KEYWORDS: Energy transfer, Gold, Data modeling, Energy efficiency, Fluorescence resonance energy transfer, Nanocrystals, Metals, Semiconductors, Quantum dots, Nanolithography
We characterize energy transfer between luminescent 1.5 nm diameter gold nanocrystal (AuNC) acceptors and three structurally/functionally-distinct classes of emissive donors including organic dyes, metal chelates and semiconductor quantum dots (QDs). Energy transfer efficiencies within the donor-AuNC assemblies were evaluated with steady-state and time-resolved measurements. Donor quenching was observed for every donor-acceptor pair although AuNC sensitization was only observed from metal-chelates and QDs. Results were analyzed with Förster’s dipole-dipole coupling model (FRET) and dipole-metal damping models including nanosurface energy transfer (NSET) and nanovolume energy transfer (NVET). FRET dramatically underestimated energy transfer efficiencies while the damping models provided qualitatively better fits to the data although neither fully reproduces the experimental data. Analysis suggests that organic dye donor quenching without corresponding AuNC sensitization results from enhanced intersystem crossing between dye singlet and triplet states driven by AuNC magnetic dipoles. We further consider factors that account for the unique electronic properties of the ultra-small luminescent AuNCs including the high excited state densities, rapid dephasing time and strong electron confinement as well as paramagnetic properties. Overall, the results provide insight into requirements necessary for realizing applications based on AuNC acceptor sensitization.
S. Rolston, J. R. Anderson, U. Chukwu, J. Grover, J. Hertzberg, J. Hoffman, P. Kordell, J. Lee, C. Lobb, L. Orozco, S. Ravets, P. Solano, K. Voigt, F. Wellstood, J. Wong-Campos, G. Beadie, F. Fatemi
Hybrid quantum systems can be formed that combine the strengths of multiple platforms while avoiding the weaknesses. Here we report on progress toward a hybrid quantum system of neutral atom spins coupled to superconducting qubits. We trap laser-cooled rubidium atoms in the evanescent field of an ultrathin optical fiber, which will be suspended a few microns above a superconducting circuit that resonates at the hyperfine frequency of the Rb atoms, allowing magnetic coupling between the atoms and superconductor. As this will be done in a dilution refrigerator environment, the technical demands on the optical fiber is severe. We have developed and optimized a tapered fiber fabrication system, achieving optical transmission in excess of 99.95% , and fibers that can sustain 400 mW of optical power in a UHV environment. We have also optimized tapered fibers that can support higher order optical modes with high transmission (> 97%), which may be useful for different optical potential geometries. We have developed an in-situ tunable high-Q superconducting microwave resonator that can be tuned to within the resonator linewidth of the 6.8 GHz frequency of the Rb hyperfine transition.
We have demonstrated efficient propagation of the first excited TE01, TM01, and HE21 modes in a nanofiber
with a radius of 400 nm. As we decrease the taper angle from 4 mrad to 1 mrad, the propagation becomes more
adiabatic and the transmission improves from 20% to 85%. We have also demonstrated that the choice of drawn
fiber can have a significant impact on the propagation characteristics.
Quantum memory is regarded as one of the essential components in the fields of quantum computing and quantum
communication. Warm atomic vapor cells for quantum memory, as originally described in DLCZ (for Duan, Lukin,
Cirac, and Zoller) protocol, are appealing due to the perceived reduction in experimental complexity and commercial
availability. However, published studies on quantum memory using warm vapor cells were performed under widely
dissimilar experimental conditions and reported ambiguous results. In order for the memory to exhibit non-classical
behavior to a high degree of certainty, the cross-correlation value between the Stokes and anti-Stokes photons needs to
be greater than two. In this work we demonstrate quantum memory with cross-correlation value between the Stokes and
anti-Stokes photons greater than two lasting for 4 μs using warm Rb vapor with buffer gas for nearly co-propagating
write and read beams.
Quantum memory is considered to be one of the key elements in the fields of quantum computing and quantum
communication. Warm atomic vapor cells for quantum memory in DLCZ (for Duan, Lukin, Cirac, and Zoller) protocol
are appealing due to the perceived reduction in experimental complexity and commercial availability. However, reported
results on quantum memory using warm vapor cells were done under widely different experimental conditions and
produced ambiguous results. In order for the memory to exhibit non-classical behavior, to a high degree of certainty, the
cross-correlation value between the Stokes and anti-Stokes photons needs to be greater than two. In this work we
demonstrate quantum memory with cross-correlation value between the Stokes and anti-Stokes photons greater than two
lasting for 4 μs using warm Rb vapor with buffer gas for nearly co-propagating write and read beams.
Pulsed coherent population trapping in atomic vapor provides a convenient method for generating frequency
narrowed atomic resonance using Ramsey interference. Here, we present our experimental results showing
high-contrast and sub-kilohertz Ramsey interference fringes produced by coherently prepared 85Rb atoms
using Raman excitation formed in D1 line transitions. A test system for atomic clock has been constructed to
measure light shift for both continuous and pulsed Raman excitation cases. Our measurements show that
light shift measured using pulsed Raman excitation, is reduced compared to the continuous excitation case.
Our ability to measure light shift is currently limited by the resolution of the frequency counter, and
performance of the locking electronics used.
The phenomenon of all-optical Ramsey interference using pulsed coherent population trapping
(CPT) beams provides a new avenue for developing frequency standards using atomic vapor. In
this study, we show that frequency narrowed Ramsey fringes can be produced in rubidium vapor
without the effect of power broadening. We observed fringes of width as narrow as 1 kHz using
a buffer-gas filled rubidium cell. A compact injection-locked laser (ILL) system was used to
generate CPT beams. Studies also show that ac Stark effect on Ramsey fringes can be reduced,
and higher frequency stability can be achieved in a clock application. The results are
encouraging to propose an architecture for development of a pulsed CPT Ramsey clock. In this
paper, we also provide related discussions on clock frequency stability, and our plans for future
experiments.
Application of slow light linear delay to squint-free (true-time delay) steering of phased array radar antennae
is discussed. Theoretical analysis is provided on true-time delay radar requirements, including delay precision,
amplitude precision, and bandwidth. We also discuss an improvement to the slow light technique based on
stimulated Brillouin scattering by using a Faraday rotator mirror that provides temporally stable, linear (with
pump power) delay, applicable to practical implementations. Future directions are considered.
We demonstrate the generation of single-beam dark toroidal optical intensity distributions, which are of interest for
neutral atom storage and atom interferometry. We demonstrate experimentally and numerically optical potentials that
contain a ring-shaped intensity minimum, bounded in all directions by higher intensity. We use a spatial light modulator
to alter the phase of an incident laser beam, and analyze the resulting optical propagation characteristics. For small
toroidal traps (< 50 &mgr;m diameter), we find an optimal superposition of Laguerre-Gaussian modes that allows the
formation of single-beam toroidal traps. We generate larger toroidal bottle traps by focusing hollow beams with toroidal
lenses imprinted onto the spatial light modulator.
We demonstrate an experimental technique for manipulating atom clouds with high-speed and high resolution. By
combining holographically engineered laser beams from a spatial light modulator with acousto-optic deflection, we
manipulate the spatial locations of multiple cold atom clouds held in dark optical traps with individual site control.
Additionally, we demonstrate smooth 2-dimensional motion of atomic ensembles.
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