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Register a new userPhoton-photon interactions in Rydberg-atom arrays
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We investigate the interaction of weak light fields with two-dimensional lattices of atoms, in which two-photon coupling establishes conditions of electromagnetically induced transparency and excites 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 interactions to long-range Rydberg-state interactions that span the entire array. 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. Such strong photon-photon interactions in the absence of otherwise detrimental photon losses in Rydberg-EIT arrays opens up a promising approach for the generation and manipulation of quantum light, and the exploration of many-body phenomena with interacting photons.
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We study theoretically the interaction between two photons in a nonlinear cavity. The photons are loaded into the cavity via a method we propose here, in which the input/output coupling of the cavity is effectively controlled via a tunable coupling to a second cavity mode that is itself strongly output-coupled. Incoming photon wave packets can be loaded into the cavity with high fidelity when the timescale of the control is smaller than the duration of the wave packets. Dynamically coupled cavities can be used to avoid limitations in the photon-photon interaction time set by the delay-bandwidth product of passive cavities. Additionally, they enable the elimination of wave packet distortions caused by dispersive cavity transmission and reflection. We consider three kinds of nonlinearities, those arising from $chi^{scriptscriptstyle(2)}$ and $chi^{scriptscriptstyle(3)}$ materials and that due to an interaction with a two-level emitter. To analyze the input and output of few-photon wave packets we use a Schrodinger-picture formalism in which travelling-wave fields are discretized into infinitesimal time-bins. We suggest that dynamically coupled cavities provide a very useful tool for improving the performance of quantum devices relying on cavity-enhanced light-matter interactions such as single-photon sources and atom-like quantum memories with photon interfaces. As an example, we present simulation results showing that high fidelity two-qubit entangling gates may be constructed using any of the considered nonlinear interactions.
An experiment is performed where a single rubidium atom trapped within a high-finesse optical cavity emits two independently triggered entangled photons. The entanglement is mediated by the atom and is characterized both by a Bell inequality violation of S=2.5, as well as full quantum-state tomography, resulting in a fidelity exceeding F=90%. The combination of cavity-QED and trapped atom techniques makes our protocol inherently deterministic - an essential step for the generation of scalable entanglement between the nodes of a distributed quantum network.
Quantum entanglement involving coherent superpositions of macroscopically distinct states is among the most striking features of quantum theory, but its realization is challenging, since such states are extremely fragile. Using a programmable quantum simulator based on neutral atom arrays with interactions mediated by Rydberg states, we demonstrate the deterministic generation of Schrodinger cat states of the Greenberger-Horne-Zeilinger (GHZ) type with up to 20 qubits. Our approach is based on engineering the energy spectrum and using optimal control of the many-body system. We further demonstrate entanglement manipulation by using GHZ states to distribute entanglement to distant sites in the array, establishing important ingredients for quantum information processing and quantum metrology.
We report the observation of entanglement between a single trapped atom and a single photon at remote locations. The degree of coherence of the entangled atom-photon pair is verified via appropriate local correlation measurements, after communicating the photon via an optical fiber link of 300 m length. In addition we measured the temporal evolution of the atomic density matrix after projecting the atom via a state measurement of the photon onto several well defined spin states. We find that the state of the single atom dephases on a timescale of 150 $mu$s, which represents an important step toward long-distance quantum networking with individual neutral atoms.
We propose a new method to create two-photon states in a controllable way using interaction between the Rydberg atoms during the storage and retrieval of slow light. A distinctive feature of the suggested procedure is that the slow light is stored into a superposition of two atomic coherences under conditions of electromagnetically induced transparency (EIT). Interaction between the atoms during the storage period creates entangled pairs of atoms in a superposition state that is orthogonal to the initially stored state. Restoring the slow light from this new atomic state one can produce a two photon state with a second-order correlation function determined by the atom-atom interaction and the storage time. Therefore the measurement of the restored light allows one to probe the atom-atom coupling by optical means with a sensitivity that can be increased by extending the storage time. As a realization of this idea we consider a many-body Ramsey-type technique which involves pi/2 pulses creating a superposition of Rydberg states at the beginning and the end of the storage period. In that case the regenerated light is due to the resonance dipole-dipole interaction between the atoms in the Rydberg states.
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