Quantum Nondemolition Measurements

TLDR

Some future gravitational‑wave antennas will be ~100‑kg cylinders whose end‑to‑end vibrations must be measured with 10^(-19) cm precision so that they behave quantum mechanically, and the vibration amplitude must be measured repeatedly without perturbation (quantum nondemolition measurement). The article aims to describe the new electronic techniques required for quantum nondemolition measurements. It develops the theory underlying these techniques. Quantum nondemolition measurements may find application elsewhere in science and technology.

Abstract

Some future gravitational-wave antennas will be cylinders of mass approximately 100 kilograms, whose end-to-end vibrations must be measured so accurately (10(-19) centimeter) that they behave quantum mechanically. Moreover, the vibration amplitude must be measured over and over again without perturbing it (quantum nondemolition measurement). This contrasts with quantum chemistry, quantum optics, or atomic, nuclear, and elementary particle physics, where one usually makes measurements on an ensemble of identical objects and does not care whether any single object is perturbed or destroyed by the measurement. This article describes the new electronic techniques required for quantum nondemolition measurements and the theory underlying them. Quantum nondemolition measurements may find application elsewhere in science and technology.