K. L. Silverman | Searcharxiv

arXiv2018

Demonstrating sub-3 ps temporal resolution in a superconducting nanowire single-photon detector

Improving the temporal resolution of single photon detectors has an impact on many applications, such as increased data rates and transmission distances for both classical and quantum optical communication systems, higher spatial resolution in laser ranging and observation of shorter-lived fluorophores in biomedical imaging. In recent years, superconducting nanowire single-photon detectors (SNSPDs) have emerged as the highest efficiency time-resolving single-photon counting detectors available in the near infrared. As the detection mechanism in SNSPDs occurs on picosecond time scales, SNSPDs have been demonstrated with exquisite temporal resolution below 15 ps. We reduce this value to 2.7$\pm$0.2 ps at 400 nm and 4.6$\pm$0.2 ps at 1550 nm, using a specialized niobium nitride (NbN) SNSPD. The observed photon-energy dependence of the temporal resolution and detection latency suggests that intrinsic effects make a significant contribution.

physics.ins-det↗

arXiv2014

Homogeneous Linewidth Narrowing of the Charged Exciton via Nuclear Spin Screening in an InAs/GaAs Quantum Dot Ensemble

In semiconductor quantum dots, the electron hyperfine interaction with the nuclear spin bath is the leading source of spin decoherence at cryogenic temperature. Using high-resolution two-color differential transmission spectroscopy, we demonstrate that such electron-nuclear coupling also imposes a lower limit for the positively charged exciton dephasing rate, γ, in an ensemble of InAs/GaAs quantum dots. We find that the dephasing rate is sensitive to the strength of the hyperfine interaction, which can be controlled through the application of an external magnetic field in the Faraday configuration. At zero applied field, strong electron-nuclear coupling induces additional dephasing beyond the radiative limit and γ= 230 MHz (0.95 μeV). Screening of the hyperfine interaction is achieved for an external field of ~1 T, resulting in γ= 172 MHz (0.71 μeV) limited only by spontaneous recombination. On the other hand, application of a Voigt magnetic field mixes the spin eigenstates, which increases the dephasing rate by up to 75%. These results are reproduced with a simple and intuitive model that captures the essential features of the electron hyperfine interaction and its influence on γ.

cond-mat.mes-hall↗