Abstract
Projectors are a simple but powerful tool for manipulating and probing quantum systems. For instance, projecting two-qubit systems onto maximally entangled states can enable quantum teleportation. While such projectors have been extensively studied, partially-entangling projectors have been largely overlooked, especially experimentally, despite their important role in quantum foundations and quantum information. Here, we propose a way to project two polarized photons onto any state with a single experimental setup. Our scheme does not require optical nonlinearities or additional photons. Instead, the entangling operation is provided by Hong–Ou–Mandel interference and post-selection. The efficiency of the scheme is between 50% and 100%, depending on the projector. We perform an experimental demonstration and reconstruct the operator describing our measurement using detector tomography. Finally, we flip the usual role of measurement and state in Hardy’s test by performing a partially-entangling projector on separable states. The results verify the entangling nature of our measurement with six standard deviations of confidence.
Highlights
In quantum physics, measurements are used for both controlling and probing quantum systems
Projectors are the archetypal measurement in many quantum information processing (QIP) tasks such as secure key distribution [1], state estimation [2], and testing Bell’s inequalities [3, 4]
We induce controllable polarizationdependent loss in one of the modes before and after the beam splitters (BSs) which imbalances the Hong–Ou–Mandel interference effect. This loss is achieved by a variable partially-polarizing BS (VPPBS), which we describe in detail
Summary
Abstract the terms of the Creative Projectors are a simple but powerful tool for manipulating and probing quantum systems. For. instance, projecting two-qubit systems onto maximally entangled states can enable quantum. While such projectors have been extensively studied, partially-entangling projectors this work must maintain attribution to the have been largely overlooked, especially experimentally, despite their important role in quantum author(s) and the title of the work, journal citation foundations and quantum information. Onto any state with a single experimental setup. The efficiency of the scheme is between 50% and 100%, depending on the projector. We perform an experimental demonstration and reconstruct the operator describing our measurement using detector tomography. We flip the usual role of measurement and state in. Hardy’s test by performing a partially-entangling projector on separable states.
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