591 research outputs found
Using mutual information to measure order in model glass-formers
Whether or not there is growing static order accompanying the dynamical
heterogeneity and increasing relaxation times seen in glassy systems is a
matter of dispute. An obstacle to resolving this issue is that the order is
expected to be amorphous and so not amenable to simple order parameters. We use
mutual information to provide a general measurement of order that is sensitive
to multi-particle correlations. We apply this to two glass-forming systems (2D
binary mixtures of hard disks with different size ratios to give varying
amounts of hexatic order) and show that there is little growth of amorphous
order in the system without crystalline order. In both cases we measure the
dynamical length with a four-point correlation function and find that it
increases significantly faster than the static lengths in the system as density
is increased. We further show that we can recover the known scaling of the
dynamic correlation length in a kinetically constrained model, the 2-TLG.Comment: 10 pages, 12 Figure
The Devil is in the details:Pentagonal bipyramids and dynamic arrest
Colloidal suspensions have long been studied as a model for atomic and
molecular systems, due to the ability to fluorescently label and individually
track each particle, yielding particle-resolved structural information. This
allows various local order parameters to be probed that are otherwise
inaccessible for a comparable molecular system. For phase transitions such as
crystallisation, appropriate order parameters which emphasise 6-fold symmetry
are a natural choice, but for vitrification the choice of order parameter is
less clear cut. Previous work has highlighted the importance of icosahedral
local structure as the glass transition is approached. However, counting
icosahedra or related motifs is not a continuous order parameter in the same
way as, for example, the bond-orientational order parameters and .
In this work we investigate the suitability of using pentagonal bipyramid
membership, a structure which can be assembled into larger, five-fold symmetric
structures, as a finer order parameter to investigate the glass transition. We
explore various structural and dynamic properties and show that this new
approach produces many of the same findings as simple icosahedral membership,
but we also find that large instantaneous displacements are often correlated
with significant changes in pentagonal bipyramid membership, and unlike the
population of defective icosahedra, the pentagonal bypyramid membership and
spindle number do not saturate for any measured volume fraction, but continues
to increase.Comment: accepted by JStat Mech: Theory and Experiment 201
On-chip electrically controlled routing of photons from a single quantum dot
Electrical control of on-chip routing of photons emitted by a single InAs/GaAs self-assembled quantum dot (SAQD) is demonstrated in a photonic crystal cavity-waveguide system. The SAQD is located inside an H1 cavity, which is coupled to two photonic crystal waveguides. The SAQD emission wavelength is electrically tunable by the quantum-confined Stark effect. When the SAQD emission is brought into resonance with one of two H1 cavity modes, it is preferentially routed to the waveguide to which that mode is selectively coupled. This proof of concept provides the basis for scalable, low-power, high-speed operation of single-photon routers for use in integrated quantum photonic circuits
Path-dependent initialization of a single quantum dot exciton spin in a nanophotonic waveguide
We demonstrate a scheme for in-plane initialization of a single exciton spin in an InGaAs quantum dot (QD) coupled to a GaAs nanobeam waveguide. The chiral coupling of the QD and the optical mode of the nanobeam enables spin initialization fidelity approaching unity in magnetic field B=1 T and >0.9 without the field. We further show that this in-plane excitation scheme is independent of the incident excitation laser polarization and depends solely on the excitation direction. This scheme provides a robust in-plane spin excitation basis for a photon-mediated spin network for quantum information applications
Monolithic integration of a quantum emitter with a compact on-chip beam-splitter
A fundamental component of an integrated quantum optical circuit is an on-chip beam-splitter operating at the single-photon level. Here, we demonstrate the monolithic integration of an on-demand quantum emitter in the form of a single self-assembled InGaAs quantum dot (QD) with a compact (>10 μm), air clad, free standing directional coupler acting as a beam-splitter for anti-bunched light. The device was tested by using single photons emitted by a QD embedded in one of the input arms of the device. We verified the single-photon nature of the QD signal by performing Hanbury Brown-Twiss measurements and demonstrated single-photon beam splitting by cross-correlating the signal from the separate output ports of the directional coupler
On-chip resonantly-driven quantum emitter with enhanced coherence
Advances in nanotechnology provide techniques for the realisation of integrated quantum-optical circuits for on-chip quantum information processing(QIP). The indistinguishable single photons, required for such devices can be generated by parametric down-conversion, or from quantum emitters such as colour centres and quantum dots(QDs). Among these, semiconductor QDs offer distinctive capabilities including on-demand operation, coherent control, frequency tuning and compatibility with semiconductor nanotechnology. Moreover, the coherence of QD photons can be significantly enhanced in resonance fluorescence(RF) approaching at its best the coherence of the excitation laser. However, the implementation of QD RF in scalable on-chip geometries remains challenging due to the need to suppress stray laser photons. Here we report on-chip QD RF coupled into a single-mode waveguide with negligible resonant laser background and show that the coherence is enhanced compared to off-resonant excitation. The results pave the way to a novel class of integrated quantum-optical devices for on-chip QIP with embedded resonantly-driven quantum emitters
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