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

Research in Optical Sciences

Nonlocal Quantum State Tomography of Entangled Photons

Y. Pilnyak, E. Megidish, A. Halevy, Assaf Shaham, H. S. Eisenberg

Published Jan 1, 2014• 0 citations
Publisher

Abstract

We measure the density matrices of various entangled photon states by state tomography using nonlocal projection measurements. Limitations and effects of this method are demonstrated by the dependence on initial state entanglement and steering levels.
DOI
10.1364/qim.2014.qtu2a.4

Related papers

Quantum state tomography

Muhammad Sabieh Anwar, Faizan-e-Ilahi, Syed Bilal Hyder +1 more

The entangled pairs of single photons are best described by density matrices that capture the complete description of their state. The quantum state can be disturbed from the idealist pure description due to imperfections and nonidealities. Therefore, it is important to completely measure the state of these pairs. This is a systematic protocol called quantum state tomography that achieves this measurement. In one such experiment, the entangled pair is measured along different directions by projecting it onto a series of measurement bases. The measured outcomes are then assembled with an algorithm to reproduce the density matrix. This procedure is the subject of the ninth chapter.

Institute of Physics eBooks•Aug 1, 2024•4 citations

Quantum-state tomography of single-photon entangled states

E. T. Burch, C. Henelsmith, Walker D. Larson +1 more

We have performed quantum-state tomography on several different single-photon entangled states, that is, states in which a single photon is shared between two possible paths. We begin by doing a tomographic reconstruction of density matrices in the subspace where a single photon is shared by two spatial modes. In this subspace we are able to create high-fidelity, path-entangled states. Also within this subspace we use the Akaike information criterion and Monte Carlo simulations to help us estimate the amount and source of state drift in our system. We find that the primary state drift is due to phase drifts and fluctuations on the order of $\ensuremath{\pi}/400$ in our experimental apparatus. We then use the single-photon subspace density matrices and further measurements to estimate density matrices in the larger space consisting of two modes containing up to one photon each. In this larger space we find that the concurrence of the density matrices is $C\ensuremath{\cong}0.08$ and is greater than 0 by at least 45 standard deviations, indicating that our states are indeed entangled.

Physical Review A•Sep 28, 2015•6 citations

Single Photon Entangled State Tomography in a Single Measurement Setup

Ron Ziv, Roey Shafran, Mordechai Segev

We propose a method for reconstructing density matrices of single-photon OAM-polarization entangled states using a single intensity measurement, facilitated by coupling the state to higher-order OAM modes.

•Jan 1, 2024•0 citations

Tomography and its role in Quantum Computation

William J. Munro, Daniel F. V. James, Andrew G. White +1 more

Quantum computation depends on quantum entanglement, a correlation between subsystems that cannot occur classically. A variety of theoretical measures exist for quantifying the degree entanglement in such schemes, all of which are functions of the system density matrix. How can the entanglement be measured experimentally? Using quantum tomography techniques developed for two photon entangled states, the density matrix can be reconstructed from the appropriate experimental data. In this case the state tomography gives the complete characterization of the physical system (for the relevant degree of freedom, such as spin or polarization). It gives information on both the degree of nonclassical correlation, that is entanglement, as well as the amount of decoherence in the system. In this proceedings we discuss the general state tomography procedure required to characterize a few qubit quantum computer, for any architecture.

•Mar 21, 2001•3 citations

Complete Measurement of Two-Photon Density Matrix by Single-Photon Detection

Salini Rajeev, Mayukh Lahiri

The reconstruction of density matrices from measurement data (quantum state tomography) is the most comprehensive method for assessing the accuracy and performance of quantum devices. Existing methods to reconstruct two-photon density matrices require the detection of both photons unless a priori information is available. Based on the concept of quantum-induced coherence by path identity, we present an approach to quantum state tomography that circumvents the requirement of detecting both photons. We show that an arbitrary two-qubit density matrix, which can contain up to fifteen free parameters, can be fully reconstructed from single-photon measurement data without any postselection and a priori information. In addition to advancing an alternative approach to quantum state measurement problems, our results also have notable practical implications. A practical challenge in quantum state measurement arises from the fact that effective single-photon detectors are not readily accessible for a wide spectral range. Our method, which eliminates the need for coincidence measurements, enables quantum state tomography in the case where one of the two photons is challenging or impossible to detect. It therefore opens the door to measuring quantum states hitherto inaccessible.

arXiv:2503.07999•Mar 11, 2025•1 citation

Direct measurement of the density matrix of a two-photon polarization qubit

Enrique J. Galvez, Andrew D. Goldstein, Chan Ju You +3 more

There is interest in using photon entanglement in biomedical applications. In one application, polarization entangled photons pass through brain tissue. The effect of the brain tissue on the photon entanglement is measured via the decoherence that is imparted on the entangled state. Our current method to obtain a measure of the decoherence involves quantum state tomography, where a minimum of 16 measurements are used in conjunction with tomographic optimization to obtain the density matrix representing the state of the photons. In this work we report on a method to avoid tomographic optimization on behalf of a direct measurement of the elements of the density matrix. We make preliminary comparisons between the two methods.

Optical Biopsy: Toward Real-Time Spectroscopic Imaging and Diagnosis•Mar 6, 2023•1 citation
The entangled pairs of single photons are best described by density matrices that capture the complete description of their state. The quantum state can be disturbed from the idealist pure description due to imperfections and nonidealities. Therefore, it is important to completely measure the state of these pairs. This is a systematic protocol called quantum state tomography that achieves this measurement. In one such experiment, the entangled pair is measured along different directions by projecting it onto a series of measurement bases. The measured outcomes are then assembled with an algorithm to reproduce the density matrix. This procedure is the subject of the ninth chapter.
We have performed quantum-state tomography on several different single-photon entangled states, that is, states in which a single photon is shared between two possible paths. We begin by doing a tomographic reconstruction of density matrices in the subspace where a single photon is shared by two spatial modes. In this subspace we are able to create high-fidelity, path-entangled states. Also within this subspace we use the Akaike information criterion and Monte Carlo simulations to help us estimate the amount and source of state drift in our system. We find that the primary state drift is due to phase drifts and fluctuations on the order of $\ensuremath{\pi}/400$ in our experimental apparatus. We then use the single-photon subspace density matrices and further measurements to estimate density matrices in the larger space consisting of two modes containing up to one photon each. In this larger space we find that the concurrence of the density matrices is $C\ensuremath{\cong}0.08$ and is greater than 0 by at least 45 standard deviations, indicating that our states are indeed entangled.
Quantum computation depends on quantum entanglement, a correlation between subsystems that cannot occur classically. A variety of theoretical measures exist for quantifying the degree entanglement in such schemes, all of which are functions of the system density matrix. How can the entanglement be measured experimentally? Using quantum tomography techniques developed for two photon entangled states, the density matrix can be reconstructed from the appropriate experimental data. In this case the state tomography gives the complete characterization of the physical system (for the relevant degree of freedom, such as spin or polarization). It gives information on both the degree of nonclassical correlation, that is entanglement, as well as the amount of decoherence in the system. In this proceedings we discuss the general state tomography procedure required to characterize a few qubit quantum computer, for any architecture.
The reconstruction of density matrices from measurement data (quantum state tomography) is the most comprehensive method for assessing the accuracy and performance of quantum devices. Existing methods to reconstruct two-photon density matrices require the detection of both photons unless a priori information is available. Based on the concept of quantum-induced coherence by path identity, we present an approach to quantum state tomography that circumvents the requirement of detecting both photons. We show that an arbitrary two-qubit density matrix, which can contain up to fifteen free parameters, can be fully reconstructed from single-photon measurement data without any postselection and a priori information. In addition to advancing an alternative approach to quantum state measurement problems, our results also have notable practical implications. A practical challenge in quantum state measurement arises from the fact that effective single-photon detectors are not readily accessible for a wide spectral range. Our method, which eliminates the need for coincidence measurements, enables quantum state tomography in the case where one of the two photons is challenging or impossible to detect. It therefore opens the door to measuring quantum states hitherto inaccessible.
There is interest in using photon entanglement in biomedical applications. In one application, polarization entangled photons pass through brain tissue. The effect of the brain tissue on the photon entanglement is measured via the decoherence that is imparted on the entangled state. Our current method to obtain a measure of the decoherence involves quantum state tomography, where a minimum of 16 measurements are used in conjunction with tomographic optimization to obtain the density matrix representing the state of the photons. In this work we report on a method to avoid tomographic optimization on behalf of a direct measurement of the elements of the density matrix. We make preliminary comparisons between the two methods.