Creating heralded hyper-entangled photons using Rydberg atoms

Sutapa Ghosh,Gadi Eisenstein,Nicholas Rivera,Ido Kaminer

doi:10.1038/s41377-021-00537-2

Abstract

Entangled photon pairs are a fundamental component for testing the foundations of quantum mechanics, and for modern quantum technologies such as teleportation and secured communication. Current state-of-the-art sources are based on nonlinear processes that are limited in their efficiency and wavelength tunability. This motivates the exploration of physical mechanisms for entangled photon generation, with a special interest in mechanisms that can be heralded, preferably at telecommunications wavelengths. Here we present a mechanism for the generation of heralded entangled photons from Rydberg atom cavity quantum electrodynamics (cavity QED). We propose a scheme to demonstrate the mechanism and quantify its expected performance. The heralding of the process enables non-destructive detection of the photon pairs. The entangled photons are produced by exciting a rubidium atom to a Rydberg state, from where the atom decays via two-photon emission (TPE). A Rydberg blockade helps to excite a single Rydberg excitation while the input light field is more efficiently collectively absorbed by all the atoms. The TPE rate is significantly enhanced by a designed photonic cavity, whose many resonances also translate into high-dimensional entanglement. The resulting high-dimensionally entangled photons are entangled in more than one degree of freedom: in all of their spectral components, in addition to the polarization—forming a hyper-entangled state, which is particularly interesting in high information capacity quantum communication. We characterize the photon comb states by analyzing the Hong-Ou-Mandel interference and propose proof-of-concept experiments.

Highlights

Entanglement is a unique feature of quantum mechanics that enables new possibilities in the fields of quantum information and quantum optics
It starts with preparing atoms in the excited Rydberg state 60S1/2 of rubidium atoms with two input fields, a probe beam at wavelength
two-photon emission (TPE) rates for transitions from the Rydberg states are higher than transitions from lower energy levels, the decay from the Rydberg states is still dominated by the one-photon processes

Summary

Introduction

The need to create entangled photons motivated the study of quantum optics in different physical systems, such as hot vapor[8,9], cold atoms[10], semiconductors[11,12], quantum dots[13], nitrogen-vacancy centers in diamond[14] and more[15,16,17,18]. The SPDC process has a broad emission spectrum, which decreases the coherence length of the emitted photons and limits their usefulness for long-distance quantum communication[21] This problem can be solved either by spectral filtering using optical cavities[22] or by using very narrow bandpass filters, but typically at the price of reducing the number of photon pairs generated ( further reducing the overall efficiency[15]). The high-dimensional energyentangled photons were produced by creating a photonic frequency comb[37,38] These hyper-entangled states have been distributed over a long distance[39,40] and have been applied to quantum teleportation experiments[41,42]. All these technological advances promote hyper-entanglement as a path towards robust quantum communication with higher channel capacity

Results

Discussion

Materials and methods