Quantum Limited Amplification and Detection with a Non-Linear Cavity Detector

Catherine Laflamme, Aashish A. Clerk

C. Laflamme, Aashish A. Clerk

We consider the quantum measurement properties of a driven cavity with a Kerr-type nonlinearity that is used to amplify a dispersively coupled input signal. Focusing on an operating regime that is near a bifurcation point, we derive simple asymptotic expressions describing the cavity's noise and response. We show that the cavity's backaction and imprecision noise allow for quantum-limited linear amplification and position detection only if one is able to utilize the sizable correlations between these quantities. This is possible when one amplifies a nonresonant signal but is not possible in quantum nondemolition qubit detection. We also consider the possibility of using the nonlinear cavity's backaction for cooling a mechanical mode.

Julio I. Concha, H. Vincent Poor

Matteo Rosati

Non-linear effects are believed to reduce the communication rate in fiber networks, leading to the introduction of the non-linear Shannon (NLS) limit. Here, we analyze, for the first time to our knowledge, the effect of quantum detection techniques in amplified optical fibers affected by non-linearity, by computing their Holevo channel capacity. First, we report that the Holevo capacity under lumped Raman amplification (RA) can surpass the NLS capacity of a coherent-detection system with distributed Raman amplification (DRA) for a moderate number of spans. Then, we observe that the Holevo RA system offers a reduction of amplification power costs at a fixed communication rate, with respect to the DRA coherent-detection system. Our results rely on the ability of a quantum joint-detection receiver (JDR) to better extract information from low-power, low-noise signals, determining the type of amplifier that is best suited to work in conjunction with the JDR.

Michael Renger, Stefan Pogorzalek, Qiming Chen +6 more

Aashish A. Clerk, Michel Devoret, S. M. Girvin +2 more

The topic of quantum noise has become extremely timely due to the rise of quantum information physics and the resulting interchange of ideas between the condensed matter and atomic, molecular, optical--quantum optics communities. This review gives a pedagogical introduction to the physics of quantum noise and its connections to quantum measurement and quantum amplification. After introducing quantum noise spectra and methods for their detection, the basics of weak continuous measurements are described. Particular attention is given to the treatment of the standard quantum limit on linear amplifiers and position detectors within a general linear-response framework. This approach is shown how it relates to the standard Haus-Caves quantum limit for a bosonic amplifier known in quantum optics and its application to the case of electrical circuits is illustrated, including mesoscopic detectors and resonant cavity detectors.