Experimental entanglement of four particles

Abstract

Quantum mechanics allows for many-particle wavefunctions that cannot be factorized into a product of single-particle wavefunctions, even when the constituent particles are entirely distinct. Such 'entangled' states explicitly demonstrate the non-local character of quantum theory, having potential applications in high-precision spectroscopy, quantum communication, cryptography and computation. In general, the more particles that can be entangled, the more clearly nonclassical effects are exhibited--and the more useful the states are for quantum applications. Here we implement a recently proposed entanglement technique to generate entangled states of two and four trapped ions. Coupling between the ions is provided through their collective motional degrees of freedom, but actual motional excitation is minimized. Entanglement is achieved using a single laser pulse, and the method can in principle be applied to any number of ions.

Entanglement of the orbital angular momentum states of photons

“…two-state quantum systems including recent realization of three- [3,4] and four-qubit [5,6] entanglements. Yet, an ever increasing body of theoretical work calls for entanglement in quantum system of higher dimensions [7,8].…”

Optimization of segmented linear Paul traps and transport of stored particles

“…Starting with two-qubit gate operations [2,3], long lived two-qubit entanglement [4,5,6], teleportation experiments [7,8], and different sorts of multi-qubit entangled states [9,10,4,11], the record for qubit-entanglement is currently presented in a 6-qubit cat state and a 8-qubit W-state [12,13]. Future improvement is expected using the technique of segmented linear Paul traps which allow to shuttle ions from a "processor" unit to a "memory" section [14].…”

Nonclassicality and information exchange in deterministic entanglement formation

“…Nowadays, the most accessible and controllable source of entanglement arises from the process of spontaneous parametric down-conversion of photons in nonlinear crystals [1,6]. Recently, experiments with trapped ions have also demonstrated a high degree of control on entanglement generation [7]. Technological improvements on experiments involving atoms and cavity fields in both optical [8] and microwave [9] frequency regions may lead to new scenarios for entanglement experiments involving massive particles in the near future.…”