186 research outputs found
Hydrogen refinement during solid phase epitaxy of buried amorphous silicon layers
The effect of hydrogen on the kinetics of solid phase epitaxy (SPE) have been studied in buried amorphous Si layers. The crystallization rate of the front amorphous/crystalline (a/c) interface is monitored with time resolved reflectivity.Secondary ion mass spectrometry(SIMS) is used to examine H implanted profiles at selected stages of the anneals. The H retardation of the SPE rate is determined up to a H concentration of 2.3×10²⁰ cm¯³ where the SPE rate decreases by 80%. Numerical simulations are performed to model the H diffusion, the moving a/c interfaces and the refinement of the H profile at these interfaces. Despite the high H concentration involved, a simple Fickian diffusion model results in good agreement with the SIMS data. The segregation coefficient is estimated to be 0.07 at 575 °C. A significant fraction of the H escapes from the a-Si layer during SPE especially once the two a/c interfaces meet which is signified by the lack of H-related voids after a subsequent high temperature anneal.This research was supported by a grant from the Australian
Research Council
Optical addressing of an individual erbium ion in silicon
The detection of electron spins associated with single defects in solids is a
critical operation for a range of quantum information and measurement
applications currently under development. To date, it has only been
accomplished for two centres in crystalline solids: phosphorus in silicon using
electrical readout based on a single electron transistor (SET) and
nitrogen-vacancy centres in diamond using optical readout. A spin readout
fidelity of about 90% has been demonstrated with both electrical readout and
optical readout, however, the thermal limitations of the electrical readout and
the poor photon collection efficiency of the optical readout hinder achieving
the high fidelity required for quantum information applications. Here we
demonstrate a hybrid approach using optical excitation to change the charge
state of the defect centre in a silicon-based SET, conditional on its spin
state, and then detecting this change electrically. The optical frequency
addressing in high spectral resolution conquers the thermal broadening
limitation of the previous electrical readout and charge sensing avoids the
difficulties of efficient photon collection. This is done with erbium in
silicon and has the potential to enable new architectures for quantum
information processing devices and to dramatically increase the range of defect
centres that can be exploited. Further, the efficient electrical detection of
the optical excitation of single sites in silicon is a major step in developing
an interconnect between silicon and optical based quantum computing
technologies.Comment: Corrected the third affiliation. Corrected one cross-reference of
"Fig. 3b" to "Fig. 3c". Corrected the caption of Fig. 3a by changing (+-)1 to
Exploring quantum chaos with a single nuclear spin
Most classical dynamical systems are chaotic. The trajectories of two
identical systems prepared in infinitesimally different initial conditions
diverge exponentially with time. Quantum systems, instead, exhibit
quasi-periodicity due to their discrete spectrum. Nonetheless, the dynamics of
quantum systems whose classical counterparts are chaotic are expected to show
some features that resemble chaotic motion. Among the many controversial
aspects of the quantum-classical boundary, the emergence of chaos remains among
the least experimentally verified. Time-resolved observations of quantum
chaotic dynamics are particularly rare, and as yet unachieved in a single
particle, where the subtle interplay between chaos and quantum measurement
could be explored at its deepest levels. We present here a realistic proposal
to construct a chaotic driven top from the nuclear spin of a single donor atom
in silicon, in the presence of a nuclear quadrupole interaction. This system is
exquisitely measurable and controllable, and possesses extremely long intrinsic
quantum coherence times, allowing for the observation of subtle dynamical
behavior over extended periods. We show that signatures of chaos are expected
to arise for experimentally realizable parameters of the system, allowing the
study of the relation between quantum decoherence and classical chaos, and the
observation of dynamical tunneling.Comment: revised and published versio
High-fidelity adiabatic inversion of a electron spin qubit in natural silicon
The main limitation to the high-fidelity quantum control of spins in
semiconductors is the presence of strongly fluctuating fields arising from the
nuclear spin bath of the host material. We demonstrate here a substantial
improvement in single-qubit gate fidelities for an electron spin qubit bound to
a P atom in natural silicon, by applying adiabatic inversion instead of
narrow-band pulses. We achieve an inversion fidelity of 97%, and we observe
signatures in the spin resonance spectra and the spin coherence time that are
consistent with the presence of an additional exchange-coupled donor. This work
highlights the effectiveness of adiabatic inversion techniques for spin control
in fluctuating environments.Comment: 4 pages, 2 figure
Chromium single photon emitters in diamond fabricated by ion implantation
Controlled fabrication and identification of bright single photon emitters is
at the heart of quantum optics and materials science. Here we demonstrate a
controlled engineering of a chromium bright single photon source in bulk
diamond by ion implantation. The Cr center has fully polarized emission with a
ZPL centered at 749 nm, FWHM of 4 nm, an extremely short lifetime of ~1 ns, and
a count rate of 500 kcounts/s. By combining the polarization measurements and
the vibronic spectra, a model of the center has been proposed consisting of one
interstitial chromium atom with a transition dipole along one of the
directions
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