Analog quantum simulation of chemical dynamics

Ultrafast chemical reactions are difficult to simulate because they involve entangled, many-body wavefunctions whose computational complexity grows rapidly with molecular size. In photochemistry, the breakdown of the Born–Oppenheimer approximation further complicates the problem by entangling nuclear and electronic degrees of freedom. Here, we show that analog quantum simulators can efficiently simulate molecular dynamics using commonly available bosonic modes to represent molecular vibrations. Our approach can be implemented in any device with a qudit controllably coupled to bosonic oscillators and with quantum hardware resources that scale linearly with molecular size, and offers significant resource savings compared to digital quantum simulation algorithms. Advantages of our approach include a time resolution orders of magnitude better than ultrafast spectroscopy, the ability to simulate large molecules with limited hardware using a Suzuki–Trotter expansion, and the ability to implement realistic system-bath interactions with only one additional interaction per mode. Our approach can be implemented with current technology; e.g., the conical intersection in pyrazine can be simulated using a single trapped ion. Therefore, we expect our method will enable classically intractable chemical dynamics simulations in the near term.

Dynamics governing ultrafast chemical reactions can be efficiently simulated using analog quantum simulators composed of a coupled system of qudits and bosonic modes.     

Systemic Losses Due to Counterparty Risk in a Stylized Banking System

We report a study of a stylized banking cascade model investigating systemic risk caused by counterparty failure using liabilities and assets to define banks’ balance sheet. In our stylized system, banks can be in two states: normally operating or distressed and the state of a bank changes from normally operating to distressed whenever its liabilities are larger than the banks’ assets. The banks are connected through an interbank lending network and, whenever a bank is distressed, its creditor cannot expect the loan from the distressed bank to be repaid, potentially becoming distressed themselves. We solve the problem analytically for a homogeneous system and test the robustness and generality of the results with simulations of more complex systems. We investigate the parameter space and the corresponding distribution of operating banks mapping the conditions under which the whole system is stable or unstable. This allows us to determine how financial stability of a banking system is influenced by regulatory decisions, such as leverage; we discuss the effect of central bank actions, such as quantitative easing and we determine the cost of rescuing a distressed banking system using re-capitalisation. Finally, we estimate the stability of the UK and US banking systems comparing the years 2007 and 2012 by using real data.     

Electro-elastic interactions and second order anisotropic constitutive equations

Piezoelectricity is usually expressed as an interaction between mechanical and electrical variables. The physics involved is hence governed by a coupling between Maxwell's equations of electromagnetism and the equations of elasticity. Such a coupling takes us through the piezoelectric constitutive relations. In this work, the second order anisotropic constitutive equations are treated, and in particular, the number of independent material constants is computed for all the 32 crystallographic classes.Paper presented, in reduced version, at the 12th Italian National Congress of Theoretical and Applied Mechanics (AIMETA '95), October 1995, Naples, Italy.     

Organometallic compounds in organic synthesis: reactions of some tricarbonylcyclohexadienyliumiron complexes with 1,2-bis(trimethylsiloxy)-1-cyclopentene. A novel route to 2-(substituted)-2-cyclopenten-1-ones.

1,2-Bis(trimethylsiloxy)-1-cyclopentene reacts with a range of tricarbonylcyclohexadienyliumiron cations to give initially siloxy acyloins, treatment of which with MeOH-HCl gives the 2-(substituted)-2-cyclopenten-1-one in good yields (56–78%).     

Probing the Sol-Gel Transition in SiO2 Hydrogels—A New Application of Near-Infrared Fluorescence

Picosecond time-resolved fluorescence spectroscopy has enabled us to use a near-infrared fluorescent dye to probe the sol-gel transition in SiO₂ hydrogels, polymerized from sulfuric acid and sodium silicate solution, for the first time. We compare the microviscosity surrounding the probe during the sol-to-gel transition as predicted by two alternative models which both describe the decay of fluorescence anisotropy well. The results for one rotational time and a residual anisotropy imply that macrogelation of the sol leads to relatively small changes in the mobility of the fluorophore caused by small changes in microviscosity, but after much longer times, e.g., 1500 min, the mobility of the fluorophore decreases, reflecting a rapid increase in microviscosity of over several orders in magnitude. In sharp contrast, analysis of the anisotropy in terms of two rotational times predicts little change in microviscosity over the whole polymerization process.     

Sulphur compounds in the kerosine boiling range of middle east distillates Occurrence of a bicyclic thiophene and a thienyl sulphide

A bicyclic thiophene, 1,4,4-trimethyl-4,5,6,7-tetrahydroisothianaphthene, and a thienyl sulphide, methyl 3, 4, 5-trimethyl-2-thienyl sulphide, have been isolated from a concentrate of sulphur compounds obtained in the refining of a Middle East kerosine. The structures of these compounds have been established.     

Isotherms of the rare gas solids

The experimental data of Anderson, Fugate and Swenson for the rare gas solids are recast in a dimensionless form which exhibits the close approach to the Lennard-Jones form except at the highest temperatures, and also in a form derived from the theory of finite elasticity. The latter is particularly useful when ultrasonic data furnish initial values of the modulus of compression. It also has the merit that no a priori assumptions concerning interatomic potentials are implicit, except that the strain-energy may be expanded in powers of the strain.