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Both photons and semiconductor quantum-dot (QD) spins are promising candidates for quantum information science and technology. It is of critical significance to realize high-fidelity quantum controlled gates on photon-spin hybrid systems. In this paper, based on the novel balance condition for the interaction between a single input photon and a singly charged QD embedded in an optical single-sided microcavity, we present three schemes for implementing three universal quantum controlled gates, i.e., the two-qubit controlled-NOT (CNOT) gate, the three-qubit Toffoli gate, and the three-qubit Fredkin gate, on composite hybrid quantum systems consisting of flying photons and QD-confined electron spins. By exploiting the balance condition, the noise caused by the unbalanced reflectance of the coupled and uncoupled QD-cavity systems can be efficiently suppressed, so that the fidelity of each quantum gate operation can be raised to unity in principle. The balance condition can be met without the strict requirement of strong coupling, making the high-fidelity quantum gates easier to be demonstrated in experiments. These features can improve the fidelity and feasibility of these schemes, which can be applied to large-scaled quantum computing and quantum information networks. [ABSTRACT FROM AUTHOR]

Both cavity quantum electrodynamics and linear optics are promising platforms for the implementation of coherent manipulations of quantum information, and have potential applications in the development of practical quantum devices. In this paper, we propose a simple and deterministic scheme for implementing a single-photon fully quantum router by a combination of both platforms. With this router, a polarization encoded signal photonic qubit can be coherently routed to one of two distinct spatial output ports or their coherent superposition according to the state of a control photonic qubit, while keeping the signal information stored in the signal qubit unaltered under the quantum routing operation. Our scheme has several advantages in contrast to previously published ones, and on top of that, this device meets all the requirements imposed on a fully featured quantum router and is easily scalable for multiqubit quantum routing. Moreover, it exhibits high experimental feasibility with current or near-future technologies. Therefore, this router can be integrated with protocols for the realization of quantum information processing and future complex quantum networks. [ABSTRACT FROM AUTHOR]

Abstract: In the venoms of cone snails, α conotoxins are competitive antagonists of nicotinic acetylcholine receptors. Eleven novel cDNA and eight partial gene sequences (including two pseudogenes) of α conotoxins were identified from five species of cone snail. As expected, every cDNA encodes a precursor of prepropeptide. In all the partial genes of α conotoxins identified, there is a long intron inserted at a fixed position in the pro-region, dividing the encoding region into two exons. The mutation rate in exon I (encoding the signal peptide and a part of pro-region) is much lower than that in exon II (encoding the other part of pro-region, the mature peptide and 3′ untranslational region). Interestingly, the sequences at the 5′ and 3′ end of introns are highly conserved. In addition, in the identified introns exist long dinucleotide (e.g. “GT”, “CA”) or trinucleotide (“CAT”) repeats. In the special case of Pu1.1, there are five almost identical repeats of a 150bp sequence in the long intron. Taking advantage of the conserved 3′ end sequence of intron, 16 α conotoxins, as well as a pseudogene and three κA conotoxins, were identified from their genomic DNAs. Based on the comparison of these cDNA and gene sequences, a hypothesis of the α conotoxin evolution was proposed. [Copyright &y& Elsevier]

Abstract: Remarkable sequence diversity of T-superfamily conotoxins was found in a mollusk-hunting cone snail Conus marmoreus. The sequence of mr5a purified from the snail venom was determined, while six other sequences of Mr5.1a, Mr5.1b, Mr5.2, Mr5.3, Mr5.4a, and Mr5.4b were deduced from their corresponding cDNA cloned by RACE approach. mr5a of 10 amino acid residues is one of the shortest T-superfamily conotoxins ever found. They all share a typical (–CC–CC–) Cys pattern, a conserved signal peptide and a long 3′-untranslated region. A consensus Glu residue is preceded by the second two adjacent cysteines in all these toxins except in mr5a, whereas Mr5.1a, Mr5.1b, Mr5.4a and Mr5.4b are abundant in Trp residues. The identification of these highly divergent T-superfamily conotoxins will facilitate the understanding the relationship of their structure and function. [Copyright &y& Elsevier]

Entanglement purification and concentration are effective means to deal with the influence of noise on the coherence of entangled quantum systems, which enable us to carry out secure and efficient quantum communications. However, the reliability of parity check in parity-check-based entanglement purification and concentration schemes will inevitably affect the performance of the schemes. In this paper, we propose faithful entanglement purification and concentration schemes for polarization-entangled photon pairs, using heralded high-fidelity parity-check detectors (PCDs) constructed by double-sided quantum-dot-microcavity (QD-microcavity) systems and linear-optical elements. The PCD is based on the general interaction rule between the input photon and the QD-microcavity system, without the requirement of the system to strictly satisfy the specifically ideal conditions for giant circular birefringence, which makes it more realizable in practice. Moreover, the PCD can work in a failure-heralded and fidelity-robust fashion, so it can make a correct judgement on the parity mode of a two-photon system and has no destruction on the entangled state. Our schemes can therefore realize faithful entanglement purification and concentration by utilizing the PCD, without reducing the fidelity and entanglement degree of the obtained entangled-state ensemble. These features make our schemes more feasible and useful in quantum repeaters and quantum networks. [ABSTRACT FROM AUTHOR]

Photonic hyperentanglement, which involves photons simultaneously entangled in more than one degree of freedom (DOF), has many important applications in quantum information processing, especially in high-capacity quantum communications. Interestingly, single-photon qubits encoded in the time-bin DOF are robust for long-distance transmissions in noisy channels. In this paper, we present a hyperentangled-Bell-state generation (HBSG) scheme for preparing two-photon six-qubit states which are simultaneously entangled in the polarization, spatial-mode, and time-bin DOFs. Compared with previous HBSG schemes, we construct an error-detected circuit unit with a quantum-dot (QD) spin in a double-sided optical microcavity, with which errors due to imperfect interactions between photons and QD systems can be easily detected, so that the error-detected circuit unit can relax the experimental requirement and improve the fidelity of our scheme largely. Meanwhile, our scheme is used to prepare two-photon hyperentangled states in polarization-spatial-time three DOFs, which is significant for faithful entanglement distribution and quantum repeater. These features make our scheme more feasible and useful in high-capacity and long-distance quantum communications with hyperentanglement. [ABSTRACT FROM AUTHOR]

E-payment has gradually become the mainstream globally in recent years. However, the security and anonymity of the traditional E-payment system are not perfectly guaranteed with the emergence of the quantum computer. In this paper, an E-payment security evaluation system based on quantum blind computing is proposed for evaluating the security of network transactions. Unitary operations and four-qubit cluster state are applied in this system to effectively defend against eavesdroppers. And a shared blind matrix used to encrypt the security scores prevents the curious third-party payment platform from obtaining the private data of users. Furthermore, our system guarantees that users cannot tamper with or disguise their security scores during transactions. We demonstrate the correctness and security of the system in detail and provide theoretical support for its extension to more types of evaluation systems. [ABSTRACT FROM AUTHOR]

γ-Secretase is a proteolytic membrane complex that processes a variety of substrates including the amyloid precursor protein and the Notch receptor. Earlier we showed that one of the components of this complex, nicastrin (NCT), functions as a receptor for γ-secretase substrates. A recent report challenged this, arguing instead that the Glu-333 residue of NCT predicted to participate in substrate recognition only participates in γ-secretase complex maturation and not in activity per Se. Here, we present evidence that Glu-333 directly participates in γ-secretase activity. By normalizing to the active pool of γ-secretase with two separate methods, we establish that γ-secretase complexes containing NCT-E333A are indeed deficient in intrinsic activity. We also demonstrate that the NCTE333A mutant is deficient in its binding to substrates. Moreover, we find that the cleavage of substrates by γ-secretase activity requires a free N-terminal amine but no minimal length of the extracellular N-terminal stub. Taken together, these studies provide further evidence supporting the role of NCT in substrate recognition. Finally, because γ-secretase cleaves itself during its maturation and because NCT-E333A also shows defects in γ-secretase complex maturation, we present a model whereby Glu-333 can serve a dual role via similar mechanisms in the recruitment of both Type 1 membrane proteins for activity and the presenilin intracellular loop during complex maturation. [ABSTRACT FROM AUTHOR]

Abstract: M-superfamily conotoxins can be divided into four branches (M-1, M-2, M-3 and M-4) according to the number of amino acid residues in the third Cys loop. In general, it is widely accepted that the conotoxin signal peptides of each superfamily are strictly conserved. Recently, we cloned six cDNAs of novel M-superfamily conotoxins from Conus leopardus, Conus marmoreus and Conus quercinus, belonging to either M-1 or M-3 branch. These conotoxins, judging from the putative peptide sequences deducted from cDNAs, are rich in acidic residues and share highly conserved signal and pro-peptide region. However, they are quite different from the reported conotoxins of M-2 and M-4 branches even in their signal peptides, which in general are considered highly conserved for each superfamily of conotoxins. The signal sequences of M-1 and M-3 conotoxins composed of 24 residues start with MLKMGVVL-, while those of M-2 and M-4 conotoxins composed of 25 residues start with MMSKLGVL-. It is another example that different types of signal peptides can exist within a superfamily besides the I-conotoxin superfamily. In addition to the different disulfide connectivity of M-1 conotoxins from that of M-4 or M-2 conotoxins, the sequence alignment, preferential Cys codon usage and phylogenetic tree analysis suggest that M-1 and M-3 conotoxins have much closer relationship, being different from the conotoxins of other two branches (M-4 and M-2) of M-superfamily. [Copyright &y& Elsevier]