The ordered atomic array emerges as a versatile atom-photon interface for exquisite control of light-matter interaction at the nanoscale. In particular, the one-dimensional atom-waveguide system can achieve strong coupling between a single atom and a photon, where two atomic mirrors coupled to waveguide act as a high-finesse cavity. In this work we show that under the strong-coupling regime, the mirror atoms arranged in the form of a Su-Schrieffer-Heeger chain are advantageous in decoherence suppression compared to a nontopological Bragg configuration, manifesting a significant increase in the lifetime of dressed states, substantial narrowing of the spectral linewidth, and order-of-magnitude enhancement of the cooperativity of light-matter interaction. Furthermore, subradiant dressed states with a decay rate smaller than the emission rate of a free-space atom are found in the dissipationless atomic cavity with a few mirror atoms, which cannot be achieved with a Bragg atomic mirror. A theory of the local density of states (LDOS) of the atomic cavity is presented and reveals that the decoherence suppression is directly related to the negative LDOS in a wide frequency range contributed by the bulk modes of the topological atomic cavity. This peculiar feature of the LDOS indicates the destructive quantum interference of photon scattering by the topological edge- and bulk-state channels. Our work demonstrates the great potential of topology in engineering quantum states and enhancing quantum coherence for future applications in quantum computing and quantum information processing.
The ordered atomic array emerges as a versatile atom-photon interface for exquisite control of light-matter interaction at the nanoscale. In particular, the one-dimensional atom-waveguide system can achieve strong coupling between a single atom and a photon, where two atomic mirrors coupled to waveguide act as a high-finesse cavity. In this work we show that under the strong-coupling regime, the mirror atoms arranged in the form of a Su-Schrieffer-Heeger chain are advantageous in decoherence suppression compared to a nontopological Bragg configuration, manifesting a significant increase in the lifetime of dressed states, substantial narrowing of the spectral linewidth, and order-of-magnitude enhancement of the cooperativity of light-matter interaction. Furthermore, subradiant dressed states with a decay rate smaller than the emission rate of a free-space atom are found in the dissipationless atomic cavity with a few mirror atoms, which cannot be achieved with a Bragg atomic mirror. A theory of the local density of states (LDOS) of the atomic cavity is presented and reveals that the decoherence suppression is directly related to the negative LDOS in a wide frequency range contributed by the bulk modes of the topological atomic cavity. This peculiar feature of the LDOS indicates the destructive quantum interference of photon scattering by the topological edge- and bulk-state channels. Our work demonstrates the great potential of topology in engineering quantum states and enhancing quantum coherence for future applications in quantum computing and quantum information processing.
Coherent and efficient light-matter interfaces between an atom and a single mode of the electromagnetic field are essential for quantum technologies. Traditionally, these systems employ optical cavities or waveguides to isolate a specific mode of light, but a more recent approach is to engineer antennas from ordered configurations of trapped ultracold atoms that exhibit controllable and directed scattering. In this work, we propose a method to engineer an antenna from the center-of-mass wavefunction of a single atom, which can produce directed emission and thereby exhibit strong coupling to a target mode of light in free space. We predict that the resulting single-atom cooperativity can be comparable to the current state of the art in optical cavity and waveguide QED experiments. Building on this approach, we show that a wavepacket antenna becomes a single-atom mirror in the linear response regime. We study the modified dipole-dipole interactions and band structure of chains of such emitters, which can exhibit sub- and superradiance at spacings much larger than the wavelength of the light. Extending our approach to multi-level atoms, we propose a method to achieve arbitrary spatial scattering from a single atom, including uni-directional spontaneous emission. Finally, we elucidate how our approach can enhance cooperative scattering in conventional arrays of tightly trapped atoms.
Quantum technologies, holding the promise of exponentially superior performance in comparison to their classical counterparts for certain tasks, have consistently encountered challenges, including instability in quantum light sources, quantum decoherence, and vulnerability to losses that topological photonics happens to adeptly address. Here, we theoretically put forth a quantum Su-Schrieffer-Heeger-type chain designed to greatly enhance single-photon blockade (single PB) effect with topological protection. By designing the deliberate coupling strengths, the quantum level lattices take the form of a one-dimensional array with a topological edge state in single-excitation space and a two-dimensional square breathing lattice with topological corner states in two-excitation space, resulting in enhanced single-photon excitation and the suppression of two-photon transitions. Therefore, the second-order correlation function is diminished by up to 2 orders of magnitude at the cavity resonance frequency, accompanied by stronger brightness. Furthermore, the PB effect is robust to local perturbations in cavity-qubit coupling and qubit frequency, benefitting from topological protection.
Scalable quantum computers and quantum networks require the combination of quantum processing nodes with efficient light-matter interfaces to distribute quantum information in local or long-distance quantum networks. Neutral-atom arrays have both been coupled to Rydberg states to enable high-fidelity quantum gates in universal processing architectures, and to optical cavities to realize interfaces to photons. However, combining these two capabilities and coupling atom arrays to highly excited Rydberg states in the mode of an optical cavity has been an outstanding challenge. Here we present a novel cavity-coupled Rydberg array that achieves this long-standing goal. We prepare, detect, and control individual atoms in a scalable optical tweezer array, couple them strongly to the optical mode of a high-finesse optical cavity and excite them in a controlled way to Rydberg states. We show that high-cooperativity coupling to an optical cavity -- demonstrated via the dispersive shift of the resonance of the cavity in presence of the atoms -- and strong Rydberg interactions -- demonstrated via the collective enhancement of Rydberg coupling in the atomic array -- can be achieved in our setup at the same spatial location. Our presented experimental platform opens the path to several new directions, including the realization of quantum network nodes, quantum simulation of long-range interacting, open quantum systems and photonic-state engineering leveraging high-fidelity Rydberg control.
Waveguide quantum electrodynamics with multiple atoms provides an important way to study photon transport. In this work, we study the photon transport in a one-dimensional waveguide coupled to a topological atom array. The interaction between light and topology-dressed atoms yields a rich variety of photon scattering phenomena. We find that the nonreciprocal photon reflection originates from the quantum interference of photons scattered by the dissipative edge and bulk modes in the topological atom array. The largest nonreciprocity is found at the magic atomic spacing d=3λ0/4, where λ0 is the characteristic wavelength of the waveguide. For an odd number of atoms with an extremely small free space decay, the broken inversion and time-reversal symmetries induce a giant anomalous photon loss from the waveguide to free space. Our model can be implemented in superconducting quantum circuits. This work opens a new avenue to manipulate photons via the interaction between light and topological quantum matter.
Recent experimental advances in preparing regular defect-free 2D arrays of atoms with optical traps have offered new opportunities to engineer strong collective couplings between light and atoms as quantum optical dipoles. Applications of such collective light-matter interactions include the realization of atom-thick mirrors, retrieval of quantum memories with high efficiency, or the implementation of topological quantum optics. I will present novel applications in the context of quantum networking. First, I will discuss the design of a chiral photonic quantum link, where distant single atoms interact by exchanging photons propagating in a unique direction in free space. This is achieved by coupling both single atoms, representing qubits implemented using a pair of Rydberg states, to bi-layer atomic arrays which act as quantum phased-array antennas. Exploiting the combination of a “Rydberg-dressing” laser and a control laser driving the atomic arrays, an effective Rydberg dipole-dipole interaction can be engineered between atoms and atomic arrays as quantum emitters, allowing to match the spatial modes of spontaneously emitted and absorbed photons to a Gaussian mode of interest. In this way, we realize a chiral quantum interface, i.e., where atoms couple to photonic modes with a unique direction of propagation. This setup provides a basic building block of a novel platform for quantum networks in free space, i.e., without requiring coupling atoms to modes of cavities or nanostructures, which I will illustrate with the deterministic coherent transfer of quantum states between single atoms with high fidelity. Second, I will discuss the collective radiation properties of two distant single-layer atomic arrays acting as quantum memories. This system can support a long-lived non-local superposition state of atomic excitations exhibiting strong subradiance. This “dark” mode consists of an atomic excitation which is delocalized between the two distant atomic arrays, in such a way that the overall radiation is strongly suppressed by quantum interference. I will describe the preparation of these states and their application as resource of non-local entanglement. In particular, by weakly driving the arrays, the state of the quantum memories, localized in each array, can be transferred to this “non-local” subradiant state, allowing again for a deterministic coherent quantum state transfer with high fidelity between the memories. Finally, I will discuss experimental realizations using cold atoms in optical trap arrays, and the effect of experimental imperfections in the arrays, such as finite defect probability, temperature, and depth of the optical traps.
A principal goal of distributed quantum processing is the ability to generate, manipulate, and transfer quantum states between distant nodes of a quantum network. These protocols generally require connecting photonic and material carriers of quantum information. Here we present two experimental realizations of light-matter interfaces that allow for engineered atom-photon interactions in free-space settings. First, we utilize reconfigurable arrays of trapped single atoms to study light scattering in low-dimensional systems. We observe noncollinear phase-matching geometries that have suppressed sensitivity to particle localization. We show that the scattered radiation can be controllably enhanced or diminished as a result of Bragg interference. Such scattering can be used for mapping collective states within an array of neutral atoms onto propagating light fields and for establishing quantum links between separated arrays. Second, we create a quasi-two-level system in a regime of Rydberg excitation blockade for a mesoscopic ensemble of several hundred atoms confined in a magic-wavelength optical lattice. We demonstrate coherent driving and Ramsey interference measurements of light shifts, with timescales on the order of ∼ 10 μs. Whereas the coupling producing the Rabi oscillations is enhanced by a factor of √N, there is no corresponding enhancement for the light shifts. These results may prove useful in applying collective qubits with Rydberg interactions to scalable quantum networking architectures.