[en] The probability of separating k particles from a beam of n classical distinguishable particles by a beam splitter is given by the Bernoulli distribution. When turning to indistinguishable Bose Quantum particles, this distribution is preserved by a refined interplay between interference and stimulation effects. This behaviour is demonstrated in an experiment where pairs of photons interact with an optical beam splitter. The distinguishability of the photons within a pair is changed by varying the degree of coherence

[en] By adjusting both the thickness and angle of the incidence of a birefringent channeled spectrum plate, the extraordinary and ordinary reflectivities can be equalized, thereby providing a polarization-independent beam splitter

[en] A more complete account of the phase fluctuation effect of a laser field has taken on the Autler-Townes splitting. In order to investigate the splitting induced by a nonmonochromatic single mode laser, the phase fluctuation of a laser field described by a two-dimensional Markovian process is employed in density matrix equations. The peak-height asymmetry of the Autler-Townes doublet is significantly affected by the characteristics of the phase diffusing field and verys with the pump laser detunings. It is known that the Autler-Townes effect can be used to measure accurately the correlation time of a single mode pulsed laser.

[en] As opposed to the conventional Cassegrain reflector, we introduce the metasurface lens into the design of the Cassegrain system as the primary component with the combination of a secondary metamirror. The electromagnetic fields reflected by the secondary metamirror would directly transmit through the metasurface lens, thus can remove the blockage effects from the secondary metamirror and generate well collimated beams with very low sidelobes compared with the traditional Cassegrain reflector. Especially, such a metasurface Cassegrain system also demonstrates the perfect capabilities of synthesizing the steerable beams and splitting beams when the metasurface lens is equipped with properly prescribed phase distributions. Finally, we fabricate the proposed metasurface lens based Cassegrain system and experimentally demonstrate the functionalities of generating highly directive radiations with beam scanning and beam splitting. (paper)

[en] Two different research teams have taken a big step toward atom interferometry. They have succeeded in splitting atomic beams by using atoms in spin states that neither absorb nor reemit laser light. By proper adjustment of experimental conditions, atoms are changed from one spin state to another, without passing through the intermediary excited state. The atoms in essence absorb momentum from the laser photons, without absorption or emission of photons. The change in momentum deflects atoms in the proper spin state

[en] We provide two quantum descriptions of a beam splitter with second-order nonlinearity. Models of nonlinear couplers could be the same. For simplicity, a symmetry of the device is assumed, which does not exclude various reflectivities. The models differ in taking into account the co-propagation of beams and replacing it by their counter-propagation. The unitary operators that evolve the input states into the output ones are calculated by using a momentum operator and the effective distance of presumed co-propagation and counter-propagation, respectively.

[en] We consider a new type of attack on a coherent quantum key distribution protocol [coherent one-way (COW) protocol]. The main idea of the attack consists in measuring individually the intercepted states and sending the rest of them unchanged. We have calculated the optimum values of the attack parameters for an arbitrary length of a communication channel and compared this novel attack with a standard beam-splitting attack. (paper)

[en] It is widely believed that at small x, the BFKL resummed gluon splitting function should grow as a power of 1/x. But in several recent calculations it has been found to decrease for moderately small-x before eventually rising. We show that this 'dip' structure is a rigorous feature of the P_gg splitting function for sufficiently small α_s, the minimum occurring formally at log(1/x)∼1/√α_s. We calculate the properties of the dip, including corrections of relative order √α_s, and discuss how this expansion in powers of √α_s, which is poorly convergent, can be qualitatively matched to the fully resummed result of a recent calculation, for realistic values of α_s. Finally, we note that the dip position, as a function of α_s, provides a lower bound in x below which the NNLO fixed-order expansion of the splitting function breaks down and the resummation of small-x terms is mandatory

[en] The decoy state method has been proposed to detect a photon number splitting (PNS) attack. Today, the decoy state method is considered to be an almost universal method for proving the secrecy of quantum cryptography protocols and calculating the length of a secret key. In this paper, it is shown that there exist attacks, for example, a beam splitting (BS) attack, to which the decoy state method turns out to be insensitive. The decoy state method is oriented to the detection of changes in the photocount statistics of information states and decoy states under a PNS attack. Under a BS attack, the photocount statistics is not changed. As a result, the decoy state method significantly overestimates the length of the key. Thus, the decoy state method is not a universal method that allows the detection of various attacks. Apparently, due to a large number of publications on the decoy state method, a widespread opinion has been formed that this method is universal. This fact has led to attempts to adopt this method as an international standard in quantum cryptography, which is clearly premature.

[en] We propose a scheme for purification of a general mixed entangled state. In this scheme, we start from a large number of general mixed entangled states and end up, after local operation and classical communication, with a smaller number of Bell diagonal states with higher entanglement. In particular, the scheme can purify one maximally entangled state from two entangled pairs prepared in a class of mixed entangled state. Furthermore we propose a linear optical implementation of the present scheme with polarization beam splitters and photon detectors. (paper)