Self-organized criticality emerges in dynamical complex systems driven out of equilibrium, and characterizes a wide range of classical phenomena in physics, geology and biology. However, for decades now, it remains a fundamental open question whether this broad property also finds a place in the quantum regime. In the talk, we shall present the first example of quantum self-organized criticality, emerging from quantum fluctuations and controlled by quantum coherence. We shall introduce a many-body quantum-coherently driven nanophotonic system where heavy photons interact in the presence of active nonlinearities. In this system, we shall show how quantum self-organized criticality emerges in an inherently new type of light localization, arising from two first-order phase transitions and being robust to dissipation, fluctuations and many-body interactions. The observed localization exhibits emergence of scale-invariant power laws and absence of finely-tuned control parameters. In analogy with the regime of quantum criticality at Tc = 0 in equilibrium static systems, we find that for our nonequilibrium dynamical system there exists a range of parameters for which the effective critical ‘temperature’ drops to zero, at which point we enter a fundamentally new regime of phase transitions – the quantum self-organized critical regime. We shall also approach the problem from a thermodynamic and information-theory perspective, deriving the multidimensional-state-vector Fokker-Planck (FP) equation for the distribution function of our problem, applying the maximum information entropy principle to make unbiased estimates on the probability distribution of microscopic states of our active nanosystem, and finally determining and analyzing the information gain and efficiency of the complex nanosystem close to its critical points.
Metamaterials are artificial materials with exotic physical, chemical and optical properties not found in natural materials. In the past decade they have attracted monumental attention from the scientific community owing to their applications ranging from physics to engineering. However, the conventional solid-state metamaterial platforms suffer from inevitable optical loss, defects which severely curtain their application at few-photon level. The quest for quantum optical applications with metamaterial-based technologies has stimulated researchers to engineer novel lossless materials and construct new platforms. Recently, by integrating two important and timely realms of science − trapped atom physics and metamaterials −, we proposed and theoretically demonstrated a topologically reconfigurable and lossless quantum metamaterial. The atomic lattice quantum metamaterial is immune to aforementioned critical challenges and can be employed at a single-photon level. Moreover, in stark contrast to conventional solid-state platforms, optical lattices provide the necessary freedom to precisely localize (within few nanometer of uncertainty) a probe atom, inside the atomic lattice quantum metamaterial to harness its exotic optical properties. In addition to its aforementioned novel characteristics, our atomic lattice quantum metamaterial offers a unique degree of freedom, namely all-optical control on ultrafast time scales over the photonic topological transition of isofrequency contours using weak fields, not possible with previous solid-state platforms. In this work, we leverage the tools, techniques, scientific advances in the field of atomic, molecular and optical physics, integrated with the concepts used in metamaterials to propose and theoretically demonstrate a novel platform towards quantum metamaterial with novel functionalities by bringing together the best of two worlds.
Quantum vacuum engineering is an active field of research. Here we use recent advances in the field of metasurface (2D-array of sub-wavelength scale nano-antennas) to construct an anisotropic quantum vacuum (AQV) in the vicinity of a quantum emitter located at some macroscopic distance from the metasurface. Such AQV can induce quantum interference among several atomic transitions, even when the transition dipole moment corresponding to the decay channels are orthogonal.
Recently, there have been few theoretical proposal to use metamaterials to engineer the back-action. All these approaches, which works in the near field (few tens of nanometers from the surface), suffers from trapping an atom at these distance, surface interactions like quenching, Casimir force etc. Hence it’s pivotal to construct the back-action over macroscopic distance. We harness the polarization dependent response of a metasurface to engineer the back-action of the spontaneous emission from the atom to itself. We show strong anisotropy in the decay rate of a quantum emitter which is a manifestation of AQV.
Engineering light-matter interaction over macroscopic distances opens new possibilities for long-range interaction between quantum emitters for quantum information processing, spin-optics/spintronics etc.