We study how one-particle correlations transfer to manifest as two-particle correlations in the context of parametric down-conversion (PDC), a process in which a pump photon is annihilated to produce two entangled photons. We work in the polarization degree of freedom and show that for any two-qubit generation process that is both trace-preserving and entropy-nondecreasing, the concurrence $C(\ensuremath{\rho})$ of the generated two-qubit state $\ensuremath{\rho}$ follows an intrinsic upper bound with $C(\ensuremath{\rho})\ensuremath{\le}(1+P)/2$, where $P$ is the degree of polarization of the pump photon. We also find that for the class of two-qubit states that is restricted to have only two nonzero diagonal elements such that the effective dimensionality of the two-qubit state is the same as the dimensionality of the pump polarization state, the upper bound on concurrence is the degree of polarization itself, that is, $C(\ensuremath{\rho})\ensuremath{\le}P$. Our work shows that the maximum manifestation of two-particle correlations as entanglement is dictated by one-particle correlations. The formalism developed in this work can be extended to include multiparticle systems and can thus have important implications towards deducing the upper bounds on multiparticle entanglement, for which no universally accepted measure exists.We study how one-particle correlations transfer to manifest as two-particle correlations in the context of parametric down-conversion (PDC), a process in which a pump photon is annihilated to produce two entangled photons. We work in the polarization degree of freedom and show that for any two-qubit generation process that is both trace-preserving and entropy-nondecreasing, the concurrence $C(\ensuremath{\rho})$ of the generated two-qubit state $\ensuremath{\rho}$ follows an intrinsic upper bound with $C(\ensuremath{\rho})\ensuremath{\le}(1+P)/2$, where $P$ is the degree of polarization of the pump photon. We also find that for the class of two-qubit states that is restricted to have only two nonzero diagonal elements such that the effective dimensionality of the two-qubit state is the same as the dimensionality of the pump polarization state, the upper bound on concurrence is the degree of polarization itself, that is, $C(\ensuremath{\rho})\ensuremath{\le}P$. Our work shows that the maximum manifestation of two-particle correlations as entanglement is dictated by one-particle correlations. The formalism developed in this work can be extended to include multiparticle systems and can thus have important implications towards deducing the upper bounds on multiparticle entanglement, for which no universally accepted measure exists.

arXiv:1511.09288Physical Review AJun 24, 201613 citations

Quantum Communication of Qubits by the Polarization of Photons

Masahiro Matsuoka, Takashi Yamamoto, Akio Motoyoshi

Elsevier eBooksJan 1, 19990 citations

Deterministic generation of a four-qubit W state using one- and two-qubit gates

Fırat Diker, Can Yesilyurt

We propose an optical scheme to build an entangled network composed of W state based on polarization encoded qubits (photons). This new setup consists of 2 cNOT gates, 4 V gates, 2 Hadamard gates and basic optical tools such as polarizing beamsplitters (PBSs) and path couplers (PCs). V gate is a specially-designed tool acting as a two-qubit gate which is composed of a cNOT gate, 3 PBSs and a PC. By using this gate, one benefits from the temporarily generated optical degree of freedom, which is the spatial mode of a photon in the proposed scheme. Using an extra degree of freedom allows us to perform more capable processing for W-state creation protocols. We use four photons as input, which means we do not need entanglement as a resource. Also, we show that the proposed scheme can be implemented by operating the quantum optical gates which can be realized via current photonics technology. Additionally, we provide discussions of quantum contextuality and non-locality for W states.We propose an optical scheme to build an entangled network composed of W state based on polarization encoded qubits (photons). This new setup consists of 2 cNOT gates, 4 V gates, 2 Hadamard gates and basic optical tools such as polarizing beamsplitters (PBSs) and path couplers (PCs). V gate is a specially-designed tool acting as a two-qubit gate which is composed of a cNOT gate, 3 PBSs and a PC. By using this gate, one benefits from the temporarily generated optical degree of freedom, which is the spatial mode of a photon in the proposed scheme. Using an extra degree of freedom allows us to perform more capable processing for W-state creation protocols. We use four photons as input, which means we do not need entanglement as a resource. Also, we show that the proposed scheme can be implemented by operating the quantum optical gates which can be realized via current photonics technology. Additionally, we provide discussions of quantum contextuality and non-locality for W states.

arXiv:1704.08204Apr 25, 20170 citations

Polarization in Quantum Optics

Alfredo Luis

Progress in opticsJan 1, 201619 citations

All-Photonic 2xN Cluster States in Frequency, Time and Polarization

Alexander L. Gaeta, Miri Blau, Xingchen Ji +1 more

Abstract Complex and multi-dimensional cluster states of light are a critical resource for one-way quantum computers. We exploit the frequency, time and polarization domains to generate all-photonic cluster-states in a two-dimensional, 2N qubit, in a 2xN configuration. Cluster states of two dimensions or higher can serve as a resource for universal measurement-based quantum computation, and our approach allows for the realization of measurement-based two-qubit operations in an all-photonic platform. To generate the cluster states, we employ a process in which we construct dual-rail cluster states in time, frequency and polarization, as sequences of dual-color photon pairs encoded in polarization. The demonstrated discrete-variable, multi-photon, 4- and 6-qubit 2xN cluster states are shown to have high lower-bound fidelities of 0.84 and 0.57, respectively. By implementing more frequency bins the cluster state can be extended further, as well as the use of additional photonic degrees of freedom (like spatial modes) for higher dimensional cluster-states.Abstract Complex and multi-dimensional cluster states of light are a critical resource for one-way quantum computers. We exploit the frequency, time and polarization domains to generate all-photonic cluster-states in a two-dimensional, 2N qubit, in a 2xN configuration. Cluster states of two dimensions or higher can serve as a resource for universal measurement-based quantum computation, and our approach allows for the realization of measurement-based two-qubit operations in an all-photonic platform. To generate the cluster states, we employ a process in which we construct dual-rail cluster states in time, frequency and polarization, as sequences of dual-color photon pairs encoded in polarization. The demonstrated discrete-variable, multi-photon, 4- and 6-qubit 2xN cluster states are shown to have high lower-bound fidelities of 0.84 and 0.57, respectively. By implementing more frequency bins the cluster state can be extended further, as well as the use of additional photonic degrees of freedom (like spatial modes) for higher dimensional cluster-states.

Jun 4, 20250 citations

P

is the degree of polarization of the pump photon. We also find that for the class of two-qubit states that is restricted to have only two nonzero diagonal elements such that the effective dimensionality of the two-qubit state is the same as the dimensionality of the pump polarization state, the upper bound on concurrence is the degree of polarization itself, that is, $C(\ensuremath{\rho})\ensuremath{\le}P$. Our work shows that the maximum manifestation of two-particle correlations as entanglement is dictated by one-particle correlations. The formalism developed in this work can be extended to include multiparticle systems and can thus have important implications towards deducing the upper bounds on multiparticle entanglement, for which no universally accepted measure exists.