Scientists from the FOM Foundation and Delft University of Technology have manipulated a quantum particle, merely by looking at it in a smart way. By adjusting the strength of their measurement according to earlier measurement outcomes, they managed to steer the particle towards a desired state. The scientists published their results online on 16 February 2014 in Nature Physics.

AbstractQuantum measurements not only extract information from a system but also alter its state. Although the outcome of the measurement is probabilistic, the backaction imparted on the measured system is accurately described by quantum theory1, 2, 3. Therefore, quantum measurements can be exploited for manipulating quantum systems without the need for control fields4, 5, 6. We demonstrate measurement-only state manipulation on a nuclear spin qubit in diamond by adaptive partial measurements. We implement the partial measurement via tunable correlation with an electron ancilla qubit and subsequent ancilla readout7, 8. We vary the measurement strength to observe controlled wavefunction collapse and find post-selected quantum weak values8, 9, 10. By combining a novel quantum non-demolition readout on the ancilla with real-time adaptation of the measurement strength we realize steering of the nuclear spin to a target state by measurements alone. Besides being of fundamental interest, adaptive measurements can improve metrology applications11, 12, 13 and are key to measurement-based quantum computing14, 15. – Manipulating a qubit through the backaction of sequential partial measurements and real-time feedback, M.S. Blok, C. Bonato, M.L. Markham, D.J. Twitchen, V.V. Dobrovitski, R. Hanson, Nature Physics. DOI: 10.1038/nphys2881

How does this relate to the quantum Zeno effect? Readers?

*Hat tip:* Daniel Quinones