A detection limit of 10 dB below the quantum limit is experimentally demonstrated for a mode-locked-laser-based quantum non-demolition measurement scheme. The scheme is completely collinear and exhibits a large read-out sensitivity.
Abstract Quantum non-demolition measurements are designed to circumvent the limitations imposed by Heisenberg's uncertainty principle when performing repeated measurements of quantum states. Recent progress in quantum optics has enabled the experimental realization of quantum non-demolition measurements of the photon flux of a light beam. This achievement bears on fundamental issues about the ultimate sensitivity of measurements, and may open the way for applications such as noise-free information tapping in optical telecommunications.
We show that the accuracy of atomic interferometry can be improved by using QND measurements of the atomic populations at the inputs to the interferometer. The accuracy of such a scheme surpasses the standard quantum limit of phase measurement δϕ SQL = 1/√ N and could reach the Heisenberg limit δϕ ∼ 1/ N . We propose to perform QND measurements of atomic populations with an off-resonant laser field. The conditions necessary for this kind of QND measurement could be fulfilled in a variety of ways with current experimental techniques, including magneto-optical traps and atomic cells.
According to Heisenberg’s uncertainty principle, measurement of a quantum observable introduces noise to this observable and thus limits the available precision of measurement. Quantum non-demolition measurements are designed to circumvent this limitation and have been demonstrated in detecting the photon flux of classical light beam. Quantum non-demolition measurement of a single photon is the ultimate goal because it is of great interest in fundamental physics and also a powerful tool for applications in quantum information processing. This chapter presents a brief introduction of the history and a review of the progress in quantum non-demolition measurement of light. In particular, a detailed description is presented for two works toward cavity-free schemes of quantum non-demolition measurement of single photons. Afterward, an outlook of the future in this direction is given.
We present a review of the criteria developped to characterize the efficiency of quantum non-demolition measurement devices for travelling electromagnetic waves. These criteria describe respectively the quality of the measurement, the non-destruction of the signal, and the quantum correlations between the meter read-out and the signal output. Quantitative limits can be defined with respect to these criteria, delimiting classicad and quantum domains of operation. Moreover, some questions related to the gain on the signal channel, and to repeated QND measurements, will be also discussed.