Atsushi Goto, Tadashi Shimizu, Kenjiro Hashi
We propose a method of controlling a quantum logic gate in a solid-state NMR quantum computer. A switchable inter-qubit coupling can be generated by using the longitudinal component of the Suhl-Nakamura interaction induced by a local singlet-triplet excitation in a 1-D antiferromagnet with a spin gap.
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Magnon harmonic generation in antiferromagnets: Dynamical symmetry enriched by symmetry breaking
研究反铁磁体中THz激光或GHz波驱动的谐波产生，揭示磁序和相变如何改变谐波光谱，不同于无对称性破缺系统。
It is considered the indirect inter-qubit coupling in 1D chain of atoms with nuclear spins 1/2, which plays role of qubits in the quantum register. This chain of the atoms is placed by regular way in easy-axis 3D antiferromagnetic thin plate substrate, which is cleaned from the other nuclear spin containing isotopes. It is shown that the range of indirect inter-spin coupling may run to a great number of lattice constants both near critical point of quantum phase transition in antiferromagnet of spin-flop type (control parameter is external magnetic field) and/or near homogeneous antiferromagne…
We propose a mechanism for destabilizing or stabilizing Bose-Einstein condensation (BEC) of interacting magnons in an antiferromagnet. We study how the interaction between magnons affects the magnon BEC in a two-sublattice antiferromagnet without and with an external magnetic field. We show that in the absence of the magnetic field the magnon BEC is destabilized by the attractive interband interaction, which is larger than the repulsive intraband interaction. We also show that in the presence of the magnetic field the magnon BEC is stabilized only if the magnetic field is large enough to make …
Continuous variable entanglement between magnon modes in Heisenberg antiferromagnet with Dzyaloshinskii-Moryia (DM) interaction is examined. Different bosonic modes are identified, which allows to establish a hierarchy of magnon entanglement in the ground state. We argue that entanglement between magnon modes is determined by a simple lattice specific factor, together with the ratio of the strengths of the DM and Heisenberg exchange interactions, and that magnon entanglement can be detected by means of quantum homodyne techniques. As an illustration of the relevance of our findings for possibl…
Ultrafast coherent magnon spin currents in antiferromagnets
本研究提出在宇称-时间对称反铁磁体中叠加多个相干磁振子对模式，利用线偏振光产生方向可控的超快净自旋流，并可进一步叠加正交自旋流形成圆形自旋流。
Collinear antiferromagnets (AFs) support two degenerate magnon excitations carrying opposite spin polarizations, by which magnons can function as electrons in various spin-related phenomena. In an insulating ferromagnet(F)/AF/F trilayer, we explore the magnon-mediated interlayer coupling by calculating the magnon thermal energy in the AF as a function of the orientations of the Fs. The effect manifests as an interlayer exchange interaction and a perpendicular magnetic anisotropy; they both depend on temperature and the AF thickness. In particular, the exchange interaction turns out to be antif…
Magnon-photon coupling has been experimentally realized inside a cavity and the emerging field known as cavity spintronics has attracted significant attention for its potential docking with quantum information science. However, one seldom knows whether this coupling implies an entanglement state among magnons and photons or not, which is crucial for its usage in quantum information. Here we study the entanglement properties among magnons and photons in an antiferromagnet-light system and find that the entanglement between magnon and photon is nearly zero while the magnon-magnon entanglement is…
Diverging entanglement of critical magnons in easy-axis antiferromagnets
本文研究了易轴反铁磁体在磁场下的相变不稳定性，发现子格磁子间纠缠在相界附近发散，并揭示了该临界性可延伸至腔磁子学系统引发超辐射相变，提出利用腔光子测量探测磁性相变。
Quantum Sensing of Antiferromagnetic Magnon Two-Mode Squeezed Vacuum
该研究提出利用自旋量子比特通过直接色散耦合传感反铁磁体的双模压缩真空基态，并借助量子比特光谱与驱动控制确定性生成磁振子对Fock态。
Employing the concept of two-mode squeezed states from quantum optics, we demonstrate a revealing physical picture for the antiferromagnetic ground state and excitations. Superimposed on a N{é}el ordered configuration, a spin-flip restricted to one of the sublattices is called a sublattice-magnon. We show that an antiferromagnetic spin-up magnon is comprised by a quantum superposition of states with $n+1$ spin-up and $n$ spin-down sublattice-magnons, and is thus an enormous excitation despite its unit net spin. Consequently, its large sublattice-spin can amplify its coupling to other excitatio…
Transmon probe for quantum characteristics of magnons in antiferromagnets
本研究针对反铁磁材料中磁振子量子特性探测难题，提出基于双格点反铁磁的磁振子-光子-transmon混合方案，可通过transmon量子比特的拉比频率表征磁不可见磁振子模式、手性及纠缠等量子特性，为量子传感与纳米磁学研究提供新途径。
In a collinear antiferromagnet with easy-axis anisotropy, symmetry guarantees that the spin wave modes are doubly degenerate. The two modes carry opposite spin angular momentum and exhibit opposite chirality. Using a honeycomb antiferromagnet in the presence of the Dzyaloshinskii-Moriya interaction, we show that a longitudinal temperature gradient can drive the two modes to opposite transverse directions, realizing a spin Nernst effect of magnons with vanishing thermal Hall current. We find that magnons around the Γ-point and the K-point contribute oppositely to the transverse spin transport, …
In an antiferromagnet (AF) with uniaxial anisotropy, spin-up and spin-down magnons coexist and form an intrinsic degree of freedom resembling electrons. When polarized by an adjacent ferromagnet (F), a magnonic pure spin current can be thermally generated in an AF. We explore thermal magnon transport in an insulating F/AF/F trilayer where propagating magnons inside the AF spacer can transfer angular momenta between the two Fs. We find that a sufficiently large temperature gradient can switch the downstream F via magnonic spin-transfer torque if it is initially antiparallel with the upstream F.…
Squeezing and quantum control of antiferromagnetic magnon pseudospin
研究通过量子涨落工程控制反铁磁磁子伪自旋，实现磁子模式与其它激发的耦合增强和调控，并提出量子比特光谱协议检测压缩伪自旋基态。
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