Classical-Quantum Boundary and Metrology

Dr Kavan Modi

Monash Quantum Information Science Group, Monash University

The real culprits behind the advantages offered by quantum computation remain unknown. Entanglement, non-locality, discord, and coherence are all potential candidates, but evidence remains circumstantial. On the metrology (the science of precision measurements) end, however, the situation is somewhat different as there are several striking results that challenge the conventional view that 'entanglement is the answer to all of life mysteries' . I will discuss the results that show that the quadratic enhancements in quantum metrology is independent of the entanglement resources [1]; coherent measurements, in presence of quantum correlations, lead to quadratic noise suppression [2]; and in some setups quantum Fisher information (the figure or merit in metrology) becomes a measure of quantum discord [3]. Finally, I will discuss quantum metrology with one pure qubit (and m fully mixed qubits) [4] and show that there is a dramatic quantum enhancement. I will connect this problem with the computational model known as DQC1 and prove a condition relating quantum discord with quantum enhancement. Finally, I will discuss how such a sensor can be constructed using a Rydberg atom system [5].

1. Quantum correlations in mixed-state metrology. K. Modi, H. Cable, M. Williamson, V. Vedral. Phys. Rev. X 1, 021022 (2011)
2. 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)
3. Quantum discord determines the interferometric power of quantum states. D Girolami et al. Phys. Rev. Lett. 112, 210401 (2014)
4. Power of one bit of quantum information in quantum metrology. H. Cable, M. Gu, K. Modi. Phys. Rev. A 93, 040304(R) (2016)
5. 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)

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