[Paper Review] Analogue quantum simulation of the Hawking effect in a polariton superfluid

Maxime J. Jacquet, Malo Joly+6 more|arXiv (Cornell University)|Jan 1, 2022

Quantum Electrodynamics and Casimir EffectPhysics and Astronomy55 references31 citations

TL;DR

This paper demonstrates that the Hawking effect—correlated emission from quantum vacuum fluctuations at an acoustic horizon—can be significantly enhanced in a polariton superfluid by engineering out-of-equilibrium conditions via optical bistability. By tuning the fluid's density and phase upstream of the horizon to operate near the bistable point (point C), the authors achieve a tenfold increase in both the strength and spatial extent of quantum correlations, enabling experimental detection of the Hawking effect in non-equilibrium quantum fluids.

ABSTRACT

Abstract: Quantum effects of fields on curved spacetimes may be studied in the laboratory thanks to quantum fluids. Here we use a polariton fluid to study the Hawking effect, the correlated emission from the quantum vacuum at the acoustic horizon. We show how out-of-equilibrium physics affects the dispersion relation, and hence the emission and propagation of correlated waves: the fluid properties on either side of the horizon are critical to observing the Hawking effect. We find that emission may be optimised by supporting the phase and density of the fluid upstream of the horizon in a regime of optical bistability. This opens new avenues for the observation of the Hawking effect in out-of-equilibrium systems as well as for the study of new phenomenology of fields on curved spacetimes.

Motivation & Objective

• To identify optimal conditions for observing the Hawking effect in out-of-equilibrium polariton superfluids.
• To investigate how non-equilibrium dynamics—specifically optical bistability—affect the dispersion relation and vacuum emission at the acoustic horizon.
• To optimize fluid parameters (density, phase) upstream of the horizon to maximize quantum correlation signals.
• To demonstrate that experimental detection of the Hawking effect is feasible in polariton systems by enhancing correlation strength and spatial extension.
• To establish two-point correlations as a diagnostic tool for out-of-equilibrium effects in quantum fluid systems.

Proposed method

• Utilizes a one-dimensional polariton wire with a trans-sonic flow profile to create an acoustic horizon.
• Employs a two-step pump profile: a high-intensity step to drive the fluid into the nonlinear regime and a second step to stabilize the fluid density near the bistable point (point C).
• Models the system using the truncated Wigner approximation (TWA) to simulate quantum fluctuations and compute correlation functions.
• Calculates the normalized two-point correlation function g(2)(x, x′) to quantify nonlocal quantum correlations from vacuum emission.
• Analyzes the Bogoliubov dispersion relation in the fluid frame, showing how optical bistability modifies the dispersion and enables enhanced emission.
• Uses numerical simulations with 1 million realizations to ensure statistical convergence of quantum observables.

Experimental results

Research questions

• RQ1 How does optical bistability in a polariton superfluid affect the strength and spatial extent of Hawking-like correlations?
• RQ2 What fluid density and phase configurations upstream of the horizon maximize the detectability of the Hawking effect?
• RQ3 Can out-of-equilibrium dynamics in polariton systems be harnessed to enhance vacuum emission and correlation signals?
• RQ4 How do the properties of the dispersion relation—particularly near the sonic point—impact the emission of correlated Bogoliubov excitations?
• RQ5 To what extent can two-point correlation functions serve as a diagnostic for non-equilibrium effects in quantum fluids?

Key findings

• Operating the fluid near the bistable point C (the sonic point) leads to a significant enhancement in both the strength and spatial extension of quantum correlations compared to previous configurations.
• The authors report an order of magnitude increase in the strength and length of quantum correlations from vacuum fluctuations compared to earlier studies (e.g., [32–34]).
• The presence of an attractive defect at the horizon enhances correlated emission, while a repulsive defect suppresses it, indicating that potential engineering is crucial for signal optimization.
• The correlation signal is strongest when the upstream fluid is tuned close to the bistable point C, where the dispersion relation exhibits a linear slope (sonic behavior), enabling efficient vacuum emission.
• The study identifies that fluid properties on both sides of the horizon—especially the upstream density and phase—critically determine the observability of the Hawking effect in out-of-equilibrium systems.
• The results demonstrate that optical bistability can be leveraged as a control knob to engineer favorable conditions for observing the Hawking effect in polariton-based quantum simulators.