The Dicke-Ising model, one of the few paradigmatic models of matter-light interaction, exhibits a superradiant quantum phase transition above a critical coupling strength. However, in natural optical systems, its experimental validation is hindered by a “no-go theorem.” Here, we propose a digital-analog quantum simulator for this model based on an ensemble of interacting qubits coupled to a single-mode photonic resonator. We analyze the system's free-energy landscape using field-theoretical methods and develop a digital-analog quantum algorithm that disentangles qubit and photon degrees of freedom through a parity-measurement protocol. This disentangling enables the emulation of a photonic Schrödinger cat state, which is a hallmark of the superradiant ground state in finite-size systems and can be unambiguously probed through the Wigner tomography of the resonator's field.
Optical Schrödinger cat states are non-Gaussian states with applications in quantum technologies, such as for building error-correcting states in quantum computing. Yet the efficient generation of high-fidelity optical Schrödinger cat states is an outstanding problem in quantum optics. Here, we propose using squeezed superpositions of zero and two photons,
∣θ⟩=cos(θ/2)∣0⟩+sin(θ/2)∣2⟩, as ingredients for protocols to efficiently generate high-fidelity cat states. We present a protocol using linear optics with success probability
P≳50% that can generate cat states of size
∣α∣2=5 with fidelity
F>0.99. The protocol relies only on detecting single photons and is remarkably tolerant of loss, with
2% detection loss still achieving
F>0.98 for cats with
∣α∣2=5. We also show that squeezed
θ states are ideal candidates for nonlinear photon subtraction using a two-level system with near deterministic success probability and fidelity
F>0.98 for cat states of size
∣α∣2=5. Schemes for generating
θ states using quantum emitters are also presented. Our protocols can be implemented with current state-of-the-art quantum optics experiments.
Superradiance offers an efficient approach for coupling discrete quantum emitters via collective fluorescence. In this work, we suggest a method for the controlled coupling and synchronization of distant integrated photonic emitters using superradiance. Our theoretical modeling and analysis using electromagnetic and Master Equation methods for a case of nanodiamond/SiN heterogenous photonic platform confirms efficient superradiant coupling of distant emitters and a good degree of spurious emission isolation. This approach can offer a path to the scalable generation of multipartite photonic states, such as NOON states, and can enable efficient cluster state generation and one-way quantum computing approaches.