arXiv subjects

Joanna M. Zajac

Publications and source records attributed to Joanna M. Zajac.

5 recordsLinked to original sources

arXiv2025

Density-functional theory study of the interaction between NV$^{-}$ centers and native defects in diamond

The NV$^{-}$ color center in diamond has been demonstrated as a nanoscale sensor for quantum metrology. However, the properties that make it ideal for measuring, e.g., minute electric and magnetic fields also make it sensitive to imperfections in the diamond host. In this work, we quantify the impact of nearby native defects on the many-body states of NV$^{-}$. We combine previous quantum embedding results of strain and electric-field susceptibilities of NV$^{-}$ with density-functional theory calculations on native defects. The latter are used to parametrize continuum models in order to extrapolate the effects of native defects up to the micrometer scale. We show that under ideal measuring conditions, the optical properties of NV$^{-}$ are measurably affected by the strain caused by single carbon interstitials and vacancies up to 200 nm away; in contrast, the NV$^{-}$ is measurably affected by the electric field of such charged (neutral) native defects within a micron (100 nm). Finally, we show how measuring multiple individual NV$^{-}$ centers in the vicinity of a native defect can be used to determine the nature of the defect and its charge state.

cond-mat.mtrl-sci↗

arXiv2024

Quantum embedding study of strain and charge induced Stark effects on the NV$^{-}$ center in diamond

The NV$^{-}$ color center in diamond has been demonstrated as a powerful nanosensor for quantum metrology due to the sensitivity of its optical and spin properties to external electric, magnetic, and strain fields. In view of these applications, we use quantum embedding to derive a many-body description of strain and charge induced Stark effects on the NV$^{-}$ center. We quantify how strain longitudinal to the axis of NV$^{-}$ shifts the excited states in energy, while strain with a component transverse to the NV$^{-}$ axis splits the degeneracies of the $^{3}E$ and $^{1}E$ states. The largest effects are for the optically relevant $^{3}E$ manifold, which splits into $E_{x}$ and $E_{y}$ with transverse strain. From these responses we extract strain susceptibilities for the $E_{x/y}$ states within the quasi-linear regime. Additionally, we study the many-body dipole matrix elements of the NV$^{-}$ and find a permanent dipole 1.64 D at zero strain, which is somewhat smaller than that obtained from recent density functional theory calculations. We also determine the transition dipole between the $E_{x}$ and $E_{y}$ and how it evolves with strain.

cond-mat.mtrl-sci↗

arXiv2021

Microscopic processes during ultra-fast laser generation of Frenkel defects in diamond

Engineering single atomic defects into wide bandgap materials has become an attractive field in recent years due to emerging applications such as solid-state quantum bits and sensors. The simplest atomic-scale defect is the lattice vacancy which is often a constituent part of more complex defects such as the nitrogen-vacancy (NV) centre in diamond, therefore an understanding of the formation mechanisms and precision engineering of vacancies is desirable. We present a theoretical and experimental study into the ultra-fast laser generation of vacancy-interstitial pairs (Frenkel defects) in diamond. The process is described by a set of coupled rate equations of the pulsed laser interaction with the material and of the non-equilibrium dynamics of charge carriers during and in the wake of the pulse. We find that a model for Frenkel defect generation via the recombination of a bound biexciton as the electron plasma cools provides good agreement with experimental data, reproducing an effective non-linearity of $\sim$ 40 for Frenkel defect generation with respect to laser pulse energy.

cond-mat.mtrl-sci↗

arXiv2016

Indistinguishable single photons with flexible electronic triggering

A key ingredient for quantum photonic technologies is an on-demand source of indistinguishable single photons. State-of-the-art indistinguishable single-photon sources typically employ resonant excitation pulses with fixed repetition rates, creating a string of single photons with predetermined arrival times. However, in future applications, an independent electronic signal from a larger quantum circuit or network will trigger the generation of an indistinguishable photon. Further, operating the photon source up to the limit imposed by its lifetime is desirable. Here, we report on the application of a true on-demand approach in which we can electronically trigger the precise arrival time of a single photon as well as control the excitation pulse duration based on resonance fluorescence from a single InAs/GaAs quantum dot. We investigate in detail the effect of the finite duration of an excitation $π$ pulse on the degree of photon antibunching. Finally, we demonstrate that highly indistinguishable single photons can be generated using this on-demand approach, enabling maximum flexibility for future applications.

quant-ph↗

arXiv2014

Polariton condensation in a planar microcavity with InGaAs quantum wells

Polariton lattice condensates provide a platform for on chip quantum emulations. Interactions in extended polariton lattices are currently limited by the intrinsic photonic disorder of microcavities. Here, we fabricate a strain compensated planar GaAs/AlAs microcavity with embedded InGaAs quantum wells and report on polariton condensation under non-resonant optical excitation. Evidence of polariton condensation is supported spectroscopically both in reflection and transmission geometry, whilst the observation of a second threshold to photon lasing allows us to conclusively distinguish between the strong- and weak-coupling non-linear regimes.

cond-mat.mes-hall↗