We construct new types of two-level qubit systems through incorporating non-Hermiticity with joint Parity-Time and anti-Parity-Time symmetries and present a framework to analytically find the dynamics for such systems. As a result, observe improved properties of decoherence, von Neumann entanglement entropy and quantum Fisher information. This suggests that non-Hermitian PT and APT-symmetric qubits may be better suited for quantum computing and quantum information processing than conventional Hermitian qubits.
We construct new types of two-level qubit systems through incorporating non-Hermiticity with joint Parity-Time and anti-Parity-Time symmetries and present a framework to analytically find the dynamics for such systems. As a result, observe improved properties of decoherence, von Neumann entanglement entropy and quantum Fisher information. This suggests that non-Hermitian PT and APT-symmetric qubits may be better suited for quantum computing and quantum information processing than conventional Hermitian qubits.
We investigate the dynamics of a general two-level based anti-parity-time (anti-PT)-symmetric qubit and study its decoherence as well as entanglement entropy properties. We compare our findings with that of the corresponding parity-time (PT)-symmetric and Hermitian qubits. To begin, we consider the time-dependent Dyson map to find the exact analytical dynamics for a general non-Hermitian qubit system weakly coupled with a thermal bath for pure dephasing, before specializing it to the case of a general anti-PT-symmetric qubit. Basing the comparison under the same coupling strength or increasing the non-Hermiticity, we observe that the decoherence function and entanglement entropy of the anti-PT-symmetric qubit decays and grows more slowly, respectively, compared to the PT-symmetric and Hermitian qubits. Similarly, the corresponding variance and area of Fisher information are much higher compared to the PT-symmetric and Hermitian qubits. These results demonstrate that anti-PT-symmetric qubits may be better suited for quantum computing and quantum information processing applications than conventional Hermitian or even PT-symmetric qubits.
Anti-PT-symmetric Qubit: Decoherence and Entanglement Entropy
We investigate a two-level spin system based anti-parity-time (anti-PT)-symmetric qubit and study its decoherence as well as entanglement entropy properties. We compare our findings with that of the corresponding PT-symmetric and Hermitian qubits. First we consider the time-dependent Dyson map to find the exact analytical dynamics for a general non-Hermitian qubit system coupled with a bath, then we specialize it to the case of the anti-PT-symmetric qubit. We find that the decoherence function for the anti-PT-symmetric qubit decays slower than the PT-symmetric and Hermitian qubits. For the entanglement entropy we find that for the anti-PT-symmetric qubit it grows more slowly compared to the PT-symmetric and Hermitian qubits. Similarly, we find that the corresponding variance and area of Fisher information is much higher compared to the PT-symmetric and Hermitian qubits. These results demonstrate that anti-PT-symmetric qubits may be better suited for quantum computing and quantum information processing applications than conventional Hermitian or even PT-symmetric qubits.
Abstract Non-Hermitian parity-time ( PT P T ) and anti-parity-time ( APT APT )-symmetric systems exhibit novel quantum properties and have attracted increasing interest. Although many counterintuitive phenomena in PT P T - and APT APT -symmetric systems were previously studied, coherence flow has been rarely investigated. Here, we experimentally demonstrate single-qubit coherence flow in PT P T - and APT APT -symmetric systems using an optical setup. In the symmetry unbroken regime, we observe different periodic oscillations of coherence. Particularly, we observe two complete coherence backflows in one period in the PT P T -symmetric system, while only one backflow in the APT APT -symmetric system. Moreover, in the symmetry broken regime, we observe the phenomenon of stable value of coherence flow. We derive the analytic proofs of these phenomena and show that most experimental data agree with theoretical results within one standard deviation. This work opens avenues for future study on the dynamics of coherence in PT P T - and APT APT -symmetric systems.
Abstract Parity-time-reversal (PT) symmetric quantum mechanics promotes the increasing research interest of non-Hermitian (NH) systems for the theoretical value, novel properties, and links to open and dissipative systems in various areas. Recently, anti-PT–symmetric systems and their featured properties have started to be investigated. In this work, we develop the PT and anti-PT symmetry to PT-arbitrary-phase symmetry (or PT- φ symmetry) for the first time, being analogous to bosons, fermions and anyons. It can also be seen as a complex extension of the PT symmetry, unifying the PT and anti-PT symmetries and having intermediate properties between them. Many of the established concepts and mathematics in the PT-symmetric system are still compatible. We mainly investigate quantum simulation of this novel NH system in two dimensions in detail and discuss for higher-dimensional cases in general using the linear combinations of unitaries in the scheme of duality quantum computing, enabling implementations and experimental investigations of novel properties on both small quantum devices and near-term quantum computers.
Abstract The evolution of entanglement in a non-Hermitian quantum system may behave differently compared to its Hermitian counterpart. In this paper, we investigate the entanglement dynamics of two coupled and driven non-Hermitian qubits. Through calculating the concurrence of the system, we find that the evolution of the bipartite entanglement manifests two distinct patterns in the parameter space. In the low non-Hermiticity regime, the concurrence oscillates significantly, while in the opposite regime the same quantity would trend to a stable value. We attribute this phenomenon to parity-time ( PT ) symmetry phase transition. We also study the effect of decoherence on the entanglement dynamics. Our work provides a method to stabilize entanglement by exploiting non-Hermiticity.
Improved coherence time of a non-Hermitian qubit in a PT-symmetric Environment
Quantum computing's potential for exponential speedup is fundamentally limited by decoherence, a phenomenon arising from environmental interactions. Non-Hermitian quantum mechanics, particularly PT-symmetric systems, offers a novel framework for extending coherence times. This study examines a qubit's coherence under non-Hermitian PT-symmetric dynamics, highlighting significantly enhanced coherence times compared to Hermitian setups. The effect is especially pronounced when both the system and environment exhibit PT-symmetry. Interestingly, greater environmental non-Hermiticity correlates with extended coherence, contrary to traditional expectations. These findings point to promising strategies for managing decoherence, which could significantly advance approaches to quantum information processing.