Quantum Seminar: Quantum physics with macroscopic objects
Prof. Eugene Simon Polzik, Professor of Physics, Niels Bohr Institute, University of Copenhagen
Decoherence and the non-commuting nature of quantum variables are among the main challenges on the way to complete control of macroscopic systems. For example, according to the textbook quantum mechanics, a measurement of the position of an object imposes a random quantum back action kick to its momentum. This randomness translates with time into position uncertainty, thus leading to the well known uncertainty on the measurement of motion. As a consequence, and in accordance with the Heisenberg uncertainty principle, this leads to the so-called standard quantum limit on the precision of sensing of position, force and fields. In addition, the rate at which information is extracted should be higher than the decoherence rate which typically grows with the size of the object. In this talk I will present the ideas and experimental results for measurement of motion of a mechanical oscillator with, in principle, unlimited precision. This is achieved by measuring the motion in a special reference frame with an effective negative mass and by creating an entangled state between the object and the reference frame. A necessary condition for success is the ultra-low decoherence rate of both systems. Applications to force sensing including gravitational wave detection will be discussed.