Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review A

Experimental determination of entanglement by a projective measurement

Stephen Patrick Walborn, P. H. Souto Ribeiro, L. Davidovich, Florian Mintert, Andreas Buchleitner

Published Mar 27, 2007• 58 citations
Publisher

Abstract

We describe a method in which the entanglement of any pure quantum state can be experimentally determined by a simple projective measurement, provided the state is available in a twofold copy. We propose implementations of this approach for various systems and discuss in detail its first experimental realization, which employed twin photons entangled in two degrees of freedom, prepared in identical polarization and momentum states. We analyze the effect of errors due to imperfect state preparation.

DOI
10.1103/physreva.75.032338

Related papers

Experimental determination of entanglement for arbitrary pure states

Shao-Ming Fei, Ming‐Jing Zhao, Kai Chen +1 more

We present a way of experimentally determining the concurrence in terms of the expectation values of local observables for arbitrary multipartite pure states. Instead of the joint measurements on two copies of a state in the experiment for two-qubit systems [S. P. Walborn et al., Nature (London) 440, 20 (2006)], we only need one copy of the state in every measurement for any arbitrary dimensional multipartite systems, avoiding the preparation of twin states or the imperfect copy of the state.

arXiv:0909.4851•Physical Review A•Sep 21, 2009•31 citations

Experimental Determination of Entanglement by a Projective Measurement

Stephen Patrick Walborn, P. H. Souto Ribeiro, L. Davidovich +2 more

We show that entanglement can be measured by projective measurements on two copies of a bipartite state. We present the experimental realization of this scheme, using two copies encoded into a pair of photons.

International Conference on Quantum Information•Jan 1, 2007•2 citations

Experimental measurement of multidimensional entanglement via equivalent symmetric projection

Fang‐Wen Sun, Jianming Cai, Jin‐Shi Xu +5 more

We construct a linear optics measurement process to determine the entanglement measure, named $I$ concurrence, of a set of $4\ifmmode\times\else\texttimes\fi{}4$-dimensional two-photon entangled pure states produced in the optical parametric down conversion process. In our experiment, an equivalent symmetric projection for the twofold copy of a single subsystem [presented by L. Aolita and F. Mintert, Phys. Rev. Lett. 97, 050501 (2006)] can be realized by observing the one-side two-photon coincidence without any triggering detection on the other subsystem. Here, for the first time, we realize the measurement for entanglement contained in biphoton pure states by taking advantage of the indistinguishability and the bunching effect of photons. Our method can determine the $I$ concurrence of generic high-dimensional bipartite pure states produced in the parametric down conversion process.

arXiv:0706.0935•Physical Review A•Nov 5, 2007•17 citations

Measurable entanglement for tripartite quantum pure states of qubits

Chang‐shui Yu, He‐Shan Song

We show that for tripartite quantum pure states of qubits, all the kinds of entanglement in terms of stochastic local operations and classical communications classification are experimentally measurable by simple projective measurements, provided that four copies of the composite quantum system are available. In particular, the entanglement of reduced density matrices, even though they are mixed states, can be exactly determined in experiment. Concurrence of assistance is also shown to be measurable by introducing an interesting equation with explicit physical meanings.

arXiv:0709.0804•Physical Review A•Aug 22, 2007•41 citations

One-Photon Measurement of Two-Photon Entanglement

Gabriela Barreto Lemos, Radek Łapkiewicz, Armin Hochrainer +2 more

Measuring entanglement is an essential step in a wide range of applied and foundational quantum experiments. When a two-particle quantum state is not pure, standard methods to measure the entanglement require detection of both particles. We realize a conceptually new method for verifying and measuring entanglement in a class of two-part (bipartite) mixed states. Contrary to the approaches known to date, in our experiment we verify and measure entanglement in mixed quantum bipartite states by detecting only one subsystem, the other remains undetected. Only one copy of the mixed or pure state is used but that state is in a superposition of having been created in two identical sources. We show that information shared in entangled systems can be accessed through single-particle interference patterns. Our experiment enables entanglement characterization even when one of the subsystems cannot be detected, for example, when suitable detectors are not available.

arXiv:2009.02851•Physical Review Letters•Mar 1, 2023•19 citations

Determining Complementary Properties with Quantum Clones

Guillaume Thekkadath, Rebecca Y. Saaltink, Lambert Giner +1 more

In a classical world, simultaneous measurements of complementary properties (e.g., position and momentum) give a system's state. In quantum mechanics, measurement-induced disturbance is largest for complementary properties and, hence, limits the precision with which such properties can be determined simultaneously. It is tempting to try to sidestep this disturbance by copying the system and measuring each complementary property on a separate copy. However, perfect copying is physically impossible in quantum mechanics. Here, we investigate using the closest quantum analog to this copying strategy, optimal cloning. The coherent portion of the generated clones' state corresponds to "twins" of the input system. Like perfect copies, both twins faithfully reproduce the properties of the input system. Unlike perfect copies, the twins are entangled. As such, a measurement on both twins is equivalent to a simultaneous measurement on the input system. For complementary observables, this joint measurement gives the system's state, just as in the classical case. We demonstrate this experimentally using polarized single photons.

arXiv:1701.04095•Physical Review Letters•Aug 4, 2017•14 citations
We describe a method in which the entanglement of any pure quantum state can be experimentally determined by a simple projective measurement, provided the state is available in a twofold copy. We propose implementations of this approach for various systems and discuss in detail its first experimental realization, which employed twin photons entangled in two degrees of freedom, prepared in identical polarization and momentum states. We analyze the effect of errors due to imperfect state preparation.
We construct a linear optics measurement process to determine the entanglement measure, named III concurrence, of a set of $4\ifmmode\times\else\texttimes\fi{}4$-dimensional two-photon entangled pure states produced in the optical parametric down conversion process. In our experiment, an equivalent symmetric projection for the twofold copy of a single subsystem [presented by L. Aolita and F. Mintert, Phys. Rev. Lett. 97, 050501 (2006)] can be realized by observing the one-side two-photon coincidence without any triggering detection on the other subsystem. Here, for the first time, we realize the measurement for entanglement contained in biphoton pure states by taking advantage of the indistinguishability and the bunching effect of photons. Our method can determine the III concurrence of generic high-dimensional bipartite pure states produced in the parametric down conversion process.
We show that for tripartite quantum pure states of qubits, all the kinds of entanglement in terms of stochastic local operations and classical communications classification are experimentally measurable by simple projective measurements, provided that four copies of the composite quantum system are available. In particular, the entanglement of reduced density matrices, even though they are mixed states, can be exactly determined in experiment. Concurrence of assistance is also shown to be measurable by introducing an interesting equation with explicit physical meanings.
Measuring entanglement is an essential step in a wide range of applied and foundational quantum experiments. When a two-particle quantum state is not pure, standard methods to measure the entanglement require detection of both particles. We realize a conceptually new method for verifying and measuring entanglement in a class of two-part (bipartite) mixed states. Contrary to the approaches known to date, in our experiment we verify and measure entanglement in mixed quantum bipartite states by detecting only one subsystem, the other remains undetected. Only one copy of the mixed or pure state is used but that state is in a superposition of having been created in two identical sources. We show that information shared in entangled systems can be accessed through single-particle interference patterns. Our experiment enables entanglement characterization even when one of the subsystems cannot be detected, for example, when suitable detectors are not available.
In a classical world, simultaneous measurements of complementary properties (e.g., position and momentum) give a system's state. In quantum mechanics, measurement-induced disturbance is largest for complementary properties and, hence, limits the precision with which such properties can be determined simultaneously. It is tempting to try to sidestep this disturbance by copying the system and measuring each complementary property on a separate copy. However, perfect copying is physically impossible in quantum mechanics. Here, we investigate using the closest quantum analog to this copying strategy, optimal cloning. The coherent portion of the generated clones' state corresponds to "twins" of the input system. Like perfect copies, both twins faithfully reproduce the properties of the input system. Unlike perfect copies, the twins are entangled. As such, a measurement on both twins is equivalent to a simultaneous measurement on the input system. For complementary observables, this joint measurement gives the system's state, just as in the classical case. We demonstrate this experimentally using polarized single photons.