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Physical Review Letters

Quantum Nondemolition Measurements Improved by a Squeezed Meter Input

Robert Bruckmeier, Klaus Schneider, Stephan Schiller, J. Mlynek

Published Feb 17, 1997• 35 citations
Publisher

Abstract

Continuous quantum nondemolition (QND) measurements of the amplitude quadrature of a 1064 nm wave are performed with a monolithic dual-port degenerate optical parametric amplifier (OPA). The quality of the measurement is limited in part by the quantum fluctuations carried by the vacuum meter input wave. Improved QND measurements are realized by injecting 3.4 dB amplitude-squeezed light into the meter input port of the OPA. This achieves increased squeezing and correlation of the output signal and meter waves, and both improved operation as a quantum optical tap and as a quantum state preparator. The all-solid-state system was operated for 5 h with high stability.

DOI
10.1103/physrevlett.78.1243

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Continuous quantum nondemolition (QND) measurements of the amplitude quadrature of a 1064 nm wave are performed with a monolithic dual-port degenerate optical parametric amplifier (OPA). The quality of the measurement is limited in part by the quantum fluctuations carried by the vacuum meter input wave. Improved QND measurements are realized by injecting 3.4 dB amplitude-squeezed light into the meter input port of the OPA. This achieves increased squeezing and correlation of the output signal and meter waves, and both improved operation as a quantum optical tap and as a quantum state preparator. The all-solid-state system was operated for 5 h with high stability.
A novel scheme for continuous-wave quantum nondemolition (QND) detection of optical-amplitude quadratures is implemented using a degenerate optical parametric amplifier. A monolithic ring resonator with optimizable frustrated total internal reflection coupling is used. Signal and meter output beams are squeezed by 0.5 dB and 2.2 dB, and 38% correlated. This implies the first realization of individually squeezed twin beams, as well as quantum state preparation ability for both output beams. A quantum optical tap efficiency T s + T m = 1.08 is achieved. The all-solid-state system was completely stabilized and continuously operated as a QND device for up to 36 hours.
Summary form only given. Quantum nondemolition (QND) measurements seek to measure a quantum mechanical observable precisely without disturbing the observable itself and its time evolution. They are of great importance in precision metrology and information processing at the quantum level. In this work, a new QND scheme for optical continuous-wave measurements of quadrature observables using a degenerate, type-I phasematched, dual port, optical parametric amplifier (OPA), is implemented. We employ a low-loss monolithic MgO:LiNbO/sub 3/ ring resonator.
Optical quantum nondemolition measurements are performed using a beamsplitter with a nonclassical meter input and a electro-optic feedforward loop. The nonclassical meter input is provided by a stable 4.5 dB amplitude squeezed source generated by an optical parametric amplifier. We show that the implementation of a feedforward loop gives a substantial improvement in the signal transfer efficiency. With a 92% reflective beamsplitter we measure a transfer coefficient of Ts+m = 1.81. The quantum state preparation ability of our system is evaluated using two-dimensional correlation plots. This technique allows the direct visualization of the quantum correlations between the outputs of the QND system.
Methods for the enhancement of optical quantum nondemolition (QND) measurements are discussed. We review the use of meter squeezing as a QND enhancement tool and present a method of QND enhancement using an electro-optic feed-forward amplifier. By applying a linearized theory it is shown that these techniques work very well together. The combined effect of these enhancement methods is modeled for two QND systems, a squeezed light beam splitter and an optical parametric amplifier. We also discuss the conflict between the normal QND criteria and QND systems that involve noiseless amplification. We use an additional parameter to quantify the problem. A method for correcting the effects of noiseless amplification is discussed and modeled. We also discuss a special case of QND that eliminates the optical interaction between the meter and signal input beams. This system is shown to be a very effective QND device.