Controlling the quantum motion of a levitated particle


The quantum trajectory of a silica particle trapped in an optical tweezer is measured and controlled in real time.

This is achieved by combining two techniques developed in the 60s for neural tissue imaging and space exploration and navigation: the confocal microscope and the Kalman filter.  A fiber based confocal detection scheme allows us to efficiently detect the light scattered by the particle trapped in ultra-high vacuum. The result is a continuous measurement of the position of the particle that is only 1.7 times above the Heisenberg limit. The outcome of this measurement is processed in real time by a Kalman filter, an optimal estimation algorithm that allows to reconstruct the evolution of the motional quantum state of the particle (its quantum trajectory) in real time with a purity of about 60%. Finally we use an optimal control algorithm that regulates an electric force that is applied to the particle cooling its motion, and reducing its energy to the quantum ground state, at excitation of only n=0.56 quanta. These results pave the way to full-scale control over the wavepacket dynamics of solid-state macroscopic quantum objects, and quantum limited massive inertial sensors.

Publication in Nature:
Real-time optimal quantum control of mechanical motion at room temperature
Lorenzo Magrini, Philipp Rosenzweig, Constanze Bach, Andreas Deutschmann-Olek, Sebastian G. Hofer, Sungkun Hong, Nikolai Kiesel, Andreas Kugi and Markus Aspelmeyer.
DOI: 10.1038/s41586-021-03602-3

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