arXiv subjects

K. S. Choi

Publications and source records attributed to K. S. Choi.

13 recordsLinked to original sources

arXiv2021

Melting a Rydberg ice to a topological spin liquid with cavity vacuum fluctuation

Quantum spin liquids are exotic phases of matter that are prevented from being frozen even at zero temperature, and appear disordered by local probes that monitor the subsystems. Driven by quantum fluctuations, topological spin liquids are manifested by their long-range entanglement, and are characterized by quasiparticles with fractional statistics. Here, we make contact of a 2D Rydberg ice to a QED vacuum of an ultra-high-finesse optical cavity, and dynamically promote the frustrated background field of the spin ice to a $\mathbb{Z}_2$ spin liquid. We characterize the deconfined nature of the dynamical gauge theory residing in the strongly-correlated Rydberg matter with Wilsonian loops. We observe the proliferation of vison and spinon pairs by site-resolved fluorescence imaging, and detect the exchange statistical angle $θ_{\text{top}}\simπ/2$ between the two anyons by monitoring the dynamical correlators of the fluctuating cavity photons. Our work provides the first microscopic detection of anyons in a topological quantum matter, and heralds the arrival of strongly-coupled many-body QED, where interacting matter and light are put on equal footing at the level of individual quanta.

quant-ph↗

arXiv2021

Physical limits of ultra-high-finesse optical cavities: Taming two-level systems of glassy metal oxides

The framework of tunnelling states in amorphous media provides the dissipative mechanism that imposes fundamental limits on the performances of ultra-high-Q optical and microwave resonators. In the optical domain, however, the microscopic nature of the tunnelling states and their direct consequences to the optical losses have not been characterized. In this work, we examine the interplay between glassy physics and stoichiometric point defects of ultra-low-loss dielectric mirrors, with a focus on two-level systems of oxygen defects in metal oxide, Ta$_2$O$_5$. In the context of ultra-high-finesse optical cavities, we characterize the Urbach tail of Ta$_2$O$_5$ under thermal annealing and reactive oxygen plasma. For the first time, we microscopically resolve the individual oxygen point defects on the mirror surfaces and introduce laser-assisted annealing to selectively "cure" surface defects. By exploiting these techniques, we report the realization of ultra-high-finesse optical cavity with finesse $\mathcal{F}=450,000$ and the absorption-scatter loss $ 0.1 \pm 0.2$ ppm at $852$ nm.

physics.optics↗

arXiv2021

Waveguide QED toolboxes for universal quantum matter

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.

quant-ph↗

arXiv2014

Emergence of stationary many-body entanglement in driven-dissipative Rydberg lattice gases

Non-equilibrium quantum dynamics represents an emerging paradigm for condensed matter physics, quantum information science, and statistical mechanics. Strongly interacting Rydberg atoms offer an attractive platform to study driven-dissipative dynamics of quantum spin models with long-range order. Here, we explore the conditions under which stationary many-body entanglement persists with near-unit fidelity and high scalability. In our approach, coherent many-body dynamics is driven by Rydberg-mediated laser transitions, while atoms at the lattice boundary reduce the entropy of the many-body state. Surprisingly, the many-body entanglement is established by continuously evolving a locally dissipative Rydberg system towards the steady-state, as with optical pumping. We characterize the dynamics of multipartite entanglement in a 1D lattice by way of quantum uncertainty relations, and demonstrate the long-range behavior of the stationary entanglement with finite-size scaling, reaching "hectapartite" entanglement under experimental conditions. Our work opens a route towards dissipative preparation of many-body entanglement with unprecedented scaling behavior.

quant-ph↗

arXiv2013

Atom-Light Interactions in Photonic Crystals

The integration of nanophotonics and atomic physics has been a long-sought goal that would open new frontiers for optical physics. Here, we report the development of the first integrated optical circuit with a photonic crystal capable of both localizing and interfacing atoms with guided photons in the device. By aligning the optical bands of a photonic crystal waveguide (PCW) with selected atomic transitions, our platform provides new opportunities for novel quantum transport and many-body phenomena by way of photon-mediated atomic interactions along the PCW. From reflection spectra measured with average atom number N = 1.1$\pm$0.4, we infer that atoms are localized within the PCW by Casimir-Polder and optical dipole forces. The fraction of single-atom radiative decay into the PCW is $Γ_{\rm 1D}/Γ'$ = 0.32$\pm$0.08, where $Γ_{1D}$ is the rate of emission into the guided mode and $Γ'$ is the decay rate into all other channels. $Γ_{\rm 1D}/Γ'$ is quoted without enhancement due to an external cavity and is unprecedented in all current atom-photon interfaces.

physics.optics↗

arXiv2012

Corrections to our results for optical nanofiber traps in Cesium

Several errors in Refs. [1, 2] are corrected related to the optical trapping potentials for a state-insensitive, compensated nanofiber trap for the D2 transition of atomic Cesium. Section I corrects our basic formalism in Ref. [1] for calculating dipole-force potentials. Section II corrects erroneous values for a partial lifetime and a transition wavelength in Ref. [1]. Sections III and IV present corrected figures for various trapping configurations considered in Refs. [1] and [2], respectively.

quant-ph↗

arXiv2012

Demonstration of a state-insensitive, compensated nanofiber trap

We report the experimental realization of an optical trap that localizes single Cs atoms ~215 nm from surface of a dielectric nanofiber. By operating at magic wavelengths for pairs of counter-propagating red- and blue-detuned trapping beams, differential scalar light shifts are eliminated, and vector shifts are suppressed by ~250. We thereby measure an absorption linewidth Γ/2π= 5.7 \pm 0.1 MHz for the Cs 6S1/2,F=4 - 6P3/2,F'=5 transition, where Γ/2π= 5.2 MHz in free space. Optical depth d~66 is observed, corresponding to an optical depth per atom d_1~0.08. These advances provide an important capability for the implementation of functional quantum optical networks and precision atomic spectroscopy near dielectric surfaces.

physics.atom-ph↗

arXiv2011

A state-insensitive, compensated nanofiber trap

Laser trapping and interfacing of laser-cooled atoms in an optical fiber network is an important capability for quantum information science. Following the pioneering work of Balykin et al. and Vetsch et al., we propose a robust method of trapping single Cesium atoms with a two-color state-insensitive evanescent wave around a dielectric nanofiber. Specifically, we show that vector light shifts (i.e., effective inhomogeneous Zeeman broadening of the ground states) induced by the inherent ellipticity of the forward-propagating evanescent wave can be effectively canceled by a backward-propagating evanescent wave. Furthermore, by operating the trapping lasers at the magic wavelengths, we remove the differential scalar light shift between ground and excited states, thereby allowing for resonant driving of the optical D2 transition. This scheme provides a promising approach to trap and probe neutral atoms with long trap and coherence lifetimes with realistic experimental parameters.

quant-ph↗

arXiv2010

Entanglement of spin waves among four quantum memories

Quantum networks are composed of quantum nodes that interact coherently by way of quantum channels and open a broad frontier of scientific opportunities. For example, a quantum network can serve as a `web' for connecting quantum processors for computation and communication, as well as a `simulator' for enabling investigations of quantum critical phenomena arising from interactions among the nodes mediated by the channels. The physical realization of quantum networks generically requires dynamical systems capable of generating and storing entangled states among multiple quantum memories, and of efficiently transferring stored entanglement into quantum channels for distribution across the network. While such capabilities have been demonstrated for diverse bipartite systems (i.e., N=2 quantum systems), entangled states with N > 2 have heretofore not been achieved for quantum interconnects that coherently `clock' multipartite entanglement stored in quantum memories to quantum channels. Here, we demonstrate high-fidelity measurement-induced entanglement stored in four atomic memories; user-controlled, coherent transfer of atomic entanglement to four photonic quantum channels; and the characterization of the full quadripartite entanglement by way of quantum uncertainty relations. Our work thereby provides an important tool for the distribution of multipartite entanglement across quantum networks.

quant-ph↗

arXiv2007

Mapping photonic entanglement into and out of a quantum memory

Recent developments of quantum information science critically rely on entanglement, an intriguing aspect of quantum mechanics where parts of a composite system can exhibit correlations stronger than any classical counterpart. In particular, scalable quantum networks require capabilities to create, store, and distribute entanglement among distant matter nodes via 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 via probabilistic protocols. However, an inherent drawback of this approach is the compromise between the amount of entanglement and its preparation probability, leading intrinsically to low count rate 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 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 %. Improvements of single-photon sources together with our protocol will enable "on demand" entanglement of atomic ensembles, a powerful resource for quantum networking.

quant-ph↗

arXiv2007

Heralded Entanglement between Atomic Ensembles: Preparation, Decoherence, and Scaling

Heralded entanglement between collective excitations in two atomic ensembles is probabilistically generated, stored, and converted to single photon fields. By way of the concurrence, quantitative characterizations are reported for the scaling behavior of entanglement with excitation probability and for the temporal dynamics of various correlations resulting in the decay of entanglement. A lower bound of the concurrence for the collective atomic state of 0.9\pm 0.3 is inferred. The decay of entanglement as a function of storage time is also observed, and related to the local dynamics.

quant-ph↗

arXiv2007

Towards experimental entanglement connection with atomic ensembles in the single excitation regime

We present a protocol for performing entanglement connection between pairs of atomic ensembles in the single excitation regime. Two pairs are prepared in an asynchronous fashion and then connected via a Bell measurement. The resulting state of the two remaining ensembles is mapped to photonic modes and a reduced density matrix is then reconstructed. Our observations confirm for the first time the creation of coherence between atomic systems that never interacted, a first step towards entanglement connection, a critical requirement for quantum networking and long distance quantum communications.

quant-ph↗

arXiv2006

Non-thermal origin of nonlinear transport across magnetically induced superconductor-metal-insulator transition

We have studied the effect of perpendicular magnetic fields and temperatures on the nonlinear electronic transport in amorphous Ta superconducting thin films. The films exhibit a magnetic field induced metallic behavior intervening the superconductor-insulator transition in the zero temperature limit. We show that the nonlinear transport in the superconducting and metallic phase is of non-thermal origin and accompanies an extraordinarily long voltage response time.

cond-mat.supr-con↗