CAREER: Understanding Pure Dephasing in Single Optical Emitters with Time-Resolved Hong-Ou-Mandel Spectroscopy

With support from the Chemical Structure and Dynamics (CSD) program in the Division of Chemistry, Professor Hendrik Utzat of the University of California, Berkeley, is advancing a new form of spectroscopy to study the loss of coherence in single-photon emitters critical to quantum information science (QIS) technologies. Solid-state single-photon emitters experience detrimental decoherence caused by noise from spin, charge, and atomic vibrations.

However, the relative contributions of these sources to decoherence and their atomistic origin are not well understood. Professor Utzat’s group will leverage a new type of spectroscopy based on quantum optics to disentangle the role of charge and spin noise in decoherence in single emitters within monolayers of boron nitride and quantum dots composed of metal halide perovskites.

By accessing currently experimentally challenging timescales from picoseconds to nanoseconds, foundational insights into how the condensed-phase environment interferes with the transduction between electronic and photonic coherences will be uncovered. Further impact arises from the formulation of materials design principles aimed at suppressing decoherence, leading to higher-quality single-photon emitters.

The program also supports the development of a quantum-educated U.S. workforce through an extracurricular science workshop for high school students.

Hong-Ou-Mandel spectroscopy compares the single-photon indistinguishability from solid-state emitters as a way to measure bath fluctuations on timescales ranging from picoseconds to nanoseconds. Varying photon time separations are employed to disentangle the effects of photon scattering, spin noise, and charge noise on the loss of photon indistinguishability.

This loss is probed through the reduction in time-dependent two-photon interference visibility, derived from second-order photon correlation measurements. The Utzat group will use this method to quantify the dephasing mechanisms of two emerging single-photon emitters: defects in hexagonal boron nitride and quantum dots made of lead-halide perovskites.

Specific objectives include quantifying the contributions of different dephasing pathways and uncovering their atomistic origins through temperature- and field-dependent studies combined with theoretical modeling. The broader impacts of this work involve the development of tools that address a critical measurement gap in the timescales of single-emitter dynamics.

This is important due to the universality of dephasing mechanisms in solid-state environments and the need for future quantum engineering at the single-emitter level. Students participating in this project will gain expertise in an array of principles and methods in quantum optics, which are highly relevant to advanced technology industries, including quantum sensing and quantum computing.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.