Berlin 2014 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 43: Quantum information: Concepts and methods II
Q 43.5: Talk
Thursday, March 20, 2014, 15:15–15:30, Kinosaal
Manipulating a qubit through the backaction of sequential partial measurements and real-time feedback — Cristian Bonato1, •Machiel Blok1, Matthew Markham2, Daniel Twitchen2, Viatcheslav Dobrovitski3, and Ronald Hanson1 — 1Kavli Institute of Nanoscience Delft, Delft University of Technology, PO Box 5046, 2600 GA Delft, The Netherlands — 2Element Six Ltd., Kings Ride Park, Ascot, Berkshire SL5 8BP, UK — 3Ames Laboratory and Iowa State University, Ames, Iowa 50011, USA
Quantum 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 theory. Therefore, quantum measurements can be exploited for manipulating quantum systems without the need for control fields. 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 readout. We vary the measurement strength to observe controlled wavefunction collapse and find post-selected quantum weak values. By combining a novel quantum non-demolition readout on the ancilla with real-time adaption 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 applications and are key to measurement-based quantum computing.