Generating resonating valence bond states through Dicke subradiance

TL;DR

This paper proposes a method to generate highly entangled resonating valence bond states in a system of N spins coupled to a photon mode, extending Dicke's experiment, with potential to create large RVB states through cavity decay.

Contribution

It introduces a scheme to produce RVB states via Dicke subradiance in multi-spin systems, expanding the experimental realization of entangled states.

Findings

Dark states with RVB character can be generated from initial spin states.

Probability of collapsing into a dark RVB state scales as 2/N.

Possible to generate RVB states with 20 or more spins.

Abstract

Dicke's original thought experiment with two spins coupled to a photon mode has recently been experimentally realized. We propose extending this experiment to N spins and show that it naturally gives rise to highly entangled states. In particular, it gives rise to dark states which have resonating valence bond (RVB) character. We first consider a system of N two level spins in a cavity with only one spin in the excited state. This initial state is a linear combination of a dark state and a bright state. We point out the dark state is a coherent superposition of singlets with resonating valence bond character. We show that the coupling to the photon mode takes the spin system into a mixed state with an entangled density matrix. We next consider an initial state with half of the spins in the excited state. We show that there is a non-zero probability for this to collapse into a dark state with RVB character. In the lossy cavity limit, if no photon is detected within several decay time periods, we may deduce that the spin system has collapsed onto the dark RVB state. We show that the probability for this scales as 2/N, making it possible to generate RVB states of 20 spins or more.