36 research outputs found
Mapping the energy landscape of biomolecules using single molecule force correlation spectroscopy (FCS): Theory and applications
In the current AFM experiments the distribution of unfolding times, P(t), is
measured by applying a constant stretching force f_s from which the apparent
unfolding rate is obtained. To describe the complexity of the underlying energy
landscape requires additional probes that can incorporate the dynamics of
tension propagation and relaxation of the polypeptide chain upon force quench.
We introduce a theory of force correlation spectroscopy (FCS) to map the
parameters of the energy landscape of proteins. In the FCS the joint
distribution, P(T,t) of folding and unfolding times is constructed by repeated
application of cycles of stretching at constant fs, separated by release
periods T during which the force is quenched to f_q<f_s. During the release
period, the protein can collapse to a manifold of compact states or refold. We
show that P(T,t) can be used to resolve the kinetics of unfolding as well as
formation of native contacts and to extract the parameters of the energy
landscape using chain extension as the reaction coordinate and P(T,t). We
illustrate the utility of the proposed formalism by analyzing simulations of
unfolding-refolding trajectories of a coarse-grained protein S1 with beta-sheet
architecture for several values of f_s, T and f_q=0. The simulations of
stretch-relax trajectories are used to map many of the parameters that
characterize the energy landscape of S1.Comment: 23 pages, 9 figures; accepted to Biophysical Journa
Quantum interference and manipulation of entanglement in silicon wire waveguide quantum circuits
Integrated quantum photonic waveguide circuits are a promising approach to
realizing future photonic quantum technologies. Here, we present an integrated
photonic quantum technology platform utilising the silicon-on-insulator
material system, where quantum interference and the manipulation of quantum
states of light are demonstrated in components orders of magnitude smaller than
in previous implementations. Two-photon quantum interference is presented in a
multi-mode interference coupler, and manipulation of entanglement is
demonstrated in a Mach-Zehnder interferometer, opening the way to an
all-silicon photonic quantum technology platform.Comment: 7 page
Superconducting nanowire single-photon detectors: physics and applications
Single-photon detectors based on superconducting nanowires (SSPDs or SNSPDs)
have rapidly emerged as a highly promising photon-counting technology for
infrared wavelengths. These devices offer high efficiency, low dark counts and
excellent timing resolution. In this review, we consider the basic SNSPD
operating principle and models of device behaviour. We give an overview of the
evolution of SNSPD device design and the improvements in performance which have
been achieved. We also evaluate device limitations and noise mechanisms. We
survey practical refrigeration technologies and optical coupling schemes for
SNSPDs. Finally we summarize promising application areas, ranging from quantum
cryptography to remote sensing. Our goal is to capture a detailed snapshot of
an emerging superconducting detector technology on the threshold of maturity.Comment: 27 pages, 5 figures, Review article preprint versio
Structure and spectroscopic characterization of tetrathia- and tetraselena[8]circulenes as a new class of polyaromatic heterocycles
Matrix of Integrated Superconducting Single-Photon Detectors With High Timing Resolution
Generation of 15 μm discrete frequency-entangled two-photon state in polarization-maintaining fibers
Chromosomal integration of a synthetic expression control sequence achieves poly-γ-glutamate production in a Bacillus subtilis strain
Single-Photon Detection System for Quantum Optics Applications
We describe the design and characterization of a fiber-coupled double-channel single-photon detection system based on superconducting single-photon detectors (SSPD), and its application for quantum optics experiments on semiconductor nanostructures. When operated at 2-K temperature, the system shows 10% quantum efficiency at 1.3-¿m wavelength with dark count rate below 10 counts per second and timing resolution <100 ps. The short recovery time and absence of afterpulsing leads to counting frequencies as high as 40 MHz. Moreover, the low dark count rate allows operation in continuous mode (without gating). These characteristics are very attractive-as compared to InGaAs avalanche photodiodes-for quantum optics experiments at telecommunication wavelengths. We demonstrate the use of the system in time-correlated fluorescence spectroscopy of quantum wells and in the measurement of the intensity correlation function of light emitted by semiconductor quantum dots at 1300 nm