Coupling of ultrathin tapered fibers with high-Q microsphere resonators at cryogenic temperatures and observation of phase-shift transition from undercoupling to overcoupling

TL;DR

This study demonstrates cryogenic coupling of ultrathin tapered fibers with high-Q microsphere resonators, observing a phase-shift transition from undercoupling to overcoupling, with potential applications in quantum optics.

Contribution

We achieved stable cryogenic coupling of ultrathin tapered fibers with high-Q microspheres and observed a discrete phase-shift transition, advancing control in quantum photonics.

Findings

Stable nanopositioning of fibers at cryogenic temperatures

Observation of phase-shift transition from undercoupling to overcoupling

Potential implications for quantum information processing

Abstract

We cooled ultrathin tapered fibers to cryogenic temperatures and controllably coupled them with high-Q microsphere resonators at a wavelength close to the optical transition of diamond nitrogen vacancy centers. The 310-nm-diameter tapered fibers were stably nanopositioned close to the microspheres with a positioning stability of approximately 10 nm over a temperature range of 7-28 K. A cavity-induced phase shift was observed in this temperature range, demonstrating a discrete transition from undercoupling to overcoupling.