Evidencing the squeezed dark nuclear spin state in lead halide perovskites

TL;DR

This paper demonstrates the optical creation of a long-lived, entangled dark nuclear spin state in lead halide perovskites, showing significant spin squeezing and potential for quantum information storage and enhanced measurement precision.

Contribution

It provides the first experimental evidence of a collective dark nuclear spin state in lead halide perovskites, revealing entanglement and spin squeezing in a solid-state system.

Findings

Achieved optical manipulation of nuclear spins in FAPbBr3 at cryogenic temperatures.

Observed strong spin squeezing with violation of the nuclear squeezing inequality.

Demonstrated approximately 750-body entanglement in the nuclear ensemble.

Abstract

Coherent many-body states are highly promising for robust and scalable quantum information processing. While far-reaching theoretical predictions have been made for various implementations, direct experimental evidence of their appealing properties can be challenging. Here, we demonstrate coherent optical manipulation of the nuclear spin ensemble in the lead halide perovskite semiconductor FAPbBr$_3$ (FA=formamidinium), targeting a long-postulated collective dark state that is insensitive to optical pumping. Via optical orientation of localized hole spins we drive the nuclear many-body system into an entangled state, requiring a weak magnetic field of only a few Millitesla strength at cryogenic temperatures. During its fast build-up, the nuclear polarization along the optical axis remains small, while the transverse nuclear spin fluctuations are strongly reduced, corresponding to spin squeezing as evidenced by a strong violation of the generalized nuclear squeezing-inequality with $\xi_s < 0.3$. The dark state evidenced in this process corresponds to an approximately 750-body entanglement between the nuclei. Dark nuclear spin states can be exploited to store quantum information benefiting from their long-lived many-body coherence and to perform quantum measurements with a precision beyond the standard limit.