Spin Entanglement Research Articles

The Creation of Remote Spin Entanglement with a Nanomechanical Cantilever

We consider the creation of entanglement between remote electron spins using a magnetic nanoparticle attached to a cantilever tip (CT). We assume that the frequency of the CT vibrations matches the Larmor frequency of the spin (CT–spin resonance). Under the conditions of CT–spin resonance, the CT–spin system is described using the Jaynes–Cummings model. In this work, using the evolution operator of the Jaynes–Cummings model, we show that a movable CT can create an entangled state between remote spins. The most striking result is that the entanglement between the remote spins can be achieved without measuring the vibrational state of the CT.

Protocol for certifying entanglement in surface spin systems using a scanning tunneling microscope

Certifying quantum entanglement is a critical step toward realizing quantum-coherent applications. In this work, we show that entanglement of spins can be unambiguously evidenced in a scanning tunneling microscope with electron spin resonance by exploiting the fact that entangled states undergo a free time evolution with a distinct characteristic time constant that clearly distinguishes it from the time evolution of non-entangled states. By implementing a phase control scheme, the phase of this time evolution can be mapped back onto the population of one entangled spin, which can then be read out reliably using a weakly coupled sensor spin in the junction of the scanning tunneling microscope. We demonstrate through open quantum system simulations with currently available spin coherence times of T2 ≈ 300 ns, that a signal directly correlated with the degree of entanglement can be measured at temperatures of 100–400 mK accessible in sub-Kelvin scanning tunneling microscopes.

Transfer of nonclassical correlations between bosonic field and atomic ensemble through electromagnetically induced transparency

Dark state polariton, as an important concept in the mechanism of electromagnetic induced transparency (EIT), can map the state of bosonic fields to atomic ensembles. To reflect the mapping ability of dark state polariton, we choose the odd and even bosonic coherent states as the probe field in EIT process, and employ spin squeezing, entanglement, and quantum correlation to characterize nonclassical correlations of atomic ensembles during the manipulation of the driving field. It is shown that the differences between the odd and even coherent states are comprehensively reflected in the three characterizations of nonclassical correlations generated through dark state polaritons. The even bosonic coherent states can perfectly transfer bosonic squeezing into atomic ensembles, resulting in spin squeezing. Although the odd bosonic coherent states cannot induce the spin squeezing, they have an advantage over the even bosonic coherent states in generating quantum entanglement and quantum correlations. Furthermore, we demonstrate that atomic ensembles can achieve significant spin squeezing with squeezing degree ∝ 1/N 2/3 through the one-axis twisting (OAT) model and two-axis twisting (TAT) model under the large N limit with the low excitation conditions, and the EIT mechanism was used to transfer the generated spin squeezing to the bosonic field, providing a feasible strategy for obtaining significant bosonic squeezing.

Observation of quantum entanglement with top quarks at the ATLAS detector

Entanglement is a key feature of quantum mechanics1–3, with applications in fields such as metrology, cryptography, quantum information and quantum computation4–8. It has been observed in a wide variety of systems and length scales, ranging from the microscopic9–13 to the macroscopic14–16. However, entanglement remains largely unexplored at the highest accessible energy scales. Here we report the highest-energy observation of entanglement, in top–antitop quark events produced at the Large Hadron Collider, using a proton–proton collision dataset with a centre-of-mass energy of √s = 13 TeV and an integrated luminosity of 140 inverse femtobarns (fb)−1 recorded with the ATLAS experiment. Spin entanglement is detected from the measurement of a single observable D, inferred from the angle between the charged leptons in their parent top- and antitop-quark rest frames. The observable is measured in a narrow interval around the top–antitop quark production threshold, at which the entanglement detection is expected to be significant. It is reported in a fiducial phase space defined with stable particles to minimize the uncertainties that stem from the limitations of the Monte Carlo event generators and the parton shower model in modelling top-quark pair production. The entanglement marker is measured to be D = −0.537 ± 0.002 (stat.) ± 0.019 (syst.) for 340GeV<mtt¯<380GeV\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$340\\,{\\rm{GeV}} < {m}_{t\\bar{t}} < 380\\,{\\rm{GeV}}$$\\end{document}. The observed result is more than five standard deviations from a scenario without entanglement and hence constitutes the first observation of entanglement in a pair of quarks and the highest-energy observation of entanglement so far.

Quantum tops at circular lepton colliders

We study the quantum properties of top quark pairs in lepton colliders with unpolarised beams, including spin correlations, entanglement, and violation of Bell inequalities. We present analytical results in the SM and in the SMEFT and discuss several practical aspects, like the choice of quantisation axes and tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ t\\overline{t} $$\\end{document} threshold effects. We also note a correspondence between parity symmetry and entanglement. We find that quantum observables exhibit a rich phenomenology in the SM, and can also provide additional leverage in detecting new physics residing at higher scales.

Hints of entanglement suppression in hyperon-nucleon scattering

Hyperon (Y=Σ,Λ)-nucleon (N=n,p) interactions are crucial for understanding the existence of neutron stars heavier than two solar masses. Amid renewed experimental efforts, we study YN scatterings from the perspective of quantum information, focusing on whether spin entanglement is suppressed in the s-wave channel, which is observed in np scattering and leads to enhanced global symmetries. Using global fits of phase shifts from experimental data, we find hints of entanglement suppression among the eight flavor channels in the strangeness S=−1 sector, similar to the np case. One exception is the Σ+p channel, where conflicting global fits lead to inconclusive outcome. We then propose “quantum” observables in Σ+p scattering to help resolve the differing global fits.

Speeding up squeezing with a periodically driven Dicke model

We present a simple and effective method to create highly entangled spin states on a faster timescale than that of the commonly employed one-axis twisting (OAT) model. We demonstrate that by periodically driving the Dicke Hamiltonian at a resonance frequency, the system effectively becomes a two-axis countertwisting Hamiltonian, which is known to quickly create Heisenberg limit scaled entangled states. For these states we show that simple quadrature measurements can saturate the ultimate precision limit for parameter estimation determined by the quantum Cramér-Rao bound. An example experimental realization of the periodically driven scheme is discussed with the potential to quickly generate momentum entanglement in a recently described experimental vertical cavity system. We analyze effects of collective dissipation in this vertical cavity system and find that our squeezing protocol can be more robust than the previous realization of OAT. Published by the American Physical Society 2024

Identifying Sources of Entanglement Loss in Photodriven Molecular Electron Spin Teleportation.

We report on an electron donor-electron acceptor-stable radical (D-A-R•) molecule in which an electron spin state first prepared on R• is followed by photogeneration of an entangled singlet 1[D•+-A•-] spin pair to produce D•+-A•--R•. Since the A•- and R• spins within D•+-A•--R• are uncorrelated, spin teleportation from R• to D•+ occurs with a maximal 25% efficiency only for the singlet pair 1(A•--R•) by spin-allowed electron transfer from A•- to R•. However, since 1[D•+-A•-] is sufficiently long-lived, coherent spin mixing involving the unreactive 3(A•--R•) population affects entanglement and teleportation within D•+-A•--R•. Pulse electron paramagnetic resonance experiments show a direct correlation between electron spin flip-flops and entanglement loss, providing information for designing molecular materials to serve as nanoscale quantum device interconnects.

Onset of spin entanglement in doped carbon nanotubes studied by EPR.

Nanoscale semiconductors with isolated spin impurities have been touted as promising materials for their potential use at the intersection of quantum, spin, and information technologies. Electron paramagnetic resonance (EPR) studies of spins in semiconducting carbon nanotubes have overwhelmingly focused on spins more strongly localized by sp3-type lattice defects. However, the creation of such impurities is irreversible and requires specific reactions to generate them. Shallow charge impurities, on the other hand, are more readily and widely produced by simple redox chemistry, but have not yet been investigated for their spin properties. Here, we use EPR to study p-doped (6,5) semiconducting single-wall carbon nanotubes (s-SWNTs) and elucidate the role of impurity-impurity interactions in conjunction with exchange and correlation effects for the spin behavior of this material. A quantitative comparison of the EPR signals with phenomenological modeling combined with configuration interaction electronic structure calculations of impurity pairs shows that orbital overlap, combined with exchange and correlation effects, causes the EPR signal to disappear due to spin entanglement for doping levels corresponding to impurity spacings of 14nm (at 30K). This transition is predicted to shift to higher doping levels with increasing temperature and to lower levels with increasing screening, providing an opportunity for improved spin control in doped s-SWNTs.

A Strategy for Preparing Quantum Squeezed States Using Reinforcement Learning

AbstractA scheme leveraging reinforcement learning to engineer control fields for generating non‐classical states is proposed. It is exemplified by the application to prepare spin‐squeezed states for an open collective spin model where a linear control field is designed to govern the dynamics. The reinforcement learning agent determines the temporal sequence of control pulses, commencing from a coherent spin state in an environment characterized by dissipation and dephasing. Compared to the constant control scenario, this approach provides various control sequences maintaining collective spin squeezing and entanglement. It is observed that denser application of the control pulses enhances the performance of the outcomes. However, there is a minor enhancement in the performance by adding control actions. The proposed strategy demonstrates increased effectiveness for larger systems. Thermal excitations of the reservoir are detrimental to the control outcomes. Feasible experiments are suggested to implement this control proposal based on the comparison with the others. The extensions to continuous control problems and another quantum system are discussed. The replaceability of the reinforcement learning module is also emphasized. This research paves the way for its application in manipulating other quantum systems.

Spin Entanglement – A Unifying Principle for Superconductors and Molecular Bonding

The spin-statistics theorem is generalized to include quantum entanglement. Specifically, within the context of spin entanglement, we prove that isotropically spin-correlated (ISC) states must occur in pairs. This pairing process can be composed of parallel or anti-parallel states. Consequently, the article proposes using ISC states as a unifying principle to explain better Bose-Einstein condensates, the theory of superconductivity, and molecular and atomic orbitals, all of which involve a pairing process. The theoretical framework is established in sections 1 and 2. The other qualitative sections focus primarily on the experimental evidence to support the theory.&lt;strong&gt;Keyword&lt;/strong&gt;&lt;strong&gt;s&lt;/strong&gt;Entanglement and spin-statistics; unifying principle; condensates; superconductors; molecular bonds

Entangled photon pair generation in an integrated SiC platform

Entanglement plays a vital role in quantum information processing. Owing to its unique material properties, silicon carbide recently emerged as a promising candidate for the scalable implementation of advanced quantum information processing capabilities. To date, however, only entanglement of nuclear spins has been reported in silicon carbide, while an entangled photon source, whether it is based on bulk or chip-scale technologies, has remained elusive. Here, we report the demonstration of an entangled photon source in an integrated silicon carbide platform for the first time. Specifically, strongly correlated photon pairs are efficiently generated at the telecom C-band wavelength through implementing spontaneous four-wave mixing in a compact microring resonator in the 4H-silicon-carbide-on-insulator platform. The maximum coincidence-to-accidental ratio exceeds 600 at a pump power of 0.17 mW, corresponding to a pair generation rate of (9 ± 1) × 103 pairs/s. Energy-time entanglement is created and verified for such signal-idler photon pairs, with the two-photon interference fringes exhibiting a visibility larger than 99%. The heralded single-photon properties are also measured, with the heralded g(2)(0) on the order of 10−3, demonstrating the SiC platform as a prospective fully integrated, complementary metal-oxide-semiconductor compatible single-photon source for quantum applications.

Evidence of a significant full tripartite entanglement in a mixed spin-(1/2,1) Heisenberg tetramer

We rigorously analyze the full tripartite entanglement of a mixed spin-(1/2,1) Heisenberg tetramer in the presence of an external magnetic field. The tetramer consists of two mixed spin-(1/2,1) dimers arranged to form a square plaquette, with distinct exchange couplings J and J1 between spins from the same and different dimers, respectively. The full tripartite entanglement is classified according to the tripartite negativity NABC defined as a geometric mean of all possible bipartite negativities NA|BC, NB|AC, and NC|AB, when the degrees of freedom of the fourth spin D of the tetrapartite system ABCD are traced out. We demonstrate that for J1/J>1, both trimeric subsystems 1/2-1-1 and 1/2-1/2-1 exhibit tripartite entanglement mediated through the central spin. This entanglement becomes more robust upon the application of an external magnetic field. The opposite limit J1/J<1 leads to the spontaneous emergence of full tripartite entanglement solely within the subsystem 1/2-1-1. However, the increasing magnetic field swiftly disrupts the three-particle correlation across the relevant ground-state phase boundary. Additionally, we identify that in the isotropic limit J1/J=1, the ground-state degeneracy significantly reduces the strength of full tripartite entanglement and favors nontrivial subtypes of full nonseparable states with none or just one spin-dimer entanglement. Finally, we discuss in detail the thermal stability of all fully tripartite nonseparable states.

Correction: Hubbard interaction induced non-symmetric spin and pseudo-spin entanglement at different valleys of graphene

Correction: Hubbard interaction induced non-symmetric spin and pseudo-spin entanglement at different valleys of graphene

Hyperon physics at BESIII

Spin polarization and entanglement are utilized by the BESIII experiment to learn more about the production and decay properties of hyperon-antihyperon pairs in a series of recent analyses of its unprecedented datasets at the J/\psiJ/ψ and \psi'ψ′ resonances. This has lead to the observation of significant transverse polarisation in decays of J/\psiJ/ψ or \psi'ψ′ into \Lambda \bar{\Lambda}ΛΛ‾, \Sigma \bar{\Sigma}ΣΣ‾, \Xi \bar{\Xi}ΞΞ‾, and \Omega \bar{\Omega}ΩΩ‾. Because of the non-zero polarization, the decay parameters for the most common hadronic weak decays of both hyperons and antihyperons could be determined independently for the first time. Comparing these to each other yields precise tests of direct, \Delta S = 1ΔS=1 CP-violation that complement measurements of kaon decays.

Entanglement in Few-Nucleon Scattering Events

We investigate the spin entanglement in few-nucleon scattering processes involving nucleons and deuterons. For this purpose, we consider the entanglement power introduced by Beane et al. We analyze different entanglement entropies as a basis to define the entanglement power of the strong interaction and calculate the corresponding entanglement powers for proton–neutron, neutron–deuteron, proton–deuteron, and deuteron–deuteron scattering. For the latter two processes, we also take into account the modification from the Coulomb interaction. In contrast to proton–neutron scattering, no universal low-energy features are evident in the spin entanglement in neutron–deuteron, proton–deuteron, and deuteron–deuteron scattering.

Quantum degeneracy and spin entanglement in ideal quantum gases

Quantum degeneracy is the central many-body feature of ideal quantum gases stemming from quantum mechanics. In this work we address its relationship to the most fundamental form of non-classicality in many-body system, i.e. many-body entanglement. We aim at establishing a quantitative link between quantum degeneracy and entanglement in spinful ideal gases, using entanglement witness criteria based on the variance of the collective spin of the spin ensemble. We show that spin-1/2 ideal Bose gases do not possess entanglement which can be revealed from such entanglement criteria. On the contrary, ideal spin-1/2 Fermi gases exhibit spin entanglement revealed by the collective-spin variances upon entering quantum degeneracy, due to the formation of highly non-local spin singlets. We map out the regime of detectable spin entanglement for Fermi gases in free space as well as in a parabolic trap, and probe the robustness of spin entanglement to thermal effects and spin imbalance. Spin entanglement in degenerate Fermi gases is amenable to experimental observation using state-of-the-art spin detection techniques in ultracold atoms.

One-ninth magnetization plateau stabilized by spin entanglement in a kagome antiferromagnet

One-ninth magnetization plateau stabilized by spin entanglement in a kagome antiferromagnet

Influence of the interaction geometry on the fidelity of the two-qubit Rydberg blockade gate

We present a comparative analysis of physical constraints limiting the quality of spin entanglement created using the Rydberg blockade technique in an ensemble of trapped neutral 87Rb atoms. Based on the approach developed earlier in Phys. Rev. A 106, 042410 (2022)PLRAAN1050-294710.1103/PhysRevA.106.042410, we consider the complete multilevel Zeeman structure of the interacting atoms and apply our simulations to two excitation geometries featured by different transition types, both feasible for experimental verification. We demonstrate that the blockade shift strongly depends not only on the interatomic separation but also on the angular position of the atom pair with respect to the quantization axis determined by polarization of the driving fields. As an example, we have estimated fidelity for a promising design of a CZ gate, recently proposed by Levine et al. [Phys. Rev. Lett. 123, 230501 (2019)PRLTAO0031-900710.1103/PhysRevLett.123.230501] for various possible experimental geometries. Anisotropic effects in entangling gates considered here are important for the optimal choice of proper geometry for quantum computing in two- and three-dimensional arrays of atomic qubits and are of considerable interest for quantum simulators, especially those that are designed for anisotropic physical models.

Triplet-mediated spin entanglement between organic radicals: integrating first principles and open-quantum-system simulations

Controlling molecular spin quantum bits optically offers the potential to effectively reduce decoherence and raise the working temperature of quantum computers. Here, exchange interactions and spin dynamics, as mediated by an optically driven triplet state, are calculated for a molecule that consists of a pair of radicals and represents a potential quantum-circuit building block. Consistent with the previous experimental observation of spin coherence induced by the triplet state, our work demonstrates an optically driven quantum gate operation scheme in a molecule. A technological blueprint combining a two-dimensional molecular network and programmable nanophotonics, both of which are sufficiently developed, is proposed. We thus realize computational exploration of chemical databases to identify suitable candidates for molecular spin quantum bits and couplers to be hybridized with nanophotonic devices. The work presented here is proposed to realize a new approach for exploring molecular excited states and click chemistry, toward advancing molecular quantum technology.