A distinctive feature of non-Hermitian systems is the skin effect, which has recently attracted widespread attention. Quantum walks provide a powerful platform for investigating the underlying mechanisms of the non-Hermitian skin effect. Additionally, hybrid entanglement generation in quantum walks is recognized as another crucial property. However, experimentally investigating the influence of skin effect on the evolution of entanglement dynamics in the non-Hermitian systems remains a challenge. In this paper, we present a flexible implementation of 20-step discrete-time quantum walks using an optimized time-multiplexed loop configuration. By optimizing the coin parameter, we achieve maximal coin-position entanglement after 20-step quantum walks. Moreover, we experimentally measure the polarization-averaged growth rates and the evolution of coin-position entanglement under specific coin and loss parameters. We observe the asymmetric Lyapunov exponent profiles and the entanglement suppression induced by the non-Hermitian skin effect. Interestingly, this entanglement suppression weakens with increasing coin parameters and enhances with increasing loss parameters and evolution steps. Our results demonstrate the potential of quantum walks as a powerful platform for investigating hybrid entanglement properties and skin effects in non-Hermitian systems.
A distinctive feature of non-Hermitian systems is the skin effect, which has recently attracted widespread attention. Quantum walks provide a powerful platform for investigating the underlying mechanisms of the non-Hermitian skin effect. Additionally, hybrid entanglement generation in quantum walks is recognized as another crucial property. However, experimentally investigating the influence of skin effect on the evolution of entanglement dynamics in the non-Hermitian systems remains a challenge. In this paper, we present a flexible implementation of 20-step discrete-time quantum walks using an optimized time-multiplexed loop configuration. By optimizing the coin parameter, we achieve maximal coin-position entanglement after 20-step quantum walks. Moreover, we experimentally measure the polarization-averaged growth rates and the evolution of coin-position entanglement under specific coin and loss parameters. We observe the asymmetric Lyapunov exponent profiles and the entanglement suppression induced by the non-Hermitian skin effect. Interestingly, this entanglement suppression weakens with increasing coin parameters and enhances with increasing loss parameters and evolution steps. Our results demonstrate the potential of quantum walks as a powerful platform for investigating hybrid entanglement properties and skin effects in non-Hermitian systems.
In this paper, we investigate the enhancement of delocalization and coin-position entanglement in asymmetric discrete-time quantum walks (DTQWs). The asymmetry results from asymmetric coin operations, asymmetric initial states, and asymmetric polarization-dependent losses. By varying these asymmetry factors, the inverse participation ratio and entanglement entropy of the walker are numerically calculated for different coin and loss parameters, both for symmetric and asymmetric initial states. We then experimentally implement a 16-step asymmetric DTQW using a time-multiplexing fiber loop structure. By choosing an asymmetric initial state, both coin-position entanglement and delocalization are simultaneously enhanced under specific coin parameters. Moreover, we observe that with finite asymmetric polarization-dependent loss, the photon probability on the left side decreases significantly, while that on the right side increases and becomes more localized. Interestingly, under specific coin parameters, the entanglement and delocalization exhibit improved robustness against polarization-dependent loss. These results demonstrate that the DTQWs constitute an ideal platform for investigating photonic delocalization and hybrid entanglement.
In this paper, we investigate the enhancement of delocalization and coin-position entanglement in asymmetric discrete-time quantum walks (DTQWs). The asymmetry results from asymmetric coin operations, asymmetric initial states, and asymmetric polarization-dependent losses. By varying these asymmetry factors, the inverse participation ratio and entanglement entropy of the walker are numerically calculated for different coin and loss parameters, both for symmetric and asymmetric initial states. We then experimentally implement a 16-step asymmetric DTQW using a time-multiplexing fiber loop structure. By choosing an asymmetric initial state, both coin-position entanglement and delocalization are simultaneously enhanced under specific coin parameters. Moreover, we observe that with finite asymmetric polarization-dependent loss, the photon probability on the left side decreases significantly, while that on the right side increases and becomes more localized. Interestingly, under specific coin parameters, the entanglement and delocalization exhibit improved robustness against polarization-dependent loss. These results demonstrate that the DTQWs constitute an ideal platform for investigating photonic delocalization and hybrid entanglement.
Abstract Quantum walks hold enormous potential applications in various areas such as quantum computing and quantum simulation. Discrete-time quantum walks on a ladder offer greater prospects compared to traditional quantum walks, especially in addressing physical problems in higher-dimension coupled systems. Here we give an experimental proposal of quantum walks on a two-leg ladder using linear optics, and further apply it to non-Hermitian systems by introducing loss-based non-unitary evolutions. Non-Hermitian systems under nonreciprocity-induced evolution present an exotic phenomenon, known as the non-Hermitian skin effect (NHSE). In a two-leg non-Hermitian system with the same preferred direction of NHSE, the direction has recently been found to reverse when interchain couplings are introduced. Based on quantum walks on a ladder, we also propose an experimentally feasible scheme to demonstrate the direction reversal of NHSE. Through the simulated results we show that particles on each chain accumulate to the preferred boundary driven by nonreciprocal hopping, while particles are transported in the opposite direction when interchain hopping is allowed, clearly demonstrating the existence of reversed NHSE. Our work further expands the application of the quantum walk platform and opens a door for the experimental investigation of reversed NHSE.
Quantum walks have demonstrated capabilities that surpass classical approaches across a range of applications, including quantum computing, quantum simulation, quantum information processing, etc. Recently, quantum walks in non-Hermitian systems have garnered significant attention. The authors experimentally realize here a non-Hermitian photonic lattice on a silicon chip, observing asymmetric quantum walks of single photons induced by the non-Hermitian skin effect. Notably, they investigate the entanglement dynamics of correlated photons, revealing a suppression of entanglement in these non-Hermitian systems.
We study maximal coin-position entanglement generation via a discrete-time quantum walk, in which the coin operation is randomly selected from one of two coin operators set at each step. We solve maximal entanglement generation as an optimization problem with quantum process fidelity as the cost function. Then we determine the maximal entanglement that can be rigorously generated for any step beyond the second regardless of initial conditions with appropriate coin sequences. The simplest coin sequence comprising Hadamard and identity operations is equivalent to the generalized elephant quantum walk, which exhibits an increasingly faster spreading in terms of probability distribution. Experimentally, we demonstrate a ten-step quantum walk driven by such coin sequences with linear optics and thereby show the desired high-dimensional bipartite entanglement as well as the transport behavior of faster spreading.
Discrete-time quantum walks are powerful platforms for simulating quantum transport and information processing. Here we introduce a walker on a one-dimensional lattice whose motion is controlled by three entangled coins, each initialized with the Hadamard gate, aiming to maximize information flow. The walker moves only when all three coins yield the same outcome (HHH or TTT), thus coupling the 8-dimensional coin Hilbert space to the position degree of freedom. By analyzing fully separable, fully entangled (GHZ-type) and intermediate initial states, and using the von Neumann entropy of reduced subsystems, we compute the mutual information I(C;P;t) between coin and position. The results show that initial three-partite entanglement accelerates the growth of mutual information by up to 18\% after ten steps (when compared to the lower of the two separable states), although it exhibits short-term non-monotonic dynamics due to quantum interference. For the first time, we introduce a tunable parameter α (amplitude of non-displacement states) and show that the GHZ state reaches a maximum of mutual information at α≈0.71 - a key finding for optimal control of information flow. Finally, an integrated photonic implementation using polarization, spatial modes and time bins is proposed, where α can be tuned with nonlinear or electro-optic elements. A scalable numerical framework (Python code) for simulations up to t=5 steps is provided. Our findings establish three-partite entanglement as a dynamical resource for maximizing information flow and spatial spreading, with direct applications in quantum state transfer, entanglement-assisted sensing and programmable photonic quantum processors.