The challenge of detecting gravitational radiation is creating a new chapter in quantum electronics: Quantum nondemolition measurements

Future gravitational wave antennas will be approximately 100 kilogram cylinders, whose end-to-end vibrations must be measured so accurately (10 to the -19th power centimeters) 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 measurements are usually made on an ensemble of identical objects, and care is not given to whether any single object is perturbed or destroyed by the measurement. Electronic techniques required for quantum nondemolition measurements are described as well as the theory underlying them.