Imperfect measurements and conjugate observables

Claudio Carmeli, Teiko Heinosaari, Alessandro Toigo

We present a unified treatment of sequential measurements of two conjugate observables. Our approach is to derive a mathematical structure theorem for all the relevant covariant instruments. As a consequence of this result, we show that every Weyl–Heisenberg covariant observable can be implemented as a sequential measurement of two conjugate observables. This method is applicable both in finite- and infinite-dimensional Hilbert spaces, therefore covering sequential spin component measurements as well as position-momentum sequential measurements.

Li‐Gang Wang, M. Al-Amri, Muhammad Suhail Zubairy

In traditional Hanbury Brown--Twiss (HBT) schemes, thermal intensity-intensity correlations (IICs) are phase insensitive. Here we propose a modified HBT scheme with phase conjugation to demonstrate phase-sensitive and nonfactorizable features of thermal IIC speckles. It shows that the novel phase-sensitive features originate from the correlation between the original and phase-conjugated thermal light. Our numerical simulation confirms the possibility of experimental realization, even for the cases of the imperfect phase conjugation. Unlike two-photon speckles, our scheme uses thermal light sources, not the entangled two-photon sources. Our result provides deeper insight into thermal correlations and may lead to significant applications in imaging and speckle technologies.

K. Heyde, John L. Wood

G.M. D'Ariano, P. Lo Presti, M.F. Sacchi

S. Adarsh, P. N. Bala Subramanian, Sreeraj T. P

Simultaneous decoherence of conjugate observables of an open quantum system leads to a classical statistical mechanical description with constant phase space probability density in terms of a uniform ensemble. We investigate a scenario where this may be realized by measurement of basic conjugate observables of a quantum system by the environment.