Ultimate Limits of quantum metrology assisted by error correction and fast control

Ultimate Limits of quantum metrology assisted by error correction and fast control

Seminar author:Michalis Skotiniotis

Event date and time:11/24/2015 02:30:pm

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We consider ultimate limits on how precise a parameter, such as frequency or magnetic field strength, can be estimated in the presence of general noise.  We show that the usage of full quantum control, in particular of auxiliary systems and fast continuous quantum error correction, allows one to improve the achievable accuracy. When an overall Hamiltonian description is appropriate, we find that a quadratic improvement (Heisenberg scaling) is achievable for all kinds of noise except noise generated by the Hamiltonian to be estimated. For generic incoherent noise processes we show that despite full quantum control the possible improvement is limited to an overall constant factor over the standard quantum limit.  However, a significant improvement is still possible for limited resources. We introduce a simple experimentally accessible sequential scheme, making use of a single sensing system plus one auxiliary system, that outperforms entanglement-based schemes without error correction operating with a finite number of parallel systems.