6 research outputs found
Trion Species-Resolved Quantum Beats in MoSe2
Monolayer photonic materials offer a tremendous potential for on-chip
optoelectronic devices. Their realization requires knowledge of optical
coherence properties of excitons and trions that have so far been limited to
nonlinear optical experiments carried out with strongly inhomogenously
broadened material. Here we employ h-BN encapsulated and electrically gated
MoSe2 to reveal coherence properties of trion-species directly in the linear
optical response. Autocorrelation measurements reveal long dephasing times up
to T2=1.16+-0.05 ps for positively charged excitons. Gate dependent
measurements provide evidence that the positively-charged trion forms via
spatially localized hole states making this trion less prone to dephasing in
the presence of elevated hole carrier concentrations. Quantum beat signatures
demonstrate coherent coupling between excitons and trions that have a dephasing
time up to 0.6 ps, a two-fold increase over those in previous reports. A key
merit of the prolonged exciton/trion coherences is that they were achieved in a
linear optical experiment, and thus are directly relevant to applications in
nanolasers, coherent control, and on-chip quantum information processing
requiring long photon coherence.Comment: 21 pages, 6 figures, 2 SOI figure
Quantum Light Signatures and Nanosecond Spectral Diffusion from Cavity-Embedded Carbon Nanotubes
Single-walled carbon nanotubes (SWCNTs) are considered
for novel
optoelectronic and quantum photonic devices, such as single photon
sources, but methods must be developed to enhance the light extraction
and spectral purity, while simultaneously preventing multiphoton emission
as well as spectral diffusion and blinking in dielectric environments
of a cavity. Here we demonstrate that utilization of nonpolar polystyrene
as a cavity dielectric completely removes spectral diffusion and blinking
in individual SWCNTs on the millisecond to multisecond time scale,
despite the presence of surfactants. With these cavity-embedded SWCNT
samples, providing a 50-fold enhanced exciton emission into the far
field, we have been able to carry out photophysical studies for the
first time with nanosecond timing resolution. We uncovered that fast
spectral diffusion processes (1–3 ns) remain that make significant
contributions to the spectral purity, thereby limiting the use of
SWCNTs in quantum optical applications requiring indistinguishable
photons. Measured quantum light signatures reveal pronounced photon
antibunching (<i>g</i><sup>2</sup>(0) = 0.15) accompanied
by side-peak bunching signatures indicative of residual blinking on
the submicrosecond time scale. The demonstrated enhanced single photon
emission from cavity-embedded SWCNTs is promising for applications
in quantum key distribution, while the demonstrated passivation effect
of polystyrene with respect to the stability of the optical emission
opens a novel pathway toward optoelectronic devices with enhanced
performance
Strong Acoustic Phonon Localization in Copolymer-Wrapped Carbon Nanotubes
Understanding and controlling exciton–phonon interactions in carbon nanotubes has important implications for producing efficient nanophotonic devices. Here we show that laser vaporization-grown carbon nanotubes display ultranarrow luminescence line widths (120 μeV) and well-resolved acoustic phonon sidebands at low temperatures when dispersed with a polyfluorene copolymer. Remarkably, we do not observe a correlation of the zero-phonon line width with <sup>13</sup>C atomic concentration, as would be expected for pure dephasing of excitons with acoustic phonons. We demonstrate that the ultranarrow and phonon sideband-resolved emission spectra can be fully described by a model assuming extrinsic acoustic phonon localization at the nanoscale, which holds down to 6-fold narrower spectral line width compared to previous work. Interestingly, both exciton and acoustic phonon wave functions are strongly spatially localized within 5 nm, possibly mediated by the copolymer backbone, opening future opportunities to engineer dephasing and optical bandwidth for applications in quantum photonics and cavity optomechanics
Nonmagnetic Quantum Emitters in Boron Nitride with Ultranarrow and Sideband-Free Emission Spectra
Hexagonal boron nitride
(hBN) is an emerging material in nanophotonics
and an attractive host for color centers for quantum photonic devices.
Here, we show that optical emission from individual quantum emitters
in hBN is spatially correlated with structural defects and can display
ultranarrow zero-phonon line width down to 45 μeV if spectral
diffusion is effectively eliminated by proper surface passivation.
We demonstrate that undesired emission into phonon sidebands is largely
absent for this type of emitter. In addition, magneto-optical characterization
reveals cycling optical transitions with an upper bound for the g-factor
of 0.2 ± 0.2. Spin-polarized density functional theory calculations
predict possible commensurate transitions between like-spin electron
states, which are in excellent agreement with the experimental nonmagnetic
defect center emission. Our results constitute a step toward the realization
of narrowband quantum light sources and the development of spin–photon
interfaces within 2D materials for future chip-scale quantum networks
Broadband Light Collection Efficiency Enhancement of Carbon Nanotube Excitons Coupled to Metallo-Dielectric Antenna Arrays
The realization of
on-chip quantum networks ideally requires lossless
interfaces between photons and solid-state quantum emitters. We propose
and demonstrate on-chip arrays of metallo-dielectric antennas (MDA)
that are tailored toward efficient and broadband light collection
from individual embedded carbon nanotube quantum emitters by trapping
air gaps on chip that form cavity modes. Scalable implementation is
realized by employing polymer layer dry-transfer techniques that avoid
solvent incompatibility issues, as well as a planar design that avoids
solid-immersion lenses. Cryogenic measurements demonstrate 7-fold
enhanced exciton intensity when compared to emitters located on bare
wafers, corresponding to a light collection efficiency (LCE) up to
92% in the best case (average LCE of 69%) into a narrow output cone
of ±15° that enables a priori fiber-to-chip butt coupling.
The demonstrated MDA arrays are directly compatible with other quantum
systems, particularly 2D materials, toward enabling efficient on-chip
quantum light sources or spin-photon interfaces requiring unity light
collection, both at cryogenic or room temperature
Low-Temperature Single Carbon Nanotube Spectroscopy of sp<sup>3</sup> Quantum Defects
Aiming
to unravel the relationship between chemical configuration
and electronic structure of sp<sup>3</sup> defects of aryl-functionalized
(6,5) single-walled carbon nanotubes (SWCNTs), we perform low-temperature
single nanotube photoluminescence (PL) spectroscopy studies and correlate
our observations with quantum chemistry simulations. We observe sharp
emission peaks from individual defect sites that are spread over an
extremely broad, 1000–1350 nm, spectral range. Our simulations
allow us to attribute this spectral diversity to the occurrence of
six chemically and energetically distinct defect states resulting
from topological variation in the chemical binding configuration of
the monovalent aryl groups. Both PL emission efficiency and spectral
line width of the defect states are strongly influenced by the local
dielectric environment. Wrapping the SWCNT with a polyfluorene polymer
provides the best isolation from the environment and yields the brightest
emission with near-resolution limited spectral line width of 270 μeV,
as well as spectrally resolved emission wings associated with localized
acoustic phonons. Pump-dependent studies further revealed that the
defect states are capable of emitting single, sharp, isolated PL peaks
over 3 orders of magnitude increase in pump power, a key characteristic
of two-level systems and an important prerequisite for single-photon
emission with high purity. These findings point to the tremendous
potential of sp<sup>3</sup> defects in development of room temperature
quantum light sources capable of operating at telecommunication wavelengths
as the emission of the defect states can readily be extended to this
range <i>via</i> use of larger diameter SWCNTs