Entanglement is a key resource for quantum information technologies ranging from quantum sensing to quantum computing. Conventionally, the entanglement between two coupled qubits is established at the timescale of the inverse of the coupling strength. In this Letter, we study two weakly coupled non-Hermitian qubits and observe entanglement generation at a significantly shorter timescale by proximity to a higher-order exceptional point. We establish a non-Hermitian perturbation theory based on constructing a biorthogonal complete basis and further identify the optimal condition to obtain the maximally entangled state. Our study of speeding up entanglement generation in non-Hermitian quantum systems opens new avenues for harnessing coherent nonunitary dissipation for quantum technologies.
Entanglement is a key resource for quantum information technologies ranging from quantum sensing to quantum computing. Conventionally, the entanglement between two coupled qubits is established at the timescale of the inverse of the coupling strength. In this Letter, we study two weakly coupled non-Hermitian qubits and observe entanglement generation at a significantly shorter timescale by proximity to a higher-order exceptional point. We establish a non-Hermitian perturbation theory based on constructing a biorthogonal complete basis and further identify the optimal condition to obtain the maximally entangled state. Our study of speeding up entanglement generation in non-Hermitian quantum systems opens new avenues for harnessing coherent nonunitary dissipation for quantum technologies.
Abstract Open quantum systems are susceptible to losses in information, energy, and particles due to their surrounding environment. One novel strategy to mitigate these losses is to transform them into advantages for quantum technologies through tailored non-Hermitian quantum systems. In this work, we theoretically propose a fast generation of multipartite entanglement in non-Hermitian qubits. Our findings reveal that weakly coupled non-Hermitian qubits can accelerate multiparty entanglement generation by thousands of times compared to Hermitian qubits, in particular when approaching the 2 n -th order exceptional points of n qubits in the P T − symmetric regime. Furthermore, we show that Hermitian qubits can generate GHZ states with a high fidelity more than 0.9995 in a timescale comparable to that of non-Hermitian qubits, but at the expense of intense driving and large coupling constant. Our approach is scalable to a large number of qubits, presenting a promising pathway for advancing quantum technologies through the non-Hermiticity and higher-order exceptional points in many-body quantum systems.
Although non-Hermitian dynamics near exceptional points (EPs) provide a route to accelerated entanglement generation, entanglement can also be generated far from EPs at comparable or even higher rates. However, the behavior of such entanglement in open systems remains largely unexplored, rendering it highly susceptible to environmental noise. Here, we study entanglement dynamics in two coupled qubits described by a non-Hermitian Hamiltonian, where the dissipative rates are subject to stochastic noise. We focus on the regime away from EPs. Our approach demonstrates that, even in the presence of classical noise, rich dynamical control can be achieved, enabling highly efficient entanglement generation with a timescale that is significantly shorter than that of both Hermitian systems and EP-based non-Hermitian protocols. Additionally, the timescale is independent of the number of qubits, highlighting favorable scalability for multipartite entanglement generation and facilitating integration into future photonic quantum processors.
We propose an enhanced entanglement generation scheme in the non-Hermitian system by introducing an ancillary qubit with adjustable driven field to control the target entanglement, making this model more suitable for the switch operation at the quantum interface. Moreover, through adiabatic elimination, the mode of the qubit has been eliminated, and direct coupling between the cavities has been realized. The effective coupling strength between two non-Hermitian microwave cavities can be adjusted as an optimal value to satisfy a specific phase condition that realizes the maximally entangled state on a timescale. To prove the ability of our scheme to improve the performances of entanglement generation in the non-Hermitian system, the numerical simulations are performed based on a model where two microwave cavities are indirectly coupled through a superconducting qubit. It is evident that non-Hermitian cavities can be entangled significantly faster than Hermitian cavities, with the relative speedup increasing significantly as the perturbation is decreased, and the fourth-order exceptional points at J=0 are approached. Last but not least, our scheme has good robustness against parameter errors, crosstalk, and Gaussian white noise and is a feasible scheme for enhanced entanglement generation via approaching to higher-order exceptional points in a non-Hermitian network system.
Entanglement generation is a cornerstone of quantum information science, yet its speed in Hermitian systems is fundamentally constrained by the coupling strength, a restriction known as the quantum speed limit. Here we demonstrate that this bound can be beaten by exploiting the unique topology of non-Hermitian systems near exceptional points (EPs). Using a pair of trapped ions, we engineer a parity-time symmetric Hamiltonian where the coalescence of eigenstates near the EP distorts the Hilbert space geometry, providing a shortcut for quantum state evolution. We observe that, as the system approaches the EP, the time required to generate a maximally entangled state is markedly reduced with respect to the limits imposed by the equivalent Hermitian interaction. We further uncover a fundamental physical trade-off whereby the acceleration of entanglement is intrinsically coupled to a reduction in the success probability, revealing the information cost of non-Hermitian speedup. Our results suggest that tailored dissipation, rather than being a source of decoherence, can serve as a powerful resource for accelerating quantum dynamics, offering a new paradigm for designing high-speed quantum gates and sensors in hardware-constrained platforms.
The exploration of the effect of non-Hermitian (NH) in quantum systems is gaining renewed momentum as a result of the recent progress in experiments. It has been indicated that the ability to engineer the orders of exceptional points (EPs) can be fundamental to its applications in quantum control, such as accelerating entanglement generation; however, an initial survey of the interactions between different orders of EPs is still missing. In this work, we try to partially address this issue by employing a non-reciprocally coupled cavity system which can be experimentally realizable with a two-dimensional reconfigurable NH gauged laser array. With deliberate design, our systems display both second and third orders of EPs. The sign of a novel, purely quantum continuous entanglement phase transition is observed, which reveals how multi-EP interactions alter entanglement dynamics across different regimes while maintaining accelerated generation. Our findings reveil the genuinely quantum NH physics of higher-order EPs, which has opened up a new avenue for future investigations of the higher-order degeneracy application and the dynamic phase transitions of quantum systems.
As a most important feature of non-Hermitian systems, exceptional points (EPs) lead to a variety of unconventional phenomena and applications. Here, we study a generic model composed of two coupled non-Hermitian qubits; the EPs can be easily obtained in this system by adjusting the driving amplitude applied to the qubits. The diverse entanglement dynamics on the two sides of the original fourth-order EP ($\mathrm{EP}{4}^{\ensuremath{'}}$) and second-order EP (EP2) can be observed simultaneously in the weak coupling regime. With the increase of the coupling strength, the $\mathrm{EP}{4}^{\ensuremath{'}}$ is replaced by an additional EP2, leading to the disappearance of the entanglement dynamics change induced by $\mathrm{EP}{4}^{\ensuremath{'}}$ in the strong coupling regime. Considering the case of Ising-type interaction, we also realize EP-induced entanglement dynamics changing without the driving field. Our study paves the way for the investigation of EP-induced quantum effects and applications of EP-related quantum technologies.