Strong converse rates for classical communication over thermal and additive noise bosonic channels

We prove that several known upper bounds on the classical capacity of thermal and additive noise bosonic channels are actually strong converse rates. Our results strengthen the interpretation of these upper bounds, in the sense that we now know that the probability of correctly decoding a classical message rapidly converges to zero in the limit of many channel uses if the communication rate exceeds these upper bounds. In order for these theorems to hold, we need to impose a maximum photon number constraint on the states input to the channel (the strong converse property need not hold if there is only a mean photon number constraint). Our first theorem demonstrates that Koenig and Smith's upper bound on the classical capacity of the thermal bosonic channel is a strong converse rate, and we prove this result by utilizing the structural decomposition of a thermal channel into a pure-loss channel followed by an amplifier channel. Our second theorem demonstrates that Giovannetti et al.'s upper bound on the classical capacity of a thermal bosonic channel corresponds to a strong converse rate, and we prove this result by relating success probability to rate, the effective dimension of the output space, and the purity of the channel as measured by the Renyi collision entropy. Finally, we use similar techniques to prove that similar previously known upper bounds on the classical capacity of an additive noise bosonic channel correspond to strong converse rates.Comment: Accepted for publication in Physical Review A; minor changes in the text and few reference

Role Of Gravin In Endothelial Wound Healing

ABSTRACT Gravin (AKAP12), a 300 kDa AKAP, is widely distributed in cells and binds to several signaling molecules including PKA-RII subunits, PKCα, PDE4, β2 adrenoreceptor and actin cytoskeleton. Initial characterization of gravin has revealed that this protein is undetectable in endothelia in vivo but expressed at the periphery of cultured endothelial cell (EC). Although the precise role of gravin in human ECs is not yet known, the cortical distribution of gravin in EC suggests that it may be involved in cAMP regulation by targeting PKA and PDE4 to plasma membrane. Several studies indicate that localization of PKA activity by A-kinase anchoring proteins (AKAPs) to the leading edge and other cytoskeletal regulators is an important factor in cell migration. SSeCKS, the rodent orthologue of gravin is reported to be involved in cell migration and regulation of actin cytoskeleton in cancer cell lines. Further, Western blot analysis, in the current study reveals that gravin upregulation in EC is associated with an active state, when cells are at a low cell density culture condition that promotes migration and proliferation, whereas downregulation occurs when cells became confluent and quiescent, indicating that gravin may have a functional role in ECs during their proliferative and migratory stage. Therefore, based on these findings, we hypothesized that gravin may play a role in EC migration. To test this hypothesis, following experiments were conducted. First, the effect of gravin knockdown on EC migration was determined in a scratch wound and a 96-well based cell migration assay using antisense oligonucleotide and siRNA treatments. The effect of antisense oligonucleotide and siRNA treatments on gravin expression was assessed by Western blotting and cell based ELISA. Finally, the reorganization of cortical actin band was quantitatively analyzed in antisense oligonucleotide treated cells to determine a role for gravin in actin cytoskeleton remodeling. A significantly reduced distance, that wound edge moved after 18-20hr, was observed in both antisense oligonucleotide and siRNA treated cells in a scratch wound model. Consistent with this, the number of cells present in the cell free zone after 42-44hr was also reduced significantly in the cells treated with antisense oligonucleotide and siRNA treatments in a 96-well cell migration assay. Finally, antisense oligonucleotide treatment also reduced the length of cortical actin band normalized with the free edge (edge not touching adjacent cells) of cells at the wound edge, which further revealed that gravin was also involved in cortical actin remodeling in migrating EC. This study proposes a possible mechanism for gravin mediated EC migration which involves the formation of a gravin-PKA-PDE4 functional complex, facilitating a compartmentalized regulation of cAMP/PKA dynamics that induces cortical actin remodeling and EC migration. In summary, the present study provides a new insight into the control of gravin expression in cultured EC and the role of gravin in EC migration and wound healing

Topics in Quantum Metrology, Control, and Communications

Noise present in an environment has significant impacts on a quantum system affecting properties like coherence, entanglement and other metrological features of a quantum state. In this dissertation, we address the effects of different types of noise that are present in a communication channel (or medium) and an interferometric setup, and analyze their effects in the contexts of preserving coherence and entanglement, phase sensitivity, and limits on rate of communication through noisy channels. We first consider quantum optical phase estimation in quantum metrology when phase fluctuations are introduced in the system by its interaction with a noisy environment. By considering path-entangled dual-mode photon Fock states in a Mach-Zehnder optical interferometric configuration, we show that such phase fluctuations affect phase sensitivity and visibility by adding noise to the phase to be estimated. We also demonstrate that the optimal detection strategy for estimating a phase in the presence of such phase noise is provided by the parity detection scheme. We then investigate the random birefringent noise present in an optical fiber affecting the coherence properties of a single photon polarization qubit propagating through it. We show that a simple but effective control technique, called dynamical decoupling, can be used to suppress the effects of the dephasing noise, thereby preserving its ability to carry the encoded quantum information in a long-distance optical fiber communication system. Optical amplifiers and attenuators can also add noise to an entangled quantum system, deteriorating the non-classical properties of the state. We show this by considering a two-mode squeezed vacuum state, which is a Gaussian entangled state, propagating through a noisy medium, and characterizing the loss of entanglement in the covariance matrix and the symplectic formalism for this state. Finally, we discuss limits on the rate of communication in the context of sending messages through noisy optical quantum communication channels. In particular, we prove that a strong converse theorem holds under a maximum photon number constraint for these channels, guaranteeing that the success probability in decoding the message vanishes in the asymptotic limit for the rate exceeding the capacity of the channels

Death of A Poet

Today, as usual, I picked up the newspaper from the dinner table. My wife keeps it handy on it for me. She knows my habit of reading newspaper, while she’s working away in the kitchen attached to the dinner room, to prepare tea and breakfast for me and for herself. We talk about diverse things over tea and breakfast, at the table. Our son, our only child is studying away at an engineering college over in Kolkata. We keep this time reserved for a conjugal chat, for the rest of the day we remain busy. I in writing poetry and criticism and participating in literary activities and she with household workWhile I was glancing through the newspaper, my ears attuned to the jingling of utensils moving about in the kitchen, my eyes was stuck by an obituary of Rebati Guha which said he died yesterday evening in a hospital. It flung me extremely surprised, for I had not expected his death so quick, though he had been admitted to the hospital a few days ago. I had meant to visit him at the hospital today. The newspaper had said his condition was not so serious that it would occasion his death so soon. Looking up from the newspaper, I shouted to my wife who was sieving tea into a cup, ‘Look, Sumita. Rebati Guha died yesterday evening.’ She received the news nonchalantly, as if she were habituated to hearing of deaths occurring everyday around her. I felt sort of disappointed; I had thought she would show interest and empathize. Many a time I had told her how much I adored him and how his poetry inspired mine. ‘Yesterday I heard of his death over TV.’ she said indifferently. She had already sieved the tea into two cups, ‘You didn’t tell me he died!’ I said, exasperated and offended ‘You know how I…’ She cut me short. “My ears have already go rotten, hearing your rigmarole,’ she said. She came over and placed on the table one of the two cups and a saucer containing two baked breads, one on the other and some curry on top and hers and sat across

Strong converse for the classical capacity of optical quantum communication channels

We establish the classical capacity of optical quantum channels as a sharp transition between two regimes---one which is an error-free regime for communication rates below the capacity, and the other in which the probability of correctly decoding a classical message converges exponentially fast to zero if the communication rate exceeds the classical capacity. This result is obtained by proving a strong converse theorem for the classical capacity of all phase-insensitive bosonic Gaussian channels, a well-established model of optical quantum communication channels, such as lossy optical fibers, amplifier and free-space communication. The theorem holds under a particular photon-number occupation constraint, which we describe in detail in the paper. Our result bolsters the understanding of the classical capacity of these channels and opens the path to applications, such as proving the security of noisy quantum storage models of cryptography with optical links.Comment: 15 pages, final version accepted into IEEE Transactions on Information Theory. arXiv admin note: text overlap with arXiv:1312.328