Jul 2026· International Journal of Quantum Information· Vol 24· 0 citations
Abstract
Real-time monitoring of weak entanglement in noisy fiber links is a practical bottleneck for entanglement-based quantum key distribution (QKD). Standard concurrence and negativity vanish with vanishing gradient near the separability boundary and are not optimized for hardware-level line-rate monitoring. We propose a closed-form, noise-robust entanglement indicator [Formula: see text] for two-qubit mixed states, constructed by regularizing the Wootters concurrence with a determinant-based spectral penalty. [Formula: see text] requires no iterative optimization, retains a nonvanishing gradient along typical QKD noise trajectories, and has an average computation time of 0.189 ms per state. Numerical simulations over 100,000 random states show strong linear correlation with negativity (Pearson 0.986) and entanglement of formation (0.968). Under 12 common LOCC channels relevant to QKD, [Formula: see text] is nonincreasing in 100% of tested cases. A field-programmable gate array (FPGA) implementation achieves 210 ns latency, enabling real-time link health monitoring in metropolitan QKD networks.
We study correlation-based entanglement evaluation in rank-2 mixed states of two- and multi-qubit systems. The relevant two-dimensional subspace is treated as a logical qubit embedded in the physical Hilbert space, and factorizable realizations of its logical Pauli operators are classified. For two qubits, this yields...
We systematically characterize quantum entanglement in all sixteen combinations of two-qubit Bell states across three operational regimes: pure superposition, noiseless mixing, and asymmetric mixing of one noisy and one pure Bell state. For pure superpositions, we calculate the von Neumann entropy and show that entangl...
Nishantkumar Chaudhari, J. V. Van Huele· 0 citations
An ideal CNOT maps the phase of a coherent qubit onto the coherence between $\ket{00}$ and $\ket{11}$ of a two-qubit state, producing an output that carries both entanglement and estimable phase information. We ask how post-gate noise degrades these two quantities, and find that they are not lost together. For the phas...
Asad Ali, H. Kuniyil, M. T. Rahim et al.· 0 citations
Identifying the entanglement structure of a many-body quantum state, namely how its constituents partition into unentangled blocks, is a central task in quantum information science, yet conventional tomography scales exponentially with system size. Here we introduce a scalable framework that recognizes large-scale enta...
Entangled photons play a crucial role in quantum applications, and determining and characterising their entanglement is vital to using them effectively. High-dimensional entangled states offer richer possibilities, but their additional measurement degrees of freedom make them increasingly demanding to characterise. How...
Xu-Kang Tan, Jesvita Menezes, Sanjan D. Murthy et al.· 0 citations
The entanglement-breaking index of a quantum channel is the smallest number of self-compositions after which the channel destroys all entanglement with any reference system. A photonic experiment has fixed an index of 2; to our knowledge no larger index has been located by measuring the n-round channel across rounds. W...
Eran Kopel· 2 citations· ⚡1
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