George Vasilakis


Quantum back-action-evading measurement of motion in a negative mass reference frame



The knowledge an observer can obtain about an object is limited by the disturbance, known as back-action, introduced to the object from the quantum measurement. A textbook example is the continuous measurement of the position of an object which imposes a random quantum back-action perturbation on its momentum. This randomness translates with time into the position uncertainty, thus leading to the Heisenberg uncertainty on the measurement of motion.


However, precision beyond the Heisenberg limit in position and momentum can be realized if the measurement of motion is performed in a quantum frame with an effective negative mass. In such a measurement, the quantum back action is evaded due to the destructive interference of the back action on the object and on the reference frame. The reference frame can be implemented with an oscillator which has its first excited state energy below the ground state energy, as is the case for an atomic spin oscillator oriented along a static magnetic field.


In this talk I will report on an experiment where the motion of the oscillator is tracked in the reference frame of a spin oscillator by probing this hybrid quantum system with light. The mechanical oscillator is a macroscopic, millimeter size, cryogenically cooled membrane. The atomic oscillator is a long-lived collective spin of an atomic ensemble at room temperature. I will demonstrate the evasion of the quantum back-action of the measurement in the hybrid system and study the interference effects of the two oscillators. The system paves the way for entanglement between macroscopic objects and can find applications in force, gravitation and acceleration sensing beyond the standard quantum limit.

Date: 22/11/2017
Time:11:00 (coffee & cookies will be served at 00:00)
Place:FORTH Seminar Room 1