Quantum Entanglement Revived by Symmetry Operations

Quantum entanglement, a phenomenon where particles remain connected regardless of distance, is crucial for technologies like quantum computing and secure communication. However, when particles accelerate, this entanglement degrades, limiting practical applications. Researchers have now demonstrated that applying local symmetric operations can recover lost entanglement and coherence, offering a way to maintain quantum advantages even under acceleration.

The key finding is that entanglement and non-local advantage of quantum coherence (NLa), which measures how well quantum systems outperform classical ones, can be restored using parity-time (PT)-symmetric operations. When only one qubit (a quantum bit) accelerates, applying these operations on both qubits significantly improves entanglement, as shown by the negativity measure increasing from low values at high acceleration. For instance, with an acceleration parameter r=0.8, negativity drops sharply without intervention, but with PT-symmetric operations, it remains higher, indicating better preservation of quantum links.

Ology involved simulating a system starting in a maximally entangled Bell state, where one or both qubits were accelerated. The researchers applied PT-symmetric operators, non-Hermitian transformations that can counteract decoherence, to the qubits. They tested scenarios like applying the operator to one or both qubits and measured changes in entanglement (using negativity) and NLa over time and acceleration levels.

Analysis, based on figures from the paper, shows that without PT-symmetric operations, negativity decreases as acceleration rises—for example, in Figure 1, it drops to near zero at r=0.8 when both qubits accelerate. With operations, Figure 3 illustrates that negativity improves, especially at smaller operator strengths (e.g., θ=π/6), and fluctuations are reduced. Similarly, NLa, which decays rapidly under acceleration (Figure 2), rebounds when operations are applied on both qubits, as seen in Figure 9, where it survives even at high accelerations.

This matters because maintaining quantum coherence under acceleration could enhance real-world technologies. For example, in quantum satellites or high-speed communication systems, particles often accelerate, leading to data loss. By using symmetric operations, these systems could operate more reliably, improving encryption and computing power without needing slower speeds.

Limitations noted in the study include the dependence on operator strength and acceleration levels. At higher strengths (e.g., θ=π/3), improvements are less effective, and entanglement can still vanish under certain conditions, as shown in Figure 4. Additionally, when both qubits accelerate, recovery is harder, indicating that works best in controlled scenarios with partial acceleration.