Clustering a large number of compounds. 2. Using the Connection Machine

About 230,000 compounds in the National Cancer Institute Repository are available for screening under a new protocol. This paper is the second on an project to extract a representative sample of these compounds by clustering. The clustering program was implemented on the Connection Machine, a massively parallel computer with 16K processing elements. This implementation reduced a formidable task to a relatively routine run.     

Nanoscale molecular superfluidity of hydrogen

We present a microscopic quantum theoretical analysis of the nanoscale superfluid properties of solvating clusters of para-H2 around the linear OCS molecule. Path-integral calculations with N=17 para-H2 molecules, constituting a full solvation shell, show the appearance of a significant superfluid response to rotation around the molecular axis at T=0.15 K. This low-temperature superfluid response is highly anisotropic and drops sharply as the temperature increases to T approximately 0.3 K. These calculations provide definitive theoretical evidence that an anisotropic superfluid state exists for molecular hydrogen in this microscopic solvation layer.     

Onset of superfluidity in small CO2(4He)N clusters

We provide definitive theoretical evidence for the onset of superfluidity in small helium clusters doped with molecules at less than one solvation shell, with quantitative analysis of spectroscopic constants for CO2 in (4)He(N) in terms of nonclassical rotational inertia and helium superfluidity calculated by path integral methods. We find a significant superfluid response for N>/=5, with essentially unit response to rotations around the CO2 axis and partial response to rotations about an axis perpendicular to the CO2 axis for N>/=6. This anisotropic superfluid response is shown to be responsible for the N dependence of measured CO2 rotational spectra in (4)He(N).     

Ohmic and step noise from a single trapping center hybridized with a Fermi sea

We show that single electron tunneling devices such as the Cooper-pair box or double quantum dot can be sensitive to the zero-point fluctuation of a single trapping center hybridized with a Fermi sea. If the trap energy level is close to the Fermi sea and has linewidth gamma > k(B)T, its noise spectrum has an Ohmic Johnson-Nyquist form, whereas for gamma < k(B)T the noise has a Lorentzian form expected from the semiclassical limit. Trap levels above the Fermi level are shown to lead to steps in the noise spectrum that can be used to probe their energetics, allowing the identification of individual trapping centers coupled to the device.     

Minimum construction of two-qubit quantum operations

Optimal construction of quantum operations is a fundamental problem in the realization of quantum computation. We here introduce a newly discovered quantum gate, B, that can implement any arbitrary two-qubit quantum operation with minimal number of both two- and single-qubit gates. We show this by giving an analytic circuit that implements a generic nonlocal two-qubit operation from just two applications of the B gate. Realization of the B gate is illustrated with an example of charge-coupled superconducting qubits for which the B gate is seen to be generated in shorter time than the CNOT gate.