Vacuum Noise Research Articles

Absolute standardless calibration of photodetectors based on quantum two-photon fields

A new method of absolute calibration of photodetectors based on a nonclassical effect in nonlinear optics is discussed. The combined influence of a monochromatic flux of pump photons and quantum vacuum noise on a nonlinear crystal with no center of symmetry results in the appearance of rigorously correlated pairs of photons with continuous spectral distribution in the spontaneous parametric scattering of light (spontaneous parametric downconversion) process. The presence of an optical field in a broad spectral range created by the two-photon states (biphotons) makes it possible to develop a new method of measuring the spectral distribution of the absolute value of the quantum efficiency of photodetectors, both in photon counting and in analog regimes, that does not use any calibrated standard light sources (étalons). The feasibility of the method is demonstrated on different types of photomultiplier tube.

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.

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.

Characterization of Noise Generated by a Dry Pump by Using a Vane Vacuum Pump and Noise Reduction Methods

Characterization of Noise Generated by a Dry Pump by Using a Vane Vacuum Pump and Noise Reduction Methods

Asymmetric Light and Multiphoton Processes

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.

Effects of a squeezed vacuum on a laser exhibiting phase locking: An application to a laser with injected atomic coherence.

We study the steady-state operation and noise properties of a laser (or maser) exhibiting phase locking when an ordinary vacuum is replaced by a squeezed vacuum. Such a phase-sensitive laser can be realized by preparing the active medium initially in a coherent superposition of levels involved in the laser transition. We develop a general formalism to treat number-phase fluctuations and quadrature fluctuations. When applied to a one-photon laser with injected atomic coherence, we find that not only is a complete quenching of the (spontaneous-emission) quantum noise possible, but the field can actually be in a squeezed state. The variance in either amplitude or phase quadrature can be below the vacuum noise level by a factor of 2 (50%) at the expense of enhanced fluctuations in the other quadrature.

Squeezing the Vacuum in Atom-Field Interactions

We discuss the squeezing of vacuum fluctuations by resonant interaction with a suitably prepared atom. We demonstrate the crucial role of atomic dipole fluctuations in modifying the vacuum noise. We show how the generation of field squeezing in spontaneous and fluorescent processes is dependent on the squeezing of the atomic dipole.

Measurement of noise nonlinearity factor of vacuum noise diodes

Measurement of noise nonlinearity factor of vacuum noise diodes

Squeezed-state generation by the normal modes of a coupled system.

A new regime for the generation of squeezed states of the electromagnetic field is described for a collection of atoms within a high-finesse cavity. The process responsible for squeezing is a coupling-induced splitting in the normal-mode structure of the atom-field system. A theoretical analysis is presented that predicts large degrees of squeezing for modest operating conditions. An experimental investigation of this regime has produced noise reductions of 30% relative to the vacuum noise level.

Still More Squeezing of Optical Noise

Quantum optics experimenters have been pushing hard to generate greater “squeezing.” This drive was encouraged by last year's milestone demonstration at AT&T Bell Labs that the noise from an optical cavity had been measurably squeezed, that is, that the noise in one phase of the signal had been reduced below the level normally associated with quantum mechanical fluctuations in the vacuum field. Until then, that vacuum noise level had represented the fundamental quantum limit to precision in optical experiments. The Bell Labs experiment reduced the noise by 7–10% below this normal quantum limit (see PHYSICS TODAY, March 1986, page 17), and several experiments since then have achieved noise reductions of at least 20%. The most spectacular results to date have been obtained by a team at the University of Texas at Austin consisting of Ling-An Wu, Min Xiao, H. Jeffrey Kimble, John L. Hall (of the Joint Institute for Laboratory Astrophysics) and Huifa Wu, who have observed noise reductions to more than 60% below the normal level.

Four-mode squeezing.

The four-wave-mixing interactions produced by pumping at two well-separated frequencies can couple four different radiation modes to generate a new kind of squeezed state of light. A dual-frequency homodyne detection scheme is described and is used to observe this type of nonclassical correlation. Initial experimental results in an optical fiber show a noise level 20% below the vacuum noise level for the output of the dual-frequency detector, even though the noise at each individual detector remains above the vacuum level.

Generation of squeezed states by parametric down conversion.

Squeezed states of the electromagnetic field are generated by degenerate parametric down conversion in an optical cavity. Noise reductions greater than 50% relative to the vacuum noise level are observed in a balanced homodyne detector. A quantitative comparison with theory suggests that the observed squeezing results from a field that in the absence of linear attenuation would be squeezed by greater then tenfold.

Vacuum Noise and Stress Induced by Uniform Acceleration

This is a comprehensive account of a particular recent development concerning the thermal character inherent in the quantum field as viewed from a uniformly accelerated frame of reference. That is, the power spectrum of the vacuum noise (or the detector-response function) seen by a uniformly accelerated observer in flat spacetimes of arbitrary dimensions is investigated and is shown to exhibit the phenomenon of the apparent inversion of statistics in odd dimensions. Its relation to the thermalization theorem is clarified. Also discussed are the closely related phenomena occurring in the vacuum stress of the Rindler manifold and in the noise seen by a comoving observer in the de Sitter spacetime, as well as those associated with the circular motion in the flat spacetime.

Observation of squeezed states generated by four-wave mixing in an optical cavity.

Squeezed states of the electromagnetic field have been generated by nondegenerate four-wave mixing due to Na atoms in an optical cavity. The optical noise in the cavity, comprised of primarily vacuum fluctuations and a small component of spontaneous emission from the pumped Na atoms, is amplified in one quadrature of the optical field and deamplified in the other quadrature. These quadrature components are measured with a balanced homodyne detector. The total noise level in the deamplified quadrature drops below the vacuum noise level.

On the Response of a Rindler Particle Detector. III

We investigate the power spectrum of the vacuum noise of a free Dirac field seen by a uniformly accelerated observer in the Minkowski manifold of arbitrary dimension. When the field is massless, it is found to be of Fermi-Dirac type if the dimension of the manifold is even and to be Planckian otherwise. We then consider a simple model of a particle detector of the De Witt monopole type coupled to the Dirac field. When the detector is uniformly accelerated, its response is shown to be expressible in terms of the above power spectrum. These conclusions apply also to a comoving observer (or detector) in the de Sitter manifold if the field is in the conformal vacuum.