Generation of tunable quantum entanglement via nonlinearity symmetry breaking in semiconductor metasurfaces

TL;DR

This paper demonstrates a novel semiconductor metasurface that uses symmetry-breaking in nonlinear polarization to achieve fast, tunable biphoton entanglement, surpassing existing sources in performance and enabling customizable quantum states.

Contribution

It introduces a new method of symmetry-breaking in nonlinear metasurfaces to generate tunable biphoton entanglement at picosecond speeds, a significant advancement over prior symmetric approaches.

Findings

Achieved continuous polarization entanglement tuning from near-unentangled to Bell states.

Demonstrated ultra-high coincidence-to-accidental ratio of approximately 7×10^4.

Outperformed existing semiconductor flat optics by two orders of magnitude.

Abstract

Tunable biphoton quantum entanglement generated from nonlinear processes is highly desirable for cutting-edge quantum technologies, yet its tunability is substantially constrained by the symmetry of material nonlinear tensors. Here, we overcome this constraint by introducing symmetry-breaking in nonlinear polarization to generate optically tunable biphoton entanglement at picosecond speeds. Asymmetric optical responses have made breakthroughs in classical applications like non-reciprocal light transmission. We now experimentally demonstrate the nonlinear asymmetry response for biphoton entanglement using a semiconductor metasurface incorporating [110] InGaP nano-resonators with structural asymmetry. We realize continuous tuning of polarization entanglement from near-unentangled states to a Bell state. This tunability can also extend to produce tailored hyperentanglement. Furthermore, our nanoscale entanglement source features an ultra-high coincidence-to-accidental ratio of $\approx7\times10^4$, outperforming existing semiconductor flat optics by two orders of magnitude. Introducing asymmetric nonlinear response in quantum metasurfaces opens new directions for tailoring on-demand quantum states and beyond.