Quantum Light Signatures and Nanosecond Spectral Diffusion from Cavity-Embedded Carbon Nanotubes William Walden-Newman, Ibrahim Sarpkaya, and Stefan Strauf* Department of Physics and Engineering Physics, Stevens Institute of Technology, Castle Point on the Hudson, Hoboken, New Jersey 07030, United States * S Supporting Information ABSTRACT: Single-walled carbon nanotubes (SWCNTs) are considered for novel optoelectronic and quantum photonic devices, such as single photon sources, but methods must be developed to enhance the light extraction and spectral purity, while simultaneously preventing multiphoton emission as well as spectral diffusion and blinking in dielectric environments of a cavity. Here we demonstrate that utilization of nonpolar polystyrene as a cavity dielectric completely removes spectral diffusion and blinking in individual SWCNTs on the millisecond to multisecond time scale, despite the presence of surfactants. With these cavity-embedded SWCNT samples, providing a 50-fold enhanced exciton emission into the far field, we have been able to carry out photophysical studies for the first time with nanosecond timing resolution. We uncovered that fast spectral diffusion processes (1-3 ns) remain that make significant contributions to the spectral purity, thereby limiting the use of SWCNTs in quantum optical applications requiring indistinguishable photons. Measured quantum light signatures reveal pronounced photon antibunching (g 2 (0) = 0.15) accompanied by side-peak bunching signatures indicative of residual blinking on the submicrosecond time scale. The demonstrated enhanced single photon emission from cavity-embedded SWCNTs is promising for applications in quantum key distribution, while the demonstrated passivation effect of polystyrene with respect to the stability of the optical emission opens a novel pathway toward optoelectronic devices with enhanced performance. KEYWORDS: Single-walled carbon nanotubes, photon antibunching, blinking, spectral diffusion, single photon source, cavity, polystyrene S ingle-walled carbon nanotubes (SWCNTs) display out- standing optical properties, such as optical recombination, that arises from excitons with binding energies of several hundred meV 1 and emission wavelengths that extend into the telecom band which are controlled by the chirality. 2,3 Toward optoelectronic devices utilizing individual SWCNTs, 4 electrical injection was demonstrated in a field effect transistor geometry 5 as well as monolithic integration in a planar cavity giving rise to directional emission and a four-fold enhanced exciton emission rate. 6 Recently it was also demonstrated that individual SWCNTs display photon antibunching at cryogenic temper- atures, 7 i.e., emission of nonclassical light from a quantum emitter with a one-dimensional density of states. These optical properties suggest that SWCNTs are ideal candidates for the next generation single photon sources, 8 which can operate at room temperature under electrical injection in the telecom band as required for practical applications in quantum cryptography. 9 For optical quantum information processing, however, the requirements are more stringent and require indistinguishable single photons, if entanglement is created by bunching at the beam splitter. 10 Hence, the quantum emitter must display photon antibunching combined with a high photon collection efficiency, long dephasing times, and a high spectral purity in order to prevent two-photon interference from diminishing. A detrimental effect on spectral purity of a quantum emitter is inhomogeneous broadening of the intrinsic photolumines- cence (PL) line width brought about by spectral diffusion (SD). 11 Spin and charge fluctuations in the vicinity of the photoemitter create a Stark-effect induced variability in the emission wavelength over time, 12 in addition to broadening caused by spontaneous emission, pure dephasing, 13 and unintentional doping. 14 Previous studies at room 15 and cryogenic 16 temperatures have found SD at a millisecond to multisecond time scale, giving rise to pronounced spectral broadening for substrate-deposited SWCNTs. It was also shown that SD can be suppressed, at least on the millisecond time scale, by suspending SWCNTs in air between supports and in the absence of surfactant wrapping. 17 However, nonencapsulated, free-standing SWCNTs 18 are brittle and might be disadvantageous in light of optoelectronic device integration into cavities for enhanced light extraction. To overcome this limitation, we recently demonstrated that both Received: December 13, 2011 Revised: March 21, 2012 Published: March 22, 2012 Letter pubs.acs.org/NanoLett © 2012 American Chemical Society 1934 dx.doi.org/10.1021/nl204402v | Nano Lett. 2012, 12, 1934-1941