Response in violation of Bell inequality to imperfect photon addition and subtraction in noisy squeezed states of light

TL;DR

This paper studies how photon addition and subtraction affect Bell inequality violations in noisy two-mode squeezed states, revealing conditions where these operations enhance quantum correlations despite noise.

Contribution

It demonstrates that photon addition and subtraction can activate or enhance Bell inequality violations in noisy states, offering insights into quantum correlation robustness.

Findings

Photon subtraction can outperform addition at low squeezing and photon numbers.

Photon addition/subtraction can counteract noise effects, increasing Bell violation.

Violation decreases under noise but can be revived by photon operations.

Abstract

Violation of Bell inequality is a prominent detection method for quantum correlations present in composite quantum systems, both in finite and infinite dimensions. We investigate the consequence on the violation of local realism based on pseduospin operators when photons are added or subtracted in a single mode or in both the modes of the two-mode squeezed states of light in presence of noise. In the noiseless situation, we show that for addition (subtraction) of photons in a single mode, there is an overall enhancement in the maximal violation, although we observe an interplay between monotonicity and non-monotonicity in the violation of Bell inequality depending on the squeezing strength. Moreover, we report that for low squeezing or low number of photons added or subtracted, subtraction in both the modes can lead to higher violation of local realism than that in the case of addition. For any choice of parameters, such ordering is not seen if one compares their entanglement contents. In the event of a faulty twin-beam generator, we obtain a lower-than-expected squeezing in the state. In such a case, or in imperfect photon addition (subtraction), or under local noise, we find that the violation of local realism by the noise-affected two-mode squeezed states always decreases. Interestingly however, we notice that photon addition (subtraction) can in general help to conquer the ill-effects of noise by enhancing the violation of local realism or by transforming non-violating states to violating ones, thereby acting as an activating agent.