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Quantum Electronics and Laser Science Conference

Repeated backaction evading measurements: demonstration of a noiseless optical bus

Juan Ariel Levenson, Kamel Bencheikh, Philippe Grangier, Olivier Lopez

Published Jun 7, 1996• 0 citations
OpenAlex

Abstract

Summary form only given. We report here repeated back action evading (BAE) experiments that clearly demonstrate all quantum nondemolition (QND) features for repeated measurements. An important feature is that each of the two BAE setups, based on pulsed type-II parametric amplifiers, also have performances that are the best achieved so far, and therefore make this demonstration more convincing. The conditional variance of the signal at the output of the first device measurement is given.

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Summary form only given. We report here repeated back action evading (BAE) experiments that clearly demonstrate all quantum nondemolition (QND) features for repeated measurements. An important feature is that each of the two BAE setups, based on pulsed type-II parametric amplifiers, also have performances that are the best achieved so far, and therefore make this demonstration more convincing. The conditional variance of the signal at the output of the first device measurement is given.
Repeated backaction evading measurements have been performed for the first time. The first backaction evading device prepares the field state while the second one measures it again. The conditional variance of the signal at the output of the first device given the measurement is 1.8 dB below the shot noise and the signal to noise ratio transfer coefficient is 1.34. The conditional variance of the final signal given the first device measurement is also 1.8 dB below the shot noise and the normalized correlation between the two meter outputs is 0.3. These figures are clearly in the quantum regime, and they constitute a full demonstration of the quantum nondemolition principle.
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.
Backaction evading (BAE) measurements are described for optical parametric amplification with polarization mixing. Quantum correlations between the ``signal'' and ``meter'' outputs from the BAE device lead to an observed photocurrent variance 30% (1.5 dB) below the signal shot-noise level and to an inferred variance 44% below the vacuum-state level for determination of the signal field given the meter reading. Together with its efficient information transfer, this BAE detector functions as a quantum optical tap and is suitable for implementing quantum nondemolition detection.
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 can engineer BAE measurements. Crucially, the QND interaction condition simultaneously ensures BAE measurements and promotes the coupling operator to a QND observable. This work provides a unified structural theory for enhancing precision in quantum metrology and sensing.