MISTiQ-Light Project
Project Title: MOTT INSULATOR TRANSITION IN A QUANTUM FLUID OF LIGHT
Acronym: MISTiQ-Light
Scientific Coordinator: Quentin Glorieux
Host Institution: Laboratoire Kastler Brossel (LKB), Sorbonne Université/ENS, Paris (France)
Funding Source: ERC Consolidator Grant 2022
Project Objective
The main goal of the MISTiQ-Light project is to observe the superfluid to Mott insulator phase transition in a fluid of light and create a new photonic state with the potential to revolutionize quantum simulation and computation. This ambitious experimental challenge aims to advance both fundamental physics by exploring strongly quantum correlated and entangled states in analogue quantum simulators, and applied science by creating a giant source of single photons for large-scale photonic quantum technologies.
Scientific Challenges and Approach
Photons are excellent information carriers but typically do not interact with each other. Atoms interact but are difficult to manipulate and do not benefit from quantum optics tools for detecting quantum fluctuations and entanglement. MISTiQ-Light aims to marry these two systems to create and study new states of light, specifically focusing on synthetic photonic matter .
The project relies on engineering a quantum phase transition in a fluid of light . This involves investigating the superfluid to Mott insulator transition for light propagating in a dense cold atomic cloud . The approach uses a paraxial fluid of light, where photons acquire an effective mass due to the paraxial approximation, and strong photon-photon interactions are generated and tuned via a giant Kerr non-linearity induced by manipulating atomic coherences. In this regime, photons behave like a quantum fluid of light and their evolution mirrors that of ultracold atomic quantum gases .
Key aspects of the approach include:
- Paraxial Fluid of Light: This platform is based on the spatial evolution of a continuous laser beam propagating in a non-linear medium . Under the paraxial approximation, this system simulates the dynamics of a 2D quantum fluid, where the transverse plane is a time snapshot of the effective temporal evolution. The effective mass originates from the paraxial approximation, light intensity corresponds to fluid density, and the spatial phase gradient corresponds to fluid velocity.
- Extending to 3D: The project will extend the formalism to a fully 3-dimensional fluid of light by using a pulsed laser source, where the temporal dimension is mapped to a third effective spatial dimension (z’) in a compressed co-moving frame. Quantum effects are expected to emerge in 3D .
- Strong Interactions: A novel type of non-linear material – an ultra-high optical depth cold atomic cloud – will be built . Giant photon-photon interactions will be implemented using atomic coherences in multi-level atoms . The approach uses a N-type atomic system in a cloud of 87Rb with three laser beams (control, pump, and fluid beams) . This configuration allows for separately tuning the linear (controlling the external potential) and non-linear (controlling interactions) susceptibilities seen by the fluid beam .
- Bose-Hubbard Model: The main experimental challenge is to map the evolution of the paraxial fluid of light onto the Bose-Hubbard model. This model describes interacting bosons on a lattice, where the superfluid to Mott insulator transition is driven by two parameters: the on-site interaction energy (U) and the tunneling rate (J). The project aims to engineer the required Hamiltonian and adiabatically increase the lattice potential along the effective temporal direction (z-axis) . Numerical simulations show that the ratio U/J can be changed from 0.1 to 40, which is sufficient to probe the Mott insulator transition (expected around U/J ~ 30 in 3D) .
- Beyond Mean-Field: A necessary condition for the project’s hypothesis is that photon fluids exhibit quantum behavior beyond the mean-field approach . Novel detection schemes will be implemented to demonstrate the presence of quantum depletion, quantum correlations, and entanglement in fluids of light.
- Detection Techniques:
- Photon Resolving Camera: A prototype novel q-CMOS camera with very low noise and high quantum efficiency will allow photon-resolving quantitative imaging on each pixel. While not single-shot photon counting like a quantum gas microscope, accumulating multiple realizations can provide a clear signature of the photon variance for each pixel, characterizing the statistic. The correlation function (g(2)) can also be computed by splitting the photon stream .
- Hybrid Homodyne Detection: This complementary approach combines wave-front shaping with homodyne detection to measure fluctuations in conjugate quadratures (amplitude and phase). This will allow measurement of the spatial noise spectrum in the (x,y) direction and the temporal noise spectrum in the z’ direction, providing access to entanglement characterization .
Expected Impact
The MISTiQ-Light project, while curiosity-driven to explore uncharted quantum phenomena, is underpinned by technology development with potentially strong and diverse impacts .
- Fundamental Physics: The project will bring photon fluids into a new regime of many-body physics, enabling the study of strongly quantum correlated and entangled states in analogue quantum simulators . It will allow exploration of truly quantum effects such as the emergence of analogue phase transitions in non-equilibrium systems, quantum depletion, pre-thermal states, and entanglement dynamics in many-body systems . The platform is also suited to study non-Hermitian physics and topological states in the strongly interacting regime . Observing entanglement in a well-controlled analogue system may also provide insights into the transition from quantum to classical fluctuations in cosmology .
- Quantum Technology: A photonic Mott insulator is envisioned as a giant source of single photons (or any Fock state) with potentially several hundreds of lattice sites delivering tunable photon number-states in parallel . This new state of light is considered an ideal source for large-scale implementations of photonic quantum technologies, such as linear optics quantum computation and quantum simulation, overcoming scalability issues. The platform can deliver tunable Fock states by changing the initial filling factor . Photons can be extracted from the system for applications .