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arXiv:2010.13075 · Physical Review Applied

Topologically Protected Strong Coupling and Entanglement Between Distant Quantum Emitters

Yujing Wang, Junfeng Ren, Weixuan Zhang, Lu He, Xiangdong Zhang

Published Nov 4, 2020• 16 citations
arXivHTMLPDF

Abstract

The realization of robust strong coupling and entanglement between distant quantum emitters (QEs) is necessary for scalable quantum-information processes. However, it is hard to achieve it based on conventional systems. Here, we propose theoretically and demonstrate numerically a scheme to realize such strong coupling and entanglement. Our scheme is based on the photonic crystal platform with topologically protected edge state and zero-dimensional topological corner cavities. When the QEs are put into topological cavities, the strong coupling between them can be fulfilled with the assistance of the topologically protected interface state. Such a strong coupling can maintain a very long distance and be robust against various defects. In particular, we numerically prove that the topologically protected entanglement between two QEs can also be realized. Moreover, the duration of quantum beats for such entanglement can reach several orders longer than that for the entanglement in a conventional photonic cavity, making it beneficial for a scalable quantum-information process.

DOI
10.1103/physrevapplied.14.054007

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The realization of robust strong coupling and entanglement between distant quantum emitters (QEs) is necessary for scalable quantum-information processes. However, it is hard to achieve it based on conventional systems. Here, we propose theoretically and demonstrate numerically a scheme to realize such strong coupling and entanglement. Our scheme is based on the photonic crystal platform with topologically protected edge state and zero-dimensional topological corner cavities. When the QEs are put into topological cavities, the strong coupling between them can be fulfilled with the assistance of the topologically protected interface state. Such a strong coupling can maintain a very long distance and be robust against various defects. In particular, we numerically prove that the topologically protected entanglement between two QEs can also be realized. Moreover, the duration of quantum beats for such entanglement can reach several orders longer than that for the entanglement in a conventional photonic cavity, making it beneficial for a scalable quantum-information process.
This paper explores the potential of topological photonics for realizing long-distance quantum bit (qubit) interconnection, a critical step towards building scalable and reliable quantum computers. Conventional approaches to quantum communication face significant challenges due to photon loss in optical fibers, limiting the transmission distance and fidelity of quantum information. We investigate how the unique properties of topological photonics, specifically the utilization of light propagation within topological defects, can circumvent these limitations. The core concept involves harnessing robust, protected edge states within photonic lattices, enabling entanglement distribution and quantum communication over significantly extended distances without the deleterious effects of direct photon scattering. This paper details the theoretical framework, focusing on key aspects such as the creation and manipulation of these topological states, and the potential for building interconnected qubit networks. We present a framework for understanding the advantages of this approach and highlight key research directions.
Photon entanglement is a fundamental resource for quantum technologies, yet it is extremely fragile especially in large quantum circuitry, which is necessary for quantum information processing and computing. We propose an integrated scheme for direct topological protection of entanglement, enabling robust transport of entangled photonic states, even when the photon dynamically evolves during propagation. Our platform relies on a two-dimensional discrete-time quantum walks in synthetic dimensions, supporting topological edge states at the interface between distinct domains. Thus far, in all previous approaches for exploiting topology to protect entanglement, the protection was linked to the position of the photon in the actual structure. In contrast, our scheme relies on a synthetic temporal dimension (time bins) where the entangled state is always reproduced, despite fluctuations or variations that may emerge in the system. Thus, our scheme provides precise temporal control important for synchronization and timing in quantum computation. By suppressing phase-sensitive errors—the most critical noise source in photonic platforms—our approach can lower the physical error rate below fault-tolerance thresholds and reduce the overhead typically required for scalable quantum information processing. The robustness to errors arises from the fact that the entangled state is preserved through correlations in the synthetic (temporal) dimension. As a result, we ensure that at specific designated times, the emergent state faithfully reproduces the initial entangled state, despite the photon having taken any dynamically evolving paths. This approach establishes a robust framework for directly protecting entanglement.
Hybrid photonic nanostructures allow the engineering of novel interesting states of light. One recent example is topological photonic crystals where a nontrivial Berry phase of the photonic band structure gives rise to topologically protected unidirectionally-propagating (chiral) edge states of photons. Here we demonstrate that by coupling an array of emitters to the chiral photonic edge state one can create strongly correlated states of photons in a highly controllable way. These are topologically protected and have a number of remarkable universal properties: the outcome of scattering does not depend on the positions of emitters and is given only by universal numbers, the zeroes of Laguerre polynomials; two-photon correlation functions manifest a well-pronounced even–odd effect with respect to the number of emitters; and the result of scattering is robust with respect to fluctuations in the emitters' transition frequencies.
Abstract Entanglement and topology both portray nature at the fundamental level but in different manners. Entangled states of quantum particles are intrinsically sensitive to environment, whereas topological phases of matters represent natural robustness against environmental perturbations. Harnessing topology physics to protect entanglement thus has a great potential for reliable quantum applications. However, generating topologically-protected entanglement remains a significant challenge, which requires operating complex quantum devices in combined extreme conditions. Here we report topologically-protected quantum entanglement emitters, that emit topological Einstein-Podolsky-Rosen entangled state and topological multiphoton entangled state from a monolithically-integrated plug-and-play silicon-photonic chip in ambient conditions. The device emulating a photonic anomalous Floquet insulator allows the generation of up to four-photon topological entangled states at nontrivial edge modes. More importantly, we show that the Einstein-Podolsky-Rosen entanglement emitters can be topologically protected against artificial structure defects, by comparing tomographically measured fidelities of 0.968 ± 0.004 and 0.951 ± 0.01 for the perfect and defected emitters, respectively. Our topologically-protected entanglement emitters may find applications in photonic quantum computation and quantum simulation, and in the study of quantum topological physics.
Robust quantum state transfer (QST) is an indispensable ingredient in scalable quantum information processing. Here we present an experimentally feasible mechanism for realizing robust QST via topologically protected edge states in superconducting qubit chains. Using superconducting Xmon qubits with tunable couplings, we construct generalized Su-Schrieffer-Heeger models and analytically derive the wave functions of topological edge states. We find that such edge states can be employed as a quantum channel to realize robust QST between remote qubits. With a numerical simulation, we show that both single-qubit states and two-qubit entangled states can be robustly transferred in the presence of sizable imperfections in the qubit couplings. The transfer fidelity demonstrates a wide plateau at the value of unity in the imperfection magnitude. This approach is general and can be implemented in a variety of quantum computing platforms.
The combination of topological photonics and quantum optics has promising applications. In previous works, the role of the edge states of conventional topological optical structure in the coherent coupling between atoms has been discussed. Besides the optimistic results, we find that if the coupling coefficient between the atom and element-cavity exceeds the coupling coefficient between cavities in the array, atoms cannot be effectively coupled with each other through the edge states. Here, we generalize to higher-order structures and explore the dynamics of three atoms interacting with the cavity array based on the kagome-type optically coupled-cavity array with topologically protected corner states. Three atoms are theoretically coupled in three corner cavities, and various quantum behaviors can be displayed in different parameters. It is shown that three atoms mediated by the corner state can be coherently coupled with each other, without the constraint of the coupling coefficient, and can induce entanglement, which shows that the high-order topological optical structure has more advantages than the conventional topological optical structure in coherent coupling among qubits. In addition, we also studied atoms mediated by edge states. The results show that the atoms mediated by edge states can be coherently coupled only in the weak coupling regime, and the entanglement effect induced by the edge states is not as good as that of the corner state. It indicates that the corner state is more useful than the edge state in the second-order optical topological structure. Our results can offer references for applying optical topological structure in quantum computing and quantum communication.