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arXiv:quant-ph/0104044 · Physical Review A

Conditional generation of sub-Poissonian light from two-mode squeezed vacuum via balanced homodyne detection on idler mode

Jaromı́r Fiurášek

Published Oct 16, 2001• 8 citations
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Abstract

A simple scheme for conditional generation of nonclassical light with sub-Poissonian photon-number statistics is proposed. The method utilizes entanglement of signal and idler modes in a two-mode squeezed vacuum state generated in an optical parametric amplifier. A quadrature component of the idler mode is measured in the balanced homodyne detector and the signal mode is accepted only if the absolute value of the measured idler quadrature lies inside a certain chosen interval of quadratures. It is shown that the conditionally generated state of the signal mode can exhibit reduction of photon-number fluctuations below the coherent-state level.

DOI
10.1103/physreva.64.053817

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Summary form only given. The squeezing of an optical field is normally observed in the frequency domain using balanced homodyne detection to measure the fluctuation variance of a selected quadrature amplitude. The scheme amounts to a measurement of sub-Poissonian photon statistics and is sensitive to efficiencies as any such unconditional measurement is. Conditional measurements are independent of efficiencies. We propose a conditional homodyne detection scheme for observing the amplitude fluctuations of squeezed light. The central idea is to sample the photocurrent by triggering on a photon count and hence realize an efficiency independent measurement that resolves the quantum fluctuations in time. Our scheme directly measures the correlation function.
We report the first experimental demonstration of conditional preparation of a nonclassical state of light in the continuous variable regime. Starting from a nondegenerate optical parametric oscillator which generates above threshold quantum intensity correlated signal and idler "twin beams," we keep the recorded values of the signal intensity only when the idler intensity falls inside a band narrower than its standard deviation. By this very simple technique, we generate a sub-Poissonian state 4.4 dB (64%) below shot noise from twin beams exhibiting 7.5 dB (82%) of noise reduction in the intensity difference.
We show that a continuous range of nonclassical states of light can be generated using conditional measurements on the idler mode of an optical parametric amplifier. The output state is prepared by introducing a coherent state in the signal mode of the amplifier with a single photon in the idler mode, followed by a conditional measurement of a single photon in the output idler mode. By varying the gain of the amplifier, this approach can produce a coherent state, a photon-added state, a displaced number state, or a continuous range of other nonclassical states with intermediate properties. We note that this approach can generate a photon-added state even though the postselected amplifier does not add any photons to the signal or idler modes. The ability to generate a continuous range of nonclassical states may have practical applications in quantum information processing.
We introduce a method for the conditional generation of nonclassical states of light in a cavity. We consider two-level atoms traveling along the transverse direction to the cavity axis and show that by conditioning on one of the output measurements nonclassical field states are generated. The two-level atoms are prepared in the ground state and we conditioned them on the events in which they are also detected in the ground state. Nonclassical properties of the cavity mode are identified and characterized. This includes quadrature squeezing, sub-Poissonian photon-number distributions, and negative Wigner functions. We determine the optimal parameter regions where the corresponding nonclassical features are most distinct.
We analyze an intensity feedforward scheme to produce a sub-Poissonian (amplitude-squeezed) light beam from the intensity-correlated twin beams generated by a nondegenerate parametric amplifier. Photon-number measurement of the idler beam at the output of the parametric amplifier is linearly fed forward onto the output signal beam using an amplitude modulator. The minimum available Fano factor is shown to be 1/(2g-1), where g is the parametric amplifier gain, and is equal to the nonclassical intensity-noise-reduction factor of the twin beams at the output of the parametric amplifier. By changing the frequency of the input-signal beam, tunable sub-Poissonian light can be generated with this scheme for application in precision absorption spectroscopy.
A scheme for conditional generating Hermite polynomial excited squeezed vacuum states (HPESVS) is proposed. Injecting a two-mode squeezed vacuum state (TMSVS) into a beam splitter (BS) and counting the photons in one of the output channels, the conditional state in the other output channel is just a HPESVS. To exhibit a number of nonclassical effects and non-Gaussianity, we mainly investigate the photon number distribution, sub-Poissonian distribution, quadrature component distribution, and Wigner function of the conditional HPESVS. We find that its nonclassicality closely relates to the control parameter of the BS, the squeezed parameter of TMSVS, and the photon number of conditional measurement. These further demonstrate that performing the conditional measurement on a BS is an effective approach to generate non-Gaussian state.