🔬 optics

Nanophotonic control of collective many-body states in Kerr solitons

This paper demonstrates how a photonic-crystal lattice can be used to nanophotonically control the transition between Mott insulator and superfluid many-body states in a Kerr microresonator by modulating the coupling between discrete frequency modes.

Original authors: Yan Jin, Jizhao Zang, Sarang Yeola, Alexa R. Carollo, Nitesh Chauhan, Scott B. Papp

Published 2026-04-27

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CC BY 4.0

Original authors: Yan Jin, Jizhao Zang, Sarang Yeola, Alexa R. Carollo, Nitesh Chauhan, Scott B. Papp

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are at a massive music festival. The way the crowd behaves depends on two things: how much people want to dance with their immediate neighbors (local interaction) and how much they want to move across the entire field to find their friends (delocalization).

This paper describes a way to control "light crowds" (photons) in a tiny, microscopic ring to switch between two very different types of "dance parties": a Mott Insulator and a Superfluid.

1. The Two Dance Parties

The Mott Insulator (The "Strict Seating" Party):
Imagine a festival where every person is assigned a specific, numbered seat. Even if the music is great, everyone stays in their spot because the "rules" (interactions) are so strong that moving to a neighbor's seat is too difficult.

In the lab: The light is very orderly. Each frequency of light has almost exactly the same amount of power. It looks like a flat, steady plateau of light. It’s predictable and stable.

The Superfluid (The "Mosh Pit" Party):
Now, imagine the seats are removed. People are free to flow, wave, and rush toward the front of the stage. Because everyone is interacting and moving together, you get huge waves of energy and chaotic, beautiful patterns.

In the lab: The light is "delocalized." The power isn't even; instead, you see huge spikes and dips in the spectrum. The light modes are "talking" to each other and interfering, creating a complex, wavy pattern.

2. The "DJ" (The Photonic Crystal)

How do scientists switch between these two states? They use a tiny, engineered structure called a Photonic-Crystal (PhC) lattice.

Think of this lattice as a DJ who controls the "social rules" of the party.
By changing the physical design of the microscopic ring (the "nanophotonic control"), the scientists can adjust a setting called the Bandgap.

Increasing the Bandgap: The DJ turns up the "social distancing" rules. This suppresses the ability of different light modes to interact and swap energy. The light is forced into the Mott Insulator state—the steady, flat-top "seated" party.
Decreasing the Bandgap: The DJ removes the barriers. The light modes can now "flow" and interact wildly, turning the system into the Superfluid "mosh pit" state.

3. Why does this matter?

Why do we care about controlling "light crowds" in a tiny ring?

Programmable Light: Instead of building a new device for every task, we can use one device and simply "tune" it to change how the light behaves. It’s like having a speaker that can switch from a steady bass beat to a complex symphony just by turning a knob.
Super-Fast Data: The "Mott Insulator" state creates a very stable, uniform "comb" of light. This is perfect for high-speed internet and telecommunications, where you need many clean, distinct channels of light to carry data without them blurring into each other.
Quantum Computing: Understanding how these many-body states work is a stepping stone toward building powerful quantum computers that use light to process information in ways traditional computers never could.

In short: Scientists have found a way to use microscopic "architectural tricks" to command light to either stand perfectly still in an orderly line or flow together in a synchronized wave.

Technical Summary: Nanophotonic Control of Collective Many-Body States in Kerr Solitons

Problem

In condensed matter physics, spatially periodic systems of interacting bosons (such as ultracold atoms in optical lattices) exhibit complex many-body behaviors, most notably the transition between a Mott insulator (where particles are localized due to strong on-site repulsion) and a superfluid (where particles are delocalized and phase-coherent). While this is a well-studied phenomenon in quantum matter, achieving similar controllable transitions in driven-dissipative photonic systems has remained a challenge. The goal of this research is to engineer a nanophotonic platform where the competition between local Kerr interactions and mode coupling can be tuned to access these distinct collective many-body states of light.

Methodology

The researchers utilized photonic-crystal microresonators (PhCRs) to manipulate the Hamiltonian of a Kerr soliton system. The core methodology involves engineering a photonic bandgap (BG) through nanoscale modulation of the resonator's geometry (specifically the inner wall radius).

Hamiltonian Engineering: The total Hamiltonian ( $\hat{H}_{tot}$ ) is decomposed into three parts: $\hat{H}_{self}$ (comprising free dispersion, self-phase modulation, and the bandgap-induced hybridization), $\hat{H}_{cross}$ (comprising cross-phase modulation and four-wave mixing), and $\hat{H}_{pump}$ .
Control Mechanism: By adjusting the strength of the photonic bandgap ( $\gamma$ $γ$ ), the researchers control the balance between $\hat{H}_{self}$ $\hat{H}_{se l f}$ and $\hat{H}_{cross}$ $\hat{H}_{cr oss}$ .
- Increasing $\gamma$ enhances the effective self-interaction (driving the system toward a Mott insulator).
- Decreasing $\gamma$ restores cross-mode coupling (driving the system toward a superfluid).
Experimental Design: Two distinct PhCR architectures were used:
- Lattice BG: A periodic modulation affecting a wide range of modes ( $\mu_s$ ), creating a "lattice" of modes.
- Pump-BG: A modulation localized only at the pump mode, which isolates the interaction dynamics.
Characterization: The transition was quantified using the Coefficient of Variation (CV) of the spectral intensity. A low CV indicates a uniform "flattop" spectrum (Mott insulator), while a high CV indicates a modulated, interference-rich spectrum (superfluid).

Key Contributions

Demonstration of a Non-equilibrium Phase Transition: The paper provides the first experimental demonstration of a Mott insulator to superfluid transition in a driven-dissipative Kerr soliton system.
Programmable Hamiltonian Control: It shows that nanophotonic design (geometry) can be used as a tool for "Hamiltonian engineering," allowing researchers to deterministically design the collective state of light.
Universality: The researchers proved that this transition is universal, occurring both in extended lattice bandgaps and in localized pump-mode bandgaps.

Results

Mott Insulator Regime: When the bandgap is large, the system enters a Mott insulator state. This is characterized by a flattop frequency comb with highly uniform power distribution across modes and high phase rigidity. In the pump-BG case, the researchers achieved a CV as low as 0.24 (excluding boundary modes).
Superfluid Regime: When the bandgap is reduced, the system enters a superfluid regime. This is characterized by strong spectral modulation and interference fringes caused by long-range phase coherence and effective cross-mode coupling.
High-Power Performance: The platform is robust at high power levels. The researchers demonstrated soliton microcombs with total on-chip powers exceeding 50–90 mW at repetition rates of 100 GHz and 200 GHz, maintaining the distinct many-body characteristics even in high-power regimes.

Significance

This work bridges the gap between many-body physics and nonlinear photonics. By transforming Kerr microresonators into programmable many-body systems, it opens new frontiers in:

Programmable Photonics: Creating light states with custom-designed spectral and phase properties.
Quantum-Optical Computing & AI: Leveraging collective states for advanced information processing and photonic AI acceleration.
High-Capacity Communications: Utilizing high-power, flattop, and stable microcombs for next-generation microwave photonics and data links.