Maximally entangled states, Werner state and maximally entangled mixed states (MEMS) have been created and fully characterized by a novel high brilliance universal source of entangled photon pairs with striking spatial characteristics. Mixed states of any structure, spanning a 2 x 2 Hilbert space may be created by this source. The non local properties of the generated entanglement have been tested by standard Bell measurements. Tunable Werner states and Maximally Entangled Mixed States (MEMS) have been created by an original patchwork technique and investigated by quantum tomography. The entropic and nonlocal properties of these states have been also undertaken.Maximally entangled states, Werner state and maximally entangled mixed states (MEMS) have been created and fully characterized by a novel high brilliance universal source of entangled photon pairs with striking spatial characteristics. Mixed states of any structure, spanning a 2 x 2 Hilbert space may be created by this source. The non local properties of the generated entanglement have been tested by standard Bell measurements. Tunable Werner states and Maximally Entangled Mixed States (MEMS) have been created by an original patchwork technique and investigated by quantum tomography. The entropic and nonlocal properties of these states have been also undertaken.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIEOct 21, 20040 citations

Universal and distortion-free entanglement concentration of multiqubit quantum states in the W class

Alonso Botero, José Mejía

We propose a multipartite extension of Matsumoto and Hayashi's distortion-free entanglement concentration protocol, which takes $n$ copies of a general multipartite state and, via local measurements and produces a maximally entangled multipartite state between local spaces of dimensions $\ensuremath{\sim}{2}^{n{E}_{i}}$, where ${E}_{i}$ are the local entropies of the input state. However, the extended protocol is generally not universal in the sense that for the same measurement outcomes, the output state will still depend on the input state. Our main result is that when specialized to any state in the multiqubit W class, the protocol is also universal, so that as in the biparatite version, the output is a unique, maximally entangled state for each given set of measurement outcomes. Our analysis brings to the forefront an interesting family of maximally entangled multipartite states, which we term Kronecker states. A recurrence relation to obtain the coefficients of the W-class Kronecker states is also given.We propose a multipartite extension of Matsumoto and Hayashi's distortion-free entanglement concentration protocol, which takes $n$ copies of a general multipartite state and, via local measurements and produces a maximally entangled multipartite state between local spaces of dimensions $\ensuremath{\sim}{2}^{n{E}_{i}}$, where ${E}_{i}$ are the local entropies of the input state. However, the extended protocol is generally not universal in the sense that for the same measurement outcomes, the output state will still depend on the input state. Our main result is that when specialized to any state in the multiqubit W class, the protocol is also universal, so that as in the biparatite version, the output is a unique, maximally entangled state for each given set of measurement outcomes. Our analysis brings to the forefront an interesting family of maximally entangled multipartite states, which we term Kronecker states. A recurrence relation to obtain the coefficients of the W-class Kronecker states is also given.

arXiv:1712.09174Physical Review ASep 24, 20185 citations

Preservers of maximally entangled states

Edward Poon

Linear Algebra and its ApplicationsMar 26, 20147 citations

Typical Entanglement of Superpositions

Damien Quinn, Joshuah T. Heath, Graham Kells

We investigate universal entanglement properties inherent to superpositions of randomized states. We find that an $m$ -fold superposition of typical states may be classified into two distinct entanglement classes via the 2nd Rényi entropy density $s_2$ . The maximally entangled regime is defined by $s_2 \sim \ln (2)$ , for which superposition adds no additional entanglement. The sub-maximally entangled regime, $s_2<\ln 2$ , instead constrains the reduced density matrices of independent components to be orthogonal in the thermodynamic limit, which fixes the entanglement of the superposition to a logarithmic enhancement $ΔS(m)=\ln (m)$ . As a consequence, an exponentially large number of superpositions is required to transition from the sub-maximally entangled class to maximal entanglement. We explicitly calculate $s_2$ and the logarithmic enhancement, and demonstrate orthogonality for two canonical examples of the sub-maximally entangled regime (superpositions of pure Gaussian states and of random matrix-product states). We also examine the entanglement of superpositions of random stabilizer states, and discuss their relaxation to the Haar limit.We investigate universal entanglement properties inherent to superpositions of randomized states. We find that an $m$-fold superposition of typical states may be classified into two distinct entanglement classes via the 2nd Rényi entropy density $s_2$. The maximally entangled regime is defined by $s_2 \sim \ln (2)$, for which superposition adds no additional entanglement. The sub-maximally entangled regime, $s_2<\ln 2$, instead constrains the reduced density matrices of independent components to be orthogonal in the thermodynamic limit, which fixes the entanglement of the superposition to a logarithmic enhancement $ΔS(m)=\ln (m)$. As a consequence, an exponentially large number of superpositions is required to transition from the sub-maximally entangled class to maximal entanglement. We explicitly calculate $s_2$ and the logarithmic enhancement, and demonstrate orthogonality for two canonical examples of the sub-maximally entangled regime (superpositions of pure Gaussian states and of random matrix-product states). We also examine the entanglement of superpositions of random stabilizer states, and discuss their relaxation to the Haar limit.

quant-pharXiv:2607.06474Jul 8, 20260 citations

Characterizing qubit channels in the context of quantum teleportation

Arkaprabha Ghosal, Debarshi Das, Subhashish Banerjee

We consider a scenario where a party, say, Alice prepares a pure two-qubit (either maximally entangled or nonmaximally entangled) state and sends one half of this state to another distant party, say, Bob through a qubit (either unital or nonunital) channel. Finally, the shared state is used as a teleportation channel. In this scenario, we focus on characterizing the set of qubit channels with respect to the final state's efficacy as a resource of quantum teleportation (QT) in terms of maximal average fidelity and fidelity deviation (fluctuation in fidelity values over the input states). Importantly, we point out the existence of a subset of qubit channels for which the final state becomes useful for universal QT (having maximal average fidelity strictly greater than the classical bound and having zero fidelity deviation) when the initially prepared state is either useful for universal QT (i.e., for a maximally entangled state) or not useful for universal QT (i.e., for a subset of nonmaximally entangled pure states). Interestingly, in the latter case, we show that nonunital channels (dissipative interactions) are more effective than unital channels (nondissipative interactions) in producing useful states for universal QT from nonmaximally entangled pure states.We consider a scenario where a party, say, Alice prepares a pure two-qubit (either maximally entangled or nonmaximally entangled) state and sends one half of this state to another distant party, say, Bob through a qubit (either unital or nonunital) channel. Finally, the shared state is used as a teleportation channel. In this scenario, we focus on characterizing the set of qubit channels with respect to the final state's efficacy as a resource of quantum teleportation (QT) in terms of maximal average fidelity and fidelity deviation (fluctuation in fidelity values over the input states). Importantly, we point out the existence of a subset of qubit channels for which the final state becomes useful for universal QT (having maximal average fidelity strictly greater than the classical bound and having zero fidelity deviation) when the initially prepared state is either useful for universal QT (i.e., for a maximally entangled state) or not useful for universal QT (i.e., for a subset of nonmaximally entangled pure states). Interestingly, in the latter case, we show that nonunital channels (dissipative interactions) are more effective than unital channels (nondissipative interactions) in producing useful states for universal QT from nonmaximally entangled pure states.

arXiv:2102.02054Physical Review AMay 18, 202111 citations

We propose a multipartite extension of Matsumoto and Hayashi's distortion-free entanglement concentration protocol, which takes

n

copies of a general multipartite state and, via local measurements and produces a maximally entangled multipartite state between local spaces of dimensions $\ensuremath{\sim}{2}^{n{E}_{i}}$, where

{E}_{i}

are the local entropies of the input state. However, the extended protocol is generally not universal in the sense that for the same measurement outcomes, the output state will still depend on the input state. Our main result is that when specialized to any state in the multiqubit W class, the protocol is also universal, so that as in the biparatite version, the output is a unique, maximally entangled state for each given set of measurement outcomes. Our analysis brings to the forefront an interesting family of maximally entangled multipartite states, which we term Kronecker states. A recurrence relation to obtain the coefficients of the W-class Kronecker states is also given.

We investigate universal entanglement properties inherent to superpositions of randomized states. We find that an

m

-fold superposition of typical states may be classified into two distinct entanglement classes via the 2nd Rényi entropy density

s_2

. The maximally entangled regime is defined by

s_2 \sim \ln (2)

, for which superposition adds no additional entanglement. The sub-maximally entangled regime,

s_2<\ln 2

, instead constrains the reduced density matrices of independent components to be orthogonal in the thermodynamic limit, which fixes the entanglement of the superposition to a logarithmic enhancement

ΔS(m)=\ln (m)

. As a consequence, an exponentially large number of superpositions is required to transition from the sub-maximally entangled class to maximal entanglement. We explicitly calculate

s_2

and the logarithmic enhancement, and demonstrate orthogonality for two canonical examples of the sub-maximally entangled regime (superpositions of pure Gaussian states and of random matrix-product states). We also examine the entanglement of superpositions of random stabilizer states, and discuss their relaxation to the Haar limit.