Entanglement and Superdense Coding with Linear Optics

We discuss a scheme for a full superdense coding of entangled photon states employing only linear-optics elements. By using the mixed basis consisting of four states that are unambiguously distinguishable by a standard and polarizing beam splitters we can deterministically transfer four messages by manipulating just one of the two entangled photons. The sender achieves the determinism of the transfer either by giving up the control over 50% of sent messages (although known to her) or by discarding 33% of incoming photons.Comment: 8 pages, 1 figur

New Class of 4-Dim Kochen-Specker Sets

We find a new highly symmetrical and very numerous class (millions of non-isomorphic sets) of 4-dim Kochen-Specker (KS) vector sets. Due to the nature of their geometrical symmetries, they cannot be obtained from previously known ones. We generate the sets from a single set of 60 orthogonal spin vectors and 75 of their tetrads (which we obtained from the 600-cell) by means of our newly developed "stripping technique." We also consider "critical KS subsets" and analyze their geometry. The algorithms and programs for the generation of our KS sets are presented.Comment: 7 pages, 3 figures; to appear in J. Math. Phys. Vol.52, No. 2 (2011

Nondestructive interaction-free atom-photon controlled-NOT gate

We present a probabilistic (ideally 50%) nondestructive interaction-free atom-photon controlled-NOT gate, where nondestructive means that all four outgoing target photon modes of the gate are available and feed-forwardable. Individual atoms are controlled by a stimulated Raman adiabatic passage transition and photons by a ring resonator with two outgoing ports. Realistic estimates we obtain for ions confined in a Paul trap around which the resonator is mounted show that a strong atom-photon coupling can be achieved. It is also shown how the resonator can be used for controlling superposition of atom states.Comment: 20 pages, 5 figures, Web page: http://m3k.grad.hr/pavici

Spin-correlated interferometry with beam splitters: preselection of spin-correlated photons

A nonclassical feature of the fourth-order interference at a beam splitter, that genuine photon spin singlets are emitted in predetermined directions even when incident photons are unpolarized, has been used in a proposal for an experiment that imposes quantum spin correlation on truly independent photons. In the experiment, two photons from two such singlets interfere at a beam splitter, and as a result the other two photons - which nowhere interacted and whose paths nowhere crossed - exhibit a 100% correlation in polarization, even when no polarization has been measured in the first two photons. The propsed experiment permits closure of the remaining loopholes in the Bell theorem proof and reveals the quantum nonlocality as a property of selection, and pioneers an experimental procedure for exact preparation of unequal superposition.Comment: RevTeX, 19 pages, 3 ps figures, author's www: http://m3k.grad.hr/pavici

Retraction of "Near-Deterministic Discrimination of All Bell States with Linear Optics," Phys. Rev. Lett. 107, 080403 (2011) and Erratum Phys. Rev. Lett. 107, 219901 (2011)

The original versions (1 and 2) of this paper paper contain a fatal error. All my attempts to patch the error have failed. As a service to the community I explain the error in some detail.Comment: The original paper (v. 1 and 2) was retracted from Phys. Rev. Lett. 107, 080403 (2011) and its Erratum Phys. Rev. Lett. 107. 219901 (2011

Kochen-Specker Sets and Generalized Orthoarguesian Equations

Every set (finite or infinite) of quantum vectors (states) satisfies generalized orthoarguesian equations ($n$OA). We consider two 3-dim Kochen-Specker (KS) sets of vectors and show how each of them should be represented by means of a Hasse diagram---a lattice, an algebra of subspaces of a Hilbert space--that contains rays and planes determined by the vectors so as to satisfy $n$OA. That also shows why they cannot be represented by a special kind of Hasse diagram called a Greechie diagram, as has been erroneously done in the literature. One of the KS sets (Peres') is an example of a lattice in which 6OA pass and 7OA fails, and that closes an open question of whether the 7oa class of lattices properly contains the 6oa class. This result is important because it provides additional evidence that our previously given proof of noa =< (n+1)oa can be extended to proper inclusion noa < (n+1)oa and that nOA form an infinite sequence of successively stronger equations.Comment: 16 pages and 5 figure

Physical Theories and Their Social and Cultural Environment

Razmatrano je da li društvena i kulturna okolina prirodnih nauka, posebno fizike, može utjecati na strukturu njihovih teorija. Pokazuje se da na pojedine teorije okolina utječe, međutim, ne direktno, već preko znanstvene zajednice u procesu njene borbe za autonomiju i položaj u društvu. Posebno, takav utjecaj postoji kad god se pojave »suparničke« teorije koje su u nekom periodu empirijski nerazlučive, bez obzira na to da li je odnosno znaristveno područje u Kuhnovskoj »krizi« ili ne. Mehanizam pomoću kojeg se znanstvena zajednica homogenizira naspram šire društvene okoline, praveći utilitarističku i pragmatističku selekciju među suparničkim teorijama, je razrađen. Proces je ilustriran primjerom valno-čestične dualnosti svjetlosti i materije.The problem of whether the cultural and social environment of natural sciences, physics in particular, can influence the structure of their theories is considered. It is argued that the structure of particular theories is often influenced by the environment however not in a direct way but through the scientific community itself in the process of its struggle to gain autonomy and respectability with the outer environment. In particular, such an influence occurs whenever rival theories, empirically indistinguishable at a given time, are formulated, without regard as to whether the scientific field in question is in a Kuhnian »crisis« or not. The mechanism whereby the scientific community homogenizes itself against the outer environment, by making a utilitarian and pragmatist selection among the rival theories is elaborated. The process is illustrated by the example of the wave-particle duality of light and matter

Duration and Variability of Speech Segments in Fluent Speech of Children with and without Stuttering

The purpose of this study was to compare the duration and variability of speech segments of children who stutter with those of children who do not stutter and to identify changes in duration and variability of speech segments due to the effect of utterance length. Eighteen children participated (ranging from 6.3 to 7.9 years of age). The experimental task required the children to repeat a single word in isolation and the same word embedded in a sentence. Durations of speech segments and Coefficients of variation (Cv) were defined to assess temporal parameters of speech. Significant differences were found in the variability of speech segments on the sentence level, but not in duration. The findings supported the assumption that linguistic factors pose direct demands on the speech motor system and that the extra duration of speech segments observed in the speech of stuttering adults may be a kind of compensation strategy

Hilbert Lattice Equations

There are five known classes of lattice equations that hold in every infinite dimensional Hilbert space underlying quantum systems: generalised orthoarguesian, Mayet's E_A, Godowski, Mayet-Godowski, and Mayet's E equations. We obtain a result which opens a possibility that the first two classes coincide. We devise new algorithms to generate Mayet-Godowski equations that allow us to prove that the fourth class properly includes the third. An open problem related to the last class is answered. Finally, we show some new results on the Godowski lattices characterising the third class of equations.Comment: 24 pages, 3 figure