Some thoughts on quantum non-demolition measurements in biological systems

E. Conte

Jian Cheng Yang, Paul G. Kwiat

We theoretically study photon-photon interactions mediated by a cavity-atom system in the strong-coupling regime of cavity quantum electrodynamics (QED), which may be harnessed for quantum non-demolition (QND) measurements.

ConteE.

Takeuchi, M, Ichihara, S, Kumakura, M +4 more

We report the development of a fast pulse polarimeter for the application to quantum non-demolition measurement of atomic spin (Spin QND). The developed system was tunable to the atomic resonance of ytterbium atom and has narrow laser linewidth suitable for spin QND. Using the developed polarimeter, we successfully demonstrated the measurement of the vacuum noise, with 10^6 to 10^7 photon number per pulse.

Zhiyuan Dong, Weichao Liang, Guofeng Zhang

We establish a framework for realizing back-action-evading (BAE) measurements and quantum non-demolition (QND) variables in linear quantum systems. The key condition, a purely imaginary Hamiltonian with a real or imaginary coupling operator, enables BAE measurements of conjugate observables. Symmetric coupling further yields QND variables. For non-compliant systems, coherent feedback is designed to engineer BAE measurements. Crucially, the QND interaction condition simultaneously ensures BAE measurements and promotes the coupling operator to a QND observable.

R. J. Sewell, Marco Koschorreck, M. Napolitano +3 more

We report the first demonstration of spin squeezing of a large-spin system via quantum non-demolition (QND) measurement. We observe 2 dB of metrological squeezing in an ensemble of ~ 106 laser cooled 87Rb atoms in the F = 1 hyperfine ground state.