(Invited) Coupled Quantum Defects of DNA Functionalized Carbon Nanotubes

Abstract

Single wall carbon nanotubes (SWCNTs) with sp3 defects created via covalent bonding of organic functional groups are rapidly emerging as a new material system for chemistry, physics, material science, engineering and quantum technologies. They are often referred to as “organic color centers” as they can mimic quantum mechanical properties of solid-state color centers.1 Their unique properties include highly enhanced molecularly wavelength-tunable fluorescence and room temperature single photon generation with 99% single photon purity at 1.55 µm telecommunication wavelength.2 To date, diazonium chemistry has been the chemists’ tool of the choice for creating sp3 defects sparsely distributed at random positions along the sidewall of SWCNTs. While such distribution is ideally suited for single photon generation, an ability to incorporate multiple coupled quantum defects in a well-defined spatial pattern is highly desirable for more sophisticated quantum information science applications involving entanglement. Recent discovery of covalently functionalizing SWCNTs with single-stranded DNA (ssDNA)3 open a possible path toward achieving this goal. In this process, SWCNTs form covalent bonds to the guanine nucleotides when aqueous suspensions of SWCNTs coated with ssDNA are exposed to singlet oxygen. As a result, creating a regular array of covalent defect with spacing defined by the ssDNA sequence become a possibility. To further explore this exciting possibility, we investigated intrinsic PL emission properties of ssDNA functionalized SWCNTs through low temperature single tube PL spectroscopy. In contrast to individual aryl functionalized SWCNTs that usually emit a single sharp isolated PL peaks, multiple PL peaks with their emission wavelengths varying from 1050 to 1300 nm were observed from individual ssDNA functinalized SWCNTs. We further conducted 2nd order photon correlation (g(2)) and cross-correlation experiments to investigate their quantum light emission properties. We observed photon anti-bunching behavior when an individual PL emission peak is spectrally isolated indicating that ssDNA functionalization creates a series of quantum defects along the length of SWCNTs. Interestingly, when the g(2) experiment is performed on combined emission of multiple (2—4) PL peaks, an incomplete antibunching with g(2)(0) values in the range of 0.2-0.4 is observed. Because these values are significantly smaller than g(2)(0) values estimated for 2-4 independent quantum emitters (0.5-0.75), we interpret that the series of defects created via ssDNA functionalization are coupled. Our photon cross-correlation experiment performed between two emission peaks of the group also reveal evidence of coupling. 1 Srinivasan, K. & Zheng, M. Nat. Photon. 11, 535 (2017). 2 Brozena, A.H., Kim, M., Powell, L.R. & Wang, Y. Nat. Rev. Chem. 3, 375-392 (2019). 3 Zheng, Y., Bachilo, S. M., Weisman, R. B. ACS Nano, 13, 8222 (2019)