[Paper Review] Strain Engineering of Quantum Emitters in Hexagonal Boron Nitride

Noah Mendelson, Marcus W. Doherty+3 more|arXiv (Cornell University)|Nov 19, 2019

Graphene research and applications45 references4 citations

TL;DR

This study demonstrates strain engineering as a highly effective method to tune quantum emitters in hexagonal boron nitride (hBN), achieving reversible spectral shifts of up to 65 meV—record-breaking for 2D materials—via applied tensile strain. The work reveals strain-induced dipole rotation and provides a theoretical model linking strain to emission energy and optical transition behavior.

ABSTRACT

Quantum emitters in hexagonal boron nitride (hBN) are promising building blocks for the realization of integrated quantum photonic systems. However, their spectral inhomogeneity currently limits their potential applications. Here, we apply tensile strain to quantum emitters embedded in few-layer hBN films and realize both red and blue spectral shifts with tuning magnitudes up to 65 meV, a record for any two-dimensional quantum source. We demonstrate reversible tuning of the emission and related photophysical properties. We also observe rotation of the optical dipole in response to strain, suggesting the presence of a second excited state. We derive a theoretical model to describe strain-based tuning in hBN, and the rotation of the optical dipole. Our work demonstrates the immense potential for strain tuning of quantum emitters in layered materials to enable their employment in scalable quantum photonic networks.

Motivation & Objective

• Address the spectral inhomogeneity of quantum emitters in hBN, a major barrier to their use in integrated quantum photonic systems.
• Explore strain engineering as a dynamic, reversible method to tune emitter energy levels in 2D materials.
• Investigate the impact of strain on photophysical properties, including emission energy and optical dipole orientation.
• Develop a theoretical framework to explain strain-induced spectral shifts and dipole rotation in hBN emitters.
• Enable scalable, on-chip control of quantum emitters for future quantum networks.

Proposed method

• Application of uniaxial tensile strain to few-layer hBN films containing quantum emitters using a piezoelectric actuator setup.
• Use of confocal microspectroscopy to measure emission spectra and track spectral shifts under varying strain.
• Polarization-resolved measurements to detect rotation of the optical dipole moment under strain.
• Development of a strain-dependent Hamiltonian model to describe energy level shifts and coupling to strain fields.
• Analysis of strain-induced symmetry breaking to explain observed dipole reorientation and excited-state coupling.
• Comparison of experimental results with theoretical predictions to validate the model.

Experimental results

Research questions

• RQ1 To what extent can tensile strain tune the emission energy of quantum emitters in hBN?
• RQ2 How does applied strain affect the orientation of the optical dipole in hBN emitters?
• RQ3 Can spectral tuning be achieved reversibly and reproducibly in hBN-based quantum emitters?
• RQ4 What is the role of higher excited states in the strain response of hBN emitters?
• RQ5 How well does a theoretical model based on strain-coupled Hamiltonians describe the observed spectral and dipole behavior?

Key findings

• Tensile strain induced spectral shifts of up to 65 meV in hBN quantum emitters, the largest reported for any 2D quantum source.
• Spectral tuning was fully reversible, demonstrating stable and controllable modulation of emission energy.
• Strain caused measurable rotation of the optical dipole, indicating coupling to a second excited state or symmetry-breaking effects.
• The observed dipole rotation was consistent with a theoretical model incorporating strain-induced changes in the electronic structure.
• Theoretical modeling successfully reproduced the strain-dependent energy shifts and dipole reorientation, validating the physical mechanism.
• The results establish strain engineering as a viable, scalable method for on-chip spectral control of quantum emitters in 2D materials.