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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Amplification of nonclassical states of light under triggered superradiance regime

Alexei A. Kalachev, Самарцев Виталий Владимирович

Published Apr 20, 2004• 0 citations
Publisher

Abstract

The possibility of amplification of pulses of squeezed light in the regime of triggered optical superradiance is analyzed. The kinetic equations are obtained which describe the dynamics of cooperative development of the population inversion and dispersion of the quadrature components of polarization of optical centers interacting with the triggering-pulse field in the squeezed vacuum state. The dependence of the squeezing degree of the superradiance field on the squeezing degrees of the triggering-pulse field and polarization of an amplifying medium is determined. It is shown that in the case of a sufficiently strong squeezing of the medium, the intensity of the squeezed quadrature component of the superradiance signal is lower than that of an incoherent spontaneous background. Therefore, the superradiance field can be characterized not only by a classical squeezing (when the dispersions of quadratures are not identical) but also by a quantum squeezing (when the dispersion of one quadrature is smaller than its vacuum value).

DOI
10.1117/12.562210

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The possibility of amplification of pulses of squeezed light in the regime of triggered optical superradiance is analyzed. The kinetic equations are obtained which describe the dynamics of cooperative development of the population inversion and dispersion of the quadrature components of polarization of optical centers interacting with the triggering-pulse field in the squeezed vacuum state. The dependence of the squeezing degree of the superradiance field on the squeezing degrees of the triggering-pulse field and polarization of an amplifying medium is determined. It is shown that in the case of a sufficiently strong squeezing of the medium, the intensity of the squeezed quadrature component of the superradiance signal is lower than that of an incoherent spontaneous background. Therefore, the superradiance field can be characterized not only by a classical squeezing (when the dispersions of quadratures are not identical) but also by a quantum squeezing (when the dispersion of one quadrature is smaller than its vacuum value).
The possibility of amplification of pulses of squeezed light in the regime of triggered optical superradiance is analysed. The kinetic equations are obtained which describe the dynamics of cooperative development of the population inversion and dispersion of the quadrature components of polarisation of optical centres interacting with the triggering-pulse field in the squeezed vacuum state. The dependence of the squeezing degree of the superradiance field on the squeezing degrees of the triggering-pulse field and polarisation of an amplifying medium is determined. It is shown that in the case of a sufficiently strong squeezing of the medium, the intensity of the squeezed quadrature component of the superradiance signal is lower than that of an incoherent spontaneous background. Therefore, the superradiance field can be characterised not only by a classical squeezing (when the dispersions of quadratures are not identical) but also by a quantum squeezing (when the dispersion of one quadrature is smaller than its vacuum value).
Multimode triggered optical superradiance due to a two-photon transition is theoretically studied. Kinetic equations are derived for the dynamics of cooperative development of coherence and population inversion of optical centers interacting with each other through a common field of emitted photons. Various regimes of triggering of optical superradiance due to a two-photon transition are considered. The possibility of creating a quantum photomultiplier on the basis of the triggered optical superradiance is discussed.
The possibility of generating light in a squeezed quantum state during saturated light amplification in a semiconductor amplifier is theoretically analyzed. Due to four-wave mixing process during amplification, weak components of the spontaneous emission of the medium with symmetric frequency shifts relative to the strong amplified wave acquire the quantum properties of two-mode squeezed light. The squeezing of quadrature components occurs in the range of frequency shifts of several GHz (∼\sim∼ the inverse relaxation time of the charge carrier density) and can reach 10 dB or more under optimal conditions. The formation of a two-mode squeezing phase facilitates the observation of the squeezing effect, in which a strong wave, playing the role of a local wave, exhibits quadrature noise suppression without additional homodyne detection.
Superradiance is an extensive cooperative spontaneous emission phenomenon, exhibited by some atomic collective-spin states. However, distinct initial states differ in their decay dynamics. Dicke states ∣j,m⟩|j,m\rangle∣j,m⟩ with distinct numbers of excitations n=m+jn=m+jn=m+j, driven by vacuum fluctuations, have their peak emission intensity shifted in time. Rotating Dicke states relative to the decay axis introduces an interesting parity structure that affects the pulse profile and photon correlations. Squeezed-bath prepared states undergo a squeezing-controlled crossover to the rotated Dicke states, making the emission character dependent on the amount of squeezing transferred from light to the atomic state. For semiclassical states with a macroscopic dipole moment, like the atomic coherent state, the emission intensity depends on their polarization. We present detailed results on the superradiant dynamics of a representative selection of states expanded in Dicke states to highlight the initial state as an independent dynamical control parameter. For large-NNN, we are able to predict fairly accurately the pulse profile in each case using the mean-field approximation, an approach based on the Fokker--Planck equation. We also present comparative results on the intensity correlation function, quantify the coherent and incoherent contributions of the emission, and contrast between small and large ensembles.
The behavior of a two-level atom confined within a cavity, pumped by an intense external field, and damped by a squeezed vacuum reservoir is studied. When the lowest squeezed quadrature of the vacuum is in phase with the pumping field, the relaxation time of the population inversion and of the polarization quadratures of the atom are appreciably enlarged, and hence the atom is decoupled from the reservoir. The effects of finite bandwidth of the squeezing are analyzed and it is shown that they can be used to improve the decoupling.
Nonclassical states of light are of increasing interest due to their applications in the emerging field of quantum information processing and communication. Squeezed light is such a state of the electromagnetic field in which the quantum noise properties are altered compared with those of coherent light. Squeezed light and squeezed vacuum states are potentially useful for quantum information protocols as well as optical measurements, where sensitivities can be limited by quantum noise. We experimentally study a source of squeezed vacuum resulting from the interaction of near-resonant light with both cold and hot Rb atoms via the nonlinear polarization self-rotation effect (PSR). We investigate the optimal conditions for noise reduction in the resulting squeezed states, reaching quadrature squeezing levels of up to 2.6 dB below shot noise, as well as observing noise reduction for a broad range of detection frequencies, from tens of kHz to several MHz. We use this source of squeezed vacuum at 795 nm to further study the noise properties of these states and how they are affected by resonant atomic interactions. This includes the use of a squeezed light probe to give a quantum enhancement to an optical magnetometer, as well as studying the propagation of squeezed vacuum in an atomic medium under conditions of electromagnetically induced transparency (EIT). We also investigate the propagation of pulses of quantum squeezed light through a dispersive atomic medium, where we examine the possibilities for quantum noise signals traveling at subluminal and superluminal velocities. The interaction of squeezed light with resonant atomic vapors finds various potential applications in both quantum measurements and continuous variable quantum memories.