Minimum energy surface required by quantum memory devices.

We address the question of what physical resources are required and sufficient to store classical information. While there is no lower bound on the required energy or space to store information, we find that there is a nonzero lower bound for the product P = of these two resources. Specifically, we prove that any physical system of mass m and d degrees of freedom that stores S bits of information will have a lower bound on the product P that is proportional to d2/m(exp(S/d) - 1)2. This result is obtained in a nonrelativistic, quantum mechanical setting, and it is independent of earlier thermodynamical results such as the Bekenstein bound on the entropy of black holes.

A broad influenza virus inhibitor acting via IMP dehydrogenase and in synergism with ribavirin.

To suppress serious influenza infections in persons showing insufficient protection from the vaccines, antiviral drugs are of vital importance. There is a need for novel agents with broad activity against influenza A (IAV) and B (IBV) viruses and with targets that differ from those of the current antivirals. We here report a new small molecule influenza virus inhibitor referred to as CPD A (chemical name: N-(pyridin-3-yl)thiophene-2-carboxamide). In an influenza virus minigenome assay, this non-nucleoside compound inhibited RNA synthesis of IAV and IBV with EC50 values of 2.3 µM and 2.6 µM, respectively. Robust in vitro activity was noted against a broad panel of IAV (H1N1 and H3N2) and IBV strains, with a median EC50 value of 0.20 µM, which is 185-fold below the 50% cytotoxic concentration. The action point in the viral replication cycle was located between 1 and 5 h p.i., showing a similar profile as ribavirin. Like this nucleoside analogue, CPD A was shown to cause strong depletion of the cellular GTP pool and, accordingly, its antiviral activity was antagonized when this pool was restored with exogenous guanosine. This aligns with the observed inhibition in a cell-based IMP dehydrogenase (IMPDH) assay, which seems to require metabolic activation of CPD A since no direct inhibition was seen in an enzymatic IMPDH assay. The combination of CPD A with ribavirin, another IMPDH inhibitor, proved strongly synergistic. To conclude, we established CPD A as a new inhibitor of influenza A and B virus replication and RNA synthesis, and support the potential of IMPDH inhibitors for influenza therapy with acceptable safety profile.

Tight noise thresholds for quantum computation with perfect stabilizer operations.

We study how much noise can be tolerated by a universal gate set before it loses its quantum-computational power. Specifically we look at circuits with perfect stabilizer operations in addition to imperfect nonstabilizer gates. We prove that for all unitary single-qubit gates there exists a tight depolarizing noise threshold that determines whether the gate enables universal quantum computation or if the gate can be simulated by a mixture of Clifford gates. This exact threshold is determined by the Clifford polytope spanned by the 24 single-qubit Clifford gates. The result is in contrast to the situation wherein nonstabilizer qubit states are used; the thresholds in that case are not currently known to be tight.

Interaction between mouse adenovirus type 1 and cell surface heparan sulfate proteoglycans.

Application of human adenovirus type 5 (Ad5) derived vectors for cancer gene therapy has been limited by the poor cell surface expression, on some tumor cell types, of the primary Ad5 receptor, the coxsackie-adenovirus-receptor (CAR), as well as the accumulation of Ad5 in the liver following interaction with blood coagulation factor X (FX) and subsequent tethering of the FX-Ad5 complex to heparan sulfate proteoglycan (HSPG) on liver cells. As an alternative vector, mouse adenovirus type 1 (MAV-1) is particularly attractive, since this non-human adenovirus displays pronounced endothelial cell tropism and does not use CAR as a cellular attachment receptor. We here demonstrate that MAV-1 uses cell surface heparan sulfate proteoglycans (HSPGs) as primary cellular attachment receptor. Direct binding of MAV-1 to heparan sulfate-coated plates proved to be markedly more efficient compared to that of Ad5. Experiments with modified heparins revealed that the interaction of MAV-1 to HSPGs depends on their N-sulfation and, to a lesser extent, 6-O-sulfation rate. Whereas the interaction between Ad5 and HSPGs was enhanced by FX, this was not the case for MAV-1. A slot blot assay demonstrated the ability of MAV-1 to directly interact with FX, although the amount of FX complexed to MAV-1 was much lower than observed for Ad5. Analysis of the binding of MAV-1 and Ad5 to the NCI-60 panel of different human tumor cell lines revealed the preference of MAV-1 for ovarian carcinoma cells. Together, the data presented here enlarge our insight into the HSPG receptor usage of MAV-1 and support the development of an MAV-1-derived gene vector for human cancer therapy.

Optimal quantum circuits for general phase estimation.

We address the problem of estimating the phase phi given N copies of the phase-rotation gate uphi. We consider, for the first time, the optimization of the general case where the circuit consists of an arbitrary input state, followed by any arrangement of the N phase rotations interspersed with arbitrary quantum operations, and ending with a general measurement. Using the polynomial method, we show that, in all cases where the measure of quality of the estimate phi for phi depends only on the difference phi-phi, the optimal scheme has a very simple fixed form. This implies that an optimal general phase estimation procedure can be found by just optimizing the amplitudes of the initial state.

Experimental implementation of an adiabatic quantum optimization algorithm.

We report the realization of a nuclear magnetic resonance computer with three quantum bits that simulates an adiabatic quantum optimization algorithm. Adiabatic quantum algorithms offer new insight into how quantum resources can be used to solve hard problems. This experiment uses a particularly well-suited three quantum bit molecule and was made possible by introducing a technique that encodes general instances of the given optimization problem into an easily applicable Hamiltonian. Our results indicate an optimal run time of the adiabatic algorithm that agrees well with the prediction of a simple decoherence model.