Bonato, Cristian

Tuesday Nov 5, 2013
Time: 14:00
Place: ETH Science City, HPF G 6
Host: Atac Imamoglu

Manipulating a spin qubit by the backaction of sequential adaptive partial measurements

Cristian Bonato
Kavli Institute of Nanoscience, Delft University of Technology

In contrast to classical physics, quantum measurements foster an intriguing interplay between information gain and system disturbance. Although the outcome of the measurement is probabilistic, the back-action imparted on the measured system is accurately described by quantum theory, given the measurement outcome. Therefore, quantum measurements can be used to manipulate a quantum system without the need for control fields. 

In this seminar, I will report on the realization of qubit manipulation using sequential partial measurements with real-time feedback on a nuclear spin qubit in diamond. We control the measurement strength via tunable entanglement with an ancilla qubit (electron spin of a nitrogen-vacancy center). Using post-selection, controlled wavefunction collapse and quantum weak values (spin exceeding 10) are observed. By performing a quantum non-demolition readout on the ancilla qubit, we realize repetitive measurements without post-selection. By incorporating real-time feedback, we demonstrate measurement-only steering of a quantum system. Adaptive measurements are an essential building block for measurement-based quantum computing and enhanced-sensitivity quantum metrology.