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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

Published Jan 1, 2021• 0 citations
OpenAlex

Abstract

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.

Related papers

超流動における量子渦環生成装置の開発

ユウスケ ナゴウ, Y. Nago, 祐輔 永合

量子乱流の生成・減衰に密接に関わる量子渦の非線形運動状態の解明に向け、超流動ヘリウム中で渦環を、そのサイズと形状を制御して生成させるための装置開発に取り組んだ。渦環生成装置は超伝導細線を用いたワイヤー振動子と樹脂製細孔板から構成される。まず有限要素法による数値計算によって細孔板が接続したワイヤー形の共振装置の共振周波数を見積もった上で、細孔板の形状、サイズを決定し、3Dプリンターを用いた光造形法によって最小孔直径4umの細孔板を作製した。その後、超伝導細線をアーチ状に張ったワイヤー振動子の頂点に、細孔板を接着した。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、常流動成分による粘性の効果を示唆する線形性を確認することに成功した。しかし、量子渦、量子乱流が発生する振動速度まで上昇させることができなかった。これは、太さ156umの太い超伝導線を使用して装置を作製したが、その分硬くなったため十分な振動振幅が実現できなかったことが考えられる。そこで、新たにマニピュレータを導入して、より小サイズの細線および細孔板の取扱いを確立した。このマニピュレータを用いて太さ30umの超伝導細線振動子に、前回よりも小さいサイズの細孔板を接着した渦環生成装置を新たに作製した。再度低温超流動中で実験を行ったところ、渦・乱流生成に伴う振動の散逸の観測に成功した。細孔から渦環が放出されていると考えられる。今後、渦環が放出されていることを実証すべくさらなる装置の改良および実験を進める予定である。また、ヘルムホルツ共鳴器を用いた渦環生成装置の作製も検討する。 I developed generator devices of quantum vortex rings which can control a ring shape and size precisely in superfluid helium, for elucidation of non-linear dynamics of quantum vortices related to creation and decay of quantum turbulence. A vortex ring generator consists of a vibrating wire resonator made of a superconducting wire and a resin orifice plate. A shape and a size of the orifice plate was fixed by estimation of a resonant frequency of the device using numerical simulation with a finite element method, and the plate with a minimum diameter of 4 um was fabricated with stereolithography using a 3D printer device. Then, the plate was glued at the top of the superconducting vibrating wire with an arch shape. I checked a resonant oscillation of the device at a room temperature and then cooled it down to 1.3 K with a 4He cryostat to measure a resonant spectrum in superfluid helium. I investigated a current(force) dependence of oscillation velocity and successfully obtained its linearity due to viscosity of a normal fluid component of superfluid helium. However, an oscillation velocity did not increase exceeding the critical velocity for creation of quantum vortex and quantum turbulence. There is a possibility that the resonator did not realize high oscillation amplitude because the wire resonator consists of a thick and hence rigid superconducting wire with a size of 156 um. I then prepared a micro manipulator and devised manipulation of a thinner wire and a smaller orifice plate. I fabricated a vortex-ring generating device in which a smaller orifice plate was glued with a superconducting wire with a thickness of 30 um. I again performed oscillation measurements in superfluid helium at low temperatures and finally succeeded to observe dissipation of oscillation due to vortex/turbulence generation. It suggests vortex ring emission from the orifice. It is desirable to improve a resonator and prepare further experiments for direct verification of vortex ring emission. I will also consider fabrication of a vortex ring generating device using a Helmholtz resonator.

•Jan 1, 2020•0 citations

Vortex emission from quantum turbulence in superfluid 4 He

Y. Nago, A. Nishijima, H. Kubo +5 more

An oscillating object can stretch quantized vortices attached to it in superfluids due to the relative superflow, steadily generating quantum turbulence, even in the zero-temperature limit. We report the emission and propagation of quantized vortices from quantum turbulence generated in superfluid ${}^{4}$He at low temperatures. A vortex-free vibrating wire enables us to detect the first collision of vortex rings and therefore to measure the time-of-flight of a vortex emitted from a generator to a detector. The detection times from the start of turbulence generation exhibit an exponential distribution, suggesting that the detection is a Poisson process. Vortices are emitted continuously, but each vortex has a random flight velocity and direction. We estimated the nondetection time and mean detection period from the distribution for two flight distances. By estimating the flight velocity, we find that only vortices with velocities lower than the detector velocity can be detected, even if the sizes of the emitted vortices are smaller than the wire thickness or the vibration amplitude. The ratio of the detection rate as a function of vortex velocity suggests anisotropic emission of vortices from the quantum turbulence.

Physical Review B•Jan 22, 2013•17 citations

周波数域線形量子光回路を用いた大規模量子シミュレータの構築

アルト ホサカ, Aruto Hosaka, 有杜 保坂

本研究課題の将来的な目的は周波数多重量子状態を活用し、比較的小規模な実験系で大規模な革新的量子シミュレータの構築を行うことである。この課題内では周波数次元上に多重化された量子状態の生成を行い、さらにこれらの混合素子の開発に取り組んだ。 まず、我々は位相整合条件を設計されたPPKTP結晶を用いてスクイズド状態を周波数軸上に並行生成する実験を行った。先行研究においても周波数軸上にスクイズド光を並行生成した成果が報告されてきたが、本研究ではプログラマブルな量子シミュレータの構築に向けて、これらの周波数多重スクイズド光を独立に制御することを目指した。そのために、本研究では周波数多重スクイズド光の生成に位相整合条件を設計されたPPKTP結晶を用いた。この特殊な結晶の性質を活用することで、周波数軸上で多重化された量子状態にポンプ光スペクトルとの独立な対応関係が生じる。さらに、この結晶の励起パルスに高精度波形整形技術を組み合わせることで、生成されたスクイズド光を独立に操作した。 実際に実験によって周波数多重スクイズド光の並行生成および独立制御を行い、その成果をレーザー学会学術講演会第40回年次大会およびThe 9th "Advanced Lasers and Photon Sources Conference" (ALPS2020)において口頭発表し、論文投稿準備が完了している状態である。 また、同時に生成した周波数多重スクイズド光の活用のために非線形光学による周波数域線形回路の構築を行った。ここでは非線形媒質としてType-II PPLN結晶を採用した。この結晶を用いた周波数特性解析実験によって7モード程度の周波数域量子干渉が可能であることを実証した。しかし、高性能の周波数領域干渉のために必要な非線形効果が十分に確保できなかったために、バルクの結晶ではなく導波路構造を新たに採用することにした。そこで、導波路型のPPLN結晶のモード構造およびモード特性を数値解析により特定し、物質材料研究機構・日本碍子との共同研究により実際に導波路PPLN結晶を作製した。 The future goal of this project is to construct a large-scale quantum simulator in a relatively small experimental setup by utilizing frequency-multiplexed quantum states. In this project, we have generated multiplexed quantum states in the frequency domain and developed a linear mixer for these quantum states. First, we experimentally demonstrated the parallel generation of squeezed states in the frequency domain using a dispersion-engineered PPKTP crystal. Similar experiments have been reported even in the previous works. However, we aim to independently control these frequency-multiplexed squeezed lights for the construction of a programmable quantum simulator. For this purpose, we used a dispersion-engineered PPKTP crystal for the generation of frequency-multiplexed squeezed light. By taking advantage of the special property of the PPKTP crystal, quantum states multiplexed in the frequency domain have an independent correspondence to the spectral modes of the pump pulse. As a result, the generated squeezed light was independently manipulated by high-precision pulse shaping technic. We experimentally demonstrated the parallel generation and independent control of frequency-multiplexed squeezed states, and the results have been presented orally at the 40th Annual Conference of the Laser Society of Japan and the 9th "Advanced Lasers and Photon Sources Conference" (ALPS2020). In addition, we also constructed a frequency-domain linear circuit with nonlinear optics. In this experiment, a type-II PPLN crystal is employed as a nonlinear medium. The experimental analysis of joint spectral amplitude using this crystal showed that the 7-mode frequency-multiplexed quantum interference is possible. However, we failed to secure a sufficient amount of the nonlinear effect due to the limited pump power, so we decided to employ a waveguide crystal instead of the bulk crystal. The mode structure and properties of waveguide PPLN crystals were identified by numerical analysis, and waveguide PPLN crystals were actually fabricated in collaboration with National Institute for Materials Science and NGK Insulators.

•Jan 1, 2019•0 citations

Experiments on quantum turbulence within superfluid 3He-B

Michael Robert Lowe

This thesis describes experiments conducted on B phase 3He in the μK temperature regime to investigate the turbulent properties of quantised vortices created by driving a vibrating wire resonator above its superfluid pair breaking critical velocity. By operating several resonators as highly sensitive vortex detectors the localised effects of vortex lines have been measured. The results have shown the vortices being of greater density in the directions of the generating wire motion and the rate of production being dependent upon the generator wire velocity. The rate at which the vortices decay spatially has been shown to approximate to a simple exponential and the decay length of this exponential has been measured. Using a thermal quasiparticle beam emitted by a black body radiator, the temperature dependence of the vorticity has been investigated for several quasiparticle beam temperatures between 177μK and 275μK and several bulk superfluid temperatures between 171μK and 236μK. The vortex line density of the turbulence has been calculated using a mathematical model developed here at Lancaster and shows some dependence on the temperature of the superfluid. The method of using a quasiparticle beam emitted from a black body radiator may be developed to allow a higher resolution of investigation of vortex creation and decay.

•Jan 1, 2003•0 citations

極低温異核フェッシュバッハ分子の研究

宏平 加藤

論文提出者氏名 加藤 宏平 冷却原子実験の進展を支える技術のひとつに、フェッシュバッハ共鳴がある。フェッシュバ ッハ共鳴を利用すると原子間の相互作用の制御が可能になるだけでなく、極端に束縛エネルギ ーの小さい分子(フェッシュバッハ分子)を作ることもできる。本論文では 41 カリウム(

•Mar 24, 2015•0 citations

Creation of Quantized Vortex Rings in Superfluid Helium

George Gamota

We have produced and observed quantized vortex rings emitted from orifices when superfluid helium is forced through channels at critical velocity. The vortices are identified by measuring their velocity and size, and are found to be in the $n=1$ quantum state.

Physical Review Letters•Aug 20, 1973•33 citations
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・減衰に密接に関わる量子渦の非線形運動状態の解明に向け、超流動ヘリウム中で渦環を、そのサイズと形状を制御して生成させるための装置開発に取り組んだ。渦環生成装置は超伝導細線を用いたワイヤー振動子と樹脂製細孔板から構成される。まず有限要素法による数値計算によって細孔板が接続したワイヤー形の共振装置の共振周波数を見積もった上で、細孔板の形状、サイズを決定し、3Dプリンターを用いた光造形法によって最小孔直径4umの細孔板を作製した。その後、超伝導細線をアーチ状に張ったワイヤー振動子の頂点に、細孔板を接着した。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、常流動成分による粘性の効果を示唆する線形性を確認することに成功した。しかし、量子渦、量子乱流が発生する振動速度まで上昇させることができなかった。これは、太さ156umの太い超伝導線を使用して装置を作製したが、その分硬くなったため十分な振動振幅が実現できなかったことが考えられる。そこで、新たにマニピュレータを導入して、より小サイズの細線および細孔板の取扱いを確立した。このマニピュレータを用いて太さ30umの超伝導細線振動子に、前回よりも小さいサイズの細孔板を接着した渦環生成装置を新たに作製した。再度低温超流動中で実験を行ったところ、渦・乱流生成に伴う振動の散逸の観測に成功した。細孔から渦環が放出されていると考えられる。今後、渦環が放出されていることを実証すべくさらなる装置の改良および実験を進める予定である。また、ヘルムホルツ共鳴器を用いた渦環生成装置の作製も検討する。 I developed generator devices of quantum vortex rings which can control a ring shape and size precisely in superfluid helium, for elucidation of non-linear dynamics of quantum vortices related to creation and decay of quantum turbulence. A vortex ring generator consists of a vibrating wire resonator made of a superconducting wire and a resin orifice plate. A shape and a size of the orifice plate was fixed by estimation of a resonant frequency of the device using numerical simulation with a finite element method, and the plate with a minimum diameter of 4 um was fabricated with stereolithography using a 3D printer device. Then, the plate was glued at the top of the superconducting vibrating wire with an arch shape. I checked a resonant oscillation of the device at a room temperature and then cooled it down to 1.3 K with a 4He cryostat to measure a resonant spectrum in superfluid helium. I investigated a current(force) dependence of oscillation velocity and successfully obtained its linearity due to viscosity of a normal fluid component of superfluid helium. However, an oscillation velocity did not increase exceeding the critical velocity for creation of quantum vortex and quantum turbulence. There is a possibility that the resonator did not realize high oscillation amplitude because the wire resonator consists of a thick and hence rigid superconducting wire with a size of 156 um. I then prepared a micro manipulator and devised manipulation of a thinner wire and a smaller orifice plate. I fabricated a vortex-ring generating device in which a smaller orifice plate was glued with a superconducting wire with a thickness of 30 um. I again performed oscillation measurements in superfluid helium at low temperatures and finally succeeded to observe dissipation of oscillation due to vortex/turbulence generation. It suggests vortex ring emission from the orifice. It is desirable to improve a resonator and prepare further experiments for direct verification of vortex ring emission. I will also consider fabrication of a vortex ring generating device using a Helmholtz resonator.
An oscillating object can stretch quantized vortices attached to it in superfluids due to the relative superflow, steadily generating quantum turbulence, even in the zero-temperature limit. We report the emission and propagation of quantized vortices from quantum turbulence generated in superfluid 4{}^{4}4He at low temperatures. A vortex-free vibrating wire enables us to detect the first collision of vortex rings and therefore to measure the time-of-flight of a vortex emitted from a generator to a detector. The detection times from the start of turbulence generation exhibit an exponential distribution, suggesting that the detection is a Poisson process. Vortices are emitted continuously, but each vortex has a random flight velocity and direction. We estimated the nondetection time and mean detection period from the distribution for two flight distances. By estimating the flight velocity, we find that only vortices with velocities lower than the detector velocity can be detected, even if the sizes of the emitted vortices are smaller than the wire thickness or the vibration amplitude. The ratio of the detection rate as a function of vortex velocity suggests anisotropic emission of vortices from the quantum turbulence.
本研究課題の将来的な目的は周波数多重量子状態を活用し、比較的小規模な実験系で大規模な革新的量子シミュレータの構築を行うことである。この課題内では周波数次元上に多重化された量子状態の生成を行い、さらにこれらの混合素子の開発に取り組んだ。 まず、我々は位相整合条件を設計されたPPKTP結晶を用いてスクイズド状態を周波数軸上に並行生成する実験を行った。先行研究においても周波数軸上にスクイズド光を並行生成した成果が報告されてきたが、本研究ではプログラマブルな量子シミュレータの構築に向けて、これらの周波数多重スクイズド光を独立に制御することを目指した。そのために、本研究では周波数多重スクイズド光の生成に位相整合条件を設計されたPPKTP結晶を用いた。この特殊な結晶の性質を活用することで、周波数軸上で多重化された量子状態にポンプ光スペクトルとの独立な対応関係が生じる。さらに、この結晶の励起パルスに高精度波形整形技術を組み合わせることで、生成されたスクイズド光を独立に操作した。 実際に実験によって周波数多重スクイズド光の並行生成および独立制御を行い、その成果をレーザー学会学術講演会第40回年次大会およびThe 9th "Advanced Lasers and Photon Sources Conference" (ALPS2020)において口頭発表し、論文投稿準備が完了している状態である。 また、同時に生成した周波数多重スクイズド光の活用のために非線形光学による周波数域線形回路の構築を行った。ここでは非線形媒質としてType-II PPLN結晶を採用した。この結晶を用いた周波数特性解析実験によって7モード程度の周波数域量子干渉が可能であることを実証した。しかし、高性能の周波数領域干渉のために必要な非線形効果が十分に確保できなかったために、バルクの結晶ではなく導波路構造を新たに採用することにした。そこで、導波路型のPPLN結晶のモード構造およびモード特性を数値解析により特定し、物質材料研究機構・日本碍子との共同研究により実際に導波路PPLN結晶を作製した。 The future goal of this project is to construct a large-scale quantum simulator in a relatively small experimental setup by utilizing frequency-multiplexed quantum states. In this project, we have generated multiplexed quantum states in the frequency domain and developed a linear mixer for these quantum states. First, we experimentally demonstrated the parallel generation of squeezed states in the frequency domain using a dispersion-engineered PPKTP crystal. Similar experiments have been reported even in the previous works. However, we aim to independently control these frequency-multiplexed squeezed lights for the construction of a programmable quantum simulator. For this purpose, we used a dispersion-engineered PPKTP crystal for the generation of frequency-multiplexed squeezed light. By taking advantage of the special property of the PPKTP crystal, quantum states multiplexed in the frequency domain have an independent correspondence to the spectral modes of the pump pulse. As a result, the generated squeezed light was independently manipulated by high-precision pulse shaping technic. We experimentally demonstrated the parallel generation and independent control of frequency-multiplexed squeezed states, and the results have been presented orally at the 40th Annual Conference of the Laser Society of Japan and the 9th "Advanced Lasers and Photon Sources Conference" (ALPS2020). In addition, we also constructed a frequency-domain linear circuit with nonlinear optics. In this experiment, a type-II PPLN crystal is employed as a nonlinear medium. The experimental analysis of joint spectral amplitude using this crystal showed that the 7-mode frequency-multiplexed quantum interference is possible. However, we failed to secure a sufficient amount of the nonlinear effect due to the limited pump power, so we decided to employ a waveguide crystal instead of the bulk crystal. The mode structure and properties of waveguide PPLN crystals were identified by numerical analysis, and waveguide PPLN crystals were actually fabricated in collaboration with National Institute for Materials Science and NGK Insulators.
This thesis describes experiments conducted on B phase 3He in the μK temperature regime to investigate the turbulent properties of quantised vortices created by driving a vibrating wire resonator above its superfluid pair breaking critical velocity. By operating several resonators as highly sensitive vortex detectors the localised effects of vortex lines have been measured. The results have shown the vortices being of greater density in the directions of the generating wire motion and the rate of production being dependent upon the generator wire velocity. The rate at which the vortices decay spatially has been shown to approximate to a simple exponential and the decay length of this exponential has been measured. Using a thermal quasiparticle beam emitted by a black body radiator, the temperature dependence of the vorticity has been investigated for several quasiparticle beam temperatures between 177μK and 275μK and several bulk superfluid temperatures between 171μK and 236μK. The vortex line density of the turbulence has been calculated using a mathematical model developed here at Lancaster and shows some dependence on the temperature of the superfluid. The method of using a quasiparticle beam emitted from a black body radiator may be developed to allow a higher resolution of investigation of vortex creation and decay.
We have produced and observed quantized vortex rings emitted from orifices when superfluid helium is forced through channels at critical velocity. The vortices are identified by measuring their velocity and size, and are found to be in the n=1n=1n=1 quantum state.