Noise Squeezing Research Articles

Quantum interference of spontaneous decays: noise reduction in V lasers without inversion

For a four-level double-V laser without inversion we show that the interference of spontaneous decays leads to intensity noise squeezing. The optimum amount of noise reduction is 50%, which is the maximum squeezing in a resonant three-level inversionless Λ-laser with coherent driving and a resonant three-level Raman laser. By transforming into a combination state basis, the Mandel parameter and the output fluctuation spectrum are calculated and the mechanism is interpreted.

PHOTON NOISE SQUEEZING AND ITS PHYSICAL MECHANISM OF A DRIVEN V-TYPE THREE-LEVEL LASER

Photon noise squeezing and its physical mechanism of a driven V-type three-level laser are investigated via Scully-Lamb theory.It is shown that intracavity squeezing of 10% and extracavity squeezing of 20% can be achieved.Even if the amount of squeezing in V system is smaller than that in Λ system (intracavity squeezing and extracavity squeezing of up to 50%),both systems have the same mechanism responsible for the squeezing of photon noise.

Noise squeezing in a semiconductor laser with an inhomogeneously broadened gain line

This paper is a theoretical analysis of the noise produced by a single-mode semiconductor laser. We allow for spectral hole-burning in the gain line and for the nonlinear dependence of the carrier spontaneous recombination rate on the number of carriers in the active area. We show that these processes do not inhibit the squeezing of the outgoing photon flux noise below the shot noise level at high pump currents but that the degree of squeezing decreases considerably. Finally, we establish that these processes also considerably narrow the squeezing bandwidth.

Semiclassical model of semiconductor laser noise and amplitude noise squeezing. II. Application to complex laser structures

For pt.I see ibid., vol.33, no.11, p.2097-2104 (1997). We present noise studies of distributed feedback (DFB) laser structures, where spatial hole burning (SHB) plays a key role performed using the model described in part I of this paper with particular emphasis on the influence of SHB, on the coupling coefficient /spl kappa/L, and on the laser facet reflectivities. These structures exhibit high amplitude noise and the possible noise reduction is strongly reduced compared to Fabry-Perot structures. Distributed Bragg reflector (DBR) lasers are better candidates even if their performances are also strictly determined by SHB and the loss in the Bragg reflector. Finally, limitations due to gain suppression are demonstrated for such complex lasers structures. We conclude on the optimum laser structure for amplitude squeezed states generation.

Semiclassical model of semiconductor laser noise and amplitude noise squeezing. I. Description and application to Fabry-Perot laser

A semiclassical model of semiconductor laser noise, based on the Green's function method, is used to derive analytical formulas for the amplitude and frequency noise spectra taking into account incoming vacuum fluctuations and noise due to internal loss. This formalism also takes into account phenomena such as gain suppression as well as spatial hole burning (SHB). The amplitude noise squeezing is studied for Fabry-Perot structures pointing out the influence of the laser structural parameters. A complete agreement with already existing quantum mechanical models is found. However, extension of the model to SHB induces limitations in the squeezing performances, which are very important for more complex structures as will be pointed out in detail, in Part II.

Field dynamics, instabilities, and phase squeezing in the two-photon correlated-emission laser.

Both stationary and time-dependent regimes of operation, instabilities, and phase squeezing are investigated in the off-resonant two-photon correlated-spontaneous-emission laser by numerical calculation. Initial atomic coherence plays an essential role in lasing without population inversion, phase locking, and phase noise squeezing in the system. Under certain conditions, in the inverted and noninverted regimes alike, the output intensity exhibits bistable behaviors against the initial atomic coherence. Depending on the parameters, the whole or a portion of the upper or lower branch gives stable operations. In the inverted regime, even tristable behavior can be found in a narrow range of parameters. The field evolution and dynamics are studied. Furthermore, phase noise reduction near bistable areas is also investigated. In addition to the lower branch, where from previous studies, it has been known to exist, phase squeezing is also found on the upper branch both with and without population inversion, thus generating a bright source of phase noise squeezed light.

Noise squeezing and commutation relations in quantum-non-demolition quasistroboscopic schemes for coupled harmonic oscillators

Quantum-non-demolition measurement strategies have been studied for two coupled harmonic oscillators. An estimate for the squeezing factor in a quasistroboscopic measurement scheme has been obtained starting from the Heisenberg uncertainty principle and the commutation relation.

Raman noise and soliton squeezing

A model is constructed for the Raman effect as responsible for the self-frequency shift of solitons. The effect is related to and compared with the measured Raman gain in silica fibers. The model is quantized and includes the thermal and the quantum noise of the optical phonons generating the Raman effect. It is shown that the Raman effect causes excess noise for ultrashort pulses and limits the squeezing of subpicosecond solitons.

Multipump and quasistroboscopic back-action evasion measurements for resonant-bar gravitational-wave antennas.

A generalization of the back-action evasion (BAE) measurement technique, which we call {ital multipump} back-action evasion, has been demonstrated with a parametric electromechanical transducer similar to ones which are used on resonant-bar gravitational-wave detectors. The benefit of a BAE measurement is that the fluctuating back-action force of the transducer readout circuit acting on a test mass is squeezed, i.e., reduced in one of the quadrature phases of the test mass, thus improving the sensitivity for the detection of weak forces. The multipump BAE technique affords even greater noise squeezing than the BAE technique. Measured back-action noise squeezing factors are in quantitative agreement with the predictions of the model of a multipump BAE measurement. Using this system we have also demonstrated a quasistroboscopic position measurement which is a limiting case of a multipump back-action evasion measurement when the number of pumps becomes large. The multipump BAE technique may be used to further improve the sensitivity of resonant-bar gravitational-wave antennas.

Experimental observation of noise deamplification in a period-doubling laser

Noise deamplification has been demonstrated in a CO 2 laser with modulated losses when it is driven near period-doubling bifurcations. Noise squeezing of the quadrature component up to 8 dB has been obtained on the first ( T−2 T) bifurcation while the noise for the in-phase component is increased by 19 dB. A similar phase sensitive behaviour was also observed on the second (2 T−4 T) bifurcation. Critical exponents for the signal amplification of 2.71 and 2.93 respectively were also obtained near these period-doubling bifurcations.

Mechanical parametric amplification and thermomechanical noise squeezing.

A mechanical degenerate parametric amplifier has been devised which greatly increases the motional response of a microcantilever for small harmonic force excitations. The amplifier can improve force detection sensitivity for measurements dominated by sensor noise or backaction effects and can also produce mechanical squeezed states. In an initial squeezing demonstration, the thermal noise (Brownian motion) of the cantilever was reduced in one phase by 4.9 dB.

Effect of random noise on a mode-locked system.

We have experimentally added white noise to an analog Josephson-junction simulator in the mode-locked state. The Poincar\'e sections and power spectra of the analog simulator have been reconstructed from the resultant time-series data. A classical form of noise squeezing is observed. In addition, the power spectra associated with noisy motion about the subharmonic fixed points in the simulator's Poincar\'e section are found to be Lorentzian in shape. These observations are well accounted for by a theory of noisy mode-locked dynamics recently developed by Wiesenfeld and Satija.

Squeezing corrections to the Bloch equations

The general analysis of quantum noise shows that a squeezing noise can produce quadratic nonlinearities in the Langevin equations leading to the Bloch equations. These quadratic nonlinearities are governed by the imaginary part of the off-diagonal terms of the covariance of the noise (the squeezing terms) and imply a correction to the usual form of the Bloch equations. Here we study numerically the case of spin-one nuclei subjected to squeezing noises of particular type. We show that the corrections to the Bloch equations, suggested by the theory, to the behaviour of the macroscopic nuclear polarization in a scale of times of the order of the relaxation time can be quite substantial. In the equilibrium regime, even if the qualitative behaviour of the system is the same (exponential decay), the numerical equilibrium values predicted by the theory are consistently different from those predicted by the usual Bloch equation. We suggest that this difference might be used to test experimentally the observable effects of squeezing noises.

Observation of zero-point noise squeezing via a Josephson-parametric amplifier.

We have demonstrated (47\ifmmode\pm\else\textpm\fi{}8)% squeezing of vacuum-fluctuation noise using a Josephson-parametric amplifier operated at 19.16 GHz. The amplifier was operated at 30 mK and has a double-sideband noise temperature of 0.446 K. This is comparable to the vacuum noise floor h\ensuremath{\nu}/2k=0.460 K.