[Paper Review] Many-body cavity quantum electrodynamics with driven inhomogeneous emitters

Mi Lei, Rikuto Fukumori+5 more|arXiv (Cornell University)|Aug 8, 2022

Mechanical and Optical Resonators4 citations

TL;DR

This paper investigates strongly driven, inhomogeneous ensembles of solid-state emitters in a high-cooperativity nanophotonic cavity, demonstrating a sharp collective induced transparency (CIT) window due to quantum interference. The CIT enables nonlinear optical responses, including superradiance and subradiance, enabling applications in slow light, frequency referencing, and quantum interconnects.

ABSTRACT

Quantum emitters coupled to optical resonators are quintessential systems for exploring fundamental phenomena in cavity quantum electrodynamics (cQED) and are commonly used in quantum devices acting as qubits, memories and transducers. Many previous experimental cQED studies have focused on regimes in which a small number of identical emitters interact with a weak external drive, such that the system can be described with simple, effective models. However, the dynamics of a disordered, many-body quantum system subject to a strong drive have not been fully explored, despite its importance and potential in quantum applications. Here we study how a large, inhomogeneously broadened ensemble of solid-state emitters coupled with high cooperativity to a nanophotonic resonator behaves under strong excitation. We discover a sharp, collectively induced transparency (CIT) in the cavity reflection spectrum, resulting from quantum interference and collective response induced by the interplay between driven inhomogeneous emitters and cavity photons. Furthermore, coherent excitation within the CIT window leads to highly nonlinear optical emission, spanning from fast superradiance to slow subradiance. These phenomena in the many-body cQED regime enable new mechanisms for achieving slow light and frequency referencing, pave a way towards solid-state superradiant lasers and inform the development of ensemble-based quantum interconnects.

Motivation & Objective

• To explore the dynamics of a many-body quantum system with strongly driven, inhomogeneous emitters in a high-cooperativity cavity.
• To understand how quantum interference and collective response emerge in disordered, driven ensembles beyond the weak-drive regime.
• To demonstrate new quantum optical phenomena such as collective induced transparency (CIT) and nonlinear emission in solid-state cavity QED.
• To enable applications in slow light, frequency referencing, and quantum interconnects using collective many-body effects.

Proposed method

• Employed a nanophotonic cavity with high cooperativity to couple to an inhomogeneously broadened ensemble of rare-earth ion emitters (Yb3+ in YSO).
• Used pulsed laser excitation at variable power and detuning to probe the cavity reflection spectrum and observe collective effects.
• Applied master equation simulations to model the dynamics of coupled and uncoupled subensembles, validating the incoherent addition approach for inhomogeneous systems.
• Measured the cavity phase and reflection spectrum to confirm the presence of a π phase shift across the CIT window, indicating a Fano-like resonance.
• Engineered an optical switch based on the CIT window by using a transverse pump to control signal transmission through the cavity.
• Compared the A and I transitions of Yb3+ to analyze the impact of cooperativity and dephasing on CIT depth and width.

Experimental results

Research questions

• RQ1 How does strong driving of an inhomogeneous ensemble of emitters in a high-cooperativity cavity lead to collective quantum phenomena?
• RQ2 What is the origin and nature of the sharp collective induced transparency (CIT) window observed in the cavity reflection spectrum?
• RQ3 How do nonlinear optical responses such as superradiance and subradiance emerge within the CIT window under coherent excitation?
• RQ4 Can the CIT window be used to realize a fast, all-optical switch with high extinction ratio?
• RQ5 How do differences in cooperativity and dephasing between the A and I transitions affect the width and depth of the CIT feature?

Key findings

• A sharp, collectively induced transparency (CIT) window was observed in the cavity reflection spectrum, narrower than the inhomogeneous linewidth, arising from quantum interference between driven emitters and cavity photons.
• The CIT window enabled coherent excitation of emitters at the center of the inhomogeneous distribution, even under strong driving, with a relative π phase shift across the resonance.
• Nonlinear optical emission was observed, ranging from fast superradiance to long-lived subradiant states, with population shifting from superradiant to subradiant subspaces as excitation power increased.
• At high power (2 a.u.), the system approached a completely mixed state, with unequal population distribution among Dicke states due to differing degeneracies in the subradiant subspace.
• The CIT width was slightly narrower for the I transition than the A transition despite higher dephasing, indicating a higher effective cooperativity in the I transition.
• An all-optical switch was demonstrated with sub-microsecond response time, using the pump to toggle between full reflection (DIR) and transmission (CIT) within the narrow spectral window.