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/0405175 · Journal of Physics A Mathematical and General

Entanglement witness derived from NMR superdense coding

Robabeh Rahimi, Kazuyuki Takeda, Masanao Ozawa, Masahiro Kitagawa

Published Feb 15, 2006• 14 citations
arXivHTMLPDF

Abstract

It is shown that superdense coding (SDC) experiments by means of nuclear magnetic resonance (NMR) can show non-classical efficiency gain over classical communication only for nuclear spin polarization beyond a certain threshold, and this threshold coincides with that for non-separability of the density matrix. It is also claimed that transfer of two-bit information mediated by a single qubit in the previous NMR SDC experiments with low nuclear spin polarization is not ascribed to the non-classical effect induced by entanglement, but merely to a statistical effect in an ensemble system having a large number of molecules. Towards experimental detection of entanglement, a new class of entanglement witnesses is proposed, which is based on the measurement of nuclear spin magnetizations in the Bell basis and is suitable for actual NMR experiments.

DOI
10.1088/0305-4470/39/9/011

Related papers

NMR experimental implementation of three-parties quantum superdense coding

Daxiu Wei, Xiaodong Yang, J. L. Luo +3 more

In this study, we report an experiment realization of quantum superdense coding (QSDC) between three parties using nuclear magnetic resonance (NMR). The experimental results have shown that in terms of the QSDC schemes between multiparties proposed by Liu et al. and Crudka et al., three-qubit QSDC can transmit three bits of classical information by sending two qubits only. Our results experimentally show that quantum superdense coding, as one of the quantum information processing protocols, is superior to classical ones.

Chinese Science Bulletin•Jan 1, 2004•63 citations

Entanglement Witness for NMR Quantum Information Processing

Robabeh Rahimi, Takeda, K, Masanao Ozawa +1 more

We discuss the tricky issue of entanglement in NMR quantum information processing and particularly NMR implementation of superdense coding. The signal intensity is introduced as a critical experimental property and an experimental approach for detection of entanglement is proposed based on the signal intesity measurements in a single NMR experiment.

•Jan 1, 2004•0 citations

Studies on Entanglement in Nuclear and Electron Spin Systems for Quantum Computing

Robabeh Rahimi

In this work, we have been working on the concept of quantum entanglement. At first, we studied the theory of entanglement in its characterization and measurement, introducing a new scheme for detection of entanglement. The new approach links molecular-spin entities involving nuclear spins to quantum computing as more appropriate physical systems of interest. Then, we continued with the realization of entanglement in experiments. NMR has been the first choice due to its well approved advantages for quantum computing. NMR, however, has not been an appropriate system for demonstrating entangled states. Through a mathematical proof, NMR with low spin polarization has been invalidated for true implementations of non-local quantum algorithms, particularly supserdense coding. The point is that high spin polarization is inevitably required to acquire entanglement while in the current NMR it has been a formidable task to get highly polarized nuclear spins. In order to acquire high spin polarization, introducing electron spins can be much effective because of its three-order-of-magnitude larger gyromagnetic ratio compared to nuclear spins. Electron Nuclear DOuble Resonance (ENDOR) is spin manipulation technology that enables us to deal with both electron and nuclear spins. Thus, in this context, it can be more appropriate device for quantum computing. We emphasize that (pseudo)entanglement and interconversion between the entangled states have been realized with ENDOR on extremely stable organic molecular-spin entities. The required experimental conditions to obtain true quantum entanglement are also discussed. The appropriate entanglement witness for the corresponding ensemble quantum computing is introduced and examined.

arXiv:quant-ph/0609063•Sep 8, 2006•0 citations

On the quantumness of correlations in nuclear magnetic resonance

Diogo O. Soares-Pinto, R. Auccaise, Jonas Maziero +3 more

Nuclear magnetic resonance (NMR) was successfully employed to test several protocols and ideas in quantum information science. In most of these implementations, the existence of entanglement was ruled out. This fact introduced concerns and questions about the quantum nature of such bench tests. In this paper, we address some issues related to the non-classical aspects of NMR systems. We discuss some experiments where the quantum aspects of this system are supported by quantum correlations of separable states. Such quantumness, beyond the entanglement-separability paradigm, is revealed via a departure between the quantum and the classical versions of information theory. In this scenario, the concept of quantum discord seems to play an important role. We also present an experimental implementation of an analogue of the single-photon Mach-Zehnder interferometer employing two nuclear spins to encode the interferometric paths. This experiment illustrates how non-classical correlations of separable states may be used to simulate quantum dynamics. The results obtained are completely equivalent to the optical scenario, where entanglement (between two field modes) may be present.

arXiv:1202.1795•Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences•Sep 3, 2012•25 citations

Witnessing nonclassical correlations via a single-shot experiment on an ensemble of spins using nuclear magnetic resonance

Amandeep Singh, Arvind, Kavita Dorai

A bipartite quantum system in a mixed state can exhibit nonclassical correlations which can go beyond quantum entanglement. While quantum discord is the standard measure of quantifying such general quantum correlations, the nonclassicality can be determined by simpler means via the measurement of witness operators. We experimentally construct a positive map to witness nonclassicality of two qubits in an NMR system. The map can be decomposed in terms of measurable spin magnetizations so that a single run of an experiment on an ensemble of spins suffices to detect the nonclassicality in the state, if present. We let the state evolve in time and use the map to detect nonclassicality as a function of time. To evaluate the efficacy of the witness operator as a means to detect nonclassicality, we measure quantum discord by performing full quantum-state tomography at each time instant and obtain a fairly good match between the two methods.

arXiv:1701.00606•Physical Review A•Jun 12, 2017•7 citations

Experimental localisation of quantum entanglement through monitored classical mediator

Soham Pal, Priya Batra, Tanjung Krisnanda +2 more

Quantum entanglement is a form of correlation between quantum particles that cannot be increased via local operations and classical communication. It has therefore been proposed that an increment of quantum entanglement between probes that are interacting solely via a mediator implies non-classicality of the mediator. Indeed, under certain assumptions regarding the initial state, entanglement gain between the probes indicates quantum coherence in the mediator. Going beyond such assumptions, there exist other initial states which produce entanglement between the probes via only local interactions with a classical mediator. In this process the initial entanglement between any probe and the rest of the system "flows through" the classical mediator and gets localised between the probes. Here we theoretically characterise maximal entanglement gain via classical mediator and experimentally demonstrate, using liquid-state NMR spectroscopy, the optimal growth of quantum correlations between two nuclear spin qubits interacting through a mediator qubit in a classical state. We additionally monitor, i.e., dephase, the mediator in order to emphasise its classical character. Our results indicate the necessity of verifying features of the initial state if entanglement gain between the probes is used as a figure of merit for witnessing non-classical mediator. Such methods were proposed to have exemplary applications in quantum optomechanics, quantum biology and quantum gravity.

arXiv:1909.11030•Quantum•Jun 17, 2021•43 citations
It is shown that superdense coding (SDC) experiments by means of nuclear magnetic resonance (NMR) can show non-classical efficiency gain over classical communication only for nuclear spin polarization beyond a certain threshold, and this threshold coincides with that for non-separability of the density matrix. It is also claimed that transfer of two-bit information mediated by a single qubit in the previous NMR SDC experiments with low nuclear spin polarization is not ascribed to the non-classical effect induced by entanglement, but merely to a statistical effect in an ensemble system having a large number of molecules. Towards experimental detection of entanglement, a new class of entanglement witnesses is proposed, which is based on the measurement of nuclear spin magnetizations in the Bell basis and is suitable for actual NMR experiments.
In this study, we report an experiment realization of quantum superdense coding (QSDC) between three parties using nuclear magnetic resonance (NMR). The experimental results have shown that in terms of the QSDC schemes between multiparties proposed by Liu et al. and Crudka et al., three-qubit QSDC can transmit three bits of classical information by sending two qubits only. Our results experimentally show that quantum superdense coding, as one of the quantum information processing protocols, is superior to classical ones.
In this work, we have been working on the concept of quantum entanglement. At first, we studied the theory of entanglement in its characterization and measurement, introducing a new scheme for detection of entanglement. The new approach links molecular-spin entities involving nuclear spins to quantum computing as more appropriate physical systems of interest. Then, we continued with the realization of entanglement in experiments. NMR has been the first choice due to its well approved advantages for quantum computing. NMR, however, has not been an appropriate system for demonstrating entangled states. Through a mathematical proof, NMR with low spin polarization has been invalidated for true implementations of non-local quantum algorithms, particularly supserdense coding. The point is that high spin polarization is inevitably required to acquire entanglement while in the current NMR it has been a formidable task to get highly polarized nuclear spins. In order to acquire high spin polarization, introducing electron spins can be much effective because of its three-order-of-magnitude larger gyromagnetic ratio compared to nuclear spins. Electron Nuclear DOuble Resonance (ENDOR) is spin manipulation technology that enables us to deal with both electron and nuclear spins. Thus, in this context, it can be more appropriate device for quantum computing. We emphasize that (pseudo)entanglement and interconversion between the entangled states have been realized with ENDOR on extremely stable organic molecular-spin entities. The required experimental conditions to obtain true quantum entanglement are also discussed. The appropriate entanglement witness for the corresponding ensemble quantum computing is introduced and examined.
Nuclear magnetic resonance (NMR) was successfully employed to test several protocols and ideas in quantum information science. In most of these implementations, the existence of entanglement was ruled out. This fact introduced concerns and questions about the quantum nature of such bench tests. In this paper, we address some issues related to the non-classical aspects of NMR systems. We discuss some experiments where the quantum aspects of this system are supported by quantum correlations of separable states. Such quantumness, beyond the entanglement-separability paradigm, is revealed via a departure between the quantum and the classical versions of information theory. In this scenario, the concept of quantum discord seems to play an important role. We also present an experimental implementation of an analogue of the single-photon Mach-Zehnder interferometer employing two nuclear spins to encode the interferometric paths. This experiment illustrates how non-classical correlations of separable states may be used to simulate quantum dynamics. The results obtained are completely equivalent to the optical scenario, where entanglement (between two field modes) may be present.
A bipartite quantum system in a mixed state can exhibit nonclassical correlations which can go beyond quantum entanglement. While quantum discord is the standard measure of quantifying such general quantum correlations, the nonclassicality can be determined by simpler means via the measurement of witness operators. We experimentally construct a positive map to witness nonclassicality of two qubits in an NMR system. The map can be decomposed in terms of measurable spin magnetizations so that a single run of an experiment on an ensemble of spins suffices to detect the nonclassicality in the state, if present. We let the state evolve in time and use the map to detect nonclassicality as a function of time. To evaluate the efficacy of the witness operator as a means to detect nonclassicality, we measure quantum discord by performing full quantum-state tomography at each time instant and obtain a fairly good match between the two methods.
Quantum entanglement is a form of correlation between quantum particles that cannot be increased via local operations and classical communication. It has therefore been proposed that an increment of quantum entanglement between probes that are interacting solely via a mediator implies non-classicality of the mediator. Indeed, under certain assumptions regarding the initial state, entanglement gain between the probes indicates quantum coherence in the mediator. Going beyond such assumptions, there exist other initial states which produce entanglement between the probes via only local interactions with a classical mediator. In this process the initial entanglement between any probe and the rest of the system "flows through" the classical mediator and gets localised between the probes. Here we theoretically characterise maximal entanglement gain via classical mediator and experimentally demonstrate, using liquid-state NMR spectroscopy, the optimal growth of quantum correlations between two nuclear spin qubits interacting through a mediator qubit in a classical state. We additionally monitor, i.e., dephase, the mediator in order to emphasise its classical character. Our results indicate the necessity of verifying features of the initial state if entanglement gain between the probes is used as a figure of merit for witnessing non-classical mediator. Such methods were proposed to have exemplary applications in quantum optomechanics, quantum biology and quantum gravity.