Additional dissipation of oscillatory superflow has been observed in uniformly rotating $^{3}\mathrm{He}$ - $B$ . The damping increases linearly with angular velocity and is interpreted in terms of vortex-induced mutual friction similar to that observed in superfluid $^{4}\mathrm{He}$ . In the nonrotating state the damping is amplitude dependent, and may contain a contribution from remanent vorticity.Additional dissipation of oscillatory superflow has been observed in uniformly rotating $^{3}\mathrm{He}$-$B$. The damping increases linearly with angular velocity and is interpreted in terms of vortex-induced mutual friction similar to that observed in superfluid $^{4}\mathrm{He}$. In the nonrotating state the damping is amplitude dependent, and may contain a contribution from remanent vorticity.

Physical Review LettersMay 7, 198423 citations

The Dynamics of Quantum Correlations of Two Qubits in a Common Environment

E. N. Bratus’, Leonid Andreevich Pastur

Zurnal matematiceskoj fiziki analiza geometriiJun 25, 20200 citations

超流動ヘリウムにおける量子渦環の制御と検出

ユウスケナゴウ, Y. Nago, 祐輔永合

量子乱流の生成・減衰過程において重要要素である量子渦の非線形運動状態の解明に向け、よく制御された細孔形状の量子渦環生成装置を用いた超流動ヘリウム中の渦生成実験を行った。昨年度に確立した作製方法を基に、超伝導細線を用いたワイヤー振動子と3Dプリンターを用いて光造形法によって作製した樹脂製細孔板から構成される装置を準備した。これまでのワイヤー振動子実験でのQ値の解析結果、および細孔サイズの渦環が発生したときのエネルギー散逸の見積もり結果から、直径4um、長さ100umの細孔を180個配列した～0.2mmサイズの細孔板を作製した。これにより振動子の共振の散逸として細孔からの渦環生成の観測が期待できる。この細孔板をマイクロマニピュレータを用いて太さ30umの超伝導細線振動子に精密に位置決めして接着した。室温でこの渦環生成装置の駆動テストを行い、正常に共振していることを確認した上で、4He冷凍機を用いて温度約1.3Kまで装置を冷却し、超流動ヘリウム中での共振スペクトル測定を行った。振動速度のドライブ電流(力)依存性を調べ、量子渦・量子乱流生成に伴う振動の散逸の観測に成功した。さらに渦生成速度の温度依存性を測定した。これらの結果とファインマンの渦環生成理論や残留渦の不安定性の理論を比較、解析したところ、観測された渦生成は残留渦によるものであることがわかった。振動子単体の実験から実証はされなかったが、渦生成速度付近では細孔内または開口部に付着した残留渦が、細孔サイズの渦環を放出していると考えられる。今後、渦環検出器を開発し、将来的に渦環放出の検証を行う予定である。また、研究室ではヘルムホルツ共鳴器による超流動流れの実験も進めており、開発した細孔板を本装置に組み込んだ実験装置の開発も計画している。 I performed experiments in superfluid helium using quantum vortex ring generators with well-controlled orifice shape, for elucidation of non-linear dynamics of quantum vortex rings which is one of the key factors for creation and decay processes of quantum turbulence. Following the fabrication method which I developed in the last fiscal year, the devices consisting of a vibrating wire resonator made of a superconducting filament and a resin orifice plate made with photofabrication using a 3D printer were prepared. I fabricated the ~0.2 mm resin plate with 180 aligned orifices with a diameter of 4 um and a length of 100 um, by reference to the Q-value obtained from the previous vibrating-wire measurements and our estimation of dissipation of the vibration due to vortex-ring emission. This enables observation of vortex ring emission from the orifice as a dissipation of resonant vibration. The plate was precisely positioned and glued on a superconducting wire with a thickness of 30 um using a micromanipulator. I checked a resonant vibration of the vortex ring generator at room temperature and thereafter cooled it down to 1.3 K using a 4He cryostat, followed by resonance spectrum measurements of it in superfluid helium. A driving current (force) dependence of vibration velocity revealed a dissipation of vibration due to generation of quantum vortices and turbulence. Furthermore, a temperature dependence of the velocity of vortex generation was measured. I compared these results with Feynman's theory for vortex nucleation and the theory of instability of remanent vortices, revealing that the observed vortex generation was caused by remanent vortices attached on the generator surfaces. It is expected that remanent vortices inside the orifice or in the vicinity of the opening emitted vortex rings with the same size as the orifice, though the single generator measurement did not provide the unambiguous evidence. I will develop vortex detecting devices and perform measurements to verify vortex ring generation in the future. In addition, superfluid flow experiments using a Helmholtz resonator are ongoing in our lab, and I am therefore planning experiments by the resonator with a resin orifice plate for the future.量子乱流の生成・減衰過程において重要要素である量子渦の非線形運動状態の解明に向け、よく制御された細孔形状の量子渦環生成装置を用いた超流動ヘリウム中の渦生成実験を行った。昨年度に確立した作製方法を基に、超伝導細線を用いたワイヤー振動子と3Dプリンターを用いて光造形法によって作製した樹脂製細孔板から構成される装置を準備した。これまでのワイヤー振動子実験でのQ値の解析結果、および細孔サイズの渦環が発生したときのエネルギー散逸の見積もり結果から、直径4um、長さ100umの細孔を180個配列した～0.2mmサイズの細孔板を作製した。これにより振動子の共振の散逸として細孔からの渦環生成の観測が期待できる。この細孔板をマイクロマニピュレータを用いて太さ30umの超伝導細線振動子に精密に位置決めして接着した。室温でこの渦環生成装置の駆動テストを行い、正常に共振していることを確認した上で、4He冷凍機を用いて温度約1.3Kまで装置を冷却し、超流動ヘリウム中での共振スペクトル測定を行った。振動速度のドライブ電流(力)依存性を調べ、量子渦・量子乱流生成に伴う振動の散逸の観測に成功した。さらに渦生成速度の温度依存性を測定した。これらの結果とファインマンの渦環生成理論や残留渦の不安定性の理論を比較、解析したところ、観測された渦生成は残留渦によるものであることがわかった。振動子単体の実験から実証はされなかったが、渦生成速度付近では細孔内または開口部に付着した残留渦が、細孔サイズの渦環を放出していると考えられる。今後、渦環検出器を開発し、将来的に渦環放出の検証を行う予定である。また、研究室ではヘルムホルツ共鳴器による超流動流れの実験も進めており、開発した細孔板を本装置に組み込んだ実験装置の開発も計画している。 I performed experiments in superfluid helium using quantum vortex ring generators with well-controlled orifice shape, for elucidation of non-linear dynamics of quantum vortex rings which is one of the key factors for creation and decay processes of quantum turbulence. Following the fabrication method which I developed in the last fiscal year, the devices consisting of a vibrating wire resonator made of a superconducting filament and a resin orifice plate made with photofabrication using a 3D printer were prepared. I fabricated the ~0.2 mm resin plate with 180 aligned orifices with a diameter of 4 um and a length of 100 um, by reference to the Q-value obtained from the previous vibrating-wire measurements and our estimation of dissipation of the vibration due to vortex-ring emission. This enables observation of vortex ring emission from the orifice as a dissipation of resonant vibration. The plate was precisely positioned and glued on a superconducting wire with a thickness of 30 um using a micromanipulator. I checked a resonant vibration of the vortex ring generator at room temperature and thereafter cooled it down to 1.3 K using a 4He cryostat, followed by resonance spectrum measurements of it in superfluid helium. A driving current (force) dependence of vibration velocity revealed a dissipation of vibration due to generation of quantum vortices and turbulence. Furthermore, a temperature dependence of the velocity of vortex generation was measured. I compared these results with Feynman's theory for vortex nucleation and the theory of instability of remanent vortices, revealing that the observed vortex generation was caused by remanent vortices attached on the generator surfaces. It is expected that remanent vortices inside the orifice or in the vicinity of the opening emitted vortex rings with the same size as the orifice, though the single generator measurement did not provide the unambiguous evidence. I will develop vortex detecting devices and perform measurements to verify vortex ring generation in the future. In addition, superfluid flow experiments using a Helmholtz resonator are ongoing in our lab, and I am therefore planning experiments by the resonator with a resin orifice plate for the future.

Jan 1, 20210 citations

Sudden transition and sudden change of quantum discord in dissipative cavity quantum electrodynamics system

Qi-Liang He, Jing‐Bo Xu

The dynamics of classical correlation and quantum correlation of two qubits in an independent and common dissipative cavity are studied. We show that for an independent case, the quantum correlation keeps constant and the correlation relation decays before the critical time point Ωt¯. On the other hand t>Ωt¯, for the classical correlation does not change and the quantum correlation is lost. These situations demonstrate that the phenomenon of sudden transition between classical and quantum decoherence appears during the time evolution. For the common case, the quantum correlation dynamics is quite different. It is displayed that for some initial states, the quantum correlation can increase up to the critical point of time, after which it decreases, which means that the quantum correlation presents a sudden change of behavior in their decay rates. But for other initial states, the quantum correlation can keep increasing up to some-steady state value. Furthermore, we also investigate the nonzero quantum correlation between two qubits induced by the dissipation of the cavity.The dynamics of classical correlation and quantum correlation of two qubits in an independent and common dissipative cavity are studied. We show that for an independent case, the quantum correlation keeps constant and the correlation relation decays before the critical time point Ωt¯. On the other hand t>Ωt¯, for the classical correlation does not change and the quantum correlation is lost. These situations demonstrate that the phenomenon of sudden transition between classical and quantum decoherence appears during the time evolution. For the common case, the quantum correlation dynamics is quite different. It is displayed that for some initial states, the quantum correlation can increase up to the critical point of time, after which it decreases, which means that the quantum correlation presents a sudden change of behavior in their decay rates. But for other initial states, the quantum correlation can keep increasing up to some-steady state value. Furthermore, we also investigate the nonzero quantum correlation between two qubits induced by the dissipation of the cavity.

Journal of the Optical Society of America BJan 3, 20139 citations

Additional dissipation of oscillatory superflow has been observed in uniformly rotating

^{3}\mathrm{He}

B

. The damping increases linearly with angular velocity and is interpreted in terms of vortex-induced mutual friction similar to that observed in superfluid

^{4}\mathrm{He}

. In the nonrotating state the damping is amplitude dependent, and may contain a contribution from remanent vorticity.