field differ from those for coherent or thermal fields, which have been stressed in the title.