Squeezing Of Noise Research Articles

Quantum noise and squeezing in an optical parametric oscillator with arbitrary output-mirror coupling.

We consider here the problem of quantum noise in light produced by an optical parametric oscillator operating below threshold inside a single-sided cavity. By employing the correct boundary conditions on quantum fields at the output mirror, a procedure that is valid for arbitrary mirror transmission, we derive exact expressions for quantum-noise reduction for arbitrary pump phase and output-mirror coupling. We find that for a given output-mirror power reflectance R, squeezing of quantum noise in the intracavity field increases to a final fractional value equal to R/(1+R) as the pump intensity is increased and the oscillation threshold is approached. The output field, on the other hand, exhibits perfect squeezing of noise in one quadrature of its central Fourier component at threshold regardless of the output-mirror coupling. The present approach, which is based on boundary conditions, is quite general and applicable to any matter-field interaction problem inside a cavity.

Vacuum noise squeezing at microwave frequencies using a Josephson parametric amplifier

Experiments on generating squeezed microwave radiation at 19.16 GHz using a Josephson parametric amplifier were performed. The source of the radiation was cooled by a dilution refrigerator down to the lowest temperature of 0.030 K. At this temperature, noise at the input port of the parametric amplifier consists almost entirely of the vacuum fluctuations with a noise temperature h nu /2k of 0.46 K. The authors observed the squeezing of the microwave noise by 47+or-8% as referred to the input of the Josephson parametric amplifier. The measured double-sideband noise temperature of the amplifier is 0.446 K, which is comparable to the vacuum noise level.

Vacuum-noise squeezing at microwave frequencies using Josephson-parametric amplifier

We have performed experiments on generating squeezed microwave radiation at 19.16 GHz using a Josephson-parametric amplifier. The cold termination at the input port and the amplifier were both cooled to 30 mK. At this temperature the equilibrium fluctuations coming from the cold termination consist of vacuum fluctuations with a noise temperature hv/2 K of 0.46 K. We have observed 47 ± 8% squeezing of this vacuum noise by the Josephson-parametric amplifier. The amplifier's double-sideband noise temperature 0.446 K is comparable to the vacuum noise level.

Three-photon squeezing: exploding solutions and possible experiments

In the frame of quantum optics the properties of a parametric amplifier of the third subharmonic, described by the Hamiltonian H 3 = iκ(a +3−a 3) 3 , are considered. The average output energy turns into infinity (explodes) at certain critical values of para meters even in the absence of feedback. The photon number distribution stays smooth at the explosion moment. The processes of squeezing of the quantum noise and of the photon bunching are discussed. The value of the parameter κ is estimated for a travelling wave amplifier.

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.

Role of pumping statistics in laser dynamics: Quantum Langevin approach.

We study in detail the influence of pumping statistics on the laser dynamics. We apply the technique of quantum Langevin operators and generalize the corresponding noise operators to incorporate the statistical properties of the pump mechanism. These equations are then used to derive expressions for the phase and intensity fluctuations of lasers with various pump statistics. We find that a reduction of pump noise can lead to a significant squeezing of the photon number noise below the shot-noise limit. This is in complete agreement with our previous analysis, which used a density-operator approach.

Multisqueezing of mechanical states and back-action evasion measurements.

A technique is proposed to improve the squeezing of the mechanical noise in a back-action evasion measurement. The scheme is based on the use of a parametric multipump system and, in the limit of many pump components, approaches a stroboscopic measurement. A simple model of the back-action evasion effect for this scheme is developed. Experimental evidence of a significant increase in the squeezing with respect to the two-pump scheme and in accordance with the model is reported.

Nonlinear theory of a two-photon correlated-spontaneous-emission laser: A coherently pumped two-level–two-photon laser

We develop a nonlinear theory of a two-photon correlated-spontaneous-emission laser (CEL) by using an effective interaction Hamiltonian for a two-level system coupled by a two-photon transition. Assuming that the active atoms are prepared initially in a coherent superposition of two atomic levels involved in the two-photon transition, we derive a master equation for the field-density operator by using our quantum theory for coherently pumped lasers. The steady-state properties of the two-photon CEL are studied by converting the field master equation into a Fokker-Planck equation for the antinormal-ordering Q representation of the field-density operator. Because of the injected atomic coherence, the drift and diffusion coefficients become phase sensitive. This leads to laser phase locking and an extra two-photon CEL gain. The laser field can build up from a vacuum in the no-population-inversion region, in contrast to an ordinary two-photon laser for which triggering is needed. We find an approximate steady-state solution of the Q representation for the laser field, which consists of two identical peaks of elliptical type. We calculate the phase variance and, for any given mean photon number, obtain the minimum variance in the phase quadrature as a function of the initial atomic variables. Squeezing of the quantum noise in the phase quadrature is found and it exhibits the following features: (1) it is possible only when the laser intensity is smaller than a certain value; (2) it becomes most significant for small mean photon number, which is achievable in the no-population-inversion region; and (3) a maximum of 50% squeezing can be asymptotically approached in the small laser intensity limit. As a by-product we also study the ordinary two-photon laser and find, e.g., photon-number variance and laser linewidth.

Bistability and other effects in a nonlinear fiber-optic ring resonator

Dispersive optical bistability with a threshold cw input power of approximately 10 mW has been observed in a single-mode fiber-optic ring resonator. Light is coupled in and out of the resonator by a single-mode-fiber variable directional coupler. A fiber-optic Faraday isolator is incorporated into the ring, thus increasing the threshold for stimulated Brillouin oscillation by a factor of 100 and permitting other weaker nonlinear effects such as bistability to be observed. Phase-sensitive amplification and deamplification (squeezing) of classical time-stationary noise is demonstrated and shown to be in agreement with the theory of squeezed-state generation in such a nonlinear fiber ring resonator. Light scattering by elastic eigenmodes of the fiber (guided-acoustic-wave Brillouin scattering, GAWBS) adds noise to light circulating in the resonator and obscures the observation of squeezed quantum fluctuations. The properties of this GAWBS scattering are investigated and compared with theory.

Quantum nondemolition measurements in systems with nonstationary squeezing of quantum noise

A Weber detector with optical readout system is considered. The measuring device consists of circulators, homodyne detector and two degenerate parametric amplifiers (or four wave mixers), modifying vacuum fluctuations of the load. In this scheme the greater the squeezing of backaction noise, the smaller the measurable force acting on the mechanical resonator. Postulation of gedanken state reduction is not necessary in our model.

Generation of squeezed states of light with a fiber-optic ring interferometer.

Forward nondegenerate four-wave mixing in an optical-fiber ring resonator is proposed as a method to generate squeezed states of light. The nonlinear interactions are analyzed both with a self-consistent propagation-equation technique and with Fokker-Planck equations in the Glauber-Sudarshan P representation. Excellent squeezing is predicted at modest input power levels, with perfect quantum-noise squeezing at the critical points for optical bistability. A method to suppress the stimulated Brillouin effect is proposed and demonstrated experimentally, and the effects of forward spontaneous guided acoustic wave Brillouin scattering inside the resonator are analyzed. Methods are suggested for minimizing this noise under conditions where squeezing can be detected. Experimental apparatus and procedures are outlined for verifying the predictions of our theory and demonstrating squeezing of classical and quantum noise.

Squeezing of classical noise by nondegenerate four-wave mixing in an optical fiber

Nondegenerate four-wave mixing in an optical fiber is shown to attenuate one quadrature of random sideband fluctuations created by external modulators. A theory of the nonlinear interaction that includes nonlinear dispersion fits the results. Analogous experiments on quantum noise inputs should prove successful.