We study a quantum state transfer between two qubits interacting with the ends of a quantum wire consisting of linearly arranged spins coupled by an excitation conserving, time-independent Hamiltonian. We show that if we control the coupling between the source and the destination qubits and the ends of the wire, the evolution of the system can lead to an almost perfect transfer even in the case in which all nearest-neighbour couplings between the internal spins of the wire are equal.PACS numbers: 03.67. Hk, 03.67.Pp, 05.50.+q The problem of designing quantum networks which enable efficient high-fidelity transfer of quantum states has recently been addressed by a number of authors (see ). Ideally, such a network should meet both the simplicity and the minimal control requirements. By simplicity we mean that the network consists of typical elements coupled in a standard way so that a few networks can be combined together to form more complex systems. The minimal control requirement says that the transmission of a quantum state through the network should be possible without performing many control operations (as switching interactions on and off, measuring, encoding and decoding, etc.). A 1D quantum network (quantum wire) which fulfills both above requirements was proposed by Bose [1] who considered a spin chain with the nearest neighbour Heisenberg Hamiltonian; here the transmission of quantum state between the ends of the chain was achieved simply by a free evolution of the network. However, as was shown by Bose, if all neighbour couplings have the same strength the fidelity of a transmission decreases with the chain length n. A similar model (with the Heisenberg Hamiltonian replaced by XY one) was considered by Christandl et al. in [2]. They show that one can transfer quantum states through arbitrary long chains if spin couplings are carefully chosen in a way depending on the chain length n (see also [3][4][5][6][7][8]). Note however that this approach does not meet the simplicity requirement since one cannot merge several "modulated" quantum wires into a longer one.Here, we study a transfer of quantum states between two qubits attached to the ends of a quantum wire consisting of n linearly arranged spins. In order to fulfill the requirement of simplicity we assume that all couplings between neighbouring spins forming the quantum wire are the same (and equal to 1), while the couplings between the source and the destination qubits and the ends of the wire are equal to a. We show that one can significantly improve of the fidelity of the transfer be- * Corresponding author. Phone: +48 (61) 829-5394, fax: +48 (61) 829-5315. E-mail: tomasz@amu.edu.pl tween the source and the destination qubits by selecting the value of a appropriately. In particular, choosing a small enough, one can achieve a transfer whose fidelity can be arbitrarily close to one, even for large n.We assume that the Hamiltonian of the whole system of n + 2 qubits conserves the number of excitation (e.g., it is a XY Hamiltonian), so the state n+1 ...

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We study a quantum state transfer between spins interacting with an arbitrary network of spins coupled by uniform XX interactions. It is shown that in such a system under fairly general conditions, we can expect a nearly perfect transfer of states. Then we analyze a generalization of this model to the case of many network users, where the sender can choose which party he wants to communicate with by appropriately tuning his local magnetic field. We also remark that a similar idea can be used to create an entanglement between several spins coupled to the network.

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We study the dynamics of a generalization of a quantum coin walk on the line, which is a natural model for a diffusion modified by quantum or interference effects. In particular, our results provide surprisingly simple explanations for recurrence phenomena observed by Bouwmeester et al. [Phys. Rev. A 61, 13410 (1999)]] in their optical Galton board experiment, and a description of a stroboscopic quantum walk given by Buerschaper and Burnett [quant-ph/0406039] through numerical simulations. We also provide heuristic explanations for the behavior of our model which show, in particular, that its dynamics can be viewed as a discrete version of Bloch oscillations.

BackgroundVertical transmission is one of the transmission routes for Babesia microti, the causative agent of the zoonotic disease, babesiosis. Congenital Babesia invasions have been recorded in laboratory mice, dogs and humans. The aim of our study was to determine if vertical transmission of B. microti occurs in naturally-infected reservoir hosts of the genus Microtus.MethodsWe sampled 124 common voles, Microtus arvalis; 76 root voles, M. oeconomus and 17 field voles, M. agrestis. In total, 113 embryos were isolated from 20 pregnant females. Another 11 pregnant females were kept in the animal house at the field station in Urwitałt until they had given birth and weaned their pups (n = 62). Blood smears and/or PCR targeting the 550 bp 18S rRNA gene fragment were used for the detection of B. microti. Selected PCR products, including isolates from females/dams and their embryos/pups, were sequenced.ResultsPositive PCR reactions were obtained for 41% (89/217) of the wild-caught voles. The highest prevalence of B. microti was recorded in M. arvalis (56/124; 45.2%), then in M. oeconomus (30/76; 39.5%) and the lowest in M. agrestis (3/17; 17.7%). Babesia microti DNA was detected in 61.4% (27/44) of pregnant females. Vertical transmission was confirmed in 81% (61/75) of the embryos recovered from Babesia-positive wild-caught pregnant females. The DNA of B. microti was detected in the hearts, lungs and livers of embryos from 98% of M. arvalis, 46% of M. oeconomus and 0% of M. agrestis embryos from Babesia-positive females. Of the pups born in captivity, 90% were born to Babesia-positive dams. Babesia microti DNA was detected in 70% (35/50) of M. arvalis and 83% (5/6) of M. oeconomus pups. Congenitally acquired infections had no impact on the survival of pups over a 3-week period post partum. Among 97 B. microti sequences, two genotypes were found. The IRU1 genotype (Jena-like) was dominant in wild-caught voles (49/53; 92%), pregnant females (9/11; 82%) and dams (3/5; 60%). The IRU2 genotype (Munich-like) was dominant among B. microti positive embryos (20/27; 74%) and pups (12/17; 71%).ConclusionA high rate of vertical transmission of the two main rodent genotypes of B. microti was confirmed in two species of naturally infected voles, M. arvalis and M. oeconomus.

Prevalence and abundance of Cryptosporodium parvum and Giardia spp. were studied in 3 species of rodents from forests and abandoned agricultural fields in N.E. Poland (Clethrionomys glareolus n l 459 ; Microtus arvalis n l 274 ; Apodemus flavicollis n l 209). Overall prevalence was consistently higher in the voles compared with A. flavicollis (70n6, 73n0 and 27n8 % respectively for C. parvum and 93n9, 96n3 and 48n3 % respectively for Giardia spp.). Prevalence and abundance of infection also varied markedly across 3 years with 1998 being a year of higher prevalence and abundance with both species. Fewer older animals (especially C. glareolus and M. arvalis) carried infection with C. parvum and infections in these animals were relatively milder. Although seasonal differences were significant, no consistent pattern of changes was apparent. Host sex did not influence prevalence or abundance of infection with C. parvum, but made a small contribution to a 4-way interaction (in 5-way ANOVA) with other factors in the case of Giardia spp. The 2 species co-occurred significantly and in animals carrying both parasites there was a highly significant positive correlation between abundance of infection with each, even with between-year, seasonal, host age, sex and species differences taken into account. Quantitative associations were confined to the 2 vole species in the study. These results are discussed in relation to the importance of wild rodents as reservoir hosts and sources of infection for local human communities.

Babesia spp. (Apicomplexa, Piroplasmida) are obligate parasites of many species of mammals, causing a malaria-like infection- babesiosis. Three routes of Babesia infection have been recognized to date. The main route is by a tick bite, the second is via blood transfusion. The third, vertical route of infection is poorly recognized and understood. Our study focused on vertical transmission of B. microti in a well-established mouse model. We assessed the success of this route of infection in BALB/c mice with acute and chronic infections of B. microti. In experimental groups, females were mated on the 1st day of Babesia infection (Group G0); on the 28th day post infection (dpi) in the post- acute phase of the parasite infection (G28); and on the 90th and 150th dpi (G90 and G150 group, respectively), in the chronic phase of the parasite infection. Pups were obtained from 58% of females mated in the post-acute phase (G28) and from 33% of females in groups G90 and G150. Mice mated in the pre-acute phase of infection (G0) did not deliver pups. Congenital B. microti infections were detected by PCR amplification of Babesia 18S rDNA in almost all pups (96%) from the experimental groups G28, G90 and G150. Parasitaemia in the F1 generation was low and varied between 0.01–0.001%. Vertical transmission of B. microti was demonstrated for the first time in BALB/c mice.