Generation of total angular momentum eigenstates in remote qubits

Abstract

We propose a scheme enabling the universal coupling of angular momentum of N remote noninteracting qubits using linear optical tools only. Our system consists of N single-photon emitters in a Λ-configuration that are entangled among their long-lived ground-state qubits through suitably designed measurements of the emitted photons. In this manner, we present an experimentally feasible algorithm that is able to generate any of the 2 N symmetric and nonsymmetric total angular momentum eigenstates spanning the Hilbert space of the N -qubit compound.

Limits to multipartite entanglement generation with bosons and fermions

“…The number of distinct outcomes that the N observers can experience is, again, bound by N !, just like the generalized Schmidt rank is according to (34). If some of the objects are identical, permutations that exchange these objects do not lead to inequivalent events, just like the multiple initial occupation of any mode reduces the rank, as discussed in Section III D. The quantum properties of bosons and fermions, i.e.…”

“…they quantify the transition amplitudes that describe the processes in which an injected particle is not collected by any of the first n modes. For example, particles may be lost in free-space propagation schemes [33,34,66]. The embedding matrix U can be inverted, and the inverse scattering process on the n modes of interest (with the input and output modes exchanged) is thus described by W † , and…”

“…A free-space photon-propagation scheme [33][34][35][36][37] allows to generate a variety of entangled states. Both, entanglement projection (with consequent entanglement swapping) [35], and entanglement creation [37] are possible.…”

“…states |S, m which are simultaneous eigenstates of the total squared spin operatorŜ 2 and its z-component S z , with eigenvalues S and m, respectively, are accessible [33]. More generally, all permutation-symmetric states can be created [37], and -with few modifications of the scattering matrix -all 2 N distinct total angular momentum eigenstates [34,90].…”

“…Manifold further strategies for the creation of entangled states were proposed [32][33][34][35][36][37][38], which promise to carry on the experimental achievements [1,13,14,18,31]; but although all schemes share the same physical ingredients, no common framework permits a direct comparison. With the increasing complexity of many-photon setups, a general framework is highly desirable to achieve high success rates, a low number of components, and a comparison of competing approaches to entanglement generation [37,38].…”