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

arXiv:quant-ph/0611015 · Physical Review A

Single observable concurrence measurement without simultaneous copies

A. Salles, Fernando de Melo, J. C. Retamal, R. L. de Matos Filho, Nicim Zagury

Published Dec 11, 2006• 11 citations
arXivHTMLPDF

Abstract

We present a protocol that allows us to obtain the concurrence of any two-qubit pure state by performing a minimal and optimal tomography of one of the subsystems through measuring a single observable of an ancillary four-dimensional qudit. An implementation for a system of trapped ions is also proposed, which can be achieved with present-day experimental techniques.

DOI
10.1103/physreva.74.060303

Related papers

Measuring Multipartite Concurrence with a Single Factorizable Observable

Leandro Aolita, Florian Mintert

We show that, for any composite system with an arbitrary number of finite-dimensional subsystems, it is possible to directly measure the multipartite concurrence of pure states by detecting only one single factorizable observable, provided that two copies of the composite state are available. This result can be immediately put into practice in trapped-ion and entangled-photon experiments.

arXiv:quant-ph/0608012•Physical Review Letters•Aug 1, 2006•99 citations

Direct measurement of concurrence for atomic two-qubit pure states

Guillermo Romero, C. E. López, F. Lastra +2 more

We propose a general scheme to measure the concurrence of an arbitrary two-qubit pure state in atomic systems. The protocol is based on one- and two-qubit operations acting on two available copies of the bipartite system, and followed by a global qubit readout. We show that it is possible to encode the concurrence in the probability of finding all atomic qubits in the ground state. Two possible scenarios are considered: atoms crossing three-dimensional microwave cavities and trapped ion systems.

arXiv:quant-ph/0611016•Physical Review A•Mar 5, 2007•51 citations

Unrestricted generation of pure two-qubit states and entanglement diagnosis by single-qubit tomography

J. Gonzales, P. Sánchez, Fabio J. Auccapuclla +3 more

We present an experimental proof-of-principle for the generation and detection of pure two-qubit states that have been encoded in degrees of freedom that are common to both classical-light beams and single photons. Our protocol requires performing polarization tomography on a single qubit from a qubit pair. The degree of entanglement in the qubit pair is measured by concurrence, which can be directly extracted from intensity measurements-or photon counting-entering single-qubit polarization tomography.

Optics Letters•Jun 24, 2019•3 citations

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

Quantification of concurrence via weak measurement

Mikko Tukiainen, H. Kobayashi, Yutaka Shikano

Since entanglement is not an observable per se, measuring its value in practice is a difficult task. Here we propose a protocol for quantifying a particular entanglement measure, namely, concurrence, of an arbitrary two-qubit pure state via a single fixed measurement setup by exploiting so-called weak measurements and the associated weak values together with the properties of the Laguerre-Gaussian modes. The virtue of our technique is that it is generally applicable for all two-qubit systems and does not involve simultaneous copies of the entangled state. We also propose an explicit optical implementation of the protocol.

arXiv:1611.00149•Physical Review A•May 1, 2017•10 citations

Nearly Time-Optimal Pure State Tomography with Pauli Measurements

Sabee Grewal, Meghal Gupta, William He +2 more

We give an algorithm for pure state tomography with near-optimal copy and time complexity using only single-qubit measurements. Specifically, given $\widetilde{O}(2^n/ε)$ copies of an unknown $n$-qubit pure state $|ψ\rangle$, the algorithm performs only nonadaptive Pauli measurements, runs in time $\widetilde{O}(2^n/ε)$, and outputs $|\widehatψ \rangle$ with fidelity at least $1-ε$ with $|ψ\rangle$ with high probability. This is the first algorithm for pure state tomography that achieves near-optimal running time.

quant-pharXiv:2601.04444•Jan 9, 2026•0 citations
We present a protocol that allows us to obtain the concurrence of any two-qubit pure state by performing a minimal and optimal tomography of one of the subsystems through measuring a single observable of an ancillary four-dimensional qudit. An implementation for a system of trapped ions is also proposed, which can be achieved with present-day experimental techniques.
We present an experimental proof-of-principle for the generation and detection of pure two-qubit states that have been encoded in degrees of freedom that are common to both classical-light beams and single photons. Our protocol requires performing polarization tomography on a single qubit from a qubit pair. The degree of entanglement in the qubit pair is measured by concurrence, which can be directly extracted from intensity measurements-or photon counting-entering single-qubit polarization tomography.
Since entanglement is not an observable per se, measuring its value in practice is a difficult task. Here we propose a protocol for quantifying a particular entanglement measure, namely, concurrence, of an arbitrary two-qubit pure state via a single fixed measurement setup by exploiting so-called weak measurements and the associated weak values together with the properties of the Laguerre-Gaussian modes. The virtue of our technique is that it is generally applicable for all two-qubit systems and does not involve simultaneous copies of the entangled state. We also propose an explicit optical implementation of the protocol.
We give an algorithm for pure state tomography with near-optimal copy and time complexity using only single-qubit measurements. Specifically, given O~(2n/ε)\widetilde{O}(2^n/ε)O(2n/ε) copies of an unknown nnn-qubit pure state ∣ψ⟩|ψ\rangle∣ψ⟩, the algorithm performs only nonadaptive Pauli measurements, runs in time O~(2n/ε)\widetilde{O}(2^n/ε)O(2n/ε), and outputs ∣ψ^⟩|\widehatψ \rangle∣ψ​⟩ with fidelity at least 1−ε1-ε1−ε with ∣ψ⟩|ψ\rangle∣ψ⟩ with high probability. This is the first algorithm for pure state tomography that achieves near-optimal running time.