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Photons for Quantum Simulation

Periodic Reporting for period 1 - PhoQuS (Photons for Quantum Simulation)

Reporting period: 2018-10-01 to 2020-03-31

The aim of the PhoQuS project is to develop a novel platform for quantum simulation, based on photonic quantum fluids, realised in different photonic systems with suitable non-linearities, allowing to engineer an effective photon-photon interaction. The main objectives of this project are to fully understand the superfluid and quantum turbulent regimes for quantum fluids of light and to achieve simulations of systems of very different nature, ranging from condensed matter to astrophysics.

The PhoQuS approach merges the theoretical and experimental techniques of controlled manipulation of quantum systems (photons) with many-body and quantum field physics. The project is based on fundamental physics and will have an impact on fundamental science (quantum optics, solid state physics, cosmology, quantum gravity) and quantum technologies (quantum simulations).

The expected impact will be the enhancement of cross-disciplinary studies involving optics, general relativity, quantum field theory and solid state physics. This will lead to a deeper understanding of quantum field theories and to the development of novel concepts for the control of quantum states to be harnessed in future quantum architectures.
The main objective addressed in the first period of PhQuS is the full characterization of the properties of the quantum fluids of light obtained in the various photonic systems investigated in the project. The key goals are (1) the experimental observation and theoretical description of superfluid light, (2) the creation of optically controlled potential barriers and disordered potentials, 3) the observation of turbulent regime with the generation of various topological excitations. These achievements set the playground for the quantum simulation which will be massively addressed in the second half of the project, although some promising preliminary results have already been obtained.

In the polariton platform, the consortium investigated the subtle features of superfluidity in driven-dissipative quantum fluids of light demonstrating that they can have a strong impact on the use of these systems as quantum simulators of gravitational systems such as analog black holes. At the same time, we implemented a novel all optical technique allowing to generate at will several types of topological excitations such as quantized vortices and dark solitons. The main results are: the generation of a steady state vortex stream in the wake of an obstacle, the generation of a new kind of bound parallel dark solitons and the theoretical prediction of frozen dark-soliton snake instabilities, confirmed by the experiment. These results open unprecedented possibilities to control and manipulate collective excitations in quantum fluids of light.In polariton array geometries, the consortium investigated the physics of resonantly excited polariton fluids in lattices of GaAs-based microcavity pillars. The observation of gap solitons has been reported in the gapped flatband of a one-dimensional Lieb lattice. Moreover honeycomb lattices emulating uniaxial strained graphene have been realised. Exotic Dirac cones have been unravelled and are very promising for the exploration of quantum transport in complex media.

In the hot Rubidium vapours platform, the main result is the observation of the Bogoliubov dispersion. This result is a strong indication of the superfluid behaviour of the fluid of light generated in this system: promising experiments to check the superfluidity following the Landau criterion are currently running. All these results pave the way to quantum simulation of black holes using this platform.

In the photorefractive crystals platform the consortium achieved a direct experimental detection of the transition to superfluidity in the flow of a fluid of light past an obstacle in a bulk nonlinear crystal (WP2, Task 2.2) as well as the generation of quantum vortices. In the same platform, the first observation of topological transitions of a photon fluid in the highly nonlinear regime has been achieved, observing the transition from shock waves to soliton gases, through the generation of counter-propagating wave fronts induced by a box-shaped input state (WP2, Task 2.3). The acquired experimental capability to shape both the flow, the potential landscape and the interactions (WP2, Task 2.1) paves the way for simulation of quantum transport in complex systems.

In thermal non linear media, superfluidity and optically created obstacles were demonstrated recently as well as first examples of simulation of astrophysical processes. The first research line investigates the simulation of Penrose amplification from a black hole using a photon superfluid. A theoretical model has been developed that fully accounts for the superfluid nature of the system [Superradiant scattering in fluids of light. The second research line is based on a focusing nonlinearity system and that allows to simulate the Newton-Schrodinger equation that describes the evolution of a quantum wave-function in a Newtonian potential. Preliminary measurements have already confirmed numerical simulations reporting the thermal relaxation process of matter and the consequent formation of galaxy structures.

In photon BEC platform, the consortium developed a novel technique to realize permanent potential structuring for two-dimensional photon gases in a microcavity, allowing to realize Bose-Einstein condensation in a linear superposition of the localized wavefunctions of a double-well potential. In close connection, the dynamics of photonic condensates was investigated by developing a time-resolved theory, showing the effects of both critical and non-critical slowing down. These theoretical discoveries inspired pulsed experiments revealing the universal role of spontaneous emission/scattering in the timing jitter of the formation of Bose-Einstein condensates of all kinds). This result thus simulates the quantum statistics of the process of Bose-Einstein condensation across all physical implementations, e.g. ultracold atoms, or polaritons.

In Photon Bubbles platform ITS partner developed a theory describing the onset of a kinetic instability when two paraxial optical fluids with different streaming velocities interact via the optical nonlinearity. From numerical simulations of the nonlinear Schrödinger equation, they further characterized the onset of the instability showing vortex nucleation and excitation of turbulence. Such instabilities provide a natural route towards the investigation of quantum turbulence, structure formation and out-of-equilibrium dynamics in superfluids of light.
The expected impact will be the enhancement of cross-disciplinary studies involving optics, general relativity, quantum field theory and solid state physics. This will lead to a deeper understanding of quantum field theories and to the development of novel concepts for the control of quantum states to be harnessed in future quantum architectures.

A number of “quantum demonstrators” and prototypes should be developed in the next years, boosted by the Quantum Flagship initiative. In the long run, hopefully, fully quantum devices for computing, simulation, metrology and sensing will be realised.
Official logo of PhoQuS project