Kavan Modi, Monash University
The real culprit behind quantum advantages offered by quantum computation remains unknown. Entanglement and discord are potential candidates, but evidence remains circumstantial. On the metrology end, however, the situation is somewhat different. Quadratic quantum enhancement is known to be present independently of the entanglement resources ; quantum measurements, in presence of quantum correlations, lead to quadratic noise suppression ; and in some setups quantum Fisher information becomes a measure of quantum discord . We study quantum metrology with one pure qubit (and m fully mixed qubits)  and find a dramatic quantum enhancement that is classically unavailable. We connect this problem with DQC1 and prove a condition relating quantum discord with quantum enhancement. Finally we propose a Rydberg atom system to experimentally realise such a sensor.
- Quantum Correlations in Mixed-State Metrology. K. Modi, H. Cable, M. Williamson, V. Vedral. Phys. Rev. X 1, 021022 (2011)
- Coherent measurements in quantum metrology. K. Micadei, D. Rowlands, F. Pollock, L. C. Céleri, R. M. Serra, K. Modi. New J. Phys. 17, 023057 (2015)
- Quantum discord determines the interferometric power of quantum states. D Girolami et al. Phys. Rev. Lett. 112, 210401 (2014)
- Power of One Bit of Quantum Information in Quantum Metrology. H. Cable, M. Gu, K. Modi. Phys. Rev. A 93, 040304(R) (2016)
- Supersensitive measurement using single-atom control of an atomic ensemble. C. MacCormick, S. Bergamini, C. Mansell, H. Cable, K. Modi. Phys. Rev. A 93, 023805 (2016)