61 research outputs found
Atomic Layer Deposition Nucleation Dependence on Diamond Surface Termination
Surface termination and interfacial interactions are critical for advanced
solid-state quantum applications. In this paper, we demonstrate that atomic
layer deposition (ALD) can both provide valuable insight on the chemical
environment of the surface, having sufficient sensitivity to distinguish
between the common diamond (001) surface termination types and passivate these
interfaces as desired. We selected diamond substrates exhibiting both smooth
and anomalously rough surfaces to probe the effect of morphology on ALD
nucleation. We use high resolution in situ spectroscopic ellipsometry to
monitor the surface reaction with sub-angstrom resolution, to evaluate the
nucleation of an ALD Al2O3 process as a function of different ex and in situ
treatments to the diamond surface. In situ water dosing and high vacuum
annealing provided the most favorable environment for nucleation of
dimethylaluminum isopropoxide and water ALD. Hydrogen termination passivated
both smooth and rough surfaces while triacid cleaning passivated the smooth
surface only, with striking effectiveness.Comment: 31 pages, 14 figure
Quantifying the limits of controllability for the nitrogen-vacancy electron spin defect
Solid-state electron spin qubits, like the nitrogen-vacancy center in
diamond, rely on control sequences of population inversion to enhance
sensitivity and improve device coherence. But even for this paradigmatic
system, the fundamental limits of population inversion and potential impacts on
applications like quantum sensing have not been assessed quantitatively. Here,
we perform high accuracy simulations beyond the rotating wave approximation,
including explicit unitary simulation of neighboring nuclear spins. Using
quantum optimal control, we identify analytical pulses for the control of a
qubit subspace within the spin-1 ground state and quantify the relationship
between pulse complexity, control duration, and fidelity. We find exponentially
increasing amplitude and bandwidth requirements with reduced control duration
and further quantify the emergence of non-Markovian effects for multipulse
sequences using sub-nanosecond population inversion. From this, we determine
that the reduced fidelity and non-Markovianity is due to coherent interactions
of the electron spin with the nuclear spin environment. Ultimately, we identify
a potentially realizable regime of nanosecond control duration for
high-fidelity multipulse sequences. These results provide key insights into the
fundamental limits of quantum information processing using electron spin
defects in diamond.Comment: 9 pages, 5 figure
Photoluminescence spectra of point defects in semiconductors: validation of first principles calculations
Optically and magnetically active point defects in semiconductors are
interesting platforms for the development of solid-state quantum technologies.
Their optical properties are usually probed by measuring photoluminescence
spectra, which provide information on excitation energies and on the
interaction of electrons with lattice vibrations. We present a combined
computational and experimental study of photoluminescence spectra of defects in
diamond and SiC, aimed at assessing the validity of theoretical and numerical
approximations used in first principles calculations, including the use of the
Franck-Condon principle and the displaced harmonic oscillator approximation. We
focus on prototypical examples of solid-state qubits, the divacancy centers in
SiC and the nitrogen-vacancy in diamond, and we report computed
photoluminescence spectra as a function of temperature that are in very good
agreement with the measured ones. As expected we find that the use of hybrid
functionals leads to more accurate results than semilocal functionals.
Interestingly our calculations show that constrained density functional theory
(CDFT) and time-dependent hybrid DFT perform equally well in describing the
excited state potential energy surface of triplet states; our findings indicate
that CDFT, a relatively cheap computational approach, is sufficiently accurate
for the calculations of photoluminescence spectra of the defects studied here.
Finally, we find that only by correcting for finite-size effects and
extrapolating to the dilute limit, one can obtain a good agreement between
theory and experiment. Our results provide a detailed validation protocol of
first principles calculations of photoluminescence spectra, necessary both for
the interpretation of experiments and for robust predictions of the electronic
properties of point defects in semiconductors
- …