ETH Team Models Dissipation-Induced Superradiance for Stabilised Lasing Applications

A new understanding of how energy loss can unlock superradiance, a form of enhanced light emission, has emerged from investigations into light-matter interactions. Sebastian Schmid and colleagues at ETH, in collaboration with University of Konstanz, orica de la Materia Co, and University of Strathclyde, show that including a negative Kerr nonlinearity within a standard Dicke model overcomes limitations that usually prevent superradiance. The findings reveal that cavity dissipation not only stabilises this superradiant phase, characterised by spin inversion, but also indicates potential routes towards new lasing mechanisms and the engineering of quantum states via environmental interactions.

Stabilising superradiance via negative photonic Kerr nonlinearity in the Dicke model

A technique employing negative photonic Kerr nonlinearity, a change in light’s properties as it travels through a material, manipulated the behaviour of light within the Dicke model. This model serves as a simplified framework for understanding light-matter interactions, analogous to a basic recipe for a complex chemical reaction. Introducing this nonlinearity lowered the energy needed to initiate superradiance, overcoming a substantial energy threshold previously required and hindered by the natural diamagnetic properties of light.

Careful control of this nonlinear response stabilised a normally fleeting superradiant phase, even with deliberate energy loss from the system’s cavity. The Dicke model, a framework describing how light and matter interact, investigated light-matter interactions with a focus on achieving superradiance, a boosted emission of light. A photonic Kerr nonlinearity, a change in light’s properties as it passes through a material, reduced the energy required for superradiance, as traditional methods were often hampered by light’s natural diamagnetic properties. Stabilising the superradiant phase involved cavity dissipation, allowing energy loss to maintain the effect, a technique differing from previous closed-system approaches.

Dissipation-induced superradiance and reduced light-matter coupling thresholds

Researchers achieved a superradiant phase accompanied by spin inversion, reducing the light-matter coupling threshold to below ω0 = ωz = 1. Previously, superradiance was unattainable without exceeding this substantial threshold due to the diamagnetic nature of light. This breakthrough, utilising a negative Kerr nonlinearity within the Dicke model, circumvents limitations hindering conventional superradiance and enables dissipation-induced stabilisation of this previously unstable phase. Cavity dissipation, the deliberate loss of energy from the system, sustains the superradiant state and unlocks potential for new lasing mechanisms and the creation of engineered quantum states through environmental interactions.

This approach provides a means to control light-matter interactions, potentially advancing quantum technologies and photonics. Researchers demonstrated a superradiant phase transition accompanied by spin inversion, achieved with a low threshold for light-matter coupling, below a value of one, a state previously requiring overcoming an energy barrier due to light’s diamagnetic properties. This development relies on utilising a negative Kerr nonlinearity, where light alters a material’s refractive index, within the Dicke model of light-matter interaction, thus avoiding conventional limitations and allowing stabilisation of this unstable phase through cavity dissipation, the controlled loss of energy from the system.

Detailed calculations reveal that spin inversion, a flipping of the collective spin of the material’s atoms, occurs when the cavity occupation exceeds a specific point, dependent on the strength of the negative nonlinearity and the frequency of the cavity. Superradiance, a phenomenon where light amplifies itself through interaction with matter, is increasingly focused on for applications ranging from advanced lasers to quantum technologies. Achieving stable superradiance, however, has traditionally demanded impractically strong interactions between light and the materials used, a significant hurdle for practical devices.

Researchers found a pathway to lower the threshold for achieving this superradiance, using a ‘photonic Kerr nonlinearity’, a process where light alters the properties of the material it passes through, even though typically intense light-matter interaction is needed. This approach utilises a specific type of nonlinearity, a negative one, to induce a superradiant state alongside a reversal of spin, a fundamental property of atoms. The researchers of Strathclyde demonstrated stable superradiance, a process amplifying light, using a negative photonic Kerr nonlinearity to reverse atomic spin.

Researchers achieved a stabilised superradiant phase through manipulation of light’s nonlinear response within the Dicke model, a standard model of light-matter interaction. This approach utilises a negative Kerr nonlinearity, altering light’s properties as it travels through a material, to overcome limitations previously hindering superradiance and reduce the energy needed to initiate it. Stabilisation occurs via cavity dissipation, where controlled energy loss maintains the superradiant state, differing from traditional closed-system approaches. This finding opens questions regarding the potential for engineering quantum states via environmental interactions and designing new laser systems reliant on bath-engineered phases.

The researchers demonstrated a low-threshold superradiant phase by utilising a negative photonic Kerr nonlinearity within a standard model of light-matter interaction. This is significant because achieving stable superradiance, the amplification of light through material interaction, typically requires very strong light-matter interactions. By employing a negative nonlinearity and controlled energy loss via cavity dissipation, they stabilised superradiance and induced spin inversion. The authors suggest this work may contribute to understanding how environmental interactions can engineer quantum states and potentially inform the design of new laser systems.