Inherent Noise of Quantum-Mechanical Amplifiers

M. W. P. Strandberg

M. W. P. Strandberg

M. W. P. Strandberg

The noise figure or limiting sensitivity for both traveling-wave and resonant-cavity quantum-mechanical amplifiers, sensitive to one direction of propagation, is derived with spontaneous emission as the limiting noise. The concept of effective temperature is introduced as an analytical parameter; thus negative temperatures appear in a natural fashion. It is pointed out that the results of this calculation can be considered the solution to the problem of linear counting of coherent particles. In this case the least count is one and the signal-to-noise ratio (for constant photon flux) increases as the reciprocal of the band width. The limiting temperature sensitivity of properly designed quantum-mechanical amplifiers is given as $\frac{h\ensuremath{\nu}}{k}$ degrees because of the drastic difference between negative and positive temperatures.

Z. Y. Ou, Silvania F. Pereira, Harry J. Kimble

Quantum fluctuations in optical amplification are investigated with a nondegenerate optical parametric amplifier whose internal idler mode is coupled to a squeezed vacuum. Reductions of the inherent quantum noise of the amplifier are observed with a minimum noise level 0.7 dB below the usual noise level of the amplifier with its internal idler mode in a vacuum state. With a small coherent field as the signal input, the amplified output exhibits an improvement in signal-to-noise ratio of 0.5 dB for the case of a squeezed-vacuum as compared to a vacuum state for the amplifier's internal mode.

Dmitri A. Kouznetsov, Daniel Rohrlich

Z. Y. Ou, Silvania F. Pereira, Harry J. Kimble

Quantum fluctuations in a nondegenerate optical parametric amplifier (NOPA) are investigated experimentally with a squeezed state coupled into the internal idler mode of the NOPA. Reductions of the inherent quantum noise of the amplifier are observed with a minimum noise level 0.7 dB below the usual noise level of the amplifier with its idler mode in a vacuum state. With two correlated quantum fields as the amplifier's inputs and proper adjustment of the gain of the amplifier, it is shown that the amplifier's intrinsic quantum noise can be completely suppressed so that noise-free amplification is achieved. It is also shown that the NOPA, when coupled to either a squeezed state or a nonclassically correlated state, can realize quantum tapping of optical information.