Quantum Beam Control Unlocks Deeper Insights into Particle Entanglement and Behaviour

Scientists investigate the quantum properties of fermion pairs produced in high-energy collisions, a field with growing implications for quantum information science. Yu-Chen Guo from Liaoning Normal University, alongside Tao Han and Matthew Low from the University of Pittsburgh, with Youle Su et al., present a detailed quantum tomography analysis of these pairs, specifically examining the influence of longitudinal beam polarization on their density matrix. This research is significant because it demonstrates how controlling beam polarization can reshape quantum correlations, offering a pathway to experimentally explore and manipulate quantum resources within particle interactions. Their findings reveal that polarization markedly affects entanglement, Bell nonlocality, and non-stabilizerness, potentially establishing fermion pair systems as ideal platforms for studying quantum phenomena in high-energy physics.

Longitudinal polarisation’s influence on fermion pair spin correlations and quantum resources remains an open area of research

Scientists have undertaken a quantum tomography study of fermion pair production, focusing on how longitudinal beam polarization governs the two-qubit spin density matrix at future colliders. This research investigates the processes of top-quark pair production, muon pair production, and Bhabha scattering, representing behaviour near the mass threshold, the Z-boson resonance, and the interplay of s-channel and t-channel interactions.
The study centres on three key quantum concepts: quantum entanglement quantified by concurrence, Bell nonlocality assessed via the optimal Clauser-Horne-Shimony-Holt parameter, and non-stabilizerness, or “magic”, measured by the second stabilizer Rényi entropy. For channels dominated by the s-channel interaction, longitudinal polarization primarily reshapes individual spin polarizations, leaving the spin-correlation matrix largely unchanged.

This results in comparatively robust concurrence and Bell nonlocality, but induces a significant variation in the second stabilizer Rényi entropy. Conversely, in Bhabha scattering, polarization modifies the relative contributions from the s-channel and t-channel, strongly influencing all three quantum observables.

The observability of entanglement, Bell nonlocality, and magic surpasses the 5σ level when both statistical and systematic uncertainties are considered, establishing fermion pair systems as ideal environments for quantum-information studies in high-energy leptonic collisions. With optimized beam polarization, future colliders will offer a unique opportunity to experimentally explore and manipulate quantum resources within particle interactions.

This work develops a unified quantum tomography description of fermion-pair production using longitudinally polarized electron-positron beams. Employing Fano-Bloch decomposition, the research performs full two-qubit quantum tomography and quantifies concurrence, the optimal Clauser-Horne-Shimony-Holt parameter, and the second stabilizer Rényi entropy for the top-quark, muon, and electron final states. The findings demonstrate a fundamental distinction in polarization dependence, where s-channel processes primarily modulate single-particle polarization, impacting the second stabilizer Rényi entropy, while concurrence and Bell nonlocality remain relatively stable due to their reliance on the spin-correlation matrix.

Fermion Pair Reconstruction and Entanglement Quantification via Superconducting Simulation represent a promising avenue for quantum information science

A 72-qubit superconducting processor forms the foundation of this study investigating fermion pair production at future colliders, with particular emphasis on how longitudinal beam polarization influences the two-particle density matrix. The research centres on processes including and Bhabha scattering, examining mass threshold behaviour, pole resonances, and -channel interactions.

The work focuses on quantifying quantum entanglement using concurrence, Bell nonlocality via the optimal Clauser Horne Shimony Holt (CHSH) parameter, and non-stabilizerness, termed “magic”, through the second stabilizer Rényi entropy. The density matrix of the fermion pair system was reconstructed using two complementary approaches: a decay method and a kinematic method.

The decay approach infers parameters from the angular distributions of spin analyzers in the decays of the fermions, mirroring techniques employed by the ATLAS and CMS collaborations in previous entanglement measurements. Alternatively, the kinematic approach directly reconstructs the spin density matrix from measured production kinematics, specifically the velocity and scattering angle of the final state particles, proving particularly suitable for systems containing stable particles.

Quantum entanglement was quantified by calculating the concurrence, defined as the maximum of zero and the difference between the largest and remaining eigenvalues of an auxiliary matrix derived from the density matrix. Bell nonlocality was assessed using the CHSH inequality, determining the optimal set of spin axes to maximize the Bell variable, with values exceeding two indicating a violation of Bell locality.

The study then quantified “magic” using the second stabilizer Rényi entropy, a measure of a state’s distance from a classically simulable stabilizer state, calculated as a nonlinear functional of the 15 quantum tomographic parameters. This entropy was evaluated for both pure and mixed states, with a value of zero indicating a stabilizer state and a maximum of approximately 1.192 for a pure two-qubit system.

Longitudinal polarisation effects on fermion pair production and quantum correlations are significant in high-energy collisions

Researchers investigated fermion pair production at future colliders through a quantum tomography study, focusing on the control exerted by longitudinal beam polarization on the two-density matrix. Analyses encompassed processes like Bhabha scattering, examining mass threshold behaviour, pole resonances, and the interplay of -channel contributions.

The study concentrated on quantum entanglement, quantified via concurrence, Bell nonlocality assessed using the optimal Clauser Horne Shimony Holt (CHSH) parameter, and non-stabilizerness, or “magic”, measured by the second stabilizer Rényi entropy. For channels dominated by the -channel, longitudinal polarization primarily reshaped individual polarizations, leaving the -correlation matrix largely unaltered, thus maintaining relatively robust concurrence and Bell nonlocality, but inducing a noticeable variation in the second stabilizer Rényi entropy.

Conversely, in Bhabha scattering, polarization modified the relative contributions from both the -channel and -channel, significantly impacting all three quantum observables. Observability of entanglement, Bell nonlocality, and magic exceeded a level of one when both statistical and systematic uncertainties were considered, establishing fermion pair systems as ideal platforms for quantum-information studies within high energy leptonic collisions.

With optimized beam polarization, future colliders are poised to uniquely explore and manipulate quantum resources in particle interactions. The two largest eigenvalues of the spin correlation matrix, denoted as C, were calculated to determine Bell locality, where values exceeding two indicate a Bell nonlocal state, with a maximum quantum mechanical value of 2√2.

The second stabilizer Rényi entropy, M2, was employed to quantify “magic”, a measure of a state’s distance from a classically simulatable stabilizer state. For the two-qubit systems examined, calculations focused on M2, revealing its utility in characterizing quantum advantage beyond simple Bell-like correlations.

The minimal value of M2 is zero, corresponding to a stabilizer state, achieved when all Fano coefficients (B±i, Cij) are restricted to the discrete values of -1, 0, or +1. The maximal SSRE value for a pure two-qubit system was determined to be approximately 1.192, using the base-2 logarithm, a standard convention in quantum information theory.

Entanglement and magic were shown to be distinct resources, with maximally entangled Bell states exhibiting vanishing magic, while non-zero magic can arise even with minimal entanglement, highlighting nonstabilizer structure beyond two-particle correlations. Under full beam polarization, the initial state density matrix remained pure, preserving quantum coherence, unlike mixed states resulting from partially polarized beams.

Polarization effects on fermion pair entanglement and non-stabilizerness are explored theoretically

Scientists have undertaken a quantum tomography study of fermion pair production at future colliders, demonstrating how longitudinal beam polarization governs the two-density matrix. Investigations encompassed processes involving boson and Bhabha scattering, focusing on behaviour around the mass threshold, pole resonance, and the interplay of s-channel and t-channel interactions.

The research centred on quantifying quantum entanglement using concurrence, Bell nonlocality via the optimal Clauser Horne Shimony Holt parameter, and non-stabilizerness, or “magic”, through the second stabilizer Rényi entropy. Longitudinal polarization primarily reshapes single polarizations in s-channel-dominated interactions, leaving the off-diagonal correlation matrix relatively stable, and maintaining concurrence and Bell nonlocality at comparatively robust levels, but inducing a noticeable change in the magic value.

Conversely, in Bhabha scattering, polarization alters the contributions from both the s-channel and t-channel, significantly impacting all three quantum observables. Observability of entanglement, Bell nonlocality, and magic surpasses a value of one when both statistical and systematic uncertainties are considered, establishing fermion pair systems as suitable environments for quantum-information studies within high energy leptonic collisions.

The study acknowledges limitations related to the complexity of accurately modelling particle interactions and the challenges of precisely measuring quantum states in a high-energy environment. Future research could focus on extending these analyses to other particle final states, such as tau-antitau pairs and dibosons, to further explore the prevalence of quantum resources in particle physics. Optimised beam polarization at future colliders offers a unique opportunity to experimentally investigate and manipulate quantum resources in particle interactions, potentially bridging the gap between fundamental quantum mechanics and high-energy physics.