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Journal of Modern Optics

Asymmetric Light and Multiphoton Processes

József Janszky, Yu. Ya. Yushin

Published Jul 1, 1989• 3 citations
Publisher

Abstract

In a previous paper it was found that the squeezed vacuum light is (2n−1)!!-fold more efficient in an n-photon process than coherent light of the same intensity. It is shown here that this is true not only for the squeezed vacuum but also for light with more complicated statistics if the variances of the quadratures used in describing squeezing are sufficiently different, even in the case when both variances are above the vacuum noise level. It is found that such light can be generated more easily than the squeezed light. It is also shown that, in contrast to squeezing, this high efficiency is not destroyed by a usual linear amplifier even during very strong amplification.

DOI
10.1080/09500348914551041

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In a previous paper it was found that the squeezed vacuum light is (2n−1)!!-fold more efficient in an n-photon process than coherent light of the same intensity. It is shown here that this is true not only for the squeezed vacuum but also for light with more complicated statistics if the variances of the quadratures used in describing squeezing are sufficiently different, even in the case when both variances are above the vacuum noise level. It is found that such light can be generated more easily than the squeezed light. It is also shown that, in contrast to squeezing, this high efficiency is not destroyed by a usual linear amplifier even during very strong amplification.
The principal problem of light amplifiers is to find a means to amplify a coherent amplitude without decreasing the SNR. Consider a signal with amplitude squeezed quantum fluctuations, that is, less noise in the amplitude quadrature than the phase quadrature. The objective is to find a phase sensitive amplifier, which, while amplifying the coherent amplitude, adds quantum noise preferentially to the phase quadrature. We take as a concrete model for the amplifier an intracavity parametric amplifier. We go beyond the usual linear analysis and include the nonlinear regime where pump depletion is important. We find that in the linear region the quantum noise added by the amplification process may be reduced by squeezing the idler mode, while in the nonlinear regime the quantum fluctuations from the pump become more important. These results are of direct application to practical light amplifiers.
High-quality squeezed light is an important resource for a variety of applications. Multiple methods for generating squeezed light are known, having been demonstrated theoretically and experimentally. However, the effectiveness of these methods—in particular, the inherent limitations to the signals that can be produced—has received little consideration. Here we present a comparative theoretical analysis for generating a highly displaced squeezed light from a linear optical method—a beamsplitter mixing a squeezed vacuum and a strong coherent state—and well-studied parametric amplification methods including an optical parametric oscillator, an optical parametric amplifier, and a dissipative optomechanical squeezer seeded with coherent states. We show that the quality of highly displaced squeezed states that can be generated using these methods is limited on a fundamental level by the physical mechanism utilized; across all methods there are significant trade-offs between displacement, squeezing, and overall uncertainty. We explore the nature and extent of these trade-offs specific to each mechanism and identify the optimal operation modes for each. Finally, we identify the conditions for minimum-uncertainty squeezing in arbitrary parametric amplifying systems and show that displacing the output signal will in general violate these conditions, adding noise and degrading squeezing.
The minimum resolvable signal in optical metrology and sensing applications is usually limited by the so-called standard quantum limit. One way to improve the signal-to-noise ratio is to use squeezed states of light. Squeezed light can be generated using different types of nonlinear interactions either in solid-state nonlinear crystals or in atomic systems. One way to generate squeezed light is to use a phase sensitive amplifier that will amplify one quadrature of the considered mode and deamplify the other one. We have recently shown that metastable helium vapor at room temperature can exhibit strong four-wave mixing effects and behave like a perfect phase sensitive amplifier when it is prepared in coherent population trapping situation. In this talk, we will present the application of this phase sensitive amplification to the generation of squeezed vacuum states of light and detail the performances and limitations of the system
In this paper, we investigated the steady-state analysis of the squeezing and statistical properties of the light generated by N two-level atoms available in a closed cavity pumped by a coherent light with the cavity coupled to a singele mode vacuum reservoir. Here we consider the noise operators associated with the vacuum reservoir in normal order. Applying the solutions of the equations of evolution for the expectation values of the atomic operators and the quantum Langavin equations for the cavity mode operators, we obtain the mean photon number, the photon number variance, and the quadrature squeezing. The three-level laser generates squeezed light under certain conditions, with maximum global squeezing being 43%. Moreover, we found that the maximum local quadrature squeezing is 80:2% (and occurs at λ = 0:08). Furthermore, our results have shown that the local quadrature squeezing, unlike the local mean of the phonon number and photon number variance does not increase as the value of λ increases. It is also found that, unlike the mean photon number, the variance of the photon number, and the quadrature variance, the quadrature squeezing does not depend on the number of atoms. This implies that the quadrature squeezing of the two-mode cavity light is independent of the number of photons.
Multi-photon processes are extremely important in optics. Optical harmonics generation, multi-photon absorption, ionization, polymerization or spectroscopy are widely used in practical applications. The efficiency of these processes depends on many factors, one of them being the statistics of the incident light. Indeed, the rate of an n-photon effect scales as the nth-order autocorrelation function g(n)of the incident light [1]. Therefore light sources with high correlation functions can enhance the efficiency of such effects by several orders in magnitude compared to coherent light with the same wavelength, pulse duration and energy per pulse. Here we demonstrate this enhancement in the generation of optical harmonics from bright squeezed vacuum (BSV), which can have thermal (g(n)=n!) or superbunched (g(n)=(2n-1)!!) statistics depending on the spectral filtering [2].
A squeezed state of light is usually taken to mean a state in which the fluctuations of one of the quadratures are below the level associated with a coherent or vacuum state. These squeezed fluctuations are phase sensitive in the sense that they vary periodically as the field evolves, but the relationship between squeezing and phase fluctuations is not trivial. While squeezed states can exhibit an arbitrarily low level of phase fluctuations, the phase states, which are eigenstates of the Hermitian optical phase operator are not themselves quadrature squeezed. A phasesqueezed state is one with a lower level of phase fluctuations than a coherent state with the same mean photon number. Phase squeezing is fundamentally different from quadrature squeezing in much the same way that sub-Poissonian photon statistics is different. For this reason optimally squeezed states and states with minimum phase noise will be distinct. We derive the form of the states which minimum phase noise for a given intensity. These have an Airy function behavior for the photon number probability distribution. These phase squeezed states have a far better phase resolution than coherent states of similar intensity, but do not seem to offer a significant reduction of phase fluctuations compared with conventional squeezed states.