Interconvertibility of single-rail optical qubits

We show how to convert between partially coherent superpositions of a single photon with the vacuum using linear optics and postselection based on homodyne measurements. We introduce a generalized quantum efficiency for such states and show that any conversion that decreases this quantity is possible. We also prove that our scheme is optimal by showing that no linear optical scheme with generalized conditional measurements, and with one single-rail qubit input can improve the generalized efficiency.Comment: 3 pages, 2 figure

Can Literature Know Itself and Not Become Philosophy?

Before puzzling over some possible conjunction between literature and philosophy, one has to agree on what such concepts mean. However, as soon as one wonders about their definitions, concepts like “literature” or “the novel” on the one hand, or “philosophy” or even “concept” on the other, prove all too elusive. If one thinks they know what a novel is, it proves virtually impossible to freeze a suitable definition of the aesthetic concept. The reason for that impossibility might be that philosophy’s mission, to the extent that it reflects upon concepts, is somehow to blur them. Yet this article aims to show that it is precisely in that sense that literature, through the example of the novel, is in itself philosophical to the degree that what defines the novel is a self-reflexive interrogation of what makes it so. With the example of Virginia Woolf’s To the Lighthouse, the article concludes that there might be no intrinsic knowledge of our (aesthetic) concepts outside examples.Avant de s’interroger sur une éventuelle conjonction entre littérature et philosophie, encore faut-il s’entendre sur ce que recouvrent ces concepts. Or dès qu’on soulève la question de leur définition, les concepts de « littérature » ou de « roman » d’un côté, de « philosophie » voire de « concept » de l’autre, s’avèrent éminemment fuyants. Si on pense savoir ce qu’est un roman, en arrêter une définition acceptable s’avère quasiment impossible. La raison en est que la philosophie, en tant qu’elle s’interroge sur des concepts, a pour mission de les brouiller. Or, cet article vise à démontrer que c’est précisément en ce sens que l’écriture littéraire, à travers l’exemple du roman, est philosophique, puisque c’est aussi le propre du roman, à l’instar de To the Lighthouse de Virginia Woolf, de s’interroger sur ce qui le définit en tant que tel. De sorte qu’il n’y a de connaissance possible que dans l’exemple

The standard fair sampling assumption is not necessary to test local realism

Almost all Bell-inequality experiments to date have used postselection, and therefore relied on the fair sampling assumption for their interpretation. The standard form of the fair sampling assumption is that the loss is independent of the measurement settings, so the ensemble of detected systems provides a fair statistical sample of the total ensemble. This is often assumed to be needed to interpret Bell inequality experiments as ruling out hidden-variable theories. Here we show that it is not necessary; the loss can depend on measurement settings, provided the detection efficiency factorises as a function of the measurement settings and any hidden variable. This condition implies that Tsirelson's bound must be satisfied for entangled states. On the other hand, we show that it is possible for Tsirelson's bound to be violated while the CHSH-Bell inequality still holds for unentangled states, and present an experimentally feasible example.Comment: 12 pages, includes experimental proposa

Adaptive Optical Phase Estimation Using Time-Symmetric Quantum Smoothing

Quantum parameter estimation has many applications, from gravitational wave detection to quantum key distribution. We present the first experimental demonstration of the time-symmetric technique of quantum smoothing. We consider both adaptive and non-adaptive quantum smoothing, and show that both are better than their well-known time-asymmetric counterparts (quantum filtering). For the problem of estimating a stochastically varying phase shift on a coherent beam, our theory predicts that adaptive quantum smoothing (the best scheme) gives an estimate with a mean-square error up to $2\sqrt{2}$ times smaller than that from non-adaptive quantum filtering (the standard quantum limit). The experimentally measured improvement is $2.24 \pm 0.14$