We present a scheme for coherently manipulating quantum states of photons by incorporating multiple photonic modes in a system with long-range interactions. The presence of nonlocal photon-photon interactions destroys the energy- or momentum-matching conditions between distinct propagating polaritons and consequently gives rise to blockaded effective coupling between the corresponding polaritons. Such a blockade mechanism protects the system from interaction-induced dissipations and enables highly tunable few-photon nonlinearities. Taking the Rydberg atomic ensemble as an example, we illustrate several intriguing phenomena based on the proposed scheme, e.g., the deterministic generation of entangled photon pairs, the nonlinear beam splitting, as well as the establishment of a tunable dressed interaction between individual photons.
We present a scheme for coherently manipulating quantum states of photons by incorporating multiple photonic modes in a system with long-range interactions. The presence of nonlocal photon-photon interactions destroys the energy- or momentum-matching conditions between distinct propagating polaritons and consequently gives rise to blockaded effective coupling between the corresponding polaritons. Such a blockade mechanism protects the system from interaction-induced dissipations and enables highly tunable few-photon nonlinearities. Taking the Rydberg atomic ensemble as an example, we illustrate several intriguing phenomena based on the proposed scheme, e.g., the deterministic generation of entangled photon pairs, the nonlinear beam splitting, as well as the establishment of a tunable dressed interaction between individual photons.
Realizing strong interactions between individual photons, mediated by matter, is a cornerstone for advancing photonic quantum computing and quantum nonlinear optics. In such systems, the interaction range is typically limited by the narrow bandwidth of the material excitation, resulting in a trade-off between interaction strength and pulse duration. Here, we address this limitation by exploring interactions between counter-propagating photons mediated by Rydberg polaritons. We experimentally demonstrate strong photon–photon interactions, achieving a record-long anti-correlation range exceeding 1 µs. This extended range enables photon pulses that are long enough to fit within the polariton bandwidth, yet short enough to remain within the interaction range. Under these conditions, we observe complete photon blockade of entire pulses, tunable via their relative timing. Extending to the three-photon regime, we observe enhanced interactions when a photon encounters a counter-propagating pair. These results, supported by analytical theory and numerical simulations, establish counter-propagating Rydberg polaritons as a powerful platform for engineering interactions in quantum light fields, enabling deterministic photonic operations and opening new directions in few-photon quantum dynamics.
We investigate the interaction of weak light fields with two-dimensional lattices of atoms with high lying atomic Rydberg states. This system features different interactions that act on disparate length scales, from zero-range defect scattering of atomic excitations and finite-range dipole exchange processes to long-range Rydberg-state interactions, which span the entire array and can block multiple Rydberg excitations. Analyzing their interplay, we identify conditions that yield a nonlinear quantum mirror which coherently splits incident fields into correlated photon-pairs in a single transverse mode, while transmitting single photons unaffected. In particular, we find strong anti-bunching of the transmitted light with equal-time pair correlations that decrease exponentially with an increasing range of the Rydberg blockade. Such strong photon-photon interactions in the absence of photon losses open up promising avenues for the generation and manipulation of quantum light, and the exploration of many-body phenomena with interacting photons.
Although photons do no a ect each other in vacuum, interactions between individual photons could enable a wide variety of scienti c and engineering applications. Here we report on the creation of a quantum nonlinear medium with large photon-photon interactions at the single photon level. Our approach relies on Electromagnetically Induced Transparency (EIT) techniques, in which individual photons are coherently mapped onto strongly interacting Rydberg atoms. Under EIT conditions, photons traveling in the medium are best described as part-matter part-light quantum particles, called polaritons, which experience long-range interactions through the Rydberg blockade. In particular, we demonstrate coherent photon-photon interactions, akin to those associated with conventional massive particles, paving the way for novel photonics states and quantum simulation with light.
Rydberg atoms represent a platform underpinning many recent developments in quantum computation, simulation, sensing, and metrology. They further facilitate optical nonlinearity at the single-photon level when coupled to photons propagating in atomic clouds, which form collective atomic excitations called Rydberg polaritons, strongly interacting with each other. Here, we experimentally explore interactions between a Rydberg polariton in an atomic ensemble and a single, adjacent, Rydberg atom. We discover three different regimes of quantum dynamics corresponding to polariton blockade, coherent exchange, and probabilistic hopping, which are defined by their distinct transmission characteristics, with a transition through an exceptional point occurring between blockade and coherent exchange. We investigate the applications of such interactions for fast, non-destructive detection of Rydberg atoms and present proof-of-principle demonstrations for their potential application in nonlinear photonic networks.
We show that very large nonlocal nonlinear interactions between pairs of colliding slow-light pulses can be realized in atomic vapors in the regime of electromagnetically induced transparency. These nonlinearities are mediated by strong, long-range dipole-dipole interactions between Rydberg states of the multilevel atoms in a ladder configuration. In contrast to previously studied schemes, this mechanism can yield a homogeneous conditional phase shift of $\ensuremath{\pi}$ even for weakly focused single-photon pulses, thereby allowing a deterministic realization of the photonic phase gate.
We discuss electromagnetically induced transparency in a cold ensemble of atoms optically excited to the Rydberg states. Strong dipole-dipole or van der Waals interactions between the atomic Rydberg states translate into large nonlocal nonlinearities for a propagating probe field. In the case of weak quantum fields, this can be used to attain a conditional phase shift of π between pairs of single photons realizing a deterministic photonic phase gate. For stronger fields, long-range interactions between the atoms constrain the medium to behave as a collection of superatoms, each comprising a blockade volume that can accommodate at most one Rydberg excitation. The propagation of a probe field is affected by its two-photon correlations within the blockade distance, which are strongly damped due to low saturation threshold of the superatoms. Our calculations reproduce and interpret the results of recent experiments.