150 research outputs found
Spin-Photon Dynamics of Quantum Dots in Two-mode Cavities
A quantum dot interacting with two resonant cavity modes is described by a
two-mode Jaynes-Cummings model. Depending on the quantum dot energy level
scheme, the interaction of a singly doped quantum dot with a cavity photon
generates entanglement of electron spin and cavity states or allows one to
implement a SWAP gate for spin and photon states. An undoped quantum dot in the
same structure generates pairs of polarization entangled photons from an
initial photon product state. For realistic cavity loss rates, the fidelity of
these operations is of order 80%.Comment: 6 pages, 4 figures; extended discussion of experimental
implementatio
First-principles theory of the luminescence lineshape for the triplet transition in diamond NV centre
In this work we present theoretical calculations and analysis of the vibronic
structure of the spin-triplet optical transition in diamond nitrogen-vacancy
centres. The electronic structure of the defect is described using accurate
first-principles methods based on hybrid functionals. We devise a computational
methodology to determine the coupling between electrons and phonons during an
optical transition in the dilute limit. As a result, our approach yields a
smooth spectral function of electron-phonon coupling and includes both
quasi-localized and bulk phonons on equal footings. The luminescence lineshape
is determined via the generating function approach. We obtain a highly accurate
description of the luminescence band, including all key parameters such as the
Huang-Rhys factor, the Debye-Waller factor, and the frequency of the dominant
phonon mode. More importantly, our work provides insight into the vibrational
structure of nitrogen vacancy centres, in particular the role of local modes
and vibrational resonances. In particular, we find that the pronounced mode at
65 meV is a vibrational resonance, and we quantify localization properties of
this mode. These excellent results for the benchmark diamond nitrogen-vacancy
centre provide confidence that the procedure can be applied to other defects,
including alternative systems that are being considered for applications in
quantum information processing
Quenching Spin Decoherence in Diamond through Spin Bath Polarization
We experimentally demonstrate that the decoherence of a spin by a spin bath
can be completely eliminated by fully polarizing the spin bath. We use electron
paramagnetic resonance at 240 gigahertz and 8 Tesla to study the spin coherence
time of nitrogen-vacancy centers and nitrogen impurities in diamond from
room temperature down to 1.3 K. A sharp increase of is observed below the
Zeeman energy (11.5 K). The data are well described by a suppression of the
flip-flop induced spin bath fluctuations due to thermal spin polarization.
saturates at below 2 K, where the spin bath polarization
is 99.4 %.Comment: 5 pages and 3 figure
Cavity-enhanced measurements of defect spins in silicon carbide
The identification of new solid-state defect-qubit candidates in widely used semiconductors has the potential to enable the use of nanofabricated devices for enhanced qubit measurement and control operations. In particular, the recent discovery of optically active spin states in silicon carbide thin films offers a scalable route for incorporating defect qubits into on-chip photonic devices. Here, we demonstrate the use of 3C silicon carbide photonic crystal cavities for enhanced excitation of color-center defect spin ensembles in order to increase measured photoluminescence signal count rates, optically detected magnetic-resonance signal intensities, and optical spin initialization rates. We observe an up to a factor of 30 increase in the photoluminescence and optically detected magnetic-resonance signals from Ky5 color centers excited by cavity-resonant excitation and increase the rate of ground-state spin initialization by approximately a factor of 2. Furthermore, we show that the 705-fold reduction in excitation mode volume and enhanced excitation and collection efficiencies provided by the structures can be used to overcome inhomogenous broadening in order to facilitate the study of defect-qubit subensemble properties. These results highlight some of the benefits that nanofabricated devices offer for engineering the local photonic environment of color-center defect qubits to enable applications in quantum information and sensin
Theoretical model of the dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide
Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point
defects in semiconductors is a key resource for both initializing nuclear
quantum memories and producing nuclear hyperpolarization. DNP is therefore an
important process in the field of quantum-information processing,
sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based
spintronics. DNP based on optical pumping of point defects has been
demonstrated by using the electron spin of nitrogen-vacancy (NV) center in
diamond, and more recently, by using divacancy and related defect spins in
hexagonal silicon carbide (SiC). Here, we describe a general model for these
optical DNP processes that allows the effects of many microscopic processes to
be integrated. Applying this theory, we gain a deeper insight into dynamic
nuclear spin polarization and the physics of diamond and SiC defects. Our
results are in good agreement with experimental observations and provide a
detailed and unified understanding. In particular, our findings show that the
defects' electron spin coherence times and excited state lifetimes are crucial
factors in the entire DNP process
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