Experimental Verification Demonstrates Genuine Multipartite Entanglement Activation from Two Copies of Biseparable States

Genuine multipartite entanglement, a complex form of correlation beyond simple separability, represents a crucial concept in advanced information processing and benchmarking of complex systems. Robert Stárek from Palacký University, Tim Gollerthan from Universität Innsbruck, and Olga Leskovjanová, alongside Michael Meth, Peter Tirler, and Nicolai Friis, now demonstrate a surprising phenomenon, the activation of this entanglement from multiple copies of states that, individually, do not possess it. The team experimentally verifies this activation using two copies of a biseparable three-qubit state within a trapped-ion processor, providing unambiguous evidence that challenges conventional understanding of quantum resources. This achievement highlights the potential of leveraging multiple copies of quantum states to unlock capabilities exceeding those of single states, opening new avenues for quantum technologies.

Genuine Entanglement Activated From Biseparable States

Quantum information processing relies on complex correlations between quantum particles, and a central concept is genuine multipartite entanglement (GME), a type of correlation that surpasses simple, partially entangled states. GME is crucial for characterizing and improving complex quantum systems, and serves as a valuable resource for applications like secure quantum communication. Remarkably, scientists have discovered that GME can be activated from multiple copies of biseparable quantum states, states that do not inherently possess GME individually. Researchers have experimentally demonstrated unambiguous evidence of this GME activation from multiple copies of biseparable states.

This work establishes a clear pathway towards utilizing previously considered unentangled states as a resource for quantum technologies, opening new avenues for quantum communication and computation. The experiment confirms the theoretical prediction that combining several biseparable states can generate genuine multipartite entanglement, a phenomenon crucial for advancing quantum information processing. This achievement represents a significant step forward in harnessing the full potential of quantum resources, even those initially deemed insufficient for complex quantum tasks.

Activating Entanglement in Multipartite Quantum Systems

This research investigates the fascinating phenomenon of entanglement activation in systems with multiple quantum particles. Entanglement, a key resource for advanced quantum technologies like quantum computation, communication, and sensing, involves strong correlations between particles. However, sometimes a quantum state appears to lack entanglement when measured directly. Entanglement activation refers to the ability to unlock hidden entanglement through specific quantum operations. This study focuses on genuine multipartite entanglement, a robust form of entanglement that cannot be created by simply entangling pairs of particles.

The team explored how multiple copies of a weakly entangled state can be combined to create a strongly entangled state, analogous to amplifying a signal. The experiment was conducted using trapped ions, a leading platform for quantum information processing due to their long coherence times and high degree of control. Ions served as qubits, with their internal energy levels manipulated to represent quantum states. Entanglement was created through laser pulses inducing controlled quantum interactions. Researchers used quantum state tomography to fully characterize the quantum states of the ions, reconstructing the density matrix through a series of measurements.

The researchers experimentally demonstrated the activation of genuine multipartite entanglement using multiple copies of a weakly entangled state, confirming a theoretical prediction and opening the door to practical applications. The experiment, performed on a well-controlled trapped-ion system, provides a high degree of confidence in the results and offers insights into scaling up quantum systems and creating more complex entangled states. This ability to activate entanglement has implications for enhancing the security and efficiency of quantum communication protocols, improving the performance of quantum algorithms, and developing more sensitive quantum sensors.

Two Copies Activate Genuine Three-Qubit Entanglement

Scientists have experimentally demonstrated the activation of genuine multipartite entanglement (GME) using two copies of a biseparable three-qubit state, achieved within a trapped-ion quantum processor. This work addresses a fundamental question in quantum information processing: how correlations beyond simple separability can emerge from states that do not inherently possess them. The team successfully prepared two identical copies of a three-qubit state known to be biseparable, meaning it can be decomposed into less entangled components, and then demonstrated that the combined two-copy state exhibits genuine multipartite entanglement. The research focused on a carefully constructed state, a balanced mixture of only eight distinct three-qubit configurations, designed to be robust against perturbations and minimize experimental overhead.

Through analytical and numerical calculations, scientists identified a state that is biseparable in a single copy, yet becomes genuinely multipartite entangled when two copies are considered. Experiments confirmed that this state fulfills the necessary conditions for GME activation, employing a suitable GME witness to verify the presence of these complex correlations. This achievement marks a significant step towards harnessing the potential of GME for advanced quantum technologies. The team’s approach utilizes state preparation solely with operations incapable of generating genuine multipartite entanglement or bipartite entanglement between the single copies, ensuring the observed GME arises from the activation process itself. The results provide clear evidence that multiple copies of biseparable states can exhibit entanglement beyond what is possible with individual copies, opening new avenues for exploring quantum resources and developing more powerful quantum communication and computation protocols. This work demonstrates a crucial principle for utilizing multiple copies of distributed quantum states in practical laboratory settings.

Genuine Multipartite Entanglement From Biseparable States

This research demonstrates unambiguous evidence of genuine multipartite entanglement (GME) activation from two copies of a biseparable three-qubit state, achieved using a trapped-ion processor. These findings challenge conventional understanding of quantum resources, revealing that GME can emerge from states that do not possess it individually, and highlight the potential of processing multiple copies of states to achieve capabilities beyond those of single copies. The experiment successfully verified GME activation, with the measured witness value falling well below zero with high statistical confidence. While this work represents a crucial first step, the authors acknowledge that extending these findings to higher levels of GME activation presents significant technical challenges.

The number of combinations required for preparation increases exponentially with each additional copy, and resource demands for verifying entanglement and biseparability also grow substantially. Simulations suggest that observing three-copy GME activation is achievable, though it would require considerably more measurement time and careful consideration of measurement uncertainty and fidelity. Future research will focus on exploring and utilizing GME activation in larger systems, specifically aiming to observe and harness this phenomenon across five spatially separated systems within a multi-party quantum network, leveraging states typical of those found in networks with bipartite entanglement sources.