Amplitude squeezing in a semiconductor laser using quantum nondemolition measurement and negative feedback
A new scheme for generating an amplitude-squeezed state is proposed. The photon-flux fluctuation of a semiconductor-laser output wave is measured with a quantum nondemolition (QND) detector, and is negatively fed back to the laser pumping current. The operator Langevin equations are derived by combining the quantum-mechanical analyses on the laser internal-external field fluctuations, the quantum nondemolition detector based on an optical Kerr effect, and a negative-feedback circuit. The output wave features a reduced photon number noise below the standard quantum limit, <(..delta..n)/sup 2/><, and an enhanced phase noise above that, <(..delta..psi-circumflex)/sup 2/>>(1/4)/sup -1/, while the minimum uncertainty product is still preserved. The observed photoelectron statistics in a negative-feedback GaAs laser diode using a conventional p-i-n photodiode (not a QND detector) are shown to exhibit sub-Poissonian statistics with the variance <(..delta..n)/sup 2/>apeq20.26. The measured photocurrent fluctuation spectral density is also indicated to be below the standard quantum limit by a factor of 0.2 ( = -7 dB). The experimental results also confirm that such amplitude squeezing is only observed inside the feedback loop and cannot be extracted from the loop unless a quantum nondemolition detector is used.
- Research Organization:
- Musashino Electrical Communication Laboratories, Nippon Telegraph and Telephone Corporation, Musashino-shi, Tokyo 180, Japan
- OSTI ID:
- 6009939
- Journal Information:
- Phys. Rev. A; (United States), Vol. 33:5
- Country of Publication:
- United States
- Language:
- English
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