The development and the use of quantum technologies are hindered by a fundamental challenge: Quantum materials exhibit macroscopic quantum properties at extremely low temperatures due to the loss of quantum coherence at elevated temperatures. Here, based on our recent discovery of room temperature superfluorescence in perovskites, we present the Quantum Analog of Vibration Isolation, 'QAVI', model and explain how it protects the quantum phase against dephasing at high temperatures. We then postulate the requirements for observation of macroscopic quantum phenomena at practical temperatures and propose a unified model for all macroscopic quantum phase transitions. We further present the general features of the temperature and density phase diagram of macroscopic quantum phase transitions that are mediated by the QAVI process and identify the similarities observed in the phase diagram of high Tc superconductors. Understanding this fundamental quantum coherence protection mechanism is imperative to accelerate the discovery of high temperature macroscopic quantum phenomena, and offers significant potential for developing quantum technologies functioning under practical conditions.
The development and the use of quantum technologies are hindered by a fundamental challenge: Quantum materials exhibit macroscopic quantum properties at extremely low temperatures due to the loss of quantum coherence at elevated temperatures. Here, based on our recent discovery of room temperature superfluorescence in perovskites, we present the Quantum Analog of Vibration Isolation, 'QAVI', model and explain how it protects the quantum phase against dephasing at high temperatures. We then postulate the requirements for observation of macroscopic quantum phenomena at practical temperatures and propose a unified model for all macroscopic quantum phase transitions. We further present the general features of the temperature and density phase diagram of macroscopic quantum phase transitions that are mediated by the QAVI process and identify the similarities observed in the phase diagram of high Tc superconductors. Understanding this fundamental quantum coherence protection mechanism is imperative to accelerate the discovery of high temperature macroscopic quantum phenomena, and offers significant potential for developing quantum technologies functioning under practical conditions.
Superfluorescence is a quantum optical phenomenon in which an initially excited ensemble of incoherent dipoles first acquire macroscopic coherence and then collectively recombine and radiate a burst of photons. This process is a symmetry breaking macroscopic quantum phase transition similar to superconductivity and Bose-Einstein condensation. Since quantum coherence is extremely fragile at high temperatures, similar to other macroscopic quantum phase transitions, superfluorescence has been almost always observed at cryogenic temperatures. In this presentation I will first present our results on room temperature superfluorescence in lead-halide perovskites and then present the mechanism that enables this exotic quantum phase transition at room temperature.
Macroscopic quantum coherence in solids, such as in superfluids, superconductors, and condensates, is generally limited to low temperatures because order forms within a fixed excitation spectrum whose competing states become thermally populated as temperature rises. Here, we show that strong coupling between electronic excitations and a deformable lattice enables a different route. Above a critical density, this coupling nucleates self generated confining potentials that trap the very excitations generating them. Unlike rigid external traps, these potentials can translate through the host lattice without changing their internal structure, defining a translational zero mode. Coupling to this zero mode provides a shared dynamical coordinate that lowers and isolates a single collective many body configuration, opening a density dependent gap that suppresses thermal occupation of competing states and supports off diagonal long range order at elevated temperatures. As a concrete realization, we identify high-temperature superfluorescence in lead halide perovskites as the radiative instability of this zero mode dressed ordered excitonic state. More broadly, this establishes a general route to macroscopic quantum order: not cooling within a fixed spectrum, nor pairing instabilities, but a self generated mobile confining structure whose translational zero mode reconstructs the many-body spectrum to protect coherence.
Abstract Light-matter interactions can create and manipulate collective many-body phases in solids1-3, which are promising for the realization of emerging quantum applications. However, in most cases these collective quantum states are fragile, with a short decoherence and dephasing time, limiting their existence to precision tailored structures under delicate conditions such as cryogenic temperatures and/or high magnetic fields. In this work, we discovered that the archetypal hybrid perovskite, MAPbI3 thin films, exhibit such a collective coherent quantum many-body phase, namely superfluorescence, at 78 K and above. Pulsed laser excitation first creates a population of high energy electron-hole pairs, which quickly relax to lower energy domains and then develop a macroscopic quantum coherence through spontaneous synchronization. The excitation fluence dependence of the spectroscopic features and the population kinetics in such films unambiguously confirm all the well-known characteristics of superfluorescence. These results show that the creation and manipulation of collective coherent states in hybrid perovskites can be used as the basic building blocks for quantum applications4,5.
The study of physics at the atomic scale led to the development of quantum mechanics in the early twentieth century. Since then, quantum mechanics has developed into one of the most successfully tested of all physical theories. Central to quantum mechanics is the concept of coherence. Keeping quantal coherence over large time scales or macroscopic length scales has proven to be a difficult, but fruitful endeavour both theoretically and experimentally. Two manifestations of this so-called macroscopic quantum coherence will be investigated in this thesis; the century-old field of superconductivity and the decade-old field of cold atomic gases. Yttrium barium copper oxide is a layered superconductor whose transition temperature can be changed by controlling the amount of oxygen found between the copper oxide planes. Motivated by recent experiments where the penetration depth along the direction perpendicular to the copper oxygen planes was measured on extremely underdoped samples, a theoretical model is constructed which phenomenologically explains the observed electrodynamic properties. The field of atomic physics underwent a revolution in 1994 when dilute atomic gases were cooled to nanokelvin temperatures, which resulted in the much sought after Bose-Einstein condensate. In the past decade, ultra-cold atomic experiments have been used to study fundamental quantum mechanics and more recently, with the application of optical lattices, many-body physics. The second project contained in this thesis investigates a method to engineer the emergence of Dirac Ferinions in an ultra-cold Fermionic gas with the application of an optical lattice. The Hamiltonian governing the low energy properties of this system is well known, and is shown to undergo a quantum phase transition where the low energy Fermionic quasiparticles acquire a mass, due to the appearance of "antiferromagnetic" ordering.
Metal halide perovskites (MHPs) have emerged as promising platforms for cooperative quantum emission. Superfluorescence is particularly intriguing because it arises from spontaneous synchronization of initially incoherent emitters into a macroscopic quantum state, producing delayed, intense, ultrafast bursts of coherent light. While superfluorescence has been demonstrated in perovskite nanocrystal superlattices and thin films, the mechanisms that enable its emergence at elevated temperatures, and the boundaries that separate cooperative from non-cooperative emission regimes, remain insufficiently understood.[1],[2] Addressing these knowledge gaps is essential for advancing superfluorescence toward quantum photonic applications.[3] In this talk, I present how our work tackles the challenges of identifying, and controlling superfluorescence in quasi-2D perovskite thin films. We demonstrate clear evidence to distinguish superfluorescence from amplified spontaneous emission and spontaneous emission. A comprehensive experimental phase map is constructed to reveal when and how macroscopic coherence forms, how it decays, and under what conditions it transitions into non-cooperative regimes.[4] Using quasi-2D PBA:CsPbBr3 thin films, we demonstrate superfluorescence with the lowest threshold fluence reported at 78 K in metal halide perovskites. Temperature and fluence dependent steady state and ultrafast spectroscopies resolve cooperative emission from 78 to 180 K, including a sharper coupled emission band, a delayed emission peak, ultrafast radiative lifetimes, quadratic like intensity scaling, and Burnham-Chiao ringing. We also map a phase diagram that delineates spontaneous emission, superfluorescence, and amplified spontaneous emission, and we observe deviations from ideal superfluorescence at high fluences and elevated temperatures, reflecting competing many-body and dephasing processes.[4] To interpret these observations, we introduce the ab initio quantum model Superfluorescence Non-Approximating Integrating Large Solver (SNAILS), which tracks emission density, inter emitter correlations, excited state populations, and trace distance under varying pumping and dephasing conditions.[4] Simulations reproduce delayed cooperative bursts when dephasing is weak and show rapid suppression of correlations and loss of delay when dephasing is stronger. Trace distance dynamics identify synchronization plateaus during cooperative emission and prolonged plateaus linked to subradiant or dark states under high dephasing, establishing a unified framework for cooperative emission and its breakdown in perovskite thin films. Overall, this work clarifies the optical and dynamical conditions required for macroscopic coherence in perovskites. The combined insights from phase mapping, ultrafast spectroscopy, and quantum modeling highlight strategies for lowering threshold fluence, mitigating dephasing, and extending superfluorescence toward higher temperatures.