67 research outputs found
Phonon sidebands of color centers in hexagonal boron nitride
Low temperature photoluminescence spectra of a color center in hexagonal
boron nitride are analyzed. The acoustic phonon sideband can be described by a
deformation coupling proportional to strain to a phonon bath that is
effectively two dimensional. The optical phonon band is described by Frohlich
coupling to the LO-branches, and a deformation coupling proportional to lattice
displacement for the TO-branch. The resonances expressed in the optical band
vary from defect to defect, in some emitters, coupling to out-of-plane
polarized phonons is reported.Comment: 7 pages, 4 fig
Fast preparation of single hole spin in InAs/GaAs quantum dot in Voigt geometry magnetic field
The preparation of a coherent heavy-hole spin via ionization of a
spin-polarized electron-hole pair in an InAs/GaAs quantum dot in a Voigt
geometry magnetic field is investigated. For a dot with a 17 ueV bright-exciton
fine-structure splitting, the fidelity of the spin preparation is limited to
0.75, with optimum preparation occurring when the effective fine-structure of
the bright-exciton matches the in-plane hole Zeeman energy. In principle,
higher fidelities can be achieved by minimizing the bright-exciton
fine-structure splitting.Comment: 8 pages, 10 figs, published PRB 85 155310 (2012
Charge control in InP/GaInP single quantum dots embedded in Schottky diodes
We demonstrate control by applied electric field of the charge states in
single self-assembled InP quantum dots placed in GaInP Schottky structures
grown by metalorganic vapor phase epitaxy. This has been enabled by growth
optimization leading to suppression of formation of large dots uncontrollably
accumulating charge. Using bias- and polarization-dependent
micro-photoluminescence, we identify the exciton multi-particle states and
carry out a systematic study of the neutral exciton state dipole moment and
polarizability. This analysis allows for the characterization of the exciton
wavefunction properties at the single dot level for this type of quantum dots.
Photocurrent measurements allow further characterization of exciton properties
by electrical means, opening new possibilities for resonant excitation studies
for such system.Comment: 7 pages, 4 figure
Effect of the GaAsP shell on optical properties of self-catalyzed GaAs nanowires grown on silicon
We realize growth of self-catalyzed core-shell GaAs/GaAsP nanowires (NWs) on
Si substrates using molecular-beam epitaxy. Transmission electron microscopy
(TEM) of single GaAs/GaAsP NWs confirms their high crystal quality and shows
domination of the zinc-blende phase. This is further confirmed in optics of
single NWs, studied using cw and time-resolved photoluminescence (PL). A
detailed comparison with uncapped GaAs NWs emphasizes the effect of the GaAsP
capping in suppressing the non-radiative surface states: significant PL
enhancement in the core-shell structures exceeding 2000 times at 10K is
observed; in uncapped NWs PL is quenched at 60K whereas single core-shell
GaAs/GaAsP NWs exhibit bright emission even at room temperature. From analysis
of the PL temperature dependence in both types of NW we are able to determine
the main carrier escape mechanisms leading to the PL quench
Spin-photon interface and spin-controlled photon switching in a nanobeam waveguide
Access to the electron spin is at the heart of many protocols for integrated
and distributed quantum-information processing [1-4]. For instance, interfacing
the spin-state of an electron and a photon can be utilized to perform quantum
gates between photons [2,5] or to entangle remote spin states [6-9].
Ultimately, a quantum network of entangled spins constitutes a new paradigm in
quantum optics [1]. Towards this goal, an integrated spin-photon interface
would be a major leap forward. Here we demonstrate an efficient and optically
programmable interface between the spin of an electron in a quantum dot and
photons in a nanophotonic waveguide. The spin can be deterministically prepared
with a fidelity of 96\%. Subsequently the system is used to implement a
"single-spin photonic switch", where the spin state of the electron directs the
flow of photons through the waveguide. The spin-photon interface may enable
on-chip photon-photon gates [2], single-photon transistors [10], and efficient
photonic cluster state generation [11]
Chirality of nanophotonic waveguide with embedded quantum emitter for unidirectional spin transfer
Scalable quantum technologies may be achieved by faithful conversion between matter qubits and photonic qubits in integrated circuit geometries. Within this context, quantum dots possess well-defined spin states (matter qubits), which couple efficiently to photons. By embedding them in nanophotonic waveguides, they provide a promising platform for quantum technology implementations. In this paper, we demonstrate that the naturally occurring electromagnetic field chirality that arises in nanobeam waveguides leads to unidirectional photon emission from quantum dot spin states, with resultant in-plane transfer of matter-qubit information. The chiral behaviour occurs despite the non-chiral geometry and material of the waveguides. Using dot registration techniques, we achieve a quantum emitter deterministically positioned at a chiral point and realize spin-path conversion by design. We further show that the chiral phenomena are much more tolerant to dot position than in standard photonic crystal waveguides, exhibit spin-path readout up to 95±5% and have potential to serve as the basis of spin-logic and network implementations
Characterisation of tungsten nano-wires prepared by electron and ion beam induced chemical vapour deposition
In this study we present a morphological characterisation of tungsten nano-wires prepared by electron and ion beam induced chemical vapour deposition. Our observations show that both electron and ion beam as-deposited nano-wires exhibit an amorphous like microstructure. Irradiation of the electron beam deposited wires with 200kV incident electrons in the TEM was found to cause an electron beam induced anneal resulting in the formation of a localised nano-crystalline structure. Wires deposited using 30kV Ga+ ions were found to exhibit the appearance of low temperature superconducting properties with a critical transition temperature Tc of ~5K
Prospective for graphene based thermal mid-infrared light emitting devices
We have investigated the spatial and spectral characteristics of mid-infrared thermal emission from large area Chemical Vapor Deposition (CVD) graphene, transferred onto SiO2/Si, and show that the emission is broadly that of a grey-body emitter, with emissivity values of approximately 2% and 6% for mono- and multilayer graphene. For the currents used, which could be sustained for over one hundred hours, the emission peaked at a wavelength of around 4 μm and covered the characteristic absorption of many important gases. A measurable modulation of thermal emission was obtained even when the drive current was modulated at frequencies up to 100 kHz
Low temperature electrical characterisation of tungsten nano-wires fabricated by electron and ion beam induced chemical vapour deposition
In this study we have fabricated tungsten containing nano-wires using focused electron and ion beams from a tungsten hexacarbonyl precursor. The temperature dependent conductive properties of the wires have been investigated. Although a superconducting transition (at ∼ 5.5 K) has been observed in ion beam deposited wires, electron beam deposited wires display non-metallic conduction properties consistent with a variable range hopping conduction mechanism. Micro-structural and compositional analysis has been performed using transmission electron microscopy and associated techniques. The observed disorder of the as-deposited wires, together with the higher oxygen and lower metal content of the electron beam deposited wires was found to correlate well with the low temperature electrical properties. In addition, the electron beam deposited wires were shown to be particularly susceptible to irradiation damage when illuminated using 200 kV electrons in the transmission electron microscope. With electron doses in the region of ∼ 50 A/cm2 the as-deposited disordered structure was refined locally to give regions of randomly orientated nano-crystallites
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