Kyung Soo Choi

An exciting frontier in quantum information science is the realization and control of complex quantum many-body systems. Hybrid nanophotonic system with cold atoms has emerged as the paradigmatic platform for engineering long-range spin models from the bottom up, exploiting their modal geometry and group dispersion for tailored interactions. An important challenge is the physical limitation imposed by the photonic bath, constraining the types of local Hamiltonians that decompose the available physical models and restricting the spatial dimensions to that of the dielectric media. However, at the nanoscopic scale, atom-field interaction inherently accompanies significant driven-dissipative quantum forces that may be tamed as a new form of a mediator for controlling the atomic internal states. Here, we formulate a quantum optics toolbox for constructing a universal quantum matter with individual atoms in the vicinity of 1D photonic crystal waveguides. The enabling platform synthesizes analog quantum materials of universal $2$-local Hamiltonian graphs mediated by phononic superfluids of the trapped atoms. We generalize our microscopic theory of analog universal quantum simulator to the development of dynamical gauge fields. In the spirit of gauge theories, we investigate emergent lattice models for strongly coupled SU$(n)$-constrained excitations driven by an underlying multi-body interaction. As a minimal model in the infrared, we explore the realization of an archetypical strong coupling quantum field theory, SU($n$) Wess-Zumino-Witten model, and discuss a diagnostic tool to extract the entire conformal data of the field theory by the static and dynamical correlators of the fluctuating photons in the guided mode.

Quantum networks are being developed for computation, communication and simulation. These authors demonstrate a quantum network capable of storing and reading out entanglement among multiple parties. It comprises four atomic memories connected by photonic channels, representing a significant increase in complexity in comparison with previous two-party networks.

We construct a method for verifying mode entanglement of N-mode W states. The ideal W state contains exactly one excitation symmetrically shared between N modes, but our method takes the existence of higher numbers of excitations into account, as well as the vacuum state and other deviations from the ideal state. Moreover, our method distinguishes between full N-party entanglement and states with M-party entanglement with M<N, including mixtures of the latter. We specialize to the case N=4 for illustrative purposes. In the optical case, where excitations are photons, our method can be implemented using linear optics.

Entanglement Sharing: Quantum information processing relies on the ability to generate quantum states, to entangle them, and to send and receive those quantum states reliably across networks. With quantum two-level systems, or qubits, if you want to have a large system (and solve complex problems), there is a fear that the ancillary equipment required to control the system will increase rapidly, perhaps too quickly. The use of multipartite systems, where several quantum states can be accessed in a single component, has been proposed as a solution. Papp et al. (p. 764 ) work with a multipartite system consisting of a single photon shared between four optical modes and show that the degree of entanglement can be controllably tuned. The ability to work with, and control, such entangled multipartite systems should help the development of quantum information processing.

Developments in quantum information science rely critically on entanglement-a fundamental aspect of quantum mechanics that causes parts of a composite system to show correlations stronger than can be explained classically. In particular, scalable quantum networks require the capability to create, store and distribute entanglement among distant matter nodes by means of photonic channels. Atomic ensembles can play the role of such nodes. So far, in the photon-counting regime, heralded entanglement between atomic ensembles has been successfully demonstrated through probabilistic protocols. But an inherent drawback of this approach is the compromise between the amount of entanglement and its preparation probability, leading to intrinsically low count rates for high entanglement. Here we report a protocol where entanglement between two atomic ensembles is created by coherent mapping of an entangled state of light. By splitting a single photon and performing subsequent state transfer, we separate the generation of entanglement and its storage. After a programmable delay, the stored entanglement is mapped back into photonic modes with overall efficiency of 17%. Together with improvements in single-photon sources, our protocol will allow 'on-demand' entanglement of atomic ensembles, a powerful resource for quantum information science.