Extensible quantum simulation architecture based on atom-photon bound states in an array of high-impedance resonators
Marco Scigliuzzo, Giuseppe Calajò, Francesco Ciccarello, Daniel Pérez Lozano, Andreas Bengtsson, Pasquale Scarlino, Andreas J. Wallraff, Darrick E. Chang, Per Delsing, Simone Gasparinetti
Engineering the electromagnetic environment of a quantum emitter gives rise to a plethora of exotic light-matter interactions. In particular, photonic lattices can seed long-lived atom-photon bound states inside photonic band gaps. Here we report on the concept and implementation of a novel microwave architecture consisting of an array of compact, high-impedance superconducting resonators forming a 1 GHz-wide pass band, in which we have embedded two frequency-tuneable artificial atoms. We study the atom-field interaction and access previously unexplored coupling regimes, in both the single- and double-excitation subspace. In addition, we demonstrate coherent interactions between two atom-photon bound states, in both resonant and dispersive regimes, that are suitable for the implementation of SWAP and CZ two-qubit gates. The presented architecture holds promise for quantum simulation with tuneable-range interactions and photon transport experiments in nonlinear regime.
Engineering the electromagnetic environment of a quantum emitter gives rise to a plethora of exotic light-matter interactions. In particular, photonic lattices can seed long-lived atom-photon bound states inside photonic band gaps. Here we report on the concept and implementation of a novel microwave architecture consisting of an array of compact, high-impedance superconducting resonators forming a 1 GHz-wide pass band, in which we have embedded two frequency-tuneable artificial atoms. We study the atom-field interaction and access previously unexplored coupling regimes, in both the single- and double-excitation subspace. In addition, we demonstrate coherent interactions between two atom-photon bound states, in both resonant and dispersive regimes, that are suitable for the implementation of SWAP and CZ two-qubit gates. The presented architecture holds promise for quantum simulation with tuneable-range interactions and photon transport experiments in nonlinear regime.
Quantum simulators employing cold atoms are among the most promising approaches to tackle quantum many-body problems. Nanophotonic structures are widely employed to engineer the band structure of light and are thus investigated as a means to tune the interactions between atoms placed in their vicinity. A key shortcoming of this approach is that excitations can decay into free photons, limiting the coherence of such quantum simulators. Here, we overcome this challenge by proposing to use a simple cubic three-dimensional array of atoms to produce an omnidirectional band gap for light and show that it enables coherent, dissipation-free interactions between embedded impurities. We show explicitly that the band gaps persist for moderate lattice sizes and finite filling fraction, which makes this effect readily observable in experiment. Our paper paves the way toward analog spin quantum simulators with long-range interactions using ultracold atomic lattices, and is an instance of the emerging field of atomic quantum metamaterials.
In quantum computing, precise control of system-environment coupling is essential for high-fidelity gates, measurements, and networking. We present an architecture that employs an artificial giant atom from waveguide quantum electrodynamics to tailor the interaction between a superconducting qubit and its environment. This frequency-tunable giant atom exhibits both frequency and power selectivity for photons: when resonant with the qubit, it reflects single photons emitted from the qubit while remaining transparent to strong microwave signals for readout and control. This approach surpasses the Purcell limit and significantly extends the qubit's lifetime by ten times while maintaining the readout speed, thereby improving both gate operations and readout. Our architecture holds promise for bridging circuit and waveguide quantum electrodynamics systems in quantum technology applications.
Waveguide quantum electrodynamics studies photon-mediated interactions of quantum emitters in a one-dimensional radiation channel. Although signatures of such interactions have been observed previously in a variety of physical systems, observation of coherent cooperative dynamics has been obscured by radiative decay of atoms into the waveguide. Employing transmon qubits as artificial atoms coupled to a microwave coplanar waveguide, here we observe dynamical oscillations in an open system where a designated probe qubit interacts with an entangled dark state of an array of qubits which effectively traps radiation as an atomic cavity. The qubit-cavity system is shown to achieve a large cooperativity of C=172 due to collective enhancement of photon-mediated interactions, entering the strong coupling regime. The quantum coherence of the dark state cavity is also explored through its nonlinear response at the single-excitation level. With realistic refinements, this system is suitable for studying the many-body dynamics of large (N>10) quantum spin chains, synthesizing highly non-classical radiation fields on demand, and implementing universal quantum logic operations with high fidelity on information encoded within decoherence-free subspaces.
Experiments utilizing quantum optics have progressed rapidly in last few decades, particularly in the context of quantum computation, simulation, and communication. Early work in this field focused on implementations of cavity quantum electrodynamics (QED), where atoms, either natural or artificial, are strongly coupled to the confined photonic modes of cavities. However, in recent years, achieving strong coupling between atoms and itinerant photons has also gained significant interest for its applications in quantum networking. To this end, many atomic platforms are attempting to realize the waveguide QED architecture: atoms that interact with the continua of propagating photonic modes within a waveguide. In this thesis, we realize the strong-coupling regime of a waveguide QED architecture by coupling superconducting artificial atoms, typically operated as qubits, to one-dimensional transmission lines. We first demonstrate that superconducting qubits in a waveguide QED system can be used as high-quality quantum emitters. We then leverage the quantum interference between the simultaneous emission from multiple qubits in order to generate non-classical, spatially entangled, and directional itinerant microwave photons. These types of photons are particularly useful for remote entanglement and quantum communication protocols. Finally, we demonstrate that superconducting qubits can be engineered to enter novel regimes of light-matter interactions that are difficult, or even impossible, to achieve in other atomic platforms. In particular, we realize the giant-atom regime of waveguide QED, where the atom can no longer be treated as a point-like object. We use our giant atoms to implement tunable atom-waveguide couplings, as well as decoherence-free waveguide-mediated interactions between multiple atoms.
Engineering the photonic environment using lattices of coupled resonators, which we refer to as lattice quantum electrodynamics (QED), provides a route to control both the spontaneous emission of individual quantum emitters and the photon-mediated interactions between them. Here we introduce an optical lattice QED platform based on individual dibenzoterrylene (DBT) molecules embedded in anthracene crystals and coupled to lattices of open optical microcavities. This hybrid architecture benefits from narrow-linewidth molecular emitters, site-resolved optical access, engineered coupled-resonator bands, and compatibility with established molecular frequency-tuning techniques. As a proof-of-principle demonstration, we observe emitter-photon bound states formed when the optical transition of a single molecule is tuned to the band gap of a Su-Schrieffer-Heeger (SSH) cavity lattice. These in-gap states display directional localization and photon emission on a single sublattice, inherited from the vacancy-induced topological edge modes of the underlying SSH lattice. Our results establish open-cavity lattices coupled to DBT molecules as a versatile architecture for engineering many-emitter quantum optical systems with controllable photon-mediated interactions.
Abstract Embedding tunable quantum emitters in a photonic bandgap structure enables control of dissipative and dispersive interactions between emitters and their photonic bath. Operation in the transmission band, outside the gap, allows for studying waveguide quantum electrodynamics in the slow-light regime. Alternatively, tuning the emitter into the bandgap results in finite-range emitter–emitter interactions via bound photonic states. Here, we couple a transmon qubit to a superconducting metamaterial with a deep sub-wavelength lattice constant (λ/60). The metamaterial is formed by periodically loading a transmission line with compact, low-loss, low-disorder lumped-element microwave resonators. Tuning the qubit frequency in the vicinity of a band-edge with a group index of ng = 450, we observe an anomalous Lamb shift of −28 MHz accompanied by a 24-fold enhancement in the qubit lifetime. In addition, we demonstrate selective enhancement and inhibition of spontaneous emission of different transmon transitions, which provide simultaneous access to short-lived radiatively damped and long-lived metastable qubit states.