Entanglement assisted random access codes

An (n,m,p) Random Access Code (RAC) allows to encode n bits in an m bit message, in such a way that a receiver of the message can guess any of the original $n$ bits with probability p, greater than 1/2. In Quantum RAC's (QRACs) one transmits n qubits. The full set of primitive Entanglement Assisted Random Access Codes (EARACs) is introduced, in which parties are allowed to share a two-qubit singlet. It is shown that via a concatenation of these, one can build for any n an (n,1,p) EARAC. QRAC's for n>3 exist only if parties additionally share classical randomness (SR). We show that EARACs outperform the best of known QRACs not only in the success probabilities but also in the amount of communication needed in the preparatory stage of the protocol. Upper bounds on the performance of EARACs are given, and shown to limit also QRACs.Comment: 4 pages, 1 figure, published versio

Experimental observation of four-photon entanglement from down-conversion

We observe polarization-entanglement between four photons produced from a single down-conversion source. The non-classical correlations between the measurement results violate a generalized Bell inequality for four qubits. The characteristic properties and its easy generation with high interferometric contrast make the observed four-photon state well-suited for implementing advanced quantum communication schemes such as multi-party quantum key distribution, secret sharing and telecloning.Comment: 4 pages, 3 figure

Bell Theorem for Nonclassical Part of Quantum Teleportation Process

The quantum teleportation process is composed of a joint measurement performed upon two subsystems A and B (uncorrelated), followed by a unitary transformation (parameters of which depend on the outcome of the measurement) performed upon a third subsystem C (EPR correlated with system B). The information about the outcome of the measurement is transferred by classical means. The measurement performed upon the systems A and B collapses their joint wavefunction into one of the four {\it entangled} Bell states. It is shown here that this measurement process plus a possible measurement on the third subsystem (with classical channel switched off - no additional unitary transformation performed) cannot be described by a local realistic theory.Comment: 4 pages, RevTeX, no figure

Greenberger-Horne-Zeilinger paradoxes for N quNits

In this paper we show the series of Greenberger-Horne-Zeilinger paradoxes for N maximally entangled N-dimensional quantum systems.Comment: 6 page

Self-image after a Catastrophe. Zofia Kossak-Szczucka and Jerzy Andrzejewski: Two Polish Testimonies of the Holocaust from the 1940s.

As far as the question of the Holocaust is concerned, the Polish culture is characterised by some peculiar feature. On the one hand, it embraces the texts which quite uncompromisingly describe the Polish role in extermination, noticing a continuum between collective discriminating behaviours of the non-Jewish part of the society and the exterminating activities of the Nazis. Such voices deconstruct narration, in which the Polish majority remains an isolated, bystanding and passive witness of the Holocaust, and demonstrate some forms of participation. On the other hand, the message of this kind does not permeate into social consciousness, does not become known and does not improve the knowledge of the society about itself. The studies of Protest by Zofia Kossak-Szczucka and Wielki Tydzień (“Holy Week”) by Jerzy Andrzejewski are used for the description of the mechanism of this “becoming acquainted”. A key role in this mechanism is played by preoccupation with self-image of the group. The Holocaust, to a certain degree, undermined the obviousness of Polish discriminating practices towards Jews. In the awareness of elites there appeared a premonition of other criteria of evaluation of Polish behaviours, going beyond the mentioned practices (a phantasm “eyes of the world”). In the light of such criteria, the attitude towards exterminated Jews proves to be discrediting. At the same time, there appear narrations whose aim is to restore the order of discrimination and the hierarchies connected with it, which comes down to forcing the victims into inferior position—in contrast to the dominating majority—and concealing the knowledge about participation in the crime. Consequently, culture remains in the state of unrest. Unwanted knowledge (and the feeling of guilt) returns and the attempts to become purified by the renewed concealment and repudiation of the awareness of evil always prove unsuccessful. The signs of repudiation are the recurring symptoms and repetitions of the same scenario of denial of never clearly stated accusations