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Annual Meeting Optical Society of America

Squeezing in three simple systems: degenerate parametric oscillation, intracavity frequency doubling, and optical bistability

H. J. Kimble, J. L. Hall

Published Jan 1, 1986• 1 citation
Publisher

Abstract

Squeezed states of light represent a manifestation of the nonclassical character of the electromagnetic field and hence are of great intrinsic interest in quantum optics. There are as well a number of applications in measurement science and optical communication associated with the possibility of sensitivity beyond the standard quan­tum limit. The experiments that we have undertaken attempt to explore the degree of achievable and detectable squeezing in three distinct physical systems. From a conceptual point of view each is in some sense ideal and should provide a large degree of squeezing. However, in practice each offers a potential set of advantages and disadvantages associated with technological constraints and with a lack of precise correspondence between experiment and existing theoretical models. The three experiments that we describe are as follows: (1) degenerate parametric oscillation in a doubly resonant cavity pumped by the frequency-doubled light from a Nd:YAG laser at 1.06 μm, (2) intracavity second harmonic generation in a doubly resonant cavity pumped at a fundamental wave­length of 515 nm with an Ar+ laser, and (3) optical bistability for a collection of two-level atoms within a high finesse interferometer of decay rate comparable to the inverse atomic lifetime.

DOI
10.1364/oam.1986.tua3

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Squeezed states of light represent a manifestation of the nonclassical character of the electromagnetic field and hence are of great intrinsic interest in quantum optics. There are as well a number of applications in measurement science and optical communication associated with the possibility of sensitivity beyond the standard quan­tum limit. The experiments that we have undertaken attempt to explore the degree of achievable and detectable squeezing in three distinct physical systems. From a conceptual point of view each is in some sense ideal and should provide a large degree of squeezing. However, in practice each offers a potential set of advantages and disadvantages associated with technological constraints and with a lack of precise correspondence between experiment and existing theoretical models. The three experiments that we describe are as follows: (1) degenerate parametric oscillation in a doubly resonant cavity pumped by the frequency-doubled light from a Nd:YAG laser at 1.06 μm, (2) intracavity second harmonic generation in a doubly resonant cavity pumped at a fundamental wave­length of 515 nm with an Ar+ laser, and (3) optical bistability for a collection of two-level atoms within a high finesse interferometer of decay rate comparable to the inverse atomic lifetime.
Squeezed states of the electromagnetic field are characterized by a reduction of fluctuations for one of two quadrature phase amplitudes below the level of fluctuations for the vacuum state. This reduction is a manifestly quantum or nonclassical feature which is of great interest in its own right but also potentially important for precision measurement with sensitivity beyond the shot-noise or vacuum-state limit. We describe three different experiments in which squeezed light has been generated in our laboratory involving parametric downconversion, intracavity frequency doubling, and optical bistability with two-state atoms. By employing the squeezed light produced by a subthreshold optical parametric oscillator, we have achieved improvements in sensitivity beyond the vacuum-state limit for the detection of both phase and amplitude changes of the electromagnetic field. An alternate route to sensitivity beyond the vacuum-state limit is through quantum nondemolition measurement, where we have suggested and are implementing a scheme involving parametric conversion and polarization mixing.
We have generated squeezed states of light by the process of second harmonic conversion within an optical cavity resonant at both fundamental and harmonic frequencies. The experiment consists of a standing-wave cavity containing a crystal of lithium niobate doped with magnesium oxide and driven by the field from a frequency-stabilized Nd:YAG laser (incident power, ~10 mW). The total field reflected from the cavity illuminates a pair of high quantum efficiency photodiodes, whose individual photocurrents are summed. Observations of squeezing are made by analyzing the spectral density of fluctuations for this sum photo-current while the cavity detuning is scanned through resonance. An intensity regulator holds the reflected light intensity constant during the scan by control of the incident light level. Reductions in photocurrent fluctuations of 12% relative to the vacuum-state or shot-noise level are achieved for frequency offsets near 4 MHz. Since significantly higher degrees of squeezing are predicted by our theoretical analysis, we discuss those processes that currently limit the observed noise reduction, including phase noise produced by the intracavity crystal in the absence of nonlinear conversion.
We discuss different approaches to the generation of bright amplitude-squeezed light using second-order nonlinear effects in optical cavities. A 0.2 mW beam at 1064 nm exhibiting 4 dB squeezing has been generated using a phase-sensitive type-I parametric amplifier pumped by a frequency-doubled Nd:YAG laser. In applying frequency-doubling processes to the generation of amplitude-squeezed light, the appearance of parasitic parametric oscillation must be considered. This effect has been observed in a singly-resonant frequency doubler. We also describe recent developments in optical cavity design for doubly-resonant frequency-doubling. Finally, we show theoretically that phase-mismatched second-harmonic generation in an optical cavity can be employed to generate a strong effective Kerr nonlinearity. This system appears promising for achieving optical bistability and for generating squeezed light of high power. Keywords: Non-classical light, squeezed light, amplitude squeezing, nonlinear op...
Experiments to generate squeezed states of light are described for a collection of two-level atoms within a high-finesse cavity. The investigation is conducted in a regime for which the weak-field coupling of atoms to the cavity mode produces a splitting in the normal mode structure of the atom–field system that is large compared with the atomic linewidth. Reductions in photocurrent noise of 30% (−1.55 dB) below the noise level set by the vacuum state of the field are observed in a balanced homodyne detector. A degree of squeezing of approximately 50% is inferred for the field state in the absence of propagation and detection losses. The observed spectrum of squeezing extends over a very broad range of frequencies (~±75 MHz), with the frequency of best squeezing corresponding to an offset from the optical carrier given by the normal mode splitting.
We investigate, theoretically, the generation of bright and vacuum-squeezed light as well as entanglement in intracavity, type II, phase-matched second-harmonic generation. The cavity in which the crystal is embedded is resonant at the fundamental frequency but not at the second-harmonic frequency. A simple model for the process using semiclassical theory is derived, and quadrature-squeezing spectra of the involved fundamental fields are deduced. The analysis shows that vacuum squeezing reminiscent of subthreshold optical parametric oscillator squeezing is present and, in the ideal case, perfect. Under slight modifications of the operational conditions, the system is shown to produce efficient bright, squeezed light. Furthermore, we investigate the degree of polarization squeezing and find that three Stokes parameters can be squeezed simultaneously. Finally, we gauge the process for possible entanglement.