entangler

An entangler is a device, process, or protocol that produces quantum entanglement between two or more systems. In quantum information science, entanglement refers to correlations that cannot be explained by classical statistics and cannot be written as a simple product of individual states. An entangler therefore maps at least some separable input states to entangled output states.

Entanglement can be generated by various mechanisms. Photonic entanglers often rely on nonlinear optical processes such as spontaneous parametric down-conversion or four-wave mixing, or on interference at a beamsplitter. Entanglement is created in different degrees of freedom, including polarization, time-bin, and spatial modes. Gate-based entanglers implement direct interactions between qubits to produce entanglement, using two-qubit gates such as CNOT, controlled-Z, or iSWAP. Measurement-induced entanglement uses projective measurements to herald entangled states from larger systems.

Common implementations span multiple platforms. Photonic systems use SPDC and heralding techniques to generate entangled photon pairs. Trapped-ion systems employ gates like the Mølmer–Sørensen gate to entangle internal states of ions. Superconducting-qubit architectures realize entangling gates such as CZ or iSWAP through microwave-frequency interactions. Other platforms include quantum dots and neutral atoms. Some entanglers are heralded, signaling success via detection events, while others aim to be deterministic, functioning without post-selection.

Applications and significance are broad: entanglers enable quantum teleportation, superdense coding, quantum networks, and scalable quantum computation. Performance is assessed with metrics like fidelity, concurrence, or entropy of entanglement. Practical challenges include decoherence, loss, gate imperfections, and the need for precise timing and synchronization.