Unidirectional single-photon emission from germanium-vacancy zero-phonon lines: Deterministic emitter-waveguide interfacing at plasmonic hot spots

TL;DR

This paper presents a nanophotonic platform that enables deterministic, unidirectional single-photon emission from germanium-vacancy centers in nanodiamonds, advancing solid-state quantum light sources and quantum nanophotonics.

Contribution

It introduces a novel plasmonic waveguide interface with GeV centers, achieving enhanced emission rates and unidirectional emission without relying on chiral or topological effects.

Findings

Achieved >10^6 counts/s zero-phonon line emission at cryogenic temperatures.

Demonstrated 10-fold enhancement in single-photon decay rates.

Realized unidirectional emission using a Bragg reflector in a plasmonic waveguide.

Abstract

Striving for nanometer-sized solid-state single-photon sources, we investigate atom-like quantum emitters based on single germanium vacancy (GeV) centers isolated in crystalline nanodiamonds (NDs). Cryogenic characterization indicated symmetry-protected and bright (> 10^6 counts/s with off-resonance excitation) zero-phonon optical transitions with up to 6-fold enhancement in energy splitting of their ground states as compared to that found for GeV centers in bulk diamonds (i.e., up to 870 GHz in highly strained NDs vs 150 GHz in bulk). Utilizing lithographic alignment techniques, we demonstrate an integrated nanophotonic platform for deterministic interfacing plasmonic waveguides with isolated GeV centers in NDs that enables 10-fold enhancement of single-photon decay rates along with the emission direction control by judiciously designing and positioning a Bragg reflector. This approach allows one to realize the unidirectional emission from single-photon dipolar sources introducing a novel method that is alternative to the propagation-direction-dependent techniques based on chiral interactions or topological protection. The developed plasmon-based nanophotonic platform opens thereby new perspectives for quantum nanophotonics in general and for realizing entanglement between single photons and spin qubits, in particular.