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If Alice and Bob start out with an entangled state $|Psi_{AB}rangle$, Bob may update his state to $|varphi_Brangle$ either by performing a suitable measurement himself, or by receiving the information that a measurement by Alice has steered that state. While Bobs update on his state is identical, his update on Alices state differs: if Bob has performed the measurement, he has steered the state $|chi_{leftarrow}(varphi)rangle_A$ of Alice; if Alice has made the measurement, to steer $|varphirangle_B$ on Bob she must have found a different state $|chi_{rightarrow}(varphi)rangle_A$. Based on this observation, a consequence of the well-known `Hardys ladder, we show that information from direct measurement must trump inference from steering. The erroneous belief that both paths should lead to identical conclusions can be traced to the usual prejudice that measurements should reveal a pre-existing state of affairs. We also prove a technical result on Hardys ladder: the minimum overlap between the steered and the steering state is $2sqrt{p_{0}p_{n-1}}/(p_0+p_{n-1})$, where $p_0$ and $p_{n-1}$ are the smallest (non-zero) and the largest Schmidt coefficients of $|Psirangle_{AB}$.
We report a direct measurement of the Wigner function characterizing the quantum state of a light mode. The experimental scheme is based on the representation of the Wigner function as an expectation value of a displaced photon number parity operator
It is known that photon pairs generated from pulse-pumped spontaneous parametric processes can be described by independent temporal modes and form a multi-temporal mode entangled state. However, the exact form of the temporal modes is not known even
It is difficult to evaluate the precision of quantum measurements because it is not possible to conduct a second reference measurement on the same physical system to compare the measurement outcome with a more accurate value of the measured quantity.
In comparison with entanglement and Bell nonlocality, Einstein-Podolsky-Rosen steering is a newly emerged research topic and in its incipient stage. Although Einstein-Podolsky-Rosen steering has been explored via violations of steering inequalities b
Within the framework of quantum refereed steering games, quantum steerability can be certified without any assumption on the underlying state nor the measurements involved. Such a scheme is termed the measurement-device-independent (MDI) scenario. He