3,636 research outputs found
Theoretical Studies of the Structure and Stability of Metal Chalcogenide CrnTem (1≤n≤6, 1≤m≤8) clusters
In the presented work, first principle studies on electronic structure, stability, and magnetic properties of metal chalcogenide, CrnTem clusters have been carried out within a density functional framework using generalized gradient functions to incorporate the exchange and correlation effects. The energetic and electronic stability was investigated, and it was found that they are not always correlated as seen in the cluster Cr6Te8 which has smaller gap between its HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) and a high electron affinity of 3.39 eV indicating lower electronic stability whereas higher fragmentation energy indicating energetic stability. The high electron affinity shows that the stability of Cr6Te8 cluster can be enhanced by adding charge donating ligands including PEt3 to form stable Cr6Te8(PEt3)6 clusters as seen in experiments. The other cluster of interest was Cr4Te6 in which energetic stability was accompanied with electronic inertness marked by its large HOMO-LUMO gap, non-magnetic ground state and high fragmentation energy
Achieving the physical limits of the bounded-storage model
Secure two-party cryptography is possible if the adversary's quantum storage
device suffers imperfections. For example, security can be achieved if the
adversary can store strictly less then half of the qubits transmitted during
the protocol. This special case is known as the bounded-storage model, and it
has long been an open question whether security can still be achieved if the
adversary's storage were any larger. Here, we answer this question positively
and demonstrate a two-party protocol which is secure as long as the adversary
cannot store even a small fraction of the transmitted pulses. We also show that
security can be extended to a larger class of noisy quantum memories.Comment: 10 pages (revtex), 2 figures, v2: published version, minor change
Simple approach to approximate quantum error correction based on the transpose channel
We demonstrate that there exists a universal, near-optimal recovery map—the transpose channel—for approximate quantum error-correcting codes, where optimality is defined using the worst-case fidelity. Using the transpose channel, we provide an alternative interpretation of the standard quantum error correction (QEC) conditions and generalize them to a set of conditions for approximate QEC (AQEC) codes. This forms the basis of a simple algorithm for finding AQEC codes. Our analytical approach is a departure from earlier work relying on exhaustive numerical search for the optimal recovery map, with optimality defined based on entanglement fidelity. For the practically useful case of codes encoding a single qubit of information, our algorithm is particularly easy to implement
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