Quantum metrology with imperfect measurements

Abstract

The impact of measurement imperfections on quantum metrology protocols has not been approached in a systematic manner so far. In this work, we tackle this issue by generalising firstly the notion of quantum Fisher information to account for noisy detection, and propose tractable methods allowing for its approximate evaluation. We then show that in canonical scenarios involving N probes with local measurements undergoing readout noise, the optimal sensitivity depends crucially on the control operations allowed to counterbalance the measurement imperfections—with global control operations, the ideal sensitivity (e.g., the Heisenberg scaling) can always be recovered in the asymptotic N limit, while with local control operations the quantum-enhancement of sensitivity is constrained to a constant factor. We illustrate our findings with an example of NV-centre magnetometry, as well as schemes involving spin-1/2 probes with bit-flip errors affecting their two-outcome measurements, for which we find the input states and control unitary operations sufficient to attain the ultimate asymptotic precision.

Characterizing entanglement robustness of N-qubit W superposition state against particle loss from quantum Fisher information

“…The interaction between nearby perfect local operations is inevitable [57,58]. Therefore, in this section we investigate the entanglement robustness of N -qubit reduced WS state under interacting environment.…”

The compatibility dimension of quantum measurements

“…In this article, we shall describe noisy POVMs as emergent from a physical motivated model based on an indirect measurement process with an application to the compatibility of quantum measurements. The effect of noise has recently received attention for practical reasons, in noisy quantum computers or what is known as NISQ devices see [BCLK + 22,LLSK22], in quantum metrology [LGRK22], and in the compatibility of quantum measurements [DFK19].…”