Symmetry-breaking Effects for Polariton Condensates in Double-Well Potentials

We study the existence, stability, and dynamics of symmetric and anti-symmetric states of quasi-one-dimensional polariton condensates in double-well potentials, in the presence of nonresonant pumping and nonlinear damping. Some prototypical features of the system, such as the bifurcation of asymmetric solutions, are similar to the Hamiltonian analog of the double-well system considered in the realm of atomic condensates. Nevertheless, there are also some nontrivial differences including, e.g., the unstable nature of both the parent and the daughter branch emerging in the relevant pitchfork bifurcation for slightly larger values of atom numbers. Another interesting feature that does not appear in the atomic condensate case is that the bifurcation for attractive interactions is slightly sub-critical instead of supercritical. These conclusions of the bifurcation analysis are corroborated by direct numerical simulations examining the dynamics of the system in the unstable regime.MICINN (Spain) project FIS2008- 0484

Operation of a continuous flow liquid helium magnetic microscopy cryostat as a closed cycle system

We demonstrate successful operation of a continuous flow liquid helium magnetic cryostat (Oxford Instruments, Microstat MO) in closed cycle operation using a modular cryocooling system (ColdEdge Technologies, Stinger). For the system operation, we have developed a custom gas handling manifold and we show that despite the lower cooling power of the cryocooler with respect to the nominal cryostat cooling power requirements, the magnetic cryostat can be operated in a stable manner. We provide the design of the gas handling manifold and a detailed analysis of the system performance in terms of cooling times, magnetic field ramping rates, and vibrations at the sample. Base temperatures can be reached within 10 h while the superconducting magnet can be energized at a ramping rate of 0.5 T/min. Vibrations are measured interferometrically and show amplitudes with a root mean square on the order of 5 nm, permitting the use of the system for sensitive magnetic microscopy experiments.<br/

Superconducting nanowire photon-number-resolving detector at telecommunication wavelengths

Optical-to-electrical conversion, which is the basis of theoperation of optical detectors, can be linear or nonlinear.When high sensitivities are needed, single-photon detectorsare used, which operate in a strongly nonlinear mode, theirresponse being independent of the number of detectedphotons. However, photon-number-resolving detectors areneeded, particularly in quantum optics, where n-photon statesare routinely produced. In quantum communication andquantum information processing, the photon-numberresolvingfunctionality is key to many protocols, such as theimplementation of quantum repeaters1 and linear-opticsquantum computing2. A linear detector with single-photonsensitivity can also be used for measuring a temporalwaveform at extremely low light levels, such as in longdistanceoptical communications, fluorescence spectroscopyand optical time-domain reflectometry. We demonstrate here aphoton-number-resolving detector based on parallelsuperconducting nanowires and capable of counting up to fourphotons at telecommunication wavelengths, with an ultralowdark count rate and high counting frequency

Superconducting nanowire photon-number-resolving detector at telecommunication wavelengths

Optical-to-electrical conversion, which is the basis of theoperation of optical detectors, can be linear or nonlinear.When high sensitivities are needed, single-photon detectorsare used, which operate in a strongly nonlinear mode, theirresponse being independent of the number of detectedphotons. However, photon-number-resolving detectors areneeded, particularly in quantum optics, where n-photon statesare routinely produced. In quantum communication andquantum information processing, the photon-numberresolvingfunctionality is key to many protocols, such as theimplementation of quantum repeaters1 and linear-opticsquantum computing2. A linear detector with single-photonsensitivity can also be used for measuring a temporalwaveform at extremely low light levels, such as in longdistanceoptical communications, fluorescence spectroscopyand optical time-domain reflectometry. We demonstrate here aphoton-number-resolving detector based on parallelsuperconducting nanowires and capable of counting up to fourphotons at telecommunication wavelengths, with an ultralowdark count rate and high counting frequency

Superconducting nanowire photon number resolving detector at telecom wavelength

We demonstrate a photon-number-resolving (PNR) detector, based on parallel superconducting nanowires, capable of resolving up to 5 photons in the telecommunication wavelength range, with sensitivity and speed far exceeding existing approaches. © 2008 Optical Society of America

Self-assembled circuit patterns

Abstract. Self-assembly is a process in which basic units aggregate under attractive forces to form larger compound structures. Recent theoretical work has shown that pseudo-crystalline self-assembly can be algorithmic, in the sense that complex logic can be programmed into the growth process [26]. This theoretical work builds on the theory of twodimensional tilings [8], using rigid square tiles called Wang tiles [24] for the basic units of self-assembly, and leads to Turing-universal models such as the Tile Assembly Model [28]. Using the Tile Assembly Model, we show how algorithmic self-assembly can be exploited for fabrication tasks such as constructing the patterns that define certain digital circuits, including demultiplexers, RAM arrays, pseudowavelet transforms, and Hadamard transforms. Since DNA self-assembly appears to be promising for implementing the arbitrary Wang tiles [30, 13] needed for programming in the Tile Assembly Model, algorithmic self-assembly methods such as those presented in this paper may eventually become a viable method of arranging molecular electronic components [18], such as carbon nanotubes [10, 1], into molecular-scale circuits.