JP3645345B2 - Recording / reproducing method and recording / reproducing apparatus - Google Patents

Description

と厳密に０となり、吸収が起きなくなる。これがＥＩＴである。吸収が起きなくなる物理的起源としては、｜−＞においては｜１＞→｜３＞と｜２＞→｜３＞の遷移が干渉効果によりキャンセルすると考えれば良い。
【００５６】
式（２₁ ），（２₂ ）より明らかなように、トラップ（trap）される先の準位である｜−＞は、｜１＞と｜２＞について、ラビ周波数、つまり、光強度の比により構成されている。したがって、光強度を変えることにより、｜−＞の性質を変えることができる。
【００５７】
Ωｃ＞＞Ωｐの場合には、｜−＞〜｜１＞、つまり、基底状態に近い状態にトラップされる。逆に、Ωｃ＜＜Ωｐの場合には、下の励起状態｜２＞に近い状態にトラップされる。
【００５８】
ＥＩＴが起きているときの｜１＞から｜３＞への吸収スペクトルの形状は、図２に示すように、吸収スペクトルには、Δω_p ＝Δω_c という条件を満たすω_p の位置に、吸収の穴、つまり、透明領域が生ずる。
【００５９】
Δω_c ＝０の場合には、図２（ａ）に示されるように、Δω_p ＝０、つまり、吸収スペクトルの中心に穴ができる。
【００６０】
Δω_c ≠０の場合には、図２（ｂ）に示されるように、吸収の裾の領域に穴が生ずる。
【００６１】
穴の幅は、カップリング光のラビ周波数Ωｃにほぼ等しい。したがって、穴の幅はカップリング光の強度を変えることにより制御できる。
【００６２】
次に物理構造が複数の場合（Ｎ個の場合）のＥＩＴ特性について説明する。
【００６３】
前述したように、固体系では均一幅や不均一幅が原子ガス系より広い。このため、固体系のスペクトルは、均一幅により広がった個々の物理構造のスペクトルを、その中心位置を分布させて重なり合わせた、非常に幅の広いスペクトルとなる。このような状況は、｜１＞→｜３＞の遷移だけでなく、｜２＞→｜３＞の遷移についても同様である。
【００６４】
したがって、原子ガス系で行なわれているＥＩＴ実験と同様に、ω_c を固定させた状態で観測したＥＩＴ信号は、（ε_i31 ，ε_i32 ）分布のために、ディチューニング（detuning）が等しいというＥＩＴ条件に合う物理構造の数は少なくなり、図３に示されるような極めて小さい信号となる。
【００６５】
そればかりでなく、系全体のＥＩＴ特性に対する物理構造一個の寄与がどこに現れるかなど、その特徴もあまり明瞭ではない。したがって、これまでのところ、ω_p 軸上でのω_p の吸収特性に現れる各物理構造のＥＩＴ特性は、検出が難しいだけでなく、それを制御する方法も明確でなく、何らかの応用を考えていくことは困難と考えられる。
【００６６】
本発明の単一物理構造（分子・原子）レベルでの記録・再生の根幹となる原理は、（ω_p ，ω_c ）平面上でのω_p の吸収特性変化を考えることである。これにより、以下に述べるように、物理構造のＥＩＴ特性を検出するだけでなく、個々の物理構造のＥＩＴ特性（ε_i31 ，ε_i32 ）分布を変えることも可能となり、単一物理構造レベルでの記録・再生が可能となる。
【００６７】
まず、物理構造一個に関して考える。｜１＞→｜３＞へのω_p の吸収について、カップリング光の周波数ω_c を変化させた場合の変化分を（ω_p ，ω_c ）平面上で考える。
【００６８】
図４は、Ωｐ＜Ωｃ＜（均一幅）という条件での特性である。スペクトルに現れる現象自体は、極めて単純である。図４（ａ）に示されるように、当然のことながら、ω_c ＝const.の平面で切ると物理構造一個の吸収スペクトルとなる。
【００６９】
ＥＩＴが起きる条件はΔω_p ＝Δω_c であり、（ω_p ＝ω₃₁＝２πε₃₁／ｈ、ω_c ＝ω₃₂＝２πε₃₂／ｈ）を中心としたω_p 軸と４５度の角度をなす線上で起きる。
【００７０】
図４（ｂ）は、その４５度の方向からスペクトルを見た様子であり、カップリング光のラビ周波数に相当する幅の狭い穴が開いているのが分かる。
【００７１】
この穴の部分だけを抜き出すと、図４（ｃ）に示すように、丁度単一物理構造の吸収スペクトルを４５度回転させたもので、しかも、厚みがラビ周波数程度の薄い板状スペクトルとなることが分かる。
【００７２】
次に物理構造が複数個の場合を考える。各物理構造がＥＩＴにより生ずる薄い板状の吸収の穴は、（ω_p ，ω_c ）平面上で、各物理構造の準位間エネルギーに対応した、（ω_i31 (i) ，ω_i32 (i) ）という点を中心として生ずる。
【００７３】
固体系では、不均一幅が広く、ω_i31 (i) とω_i32 (i) は各々ω_p 軸、ω_c 軸上で分散している。このため、ラビ周波数を小さくして各板の厚みを薄くすれば、図５に示すように、個々の物理構造の寄与は（ω_p ，ω_c ）平面上で完全に分離することが可能となる。
【００７４】
このように、（ω_p ，ω_c ）平面上でのω_p の吸収特性変化を考えることにより、各物理構造に起因した吸収の穴は、各物理構造毎に分離して現れ、しかも、その中心位置は（ω_i31 (i) ，ω_i32 (i) ）という点になる。
【００７５】
したがって、（ω_p ，ω_c ）平面上における系全体のＥＩＴ信号を観測し、吸収に現れる板状の穴がどこに現れるかを調べることにより、各物理構造のエネルギーε_i31 ，ε_i32 の位置が分かることになる。
【００７６】
よって、Ｎ個の物理構造における（ω_i31 ，ω_i32 ）の分布を例えばレーザ照射により変化させ、記録媒体に情報を記録した場合において、上記方法により、（ω_i31 ，ω_i32 ）の分布を検出すれば、情報の再生を行なうことができる。
【００７７】
ここで、図４、図５に示したような、（ω_p ，ω_c ）平面上でのω_p の吸収特性を検出するためには、複数のω_c に関して、ω_p の吸収を測定することが不可欠である。すなわち、複数の（ω_p ，ω_c ）組みについて吸収特性を計測することにより、記録媒体に記録された情報を再生することが好ましい。
【００７８】
この理由は、単一のω_c ＝ω_c ⁰ に関してω_p の吸収を測定したときには、図４、図５に示したような吸収特性を、ω_c ＝ω_c ⁰ （＝const.）という平面で切った断面の形状を有したスペクトルとなり、ε_i31 ，ε_i32 というエネルギーが広範囲に分布する物理構造の中で、２πε_i32 〜ｈω_c ⁰ という関係を満たす物理構造についてしか吸収の穴を検出する可能性がないからである。
【００７９】
さらに、たとえ、２πε_i32 〜ｈω_c ⁰ という関係を満たしていても、ω_c ＝ω_c ⁰ 平面上に吸収穴の極値が存在しなければ、吸収穴に対応した信号はきわめて弱く穴の位置の同定が困難となる。
【００８０】
設定したω_c ⁰ の値に関して、ω_c ＝ω_c ⁰ 上に吸収穴の極値を含むことは確率的にも希である。このことからも、単一のω_c ではなく、複数のω_c について、ω_p の吸収を測定することが、エネルギー的に分布する物理構造集団に対し、個々の物理構造に起因した吸収の穴を検出するために不可欠の要素であることが分かる。
【００８１】
図４、図５に示された吸収の穴は、単一物理構造の吸収スペクトルを４５度回転させたものであるので、長手方向、つまり、ω_c ＝ω_p ＋const.に平行な方向に関する幅は、単一物理構造スペクトルの均一幅程度である。
【００８２】
このため、各吸収の穴を検出するためには、ω_p に対応するコヒーレント光の線幅だけでなく、ω_c に対応するコヒーレント光の線幅も、均一幅と同程度もしくはそれ以下であることが望ましい。
【００８３】
また、測定時のω_p の間隔を均一幅と同程度もしくはそれ以下にするだけでなく、複数のω_c に関しその各々の間隔も均一幅と同程度もしくはそれ以下にすることが望ましい。
【００８４】
（第２の実施形態）
（ω_p ，ω_c ）平面において、ω_p に関する吸収の穴を個々検出することとともに、次のような吸収の積分強度を検出することも、本発明における記録媒体に記録した情報の再生として重要な手段である。今、（ω_p −ω_c ）＝Δωの値が一定という条件下での、
Ｉ_ab（Δω）＝∫Ｉ_ab（ω_p ；ω_p −Δω）ｄω_p
という積分を考える。
【００８５】
まず、物理構造一個の場合の特性を説明する。このＩ_ab（Δω）は、（ω_p ，ω_c ）平面において、ω_p 軸と４５度をなす方向にＩ_ab（ω_p ；ω_c ）を積分したものである。
【００８６】
図６にＩ_ab（Δω）の分布を示す。図４（ｂ）の穴に対応した幅Ω_c の狭い穴が、Δω＝ω₃₁−ω₃₂＝ω₂₁）の近傍にあり、その他の領域では一定値をとることが分かる。この一定値は、一物理構造の吸収の積分強度という、物理構造に固有の物理量、Ｉ₀ ＝∫Ｉ⁰ _ab（ω_p ）ｄω_p と一致する。
【００８７】
図７に温度を変えたときのＩ_ab（ω_p ；ω_c ）およびΔＩ_ab（ω_p ；ω_c ）の変化の様子を示す。図７から、温度上昇とともに、Ｉ_ab（ω_p ；ω_c ）およびΔＩ_ab（ω_p ；ω_c ）は全体に４５度方向に伸びるが、Ｉ_ab（Δω）は全く変化しないことが分かる。
【００８８】
図８（ａ）、図８（ｂ）に、それぞれ、物理構造が複数個の場合のＩ_ab（Δω）の分布、ΔＩ_ab（Δω）の分布を示す。Ｉ_ab（Δω）には、ＮＩ₀ をベースラインとして、そこからＩ₀ の整数倍の深さおよび幅Ω_c をもつ穴が生じる。図８（ｂ）のΔＩ_ab（Δω）の分布は、穴の部分だけを抽出した符号を逆転させたものに対応する。
【００８９】
これらの棒状のスペクトルの高さや深さをＩ₀ で割って得られる整数値は、Δω軸上において、ω₂₁の値がそのΔωに等しいような物理構造の個数を意味している。この場合にも、Ｉ_ab（Δω）およびΔＩ_ab（Δω）が温度に依存しないことは言うまでもない。
【００９０】
このようなことから、Ｉ_ab（Δω）やΔＩ_ab（Δω）を計測し、それを記録媒体に記録した情報の再生に用いれば、温度に依存しない、極めて安定な情報の再生を行なえるようになる。
【００９１】
また、Ｉ_ab（ω_p ；ω_c ）あるいはΔＩ_ab（ω_p ；ω_c ）を情報の再生として用いる場合には、（ω_i31 ，ω_i32 ）の分布について単一物理構造レベルでの再生が行なえるのに対して、Ｉ_ab（Δω）やΔＩ_ab（Δω）を情報の再生として用いる場合には、ω_i21 の分布を単一物理構造レベルで再生することが可能となる。
【００９２】
なお、吸収だけでなく、発光に関しても
Ｉ_lu（Δω）＝∫Ｉ_lu（ω_p ；ω_p −Δω）ｄω_p
もしくは
Ｉ_lu（Δω）＝∫｛Ｉ⁰ _lu（ω_p ）−Ｉ_lu（ω_p ；ω_p −Δω）｝ｄω_p
を計測して情報の再生を行なう場合にも同様な作用効果がある。
【００９３】
（第３の実施形態）
次に情報の記録について説明する。
【００９４】
本発明では、（ω_p ，ω_c ）平面における物理構造のエネルギー準位分布を変えることにより、記録媒体に情報を記録する。
【００９５】
エネルギー準位分布を変えるためには、例えば、記録媒体に光や電子線を照射したり、記録媒体に電場や磁場を印加したり、あるいは記録媒体に圧力を加えることにより、物理構造集団の一部を励起して、そのエネルギー準位を変化させてやれば良い。
【００９６】
特に、単一物理構造レベル（分子・原子レベル）での情報の記録を行なうために、本発明では、前述したＰｏｐｕｌａｔｉｏｎ Ｔｒａｐｐｉｎｇを利用し、（ω_i31 ，ω_i32 ）の分布あるいはω_i21 の分布を単一物理構造レベルで変換する。
【００９７】
具体的には、再生の場合と同様に、角周波数ω_p ，ω_c 、ラビ周波数Ω_p ，Ω_c の第１、第２のコヒーレント光を例えばレーザにより同時に記録媒体に照射して、ある物理構造をポピュレーショントラップさせた状態で、更に、電子が励起されると構造変化を起こしたり、あるいは電子がその準位からイオン化したりする準位、｜ｉ４＞へ励起するための、角周波数ω_exの第３のコヒーレント光も例えばレーザにより照射する。
【００９８】
このような手法により、どのような物理構造が状態を変えるかを図を用いて説明する。（ω_p ，ω_c ）平面において、第１、第２のコヒーレント光の照射によるポピュレーショントラップは、図９に示すように、点（ω_p ，ω_c ）を中心とした、４５度の線上に（ω_i31 ，ω_i32 ）を有する物理構造が起こす。
【００９９】
ここで、
Ω_p ＜Ω_c
の場合には、物理構造は｜ｉ１＞という状態にトラップされることになる。したがって、図１０に示すような、｜ｉ１＞と｜ｉ４＞との間の遷移を引き起こすような角周波数ω_exの第３のコヒーレント光の照射により、
ω_ex＝ω_i41
を満たす物理構造は、選択的に｜ｉ４＞へと励起され、イオン化や構造変化を起こす。そして、角周波数ω_exが異なる複数の第３のコヒーレント光を照射することにより、図１１に示すように、（ω_i31 ，ω_i32 ）の分布に穴を開けることができる。
【０１００】
また、Ω_p ＞Ω_c の場合には、物理構造は｜ｉ２＞という状態にトラップされることになる。したがって、図１２に示すような、｜ｉ２＞と｜ｉ４＞との間の遷移を引き起こすような角周波数ω_exの第３のコヒーレント光Ｌの照射により、
ω_ex＝ω_i24
を満たす物理構造は、選択的に｜ｉ４＞へと励起され、イオン化や構造変化を起こす。そして、この場合にも、角周波数ω_exが異なる複数の第３のコヒーレント光を照射することにより、図１１の場合と同様、（ω_i31 ，ω_i32 ）の分布に穴を開けることができる。
【０１０１】
なお、ポピュレーショントラップを起こしていない物理構造に対しても選択的に状態変化を起こすことも可能である。
【０１０２】
図１３に、第１、第２のコヒーレント光の照射下において、ポピュレーショントラップを起こさず、かつ第１のコヒーレント光を吸収して、｜ｉ３＞へと励起される物理構造の分布を示す。
【０１０３】
したがって、図１４に示すような、｜ｉ３＞と｜ｉ４＞との間の遷移を引き起こすような角周波数ω_exの第３のコヒーレント光の照射により、
ω_ex＝ω_i34
を満たす物理構造は、選択的に｜ｉ４＞へと励起され、イオン化や構造変化を起こす。そして、この場合にも、好ましくは角周波数ω_exが異なる複数の第３のコヒーレント光を照射することにより、図１１の場合と同様、（ω_i31 ，ω_i32 ）の分布に穴を開けることができる。
【０１０４】
（ω_i31 ，ω_i32 ）の分布を広範囲にわたって変えて情報の記録を行なう場合には、複数の（ω_p ，ω_c ）の値に対して同様な操作を行なえば良い。
【０１０５】
また、第１、第２、第３のコヒーレント光の照射とともに、電圧や磁場の印加を同時に行なうことにより、各物理構造のエネルギー準位が変わり、ω_i31 ，ω_i32 ，ω_i41 等の値が変わる。
【０１０６】
したがって、（ω_p ，ω_c ）の値を変えなくても、（ω_i31 ，ω_i32 ）の分布を変えることが可能となり、これにより、情報の記録を効率よく行なうことができる。
【０１０７】
（第４の実施形態）
本実施形態では、不純物としてＥｕを０．１モル％含むＹＡＧ結晶を記録媒体として使用する。
【０１０８】
図１５に、Ｅｕのエネルギー準位を示す。Ｅｕの基底状態は ⁷Ｆ₀ で、 ⁷Ｆ₀ から１８９５０ｃｍ^-1高エネルギー側に ⁵Ｄ₁ という励起状態があり、 ⁷Ｆ₀ との間は強い光学遷移を起こす。
【０１０９】
また、 ⁷Ｆ₀ から４６０ｃｍ^-1高エネルギー側に ⁷Ｆ₁ という励起状態があり、 ⁵Ｄ₁ との間に強い光学遷移を起こす。さらに、 ⁷Ｆ₀ から３６０００ｃｍ^-1〜４２０００ｃｍ^-1高エネルギー側付近に電荷移動状態が連続的に存在し、そこに電子が励起されたＥｕ原子は＋３価から＋２価へと価数を変える。
【０１１０】
この記録媒体を、可視域が透明な光学窓を有した温度可変のクライオスタットに入れ、液体ヘリウムによる冷却により、試料温度を４Ｋに保つ。その状態で、アルゴンイオンレーザーで励起する二本のリング色素レーザーを記録媒体に照射する。二本のリング色素レーザーを駆動するレーザー色素としては、ともにチューニングレンジが１７２４０〜１９２３０ｃｍ^-1であるクマリンを用いる。
【０１１１】
ここでは、リング色素レーザーの発振線幅は、５００ｋＨｚ＝０．００００１７ｃｍ^-1となるように調整する。また、リング色素レーザーのうち一つ（Ｌ１）は、その発振周波数ω_p を１８９５０ｃｍ^-1近傍、もう一つ（Ｌ２）はその発振周波数ω_c を１８４９０ｃｍ^-1近傍を掃引するように調整する。レーザー光強度は、レーザーＬ１，Ｌ２のラビ周波数がそれぞれ３ＭＨｚ、１７ＭＨｚとなるように設定する。
【０１１２】
先ず、記録媒体に情報を記録する前におけるＥｕのエネルギー分布の検出を以下のような手法により行なった。すなわち、記録媒体に新しい情報を記録する前に記録されている情報の再生を以下のような手法により行なった。
【０１１３】
まず、レーザーＬ２は照射せず、レーザーＬ１の発振周波数を１８９４５．００００ｃｍ^-1から１８９５５．００００ｃｍ^-1まで連続的に変化させ、レーザーＬ１の吸収スペクトル、Ｉ⁰ _ab（ω_p ）を検出する。
【０１１４】
次にレーザーＬ２の発振周波数を１８４８５．００００ｃｍ^-1に固定し、レーザーＬ１の発振周波数を１８９４５．００００ｃｍ^-1から１８９５５．００００ｃｍ^-1まで連続的に変化させ、レーザーＬ１の吸収スペクトル、Ｉ_ab（ω_p ；ω_c ）を検出し、Ｉ⁰ _ab（ω_p ）との差、ΔＩ_ab（ω_p ；ω_c ）＝Ｉ⁰ _ab（ω_p ）−Ｉ_ab（ω_p ；ω_c ）を求める。
【０１１５】
次にレーザーＬ２の発振周波数を０．０００２ｃｍ^-1増加させ１８４８５．０００２ｃｍ^-1に固定し、再度レーザーＬ１の発振周波数を１８９４５．００００ｃｍ^-1から１８９５５．００００ｃｍ^-1まで連続的に変化させ、レーザーＬ１の吸収スペクトル、Ｉ_ab（ω_p ；ω_c ）を検出し、ΔＩ_ab（ω_p ；ω_c ）を求める。
【０１１６】
このようにレーザーＬ２の発振周波数を順次０．０００２ｃｍ^-1ずつ増加させその都度レーザーＬ１の吸収スペクトルを検出するプロセスを、レーザーＬ２の発振周波数が１８４９５．００００ｃｍ^-1になるまで続ける。
【０１１７】
図１６は、このようにして得られたΔＩ_ab（ω_p ；ω_c ）の一部を、レーザーＬ１の発振周波数ω_p とレーザーＬ２の発振周波数ω_c を二つの座標軸とした（ω_p ，ω_c ）平面に図示したものである。図１６から、各擬原子（物理構造）のＥＩＴに伴う吸収の穴が観測されていることが分かる。
【０１１８】
図１７は、Δω＝ω_p −ω_c の値を、１２ＭＨｚ＝０．０００４ｃｍ^-1毎に設定して、
ΔＩ_ab（Δω）＝∫｛Ｉ⁰ _ab（ω_p ）−Ｉ_ab（ω_p ；ω_p −Δω）｝ｄω_p
という積分強度を、各Δωについて求めたものである。ΔＩ_ab（Δω）の値は、ある一定値を単位としたその整数倍になっていることが観測された。
【０１１９】
次にこの記録媒体に新しい情報を記録する場合について説明する。
【０１２０】
情報の記録を行なうには、ラビ周波数を各々１７ＭＨｚ，３ＭＨｚに設定したレーザーＬ１，Ｌ２を照射するとともに、更にもう一台のリング色素レーザーＬ３（発振周波数ω_ex）を用意し、クマリン色素励起の出力光をＢＢＯ結晶に照射することにより得られる２倍波を、記録媒体に照射する。
【０１２１】
情報の記録は、以下のような条件で順次行なった。
【０１２２】
（１）ω_p ＝１８９５２．００２０ｃｍ^-1，ω_c ＝１８４８６．００００ｃｍ^-1，ω_ex＝３８０００〜４００００ｃｍ^-1
（２）ω_p ＝１８９５２．００００ｃｍ^-1，ω_c ＝１８４８６．００２０ｃｍ^-1，ω_ex＝４００００〜４２０００ｃｍ^-1
（３）ω_p ＝１８９５２．００００ｃｍ^-1，ω_c ＝１８４８６．０１２０ｃｍ^-1，ω_ex＝３８０００〜４００００ｃｍ^-1
図１８、図１９、図２０は、それぞれ、（１）〜（３）の各手順の後に、レーザーＬ３の照射を止め、ラビ周波数を各々３ＭＨｚ，１７ＭＨｚに設定し直したレーザーＬ１，Ｌ２を照射し、ΔＩ_ab（ω_p ；ω_c ）を測定した結果である。
【０１２３】
図１６との比較から分かるように、各物理構造の吸収の穴の中で、記録に用いたω_p ，ω_c の値と４５度をなす方向に位置する穴の幾つかが消失していることが分かる。また、新たな記録を行なっても、それまでに記録した情報は変化しないことも分かる。
【０１２４】
図２１は、（３）の手順後に、測定したΔＩ_ab（Δω）の結果である。
【０１２５】
図２１から分かるように、Δω＝４６５．９８８０ｃｍ^-1におけるΔＩ_ab（Δω）の値は５から２へ、Δω＝４６５．９９８０ｃｍ^-1におけるΔＩ_ab（Δω）の値は５から１へ、さらにΔω＝４６６．００２０ｃｍ^-1におけるΔＩ_ab（Δω）の値は４から１へと変化した。
【０１２６】
なお、試料温度を室温に上げてから再度このΔＩ_ab（Δω）の測定を行なったところ、図２１と同じ測定結果が得られ、ΔＩ_ab（Δω）を記録データとする、本実施形態の記録方法の温度に対する安定性が確認された。
【０１２７】
（第５の実施形態）
第４の実施形態の場合と同様に、不純物としてＥｕを０．０１モル％含むＹＡＧ結晶を記録媒体に用いた。ただし、本実施形態では、ＹＡＧ結晶の二つの側面にＡｕを蒸着し電極を形成してある。この電極は外場としての電場を記録媒体に与えるためのものである。
【０１２８】
本実施形態では、以下のようにして記録媒体に情報を記録する。
【０１２９】
すなわち、記録媒体に、角周波数ω_p が１８９５２．００２０ｃｍ^-1に固定されたレーザーＬ１、角周波数ω_c が１８４８６．００００ｃｍ^-1に固定されたレーザーＬ２を照射した状態で、記録媒体に、１分間で角周波数ω_exが３８０００から４００００ｃｍ^-1まで掃引されたレーザー３Ｌを照射する。また、電極には、０Ｖから５Ｖの間を１Ｈｚで三角波掃引した電圧を印加する。
【０１３０】
図２２、図２３は、それぞれ、記録の前後でのΔＩ_ab（Δω）の変化を示す図である。
【０１３１】
第１の実施形態では、Δωの値が、角周波数ω_p と角周波数ω_c の差に等しいところで、ΔＩ_ab（Δω）の値が変化し記録が行なわれたが、本実施形態では、Δω＝４６５．９９８０ｃｍ^-1のところだけでなく、より幅広い領域でΔＩ_ab（Δω）の値が変化している。
【０１３２】
これは、角周波数ω_p ，ω_c の値が固定されていても、電場により各物理構造のエネルギー準位が変化し、各電場によりポピュレーショントラップの条件を満たす物理構造が変わり、その結果｜ｉ４＞へと励起される物理構造が増えたためである。このように電場を利用することにより、効率的に記録媒体に情報を記録できることが確認された。
【０１３３】
なお、本実施形態では、外場として電場の場合について説明したが、磁場、温度、圧力等の他の外場の場合についても、同様に個々の物理構造の光学スペクトル等の変化を検出できる。
【０１３４】
（第６の実施形態）
本実施形態では、第４、第５の実施形態の場合と同様に、不純物としてＥｕを０．１モル％含むＹＡＧ結晶を記録媒体に用いる。本実施形態の特徴は、光の吸収ではなく蛍光を計測することにより記録されている情報の再生を行なうことにある。
【０１３５】
本実施形態の記録媒体は、図２４に示すように、 ⁵Ｄ₁ から約２４１５ｃｍ^-1高エネルギー側に ⁵Ｄ₂ という励起状態があり、この状態から⁷ Ｆ₀ に電子が遷移する際に、２１３６０ｃｍ^-1程度の波数の強い蛍光を示す。
【０１３６】
したがって、ポピュレーショントラップされずに、 ⁵Ｄ₁ へ励起されたＥｕ原子に関して、第３のコヒーレント光として２３００〜２５００ｃｍ^-1近傍の赤外線を発振するＰｂ_1-x Ｃｄ_x Ｓ、もしくはＰｂＳ_1-x Ｓｅ_x の半導体レーザーなどを用いて選択的に ⁵Ｄ₂ へ励起すれば、そこから⁷ Ｆ₀ へ励起する際の蛍光を検出できる。
【０１３７】
ここでは、第１、第２のコヒーレント光は、第４の実施形態と同一のものを用い、第３のコヒーレント光としては、特に発振周波数のピーク周波数が２４１１ｃｍ^-1、ラビ周波数０．２ＭＨｚのＰｂＳ_1-x Ｓｅ_x の半導体レーザーＬ３を用いて、記録媒体に情報を記録する前におけるＥｕのエネルギー分布の検出を以下のような手法により行なった。すなわち、記録媒体に新しい情報を記録する前に記録されている情報の再生を以下のような手法により行なった。
【０１３８】
まず、レーザーＬ２は照射せず、レーザーＬ３は照射した状態で、レーザーＬ１の発振周波数を１８９４５．００００ｃｍ^-1から１８９５５．００００ｃｍ^-1まで連続的に変化させた時に観測される２１０００ｃｍ^-1以上の波数の蛍光強度Ｉ⁰ _lu（ω_p ）を、フィルタとフォトカウンタを用いて検出する。
【０１３９】
次にレーザーＬ２の発振周波数を１８４８５．００００ｃｍ^-1に固定し、レーザーＬ３は照射した状態で、レーザーＬ１の発振周波数を１８９４５．００００ｃｍ^-1から１８９５５．００００ｃｍ^-1まで連続的に変化させた時に観測される２１０００ｃｍ^-1以上の波数の蛍光強度Ｉ_lu（ω_p ；ω_c ）を検出し、蛍光強度Ｉ⁰ _lu（ω_p ）との差、ΔＩ_lu（ω_p ；ω_c ）＝Ｉ⁰ _lu（ω_p ）−Ｉ_lu（ω_p ；ω_c ）を求める。
【０１４０】
次にレーザーＬ２の発振周波数を０．０００２ｃｍ^-1増加させ、１８４８５．０００２ｃｍ^-1に固定し、レーザーＬ３は照射した状態で、レーザーＬ１の発振周波数を１８９４５．００００ｃｍ^-1から１８９５５．００００ｃｍ^-1まで連続的に変化させた時に観測される２１０００ｃｍ^-1以上の波数のＩ_lu（ω_p ；ω_c ）を検出し、ΔＩ_lu（ω_p ；ω_c ）を求める。
【０１４１】
このように、レーザーＬ２の発振周波数を順次０．０００２ｃｍ^-1増加させ、その都度発光強度Ｉ_lu（ω_p ；ω_c ）を検出し、ΔＩ_lu（ω_p ；ω_c ）を求めるプロセスを、レーザーＬ２の発振周波数が１８４９５．００００ｃｍ^-1になるまで続ける。
【０１４２】
図２５は、このようにして得られたΔＩ_lu（ω_p ；ω_c ）の一部を、レーザーＬ１の発振周波数ω_p とレーザーＬ２の発振周波数ω_c を二つの座標軸とした（ω_p ，ω_c ）平面に図示したものである。図１６と同様に、各擬原子（物理構造）のＥＩＴに伴う蛍光の穴が観測されていることが分かる。
【０１４３】
ただし、図１６との違いは、穴の個数が少ないことである。これは、レーザーＬ３の線幅が、 ⁵Ｄ₁ から ⁵Ｄ₂ への遷移の不均一幅よりも狭く、 ⁵Ｄ₁ へ励起されているＥｕ原子の全てを ⁵Ｄ₂ へ励起しているわけではないことに起因する。
【０１４４】
さらに、ＰｂＳ_1-x Ｓｅ_x 半導体レーザーＬ３に流す駆動電流を増加させて発振周波数を２４１３ｃｍ^-1に変えて、上記方法と同様にΔＩ_lu（ω_p ；ω_c ）を求めた結果を図２６に示す。
【０１４５】
（ω_p ，ω_c ）平面の領域に関しては図２５と同じであるが、図２５とは異なった擬原子（物理構造）のＥＩＴに伴う蛍光の穴が観測されていることが明確に分かる。
【０１４６】
このようにレーザーＬ３に流す駆動電流を変えて発振周波数を変化させることで、 ⁵Ｄ₁ から ⁵Ｄ₂ への遷移の不均一幅の範囲を全て走査すれば、全てのＥｕ原子に関するＥＩＴ信号（情報）を蛍光により観測（再生）できるようになる。（第７の実施形態）
ここでは、本発明の記録／再生装置を用いて、記録媒体に記録された情報を再生する方法と、新しい情報を記録する方法について具体的に説明する。
【０１４７】
図２７は、本実施形態における記録／再生装置を模式的に示す図である。情報の再生においては、２台のリング色素レーザー１１，１２からの出力光を記録媒体１３に照射する。
【０１４８】
レーザー１１の出力光は、記録媒体１３を透過した後に、出力検出用フォトマルチプライア１４に入力される。フォトマルチプライア１４の出力Ｉ^S _PM1 （ω_p ）は、アナログ信号であるので、ＡＤコンバータ１５によりデジタル信号に変換してから、データ制御用パーソナルコンピュータ１６に入力させる。
【０１４９】
ここで、記録媒体１３への入射光強度を換算するために、レーザー１１からの出力光の一部をビームスプリッタ１７により分岐させた後、フォトマルチプライア１８に入力させ、分岐光の強度であるフォトマルチプライア１８の出力^S _PM2 （ω_p ）を求める。出力Ｉ^S _PM2 （ω_p ）も、ＡＤコンバータ１９によりデジタル信号に変換してから、データ制御用パーソナルコンピュータ１６に入力させる。
【０１５０】
さらに、吸収スペクトルのデータを得るために、記録媒体１３がないときの、フォトマルチプライア１４，１８のそれぞれの出力Ｉ⁰ _PM1 （ω_p ），Ｉ^S _PM2 （ω_p ）を予め計測し、これらをデータ制御用パーソナルコンピュータ１６に入力させる。
【０１５１】
レーザー１２の出力光の照射の有無に関わらず、角振動数ω_p の吸収Ｉ_ab（ω_p ）は次式で定義される。
【０１５２】
Ｉ_ab（ω_p ）＝（１／Ｉ⁰ _PM1 （ω_p ））（Ｉ⁰ _PM1 （ω_p ）−Ｉ^S _PM1 （ω_p ）・Ｉ_PM2 （ω_p ）／Ｉ^S _PM2 （ω_p ））
データ制御用パーソナルコンピュータ１６は、この式に対応した演算処理を行ない吸収Ｉ_ab（ω_p ）を求める。また、データ制御用パーソナルコンピュータ１６にはリング色素レーザー制御用パーソナルコンピュータ２１，２８から、角振動数ω_p ，ω_c の値が信号として入力される。
【０１５３】
このような手順により、レーザー１２の照射下での吸収スペクトルデータＩ_ab（ω_p ；ω_c ）、レーザー１２を照射しない時の吸収スペクトルＩ⁰ _ab（ω_p ）が各々（ω_p ，ω_c ）の組の値、ω_p の値に対して求められ、データ制御用パーソナルコンピュータ１６のハードディスクに再生データが収納される。
【０１５４】
データ量が多い場合には、データ制御用パーソナルコンピュータ１６のハードディスクから磁気ディスク等の大容量の外部記憶装置２２にデータを転送してデータを保存することも可能である。さらに、再生データを画面上で見るような場合には、データをディスプレイ２３に転送すれば良い。
【０１５５】
記録媒体１３に新たに情報を記録するには、以下のような手順で行なう。
【０１５６】
すなわち、レーザー１１，１２の出力光に加え、リング色素レーザー２４およびエキシマレーザー２５の出力光も出力増加用の色素増幅器２６に入射する。この色素増幅器２６から出力されたレーザー光を非線形光学結晶のＢＢＯ結晶２７に入射させ、得られた２高波を記録媒体１３に照射し、第４の実施形態で説明した手法により情報を記録する。
【０１５７】
このとき、レーザー２４の発振周波数の値はパーソナルコンピュータ２８からデータ制御用パーソナルコンピュータ１６に信号として入力される。
【０１５８】
なお、上述したように、情報の記録・再生時には、レーザー１１，１２，２４の光強度をモニタすることが重要であるので、レーザー１１だけではなく、レーザー１２，２４の出力光の一部もそれぞれビームスプリッタ２９，３０により分岐させた後、それぞれの分岐光をフォトマルチプライア３１，３２に入力させ、これらフォトマルチプライア３１，３２の出力をそれぞれＡＤコンバータ３３，３４によりデジタル信号に変換して、データ制御用パーソナルコンピュータ１６に入力して、レーザー１２，２４の出力光の強度を計測する。なお、図中、３５〜４０はミラーを示している。
【０１５９】
【発明の効果】
以上詳説したように本発明によれば、ＥＩＴ現象の持つ極めて高い周波数分解能を利用するという全く新しい記録／再生原理を採用することにより、原子や分子の状態を記録単位とした情報の記録・再生を実現できるようになる。
【図面の簡単な説明】
【図１】３準位系のモデルを示す図
【図２】１個の物理構造のＥＩＴ特性を表すプローブ光の角周波数ω_p に対する吸収スペクトルを示す図
【図３】Ｎ個の物理構造のＥＩＴ特性を表すプローブ光の角周波数ω_p に対する吸収スペクトルを示す図
【図４】１個の物理構造に関し、プローブ光の角周波数ω_p に対する吸収スペクトルを示す図
【図５】Ｎ個の物理構造に関し、プローブ光の角周波数ω_p に対する吸収スペクトルに観測される吸収の穴を符号を逆転させてω_p −ω_c 平面に示す図
【図６】第２の実施形態における情報の記録原理を説明するための１物理構造の関するＩ_ab（Δω）を示す図
【図７】第２の実施形態における情報の再生原理を説明するための１物理構造に関するＩ_ab（ω_p ；ω_c ）、ΔＩ_ab（ω_p ；ω_c ）の分布を示す図
【図８】第２の実施形態における情報の再生原理を説明するためのＮ物理構造に関するＩ_ab（ω_p ；ω_c ）、ΔＩ_ab（ω_p ；ω_c ）の分布を示す図
【図９】第１、第２のコヒーレント光の照射によりポピュレーショントラップされる物理構造のエネルギー分布を示す図
【図１０】第３の実施形態においてΩ_p ＜Ω_c の場合における記録方法を説明するための図
【図１１】第１、第２のコヒーレント光の照射によりポピュレーショントラップされる物理構造の中で、第３のコヒーレント光の照射により第４の準位に励起され、イオン化や構造変化を起こす物理構造のエネルギー分布を示す図
【図１２】第３の実施形態においてΩ_p ＞Ω_c の場合における記録方法を説明するための図
【図１３】第１、第２のコヒーレント光の照射によりポピュレーショントラップされず、かつ第１のコヒーレント光を吸収して第３の準位に励起される物理構造のエネルギー分布を示す図
【図１４】ポピュレーショントラップを起こさない物理構造に対する記録方法を説明するための図
【図１５】第４の実施形態で用いたＥｕのエネルギー準位図
【図１６】第４の実施形態において、記録前に測定したΔＩ_ab（ω_p ；ω_c ）に関して、１８９５２．００００ｃｍ^-1＜ω_p ＜１８９５２．０２００ｃｍ^-1，１８４８６．００００ｃｍ^-1＜ω_c ＜１８４８６．０２００ｃｍ^-1の領域を拡大して示す図
【図１７】第４の実施例形態において、記録前に測定したΔＩ_ab（ω）に関して、４６５．９８８０ｃｍ^-1＜Δω＜４６６．００２０ｃｍ^-1の領域を拡大して示す図
【図１８】第４の実施形態において、情報の記録操作（１）の後に読み出したΔＩ_ab（ω_p ；ω_c ）を示す図
【図１９】第４の実施形態において、情報の記録操作（１），（２）の後に読み出したΔＩ_ab（ω_p ；ω_c ）を示す図
【図２０】第４の実施形態において、情報の記録操作（１），（２），（３）の後に読み出したΔＩ_ab（ω_p ；ω_c ）を示す図
【図２１】第４の実施形態において、情報の記録操作（１），（２），（３）の後に読み出したΔＩ_ab（Δω）を示す図
【図２２】第５の実施形態において、情報を記録する前のΔＩ_ab（Δω）を示す図
【図２３】第５の実施形態において、情報を記録した後のΔＩ_ab（Δω）を示す図
【図２４】第６の実施形態の記録媒体としてのＥｕを０．１モル％含むＹＡＧ結晶のエネルギー準位を示す図
【図２５】第６の実施形態の記録媒体に記録された情報を読出した結果を示す（ω_p ，ω_c ）平面
【図２６】第６の実施形態の記録媒体に記録された情報を読出した結果を示す他の（ω_p ，ω_c ）平面
【図２７】第７の実施形態の記録／再生装置を模式的に示す図
【符号の説明】
｜１＞…第１の準位
｜２＞…第２の準位
｜３＞…第３の準位
ω_p …プローブ光（第１のコヒーレント光）の周波数
ω_c …カップリング光（第２のコヒーレント光）の周波数
Ωｐ…プローブ光のラビ周波数
Ωｃ…カップリング光のラビ周波数
１１，１２…リング色素レーザー
１３…記録媒体
１４…フォトマルチプライア
１５…ＡＤコンバータ
１６…パーソナルコンピュータ
１７…ビームスプリッタ
１８…フォトマルチプライア
１９…ＡＤコンバータ
２０，２１…パーソナルコンピュータ
２２…外部記憶装置
２３…ディスプレイ
２４…リング色素レーザ
２５…エキシマレーザー
２６…色素増幅器
２７…ＢＢＯ結晶
２８…パーソナルコンピュータ
２９，３０…ビームスプリッタ
３１，３２…フォトマルチプライア
３３，３４…ＡＤコンバータ
３５〜４０…ミラー[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a recording / reproducing method and a recording / reproducing apparatus using a state of each atom or molecule as a recording unit.
[0002]
[Prior art]
In the information society in recent years, the advent of a recording / reproducing method and a recording / reproducing apparatus based on the recording / reproducing method with a dramatically higher recording density than the conventional one corresponding to the ever-increasing amount of information is expected.
[0003]
One limitation of the recording density is an atomic / molecular memory that uses the state of each atom or molecule as a recording unit. In order to realize atomic / molecular memory, technology to detect and control phenomena at the atomic / molecular level is indispensable.
[0004]
As an example of such a technology, many scanning probe technologies such as STM, AFM, or NSOM (Near-Field Scanning Optical Microscope) using a near-field of light are being studied, and actual application to memory is also attempted. Being started. However, at present, there are technical problems such as the scanning speed of the surface being too slow, and it has not been put into practical use.
[0005]
On the other hand, with the advancement of laser technology, research on new physical phenomena is progressing in the field of quantum electronics research targeting atomic gases. Typical examples are EIT (Electromagnetically Induced Transparency) and LWI (Lasing Without Inversion) based on coherent interaction between atoms and lasers.
[0006]
EIT and LWI are phenomena induced by irradiating two laser beams to an atomic system having both three levels to keep the atoms in a coherent state.
[0007]
That is, EIT is a phenomenon in which the wavelength region that should have strong absorption becomes transparent (JEField et al., Phys. Rev. Lett. 67, 3062 (1991), K.-J. Moller et al. Phys. Rev. Lett. 66, 2593 (1991)). LWI is a phenomenon in which EIT is not absorbed even when coherent light is emitted, and laser oscillation occurs even if there is no inversion distribution (SEHarris, Phys. Rev. Lett. 62, 1033 (1989). )).
[0008]
EIT has already been verified in several atomic gas systems, and a large change of several orders of magnitude in the transmission coefficient has been reported. On the other hand, with regard to LWI, some experiments have been attempted in an atomic gas system, and laser oscillation has not been achieved, but amplification of probe light has been realized (WEVeer et al., Phys. Rev. Lett. 70,3243 (1993)).
[0009]
As applications using EIT and LWI, an optical filter that transmits only light in a very narrow band, a laser in a short wavelength region in which an inversion distribution is difficult to be formed, and the like are considered.
[0010]
In addition to these, it is considered that various new applications may be born. However, when considering the feasibility of such new applications, phenomena such as EIT and LWI are realized not in atomic gas systems but in solid systems. It is better to do it.
[0011]
As an approach to solid-state systems, theoretical analysis has been carried out on impurities in semiconductor quantum wells, rubies and diamonds (Y. Zhu et al., Phys. Rev. A49, 4016). (1994), D. Huang et al., J. Opt. Soc. Am. Bll, 2258 (1994), C. Wei et al., Phys. Rev. A51, 1438 (1995)), EIT and LWI experiments No report has been made on solid systems.
[0012]
In order to realize EIT and LWI in a solid system, there are some points that must be considered unlike an atomic gas system.
[0013]
First, EIT and LWI are based on a closed three-level or four-level system, and it is essential that electrons do not escape to other levels under light irradiation. For this reason, it is necessary to select a level in which the wave function is localized and the relaxation to other levels hardly occurs as the solid state electronic state.
[0014]
As a candidate of a level satisfying such conditions, there are physical structure systems having atomic characteristics such as impurities such as transition metals and rare earths, point defects such as vacancies, and quantum structures such as quantum dots and quantum wires. The level which can be said is mentioned.
[0015]
The second point is that the spectral width of the optical transition is generally wide in a solid system. Factors that determine the spectral width are the level involved in the transition, the uniform width that occurs when the energy value fluctuates in time due to the interaction with the surroundings, and the temporal average value of the interaction There are two non-uniform widths depending on the level and due to the distribution in the level itself.
[0016]
Among the solid systems, the physical structure system described above has a relatively small width, but the uniform width and the non-uniform width are both large compared to the atomic gas system. The characteristics of EIT and LWI are determined by the resonance condition related to the frequency, and the size of the uniform width and the non-uniform width greatly affects the characteristics.
[0017]
Thus, in order to realize EIT and LWI in a solid system, the above-mentioned points must be taken into consideration. Therefore, in order to realize EIT and LWI in a solid system, an approach different from that of an atomic gas system is required. However, at present, a solid-system-specific approach necessary for realizing EIT and LWI in a solid system has not been clarified.
[0018]
Furthermore, in the case of a solid system, functions and features peculiar to the solid system and application of new EIT and LWI based thereon are expected, but no such proposal has been made so far.
[0019]
[Problems to be solved by the invention]
As described above, the advent of recording / reproducing methods and recording / reproducing apparatuses capable of recording and reproducing information at the atomic / molecular level is expected, and the super high level by scanning probe technology such as STM, AFM, NSOM, etc. Although application to density recording has been attempted, a practical level has not been realized.
[0020]
The present invention has been made in view of the above circumstances, and its object is to provide a recording / reproducing method capable of recording and reproducing information in the recording unit of the state of each atom or molecule. And providing a recording / reproducing apparatus.
[0021]
[Means for Solving the Problems]
    [Overview]
  In order to achieve the above object, the recording / reproducing method according to the present invention (Claim 1) uses, as a recording medium, a solid having a physical structure having an energy level structure composed of three or more energy levels. The number of the physical structures contained in the solid is N, the predetermined three levels of the i-th physical structure are the first, second, and third levels, and h is the Planck constant, The level energy is hω_i1/ 2π, the energy of the second level is hω_i2/ 2π, the energy of the third level is hω_i3/ 2π, | ω_i3−ω_i1|_i31 , | Ω_i3−ω_i2|_i32 , | Ω_i2−ω_i1|_i21And whenBy irradiating the recording medium with light or electron beam, applying an electric field or magnetic field to the recording medium, or applying pressure to the recording medium,(Ω in N physical structures_i31 , Ω_i32 ) To change the distribution of information on the recording medium,Based on the change in the optical spectrum of the physical structure,(Ω_i31 , Ω_i32 ) Distribution or ω_i21The information is reproduced by detecting the distribution of.
[0022]
Here, the physical structure means a quantum structure such as a quantum dot, a quantum wire, or a quantum box, a crystal defect such as a point defect, and an impurity atom. Further, the number N of physical structures is the number of physical structures included in the portion irradiated with coherent light, and may be the number of physical structures included in the entire solid that is an object to be detected. It may be the number of physical structures included in the part.
[0024]
Another recording / reproducing method according to the present invention (Claim 2) is the above recording / reproducing method (Claim 1)._i31The maximum value of max (ω_i31), Min (ω_i31) Among the N physical structures_i32The maximum value of max (ω_i32), Min (ω_i32), The angular frequency of the first coherent light is ω_p, The angular frequency of the second coherent light is ω_cMin (ω_i31) <Ω_p<Max (ω_i31), Min (ω_i32) <Ω_c<Max (ω_i32The recording medium is irradiated with the first and second coherent light satisfying the condition (2), and is generated through absorption of the first coherent light and absorption of the first coherent light in the recording medium. At least one of the fluorescence of the recording medium is a plurality of (ω_p, Ω_c) The information recorded on the recording medium is reproduced by measuring the set.
[0025]
Another recording / reproducing method according to the present invention (Claim 3) is the above recording / reproducing method (Claim 1), wherein_i31The maximum value of max (ω_i31), Min (ω_i31) Among the N physical structures_i32The maximum value of max (ω_i32), Min (ω_i32), The angular frequency of the first coherent light is ω_p, The angular frequency of the second coherent light is ω_c, Ω_p−ω_cΔω, Δω is constant, and min (ω_i31) <Ω_p<Max (ω_i31), Min (ω_i32) <Ω_c<Max (ω_i32The absorption of the first coherent light in the recording medium when the recording medium is irradiated with the first and second coherent light satisfying the condition of_ab(Ω_p; Ω_c), The fluorescence of the recording medium generated through the absorption of the first coherent light._lu(Ω_p; Ω_c) And I_ab(Δω) = ∫I_ab(Ω_p; Ω_p−Δω) dω_pAnd I_lu(Δω) = ∫I_lu(Ω_p; Ω_p−Δω) dω_pThe information recorded on the recording medium is reproduced by obtaining at least one of a plurality of different Δω.
[0026]
Another recording / reproducing method according to the present invention (Claim 4) is the recording / reproducing method (Claim 1), wherein the solid causes a change in structure when electrons are excited at the level. It has a fourth level, and the energy of this fourth level is hω_i4/ 2π, ω_i4−ω_i1|_i41, | Ω_i4−ω_i2|_i42, | Ω_i4−ω_i3|_i43, Ω among the N physical structures_i41The maximum value of max (ω_i41), Min (ω_i41) Among the N physical structures_i42The maximum value of max (ω_i42), Min (ω_i42) Among the N physical structures_i43The maximum value of max (ω_i43), Min (ω_i43), The rabbi frequency of the first coherent light is Ω_p, The rabbi frequency of the second coherent light is Ω_cWhen Ω_p<Ω_cIn this case, the first and second coherent lights, and min (ω_i41) Greater than max (ω_i41) Smaller angular frequency, or min (ω_i43) And max (ω_i43) Irradiating a third coherent light having an angular frequency smaller than_p> Ω_cIn this case, the first and second coherent lights, and min (ω_i42) And max (ω_i42) Less angular frequency, or min (ω_i43) And max (ω_i43The information is recorded on the recording medium by irradiating a third coherent light having an angular frequency smaller than ().
[0027]
Where (ω_i31, Ω_i32) Distribution, and thus ω_i21In order to efficiently change the distribution of the light, it is preferable to simultaneously apply the electric field and the magnetic field simultaneously with the irradiation of the first, second, and third coherent light.
[0028]
Information reproduction may be performed as follows.
[0029]
min (ε_i31) <Hω_p/ 2π <max (ε_i31The first coherent light when the recording medium is irradiated with the first coherent light and the recording medium is irradiated with the first and second coherent light under the conditions And the first and second coherent light in the recording medium and the fluorescence of the recording medium generated through the absorption of the first coherent light when the recording medium is irradiated with only the first coherent light. At least one of the fluorescence differences from the fluorescence of the recording medium that occurs through the absorption of the first coherent light when irradiated with a plurality of (ω_p, Ω_c) Perform by measuring the set.
[0030]
Where multiple (ω_p, Ω_c) During assembly, ω_cTwo (ω) whose absolute value of the difference between is less than or equal to the uniform width for the transition between the first level and the third level_p, Ω_c) It is preferable that a set exists.
[0031]
  The recording / reproducing apparatus according to the present invention (Claim 5) includes a solid having an energy level structure composed of energy levels of three or more levels as a recording medium, and first and second recording mediums. An optical system for irradiating the coherent light, wherein the optical system includes N as the number of the physical structures contained in the solid, and first three predetermined levels of the i-th physical structure, The second and third levels, h is the Planck constant, and the energy of the first level is hω_i1/ 2π,SaidThe energy of the second level is hω_i2/ 2π, the energy of the third level is hω_i3/ 2π, | ω_i3−ω_i1|_i31, | Ω_i3−ω_i2|_i32, Ω among the N physical structures_i31The maximum value of max (ω_i31) Among the N physical structures_i32Min (ω_i32),Among the N physical structures, ω _i31 Min (ω _i31 ) Among the N physical structures _i32 The maximum value of max (ω _i32 ),The angular frequency of the first coherent light is ω_p, The angular frequency of the first coherent light is ω_cMin (ω_i31) <Ω_p<Max (ω_i31) And min (ω_i32) <Ω_c<Max (ω_i32And a means for changing the angular frequency of the first and second coherent lights within a range that satisfies the condition of (1).
[0032]
Here, the physical structure means a quantum structure such as a quantum dot, a quantum wire, or a quantum box, a crystal defect such as a point defect, and an impurity atom.
[0033]
Another recording / reproducing apparatus according to the present invention (Claim 6) is the same as the recording / reproducing apparatus (Claim 5), except that_p−ω_cIs set to Δω, the optical system has means for changing the angular frequency of the first and second coherent light under the condition that Δω is constant.
[0034]
Here, the number N of physical structures is the number of physical structures included in the portion irradiated with coherent light, and may be the number of physical structures included in the entire solid as the object to be detected. In some cases, the number of physical structures included in this part.
[0035]
According to another recording / reproducing apparatus of the present invention (Claim 7), in the recording / reproducing apparatus (Claim 5), the solid causes a structural change when electrons are excited to the level. A fourth level, and the optical system converts the energy of the fourth level to hω_i4/ 2π, ω_i4−ω_i1|_i41, | Ω_i4−ω_i2|_i42, | Ω_i4−ω_i3|_i43, Ω among the N physical structures_i41The maximum value of max (ω_i41), Min (ω_i41) Among the N physical structures_i42The maximum value of max (ω_i42), Min (ω_i42) Among the N physical structures_i43The maximum value of max (ω_i43), Min (ω_i43), The rabbi frequency of the first coherent light is Ω_p, The rabbi frequency of the second coherent light is Ω_cWhen Ω_p<Ω_cIn this case, the first and second coherent lights and min (ω_i41) Greater than max (ω_i41) Smaller angular frequency, or min (ω_i43) And max (ω_i43) Irradiating a third coherent light having an angular frequency smaller than_p> Ω_cIn this case, the first and second coherent lights and min (ω_i42) And max (ω_i42) Less angular frequency, or min (ω_i43) And max (ω_i43And a means for irradiating a third coherent light having an angular frequency smaller than.
[0036]
According to another recording / reproducing apparatus of the present invention (Claim 8), in the recording / reproducing apparatus (Claims 5 to 7), the optical system includes the first coherent in the recording medium. And a means for measuring at least one of light absorption and fluorescence of the recording medium generated through absorption of the first coherent light.
[0037]
Further, another recording / reproducing apparatus according to the present invention (Claim 8) is the same as the recording / reproducing apparatus (Claims 5 to 7) described above._i2−ω_i1|_i21(Ω in N physical structures_i31, Ω_i32) Is changed to record information on the recording medium, and the (ω_i31, Ω_i32) Distribution or ω_i21The above information is reproduced by detecting the distribution of.
[0038]
Rabi frequency in Ω_p, The rabbi frequency of the second coherent light is Ω_cWhen Ω_p<Ω_c, The first and second coherent light and min (ω_i41) Greater than max (ω_i41) Smaller angular frequency, or min (ω_i43) And max (ω_i43) Irradiating the recording medium with a third coherent light having an angular frequency smaller than_p> Ω_c, The first and second coherent light and min (ω_i42) And max (ω_i42) Less angular frequency, or min (ω_i43) And max (ω_i43And a light irradiating means for irradiating the recording medium with a third coherent light having an angular frequency smaller than.
[0039]
Also, (ω_i31, Ω_i32) Distribution, and thus ω_i21In order to efficiently change the distribution of the light, it is preferable to simultaneously apply the electric field and the magnetic field simultaneously with the irradiation of the first, second, and third coherent light.
[0040]
Furthermore, in the present invention, the line width of the second coherent light is set to δω_c, The uniform width for the transition between the first level and the third level ω_homo31Δω_c≦ ω_homo31It is desirable to satisfy the following conditions.
[0041]
[Action]
According to the present invention, by adopting a completely new recording / reproducing principle that utilizes the extremely high frequency resolution of the EIT phenomenon, it is possible to realize recording / reproducing with the state of each atom or molecule as a recording unit. Like that.
[0042]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments (embodiments) of the present invention will be described below with reference to the drawings.
[0043]
(First embodiment)
In the following description, the first level, the second level, and the third level (state vector) are expressed as | i1>, | i2>, and | i3>, respectively.
[0044]
Regarding the relationship between the three levels and the light, there are four types of excitation (Energy Scheme) as shown in FIG. 1. Hereinafter, an explanation will be given by taking an example of an excitation type called Λ type shown in FIG. To do. In the case of the Λ type, | i1> (| 1>), | i2> (| 2>), and | i3> (| 3>) in ascending order of energy.
[0045]
In the case of the V type shown in FIG. 1B, contrary to the case of the Λ type, the three levels are | i1> (| 1>), | i2> (| 2>) and | i3> (| 3>), the same argument as in the case of the Λ type holds.
[0046]
In the case of a saddle-excited type, as shown in FIG. 1 (c), the three levels are set in order from the highest energy | i1> (| 1>), | i3> (| 3>), | I2> (| 2>) or, as shown in FIG. 1 (d), | i1> (| 1>), | i3> (| 3>), | i2> in order from the lowest energy By setting (| 2>), the same argument as in the case of the Λ type holds.
[0047]
First, an EIT characteristic with one physical structure will be described.
[0048]
The EIT is composed of three levels related to a single physical structure and two laser beams connecting the levels. In the Λ type, | i1> → | i3> and | i2> → | 3> are permissible transitions, but | 1> → | 2> is selected as a forbidden transition.
[0049]
The light that connects the ground states | 1> and | 3> is called probe light, and the light that connects the above two levels | 2> and | 3> is called coupling light.
[0050]
Also, the probe light frequency ω_pAnd | 1> → | 3> resonance frequency 2π · ε corresponding to the energy difference between levels₃₁Δω is the frequency difference from / h_p, Coupling light frequency ω_cAnd | 2> → | 3> resonance frequency 2π · ε corresponding to the energy difference between levels_{twenty one}Δω is the frequency difference from / h_cAnd
[0051]
Each intensity is expressed by a rabi frequency Ωc, Ωp defined by the following equation.
[0052]
Ωc = 2π <3 | μ · E | 2> / h (1₁)
Ωp = 2π <3 | μ · E | 1> / h (1₂)
Here, μ is an operator related to the dipole moment, and E is an operator related to the electric field.
[0053]
Next, let us consider a state in which the lower two levels as shown in the following equation are removed at each rabbi frequency to obtain a linear combination.
[0054]
* +> = (Ωc | 1> + Ωp | 2>) / (Ωc²+ Ωp²)^1/2  (2₁)
*-> = (Ωc | 1> -Ωp | 2>) / (Ωc²+ Ωp²)^1/2  (2₂)
Here, when the detuning of the two laser beams is equal, that is, Δω_c= Δω_pIn this case, considering the time variation of the population related to the three-level system, it is easily shown that the population of *-> does not increase or decrease.
[0055]
Therefore, in the steady state, the probability of occupying *-> level is 1. This is a phenomenon called population trapping. At this time, regarding the transition dipole moment between *-> and | 3>,

Strictly 0 and no absorption occurs. This is EIT. As a physical origin at which absorption does not occur, it can be considered that the transition of | 1> → | 3> and | 2> → | 3> is canceled by the interference effect in |->.
[0056]
Formula (2₁), (2₂As apparent from the above, |->, which is the level to be trapped, is constituted by the rabbi frequency, that is, the ratio of the light intensity with respect to | 1> and | 2>. Therefore, the property of |-> can be changed by changing the light intensity.
[0057]
In the case of Ωc >> Ωp, it is trapped in the state of |-> to | 1>, that is, a state close to the ground state. On the other hand, when Ωc << Ωp, it is trapped in a state close to the lower excited state | 2>.
[0058]
The shape of the absorption spectrum from | 1> to | 3> when EIT is occurring is shown in FIG._p= Δω_cΩ that satisfies the condition_pAn absorption hole, that is, a transparent region, is formed at the position of.
[0059]
Δω_cWhen = 0, as shown in FIG. 2A, Δω_p= 0, that is, a hole is formed at the center of the absorption spectrum.
[0060]
Δω_cWhen ≠ 0, as shown in FIG. 2B, a hole is formed in the region of the bottom of absorption.
[0061]
The width of the hole is substantially equal to the Rabi frequency Ωc of the coupling light. Therefore, the hole width can be controlled by changing the intensity of the coupling light.
[0062]
Next, EIT characteristics when there are a plurality of physical structures (N cases) will be described.
[0063]
As described above, the solid width and the non-uniform width are wider in the solid system than in the atomic gas system. For this reason, the spectrum of the solid system is a very wide spectrum in which the spectra of the individual physical structures spread by a uniform width are overlapped with their center positions distributed. Such a situation applies not only to the transition of | 1> → | 3> but also to the transition of | 2> → | 3>.
[0064]
Therefore, as in the EIT experiment conducted in the atomic gas system, ω_cThe EIT signal observed in a state where is fixed is (ε_i31, Ε_i32) Due to the distribution, the number of physical structures that meet the EIT condition that detuning is equal is reduced, resulting in a very small signal as shown in FIG.
[0065]
Not only that, but the characteristics such as where the contribution of one physical structure to the EIT characteristics of the whole system appears are not so clear. Thus, so far, ω_pΩ on axis_pThe EIT characteristics of each physical structure appearing in the absorption characteristics of the above are not only difficult to detect, but the method for controlling them is not clear, and it is considered difficult to consider any application.
[0066]
The fundamental principle of recording / reproduction at the single physical structure (molecule / atom) level of the present invention is (ω_p, Ω_c) On the plane_pIt is to consider the change of absorption characteristics. This not only detects the EIT characteristics of the physical structure, but also describes the EIT characteristics (ε_i31, Ε_i32) Distribution can be changed, and recording / reproduction at a single physical structure level is possible.
[0067]
First, consider one physical structure. Ω to ｜ 1> → | 3>_pThe coupling light frequency ω_cThe amount of change when (_p, Ω_c) Think on a plane.
[0068]
FIG. 4 shows the characteristics under the condition of Ωp <Ωc <(uniform width). The phenomenon itself that appears in the spectrum is very simple. As shown in FIG. 4 (a), of course, ω_cIf you cut on the plane of const.
[0069]
The condition for EIT to occur is Δω_p= Δω_cAnd (ω_p= Ω₃₁= 2πε₃₁/ H, ω_c= Ω₃₂= 2πε₃₂/ H)_pIt happens on a line that makes an angle of 45 degrees with the axis.
[0070]
FIG. 4B shows a state in which the spectrum is viewed from the direction of 45 degrees, and it can be seen that a narrow hole corresponding to the Rabi frequency of the coupling light is opened.
[0071]
When only the hole portion is extracted, as shown in FIG. 4C, the absorption spectrum of a single physical structure is rotated by 45 degrees, and a thin plate-like spectrum having a thickness of about Rabi frequency is obtained. I understand that.
[0072]
Next, consider a case where there are a plurality of physical structures. The thin plate-shaped absorption holes that each physical structure is caused by EIT are (ω_p, Ω_c) On the plane, corresponding to the energy between levels of each physical structure (ω_i31(i), ω_i32(i) It occurs centering on the point).
[0073]
In solid systems, the non-uniform width is wide and ω_i31(i) and ω_i32(i) are each ω_pAxis, ω_cDistributed on the axis. For this reason, if the rabbi frequency is reduced and the thickness of each plate is reduced, the contribution of each physical structure is (ω as shown in FIG._p, Ω_c) It is possible to completely separate on a plane.
[0074]
Thus, (ω_p, Ω_c) On the plane_pThe absorption hole due to each physical structure appears separately for each physical structure, and the center position is (ω_i31(i), ω_i32(i) It becomes point.
[0075]
Therefore, (ω_p, Ω_c) By observing the EIT signal of the whole system on the plane and examining where the plate-like hole appearing in the absorption appears, the energy ε of each physical structure_i31, Ε_i32The position of will be understood.
[0076]
Thus, (ω in N physical structures_i31, Ω_i32) Distribution is changed by, for example, laser irradiation, and information is recorded on a recording medium,_i31, Ω_i32) Is detected, information can be reproduced.
[0077]
Here, as shown in FIGS. 4 and 5, (ω_p, Ω_c) On the plane_pIn order to detect the absorption characteristics of_cWith respect to ω_pIt is essential to measure the absorption. That is, multiple (ω_p, Ω_cIt is preferable to reproduce the information recorded on the recording medium by measuring the absorption characteristics of the set.
[0078]
This is because a single ω_c= Ω_c ⁰With respect to ω_pWhen measuring the absorption of ω, the absorption characteristics as shown in FIGS._c= Ω_c ⁰(= Const.) A spectrum having a cross-sectional shape cut by a plane, ε_i31, Ε_i322πε in a physical structure with a wide distribution of energy_i32~ Hω_c ⁰This is because there is a possibility of detecting an absorption hole only for a physical structure that satisfies the above relationship.
[0079]
Furthermore, even if 2πε_i32~ Hω_c ⁰Even if the relationship_c= Ω_c ⁰If the extreme value of the absorption hole does not exist on the plane, the signal corresponding to the absorption hole is very weak and it is difficult to identify the position of the hole.
[0080]
Set ω_c ⁰For the value of ω_c= Ω_c ⁰It is rarely stochastic to include the extreme value of the absorption hole above. From this, a single ω_cNot multiple ω_cAbout ω_pIt can be seen that the measurement of the absorption of γ is an indispensable element for detecting the absorption holes due to the individual physical structures in the energetically distributed physical structure group.
[0081]
The absorption holes shown in FIG. 4 and FIG. 5 are obtained by rotating the absorption spectrum of a single physical structure by 45 degrees._c= Ω_pThe width in the direction parallel to + const. Is about the uniform width of a single physical structure spectrum.
[0082]
Therefore, to detect each absorption hole,_pAs well as the line width of coherent light corresponding to ω_cIt is desirable that the line width of the coherent light corresponding to is equal to or less than the uniform width.
[0083]
Also, ω at the time of measurement_pIs not only equal to or less than the uniform width, but also multiple ω_cIt is desirable that each of the intervals be equal to or less than the uniform width.
[0084]
(Second Embodiment)
(Ω_p, Ω_c) In the plane, ω_pIn addition to the individual detection of the absorption holes, the following integrated intensity of absorption is also an important means for reproducing the information recorded on the recording medium in the present invention. Now (ω_p−ω_c) = Δω value is constant.
I_ab(Δω) = ∫I_ab(Ω_p; Ω_p−Δω) dω_p
Think of the integral.
[0085]
First, characteristics in the case of one physical structure will be described. This I_ab(Δω) is (ω_p, Ω_c) In the plane, ω_pI in the direction of 45 degrees with the axis_ab(Ω_p; Ω_c) Is integrated.
[0086]
In FIG._abThe distribution of (Δω) is shown. Width corresponding to the hole in Fig. 4 (b)_cNarrow hole, Δω = ω₃₁−ω₃₂= Ω_{twenty one}It can be seen that the value is in the vicinity of) and takes a constant value in other regions. This constant value is a physical quantity unique to the physical structure, that is, the integrated intensity of absorption of one physical structure, I₀= ∫I⁰ _ab(Ω_pDω_pMatches.
[0087]
FIG. 7 shows I when the temperature is changed._ab(Ω_p; Ω_c) And ΔI_ab(Ω_p; Ω_c). As shown in FIG._ab(Ω_p; Ω_c) And ΔI_ab(Ω_p; Ω_c) Extends in the direction of 45 degrees, but I_abIt can be seen that (Δω) does not change at all.
[0088]
FIG. 8A and FIG. 8B show I in the case where there are a plurality of physical structures, respectively._ab(Δω) distribution, ΔI_abThe distribution of (Δω) is shown. I_ab(Δω) includes NI₀As the baseline, then I₀Integer depth and width Ω_cA hole with is produced. ΔI in FIG. 8B_abThe distribution of (Δω) corresponds to a reverse of the sign obtained by extracting only the hole portion.
[0089]
The height and depth of these rod-like spectra are defined as I₀The integer value obtained by dividing by ω is_{twenty one}Means the number of physical structures whose value is equal to Δω. Again, I_ab(Δω) and ΔI_abNeedless to say, (Δω) does not depend on temperature.
[0090]
Because of this, I_ab(Δω) and ΔI_abIf (Δω) is measured and used for reproducing information recorded on a recording medium, extremely stable information reproduction can be performed without depending on temperature.
[0091]
I_ab(Ω_p; Ω_c) Or ΔI_ab(Ω_p; Ω_c) Is used for information reproduction,_i31, Ω_i32) Can be reproduced at a single physical structure level, while I_ab(Δω) and ΔI_abWhen (Δω) is used for information reproduction, ω_i21Can be reproduced at a single physical structure level.
[0092]
Not only absorption but also emission
I_lu(Δω) = ∫I_lu(Ω_p; Ω_p−Δω) dω_p
Or
I_lu(Δω) = ∫ {I⁰ _lu(Ω_p) -I_lu(Ω_p; Ω_p−Δω)} dω_p
The same effect can be obtained when information is reproduced by measuring.
[0093]
(Third embodiment)
Next, information recording will be described.
[0094]
In the present invention, (ω_p, Ω_c) Information is recorded on the recording medium by changing the energy level distribution of the physical structure in the plane.
[0095]
In order to change the energy level distribution, for example, by irradiating the recording medium with light or an electron beam, applying an electric field or magnetic field to the recording medium, or applying pressure to the recording medium, one of the physical structure group is changed. What is necessary is just to excite a part and to change the energy level.
[0096]
In particular, in order to record information at a single physical structure level (molecular / atomic level), the present invention uses the above-mentioned Population Trapping (ω)_i31, Ω_i32) Distribution or ω_i21Transform the distribution of s at the single physical structure level.
[0097]
Specifically, as in the case of playback, the angular frequency ω_p, Ω_c, Rabi frequency Ω_p, Ω_cThe first and second coherent light beams are simultaneously irradiated onto the recording medium by, for example, a laser to cause a certain physical structure to be population trapped. An angular frequency ω for exciting to the level that ionizes from that level, | i4>_exThe third coherent light is also irradiated by a laser, for example.
[0098]
It will be described with reference to what kind of physical structure changes state by such a method. (Ω_p, Ω_c) In the plane, the population trap due to the irradiation of the first and second coherent light has a point (ω_p, Ω_c) On the 45 degree line (ω_i31, Ω_i32) Cause a physical structure.
[0099]
here,
Ω_p<Ω_c
In this case, the physical structure is trapped in a state of | i1>. Therefore, the angular frequency ω that causes a transition between | i1> and | i4> as shown in FIG._exBy irradiating the third coherent light of
ω_ex= Ω_i41
A physical structure satisfying the condition is selectively excited to | i4> to cause ionization or structural change. And angular frequency ω_exBy irradiating a plurality of third coherent lights having different values, as shown in FIG._i31, Ω_i32) Can be perforated.
[0100]
Also Ω_p> Ω_cIn this case, the physical structure is trapped in a state of | i2>. Therefore, as shown in FIG. 12, an angular frequency ω that causes a transition between | i2> and | i4>._exOf the third coherent light L of
ω_ex= Ω_i24
A physical structure satisfying the condition is selectively excited to | i4> to cause ionization or structural change. And also in this case, the angular frequency ω_exBy irradiating a plurality of third coherent lights having different values, as in the case of FIG._i31, Ω_i32) Can be perforated.
[0101]
It is also possible to selectively cause a state change even for a physical structure that has not caused a population trap.
[0102]
FIG. 13 shows the distribution of the physical structure that is excited to | i3> without causing a population trap and absorbing the first coherent light under irradiation of the first and second coherent lights.
[0103]
Therefore, the angular frequency ω that causes a transition between | i3> and | i4> as shown in FIG._exBy irradiating the third coherent light of
ω_ex= Ω_i34
A physical structure satisfying the condition is selectively excited to | i4> to cause ionization or structural change. And also in this case, preferably the angular frequency ω_exBy irradiating a plurality of third coherent lights having different values, as in the case of FIG._i31, Ω_i32) Can be perforated.
[0104]
(Ω_i31, Ω_i32) Distribution over a wide range, when recording information,_p, Ω_cThe same operation may be performed on the value of).
[0105]
In addition, by simultaneously applying the voltage and the magnetic field together with the irradiation of the first, second, and third coherent light, the energy level of each physical structure changes, and ω_i31, Ω_i32, Ω_i41The value of etc. changes.
[0106]
Therefore, (ω_p, Ω_c) Without changing the value of (ω_i31, Ω_i32) Distribution can be changed, and information can be recorded efficiently.
[0107]
(Fourth embodiment)
In this embodiment, a YAG crystal containing 0.1 mol% of Eu as an impurity is used as a recording medium.
[0108]
FIG. 15 shows the energy level of Eu. Eu ground state is⁷F₀so,⁷F₀To 18950cm^-1On the high energy side^FiveD₁There is an excited state⁷F₀A strong optical transition occurs between
[0109]
Also,⁷F₀From 460cm^-1On the high energy side⁷F₁There is an excited state^FiveD₁A strong optical transition occurs between further,⁷F₀To 36000cm^-1~ 42000cm^-1A charge transfer state continuously exists in the vicinity of the high energy side, and the Eu atom in which electrons are excited changes the valence from +3 valence to +2 valence.
[0110]
This recording medium is put into a temperature-variable cryostat having an optical window with a transparent visible region, and the sample temperature is kept at 4K by cooling with liquid helium. In this state, the recording medium is irradiated with two ring dye lasers excited by an argon ion laser. Both laser dyes that drive two ring dye lasers have a tuning range of 17240-19230 cm.^-1Use coumarin.
[0111]
Here, the oscillation line width of the ring dye laser is 500 kHz = 0.000017 cm.^-1Adjust so that One of the ring dye lasers (L1) has an oscillation frequency ω._p18950cm^-1Nearby, another (L2) is its oscillation frequency ω_c18490cm^-1Adjust to sweep the neighborhood. The laser light intensity is set so that the Rabi frequencies of the lasers L1 and L2 are 3 MHz and 17 MHz, respectively.
[0112]
First, Eu energy distribution before information was recorded on the recording medium was detected by the following method. That is, the information recorded before recording new information on the recording medium was reproduced by the following method.
[0113]
First, the laser L2 is not irradiated, and the oscillation frequency of the laser L1 is 18945.00000 cm.^-1To 18955.0000cm^-1The absorption spectrum of the laser L1, I⁰ _ab(Ω_p) Is detected.
[0114]
Next, the oscillation frequency of the laser L2 is 18485.00000 cm.^-1The laser L1 oscillation frequency is 18945.00000 cm^-1To 18955.0000cm^-1The absorption spectrum of the laser L1, I_ab(Ω_p; Ω_c) And I⁰ _ab(Ω_p), ΔI_ab(Ω_p; Ω_c) = I⁰ _ab(Ω_p) -I_ab(Ω_p; Ω_c)
[0115]
Next, the oscillation frequency of the laser L2 is 0.0002 cm.^-1Increase 18485.0002cm^-1The laser L1 oscillation frequency is again 18945.00000 cm^-1To 18955.0000cm^-1The absorption spectrum of the laser L1, I_ab(Ω_p; Ω_c) And detect ΔI_ab(Ω_p; Ω_c)
[0116]
In this way, the oscillation frequency of the laser L2 is sequentially changed to 0.0002 cm.^-1The process of detecting the absorption spectrum of the laser L1 each time it is increased, the oscillation frequency of the laser L2 is 184955000 cm^-1Continue until
[0117]
FIG. 16 shows ΔI obtained in this way._ab(Ω_p; Ω_c) Part of the oscillation frequency ω of the laser L1_pAnd laser L2 oscillation frequency ω_cAre two coordinate axes (ω_p, Ω_c) It is illustrated in the plane. From FIG. 16, it can be seen that absorption holes associated with EIT of each pseudo atom (physical structure) are observed.
[0118]
FIG. 17 shows that Δω = ω_p−ω_cThe value of 12MHz = 0.004cm^-1Set for each
ΔI_ab(Δω) = ∫ {I⁰ _ab(Ω_p) -I_ab(Ω_p; Ω_p−Δω)} dω_p
Is obtained for each Δω. ΔI_abIt was observed that the value of (Δω) was an integral multiple of a certain value as a unit.
[0119]
Next, a case where new information is recorded on this recording medium will be described.
[0120]
In order to record information, lasers L1 and L2 having a rabbi frequency set to 17 MHz and 3 MHz, respectively, are irradiated, and another ring dye laser L3 (oscillation frequency ω) is used._ex), And the recording medium is irradiated with a second harmonic obtained by irradiating the BBO crystal with output light of coumarin dye excitation.
[0121]
Information was recorded sequentially under the following conditions.
[0122]
(1) ω_p= 18952.0020cm^-1, Ω_c= 18486.000cm^-1, Ω_ex= 38000-40000cm^-1
(2) ω_p= 18952.000cm^-1, Ω_c= 18486.0020cm^-1, Ω_ex= 40000-42000cm^-1
(3) ω_p= 18952.000cm^-1, Ω_c= 18486.0120 cm^-1, Ω_ex= 38000-40000cm^-1
18, 19, and 20, the laser L <b> 3 is stopped after the steps (1) to (3), and the lasers L <b> 1 and L <b> 2 are reset with the rabbi frequencies set to 3 MHz and 17 MHz, respectively. ΔI_ab(Ω_p; Ω_c).
[0123]
As can be seen from the comparison with FIG. 16, the ω used for recording in the absorption hole of each physical structure._p, Ω_cIt can be seen that some of the holes located in the direction of 45 degrees with the value of have disappeared. It can also be seen that even if a new recording is performed, the information recorded so far does not change.
[0124]
FIG. 21 shows the measured ΔI after the procedure of (3)._abThis is a result of (Δω).
[0125]
As can be seen from FIG. 21, Δω = 4655.9880 cm.^-1ΔI at_abThe value of (Δω) is from 5 to 2, Δω = 4655.9980 cm^-1ΔI at_abThe value of (Δω) is changed from 5 to 1, and Δω = 466.0020 cm^-1ΔI at_abThe value of (Δω) changed from 4 to 1.
[0126]
It should be noted that this ΔI is again raised after the sample temperature is raised to room temperature._abWhen (Δω) was measured, the same measurement results as in FIG. 21 were obtained, and ΔI_abThe stability with respect to temperature of the recording method of this embodiment using (Δω) as recording data was confirmed.
[0127]
(Fifth embodiment)
As in the case of the fourth embodiment, a YAG crystal containing 0.01 mol% of Eu as an impurity was used for the recording medium. However, in this embodiment, Au is vapor-deposited on the two side surfaces of the YAG crystal to form electrodes. This electrode is for applying an electric field as an external field to the recording medium.
[0128]
In the present embodiment, information is recorded on a recording medium as follows.
[0129]
In other words, the angular frequency ω_pIs 1895.0020cm^-1Laser L1, fixed at the angular frequency ω_cIs 18486.0000cm^-1The recording medium is irradiated with the laser L2 fixed to the angular frequency ω in one minute on the recording medium._ex38000-40000cm^-1The laser 3L swept up to is irradiated. In addition, a voltage obtained by sweeping a triangular wave between 1 V and 5 V at 1 Hz is applied to the electrode.
[0130]
22 and 23 show ΔI before and after recording, respectively._abIt is a figure which shows the change of ((DELTA) omega).
[0131]
In the first embodiment, the value of Δω is the angular frequency ω._pAnd angular frequency ω_cWhere ΔI is equal to_abRecording was performed with the value of (Δω) changed. In this embodiment, Δω = 465.980 cm.^-1ΔI in a wider area as well as_abThe value of (Δω) has changed.
[0132]
This is the angular frequency ω_p, Ω_cEven if the value of is fixed, the energy level of each physical structure is changed by the electric field, and the physical structure that satisfies the conditions of the population trap is changed by each electric field. As a result, the physical structure excited to | i4> It is because it increased. It was confirmed that information can be efficiently recorded on a recording medium by using an electric field in this way.
[0133]
In the present embodiment, the case of an electric field as an external field has been described. However, in the case of other external fields such as a magnetic field, temperature, and pressure, a change in the optical spectrum of each physical structure can be similarly detected.
[0134]
(Sixth embodiment)
In this embodiment, as in the fourth and fifth embodiments, a YAG crystal containing 0.1 mol% of Eu as an impurity is used for the recording medium. The feature of this embodiment is that the recorded information is reproduced by measuring fluorescence instead of light absorption.
[0135]
As shown in FIG. 24, the recording medium of this embodiment is^FiveD₁About 2415cm^-1On the high energy side^FiveD₂There is an excited state, and from this state⁷F₀21360 cm when electrons transition to^-1It shows strong fluorescence with a wave number of about.
[0136]
So without being a population trap,^FiveD₁For the Eu atom excited to 2300-2500 cm as the third coherent light^-1Pb that oscillates near infrared rays_1-xCd_xS or PbS_1-xSe_xSelectively using semiconductor laser etc.^FiveD₂From there,⁷F₀Fluorescence can be detected when excited to.
[0137]
Here, the first and second coherent lights are the same as those in the fourth embodiment, and the peak frequency of the oscillation frequency is particularly 2411 cm as the third coherent light.^-1, PbS with Rabi frequency 0.2MHz_1-xSe_xUsing the semiconductor laser L3, Eu energy distribution before recording information on a recording medium was detected by the following method. That is, the information recorded before recording new information on the recording medium was reproduced by the following method.
[0138]
First, the laser L2 is not irradiated, the laser L3 is irradiated, and the oscillation frequency of the laser L1 is 18945.00000 cm.^-1To 18955.0000cm^-121000cm observed when continuously changing^-1Fluorescence intensity I at the above wave numbers⁰ _lu(Ω_p) Is detected using a filter and a photo counter.
[0139]
Next, the oscillation frequency of the laser L2 is 18485.00000 cm.^-1With the laser L3 irradiated, the oscillation frequency of the laser L1 is 18945.00000 cm^-1To 18955.0000cm^-121000cm observed when continuously changing^-1Fluorescence intensity I of the above wave number_lu(Ω_p; Ω_c) And fluorescence intensity I⁰ _lu(Ω_p), ΔI_lu(Ω_p; Ω_c) = I⁰ _lu(Ω_p) -I_lu(Ω_p; Ω_c)
[0140]
Next, the oscillation frequency of the laser L2 is 0.0002 cm.^-1Increase, 18485.0002cm^-1With the laser L3 irradiated, the oscillation frequency of the laser L1 is 18945.00000 cm^-1To 18955.0000cm^-121000cm observed when continuously changing^-1I of above wave number_lu(Ω_p; Ω_c) And detect ΔI_lu(Ω_p; Ω_c)
[0141]
Thus, the oscillation frequency of the laser L2 is sequentially changed to 0.0002 cm.^-1Increasing the emission intensity I each time_lu(Ω_p; Ω_c) And detect ΔI_lu(Ω_p; Ω_c), The laser L2 oscillation frequency is 184955.0000 cm^-1Continue until
[0142]
FIG. 25 shows ΔI obtained in this way._lu(Ω_p; Ω_c) Part of the oscillation frequency ω of the laser L1_pAnd laser L2 oscillation frequency ω_cAre two coordinate axes (ω_p, Ω_c) It is illustrated in the plane. As in FIG. 16, it can be seen that fluorescent holes associated with the EIT of each pseudo atom (physical structure) are observed.
[0143]
However, the difference from FIG. 16 is that the number of holes is small. This is because the line width of the laser L3 is^FiveD₁From^FiveD₂Narrower than the non-uniform width of the transition to^FiveD₁All of the Eu atoms excited to^FiveD₂This is due to the fact that they are not excited.
[0144]
In addition, PbS_1-xSe_xIncrease the drive current passed through the semiconductor laser L3 to increase the oscillation frequency to 2413cm^-1In the same way as above, ΔI_lu(Ω_p; Ω_c) Is shown in FIG.
[0145]
(Ω_p, Ω_c) Although the planar region is the same as that in FIG. 25, it can be clearly seen that a fluorescence hole is observed accompanying EIT of a pseudo atom (physical structure) different from that in FIG.
[0146]
In this way, by changing the drive current flowing to the laser L3 and changing the oscillation frequency,^FiveD₁From^FiveD₂If the entire range of the non-uniform width of the transition to is scanned, the EIT signal (information) regarding all Eu atoms can be observed (reproduced) by fluorescence. (Seventh embodiment)
Here, a method for reproducing information recorded on a recording medium and a method for recording new information using the recording / reproducing apparatus of the present invention will be specifically described.
[0147]
FIG. 27 is a diagram schematically showing a recording / reproducing apparatus in the present embodiment. In the reproduction of information, the recording medium 13 is irradiated with output light from the two ring dye lasers 11 and 12.
[0148]
The output light of the laser 11 passes through the recording medium 13 and is then input to the output detection photomultiplier 14. Output I of photomultiplier 14^S _PM1(Ω_p) Is an analog signal, it is converted into a digital signal by the AD converter 15 and then input to the data control personal computer 16.
[0149]
Here, in order to convert the intensity of incident light on the recording medium 13, a part of the output light from the laser 11 is branched by the beam splitter 17 and then input to the photomultiplier 18, which is the intensity of the branched light. Photomultiplier 18 output^S _PM2(Ω_p) Output I^S _PM2(Ω_p) Is also converted into a digital signal by the AD converter 19 and then input to the data control personal computer 16.
[0150]
Further, in order to obtain absorption spectrum data, the output I of each of the photomultipliers 14 and 18 when there is no recording medium 13 is obtained.⁰ _PM1(Ω_p), I^S _PM2(Ω_p) Are measured in advance, and these are input to the data control personal computer 16.
[0151]
Regardless of whether or not the output light of the laser 12 is irradiated, the angular frequency ω_pAbsorption I_ab(Ω_p) Is defined by the following equation.
[0152]
I_ab(Ω_p) = (1 / I⁰ _PM1(Ω_p)) (I⁰ _PM1(Ω_p) -I^S _PM1(Ω_p) ・ I_PM2(Ω_p) / I^S _PM2(Ω_p))
The data control personal computer 16 performs an arithmetic process corresponding to this equation and performs absorption I_ab(Ω_p) Further, the data control personal computer 16 includes an angular frequency ω from the ring dye laser control personal computers 21 and 28._p, Ω_cIs input as a signal.
[0153]
By such a procedure, the absorption spectrum data I under the irradiation of the laser 12 is obtained._ab(Ω_p; Ω_c), Absorption spectrum I when the laser 12 is not irradiated⁰ _ab(Ω_p) Each (ω_p, Ω_c) Set of values, ω_pThe reproduction data is stored in the hard disk of the personal computer 16 for data control.
[0154]
When the amount of data is large, it is also possible to transfer the data from the hard disk of the data control personal computer 16 to a large-capacity external storage device 22 such as a magnetic disk and store the data. Further, when the reproduction data is viewed on the screen, the data may be transferred to the display 23.
[0155]
In order to newly record information on the recording medium 13, the following procedure is performed.
[0156]
That is, in addition to the output lights of the lasers 11 and 12, the output lights of the ring dye laser 24 and the excimer laser 25 are also incident on the dye amplifier 26 for increasing the output. The laser light output from the dye amplifier 26 is incident on the BBO crystal 27 which is a nonlinear optical crystal, and the obtained two high waves are applied to the recording medium 13, and information is recorded by the method described in the fourth embodiment.
[0157]
At this time, the value of the oscillation frequency of the laser 24 is input from the personal computer 28 to the data control personal computer 16 as a signal.
[0158]
As described above, since it is important to monitor the light intensity of the lasers 11, 12, and 24 at the time of recording / reproducing information, not only the laser 11 but also part of the output light of the lasers 12 and 24 is included. After being branched by the beam splitters 29 and 30, the respective branched lights are input to the photomultipliers 31 and 32, and the outputs of the photomultipliers 31 and 32 are converted into digital signals by the AD converters 33 and 34, respectively. Then, the data is input to the data control personal computer 16 and the intensity of the output light of the lasers 12 and 24 is measured. In the figure, reference numerals 35 to 40 denote mirrors.
[0159]
【The invention's effect】
As described in detail above, according to the present invention, recording / reproducing information with the state of atoms and molecules as a recording unit is achieved by adopting a completely new recording / reproducing principle that utilizes the extremely high frequency resolution of the EIT phenomenon. Can be realized.
[Brief description of the drawings]
FIG. 1 shows a model of a three-level system
FIG. 2 is an angular frequency ω of probe light representing EIT characteristics of one physical structure._pOf absorption spectrum for
FIG. 3 is an angular frequency ω of probe light representing EIT characteristics of N physical structures._pOf absorption spectrum for
FIG. 4 shows an angular frequency ω of probe light with respect to one physical structure._pOf absorption spectrum for
FIG. 5 shows the angular frequency ω of the probe light with respect to N physical structures._pReversing the sign of the absorption hole observed in the absorption spectrum for ω_p−ω_cFigure shown on the plane
FIG. 6 is a diagram of I relating to one physical structure for explaining the information recording principle in the second embodiment;_abDiagram showing (Δω)
FIG. 7 is a diagram of an I physical structure for explaining the information reproduction principle in the second embodiment;_ab(Ω_p; Ω_c), ΔI_ab(Ω_p; Ω_c) Distribution
FIG. 8 is a diagram illustrating an I physical structure for explaining an information reproduction principle in the second embodiment._ab(Ω_p; Ω_c), ΔI_ab(Ω_p; Ω_c) Distribution
FIG. 9 is a diagram showing an energy distribution of a physical structure that is populated by the irradiation of the first and second coherent lights.
FIG. 10 shows Ω in the third embodiment._p<Ω_cFor explaining the recording method in the case of
FIG. 11 shows a physical structure that is excited to the fourth level by irradiation with the third coherent light, and causes ionization or structural change in the physical structure that is populated by the irradiation with the first and second coherent light. Diagram showing energy distribution of structure
FIG. 12 shows Ω in the third embodiment._p> Ω_cFor explaining the recording method in the case of
FIG. 13 is a diagram showing an energy distribution of a physical structure that is not populated by the irradiation of the first and second coherent light and is excited to the third level by absorbing the first coherent light.
FIG. 14 is a diagram for explaining a recording method for a physical structure that does not cause a population trap;
FIG. 15 is an energy level diagram of Eu used in the fourth embodiment.
FIG. 16 shows ΔI measured before recording in the fourth embodiment._ab(Ω_p; Ω_c), 18952.00000cm^-1<Ω_p<18952.0200cm^-1, 18486.0000cm^-1<Ω_c<18486.0200cm^-1The figure which expands and shows the area
FIG. 17 shows ΔI measured before recording in the fourth embodiment._abWith respect to (ω), 465.9880 cm^-1<Δω <466.0020cm^-1The figure which expands and shows the area
FIG. 18 shows ΔI read after the information recording operation (1) in the fourth embodiment._ab(Ω_p; Ω_cFigure showing
FIG. 19 shows ΔI read after information recording operations (1) and (2) in the fourth embodiment._ab(Ω_p; Ω_cFigure showing
FIG. 20 shows ΔI read after information recording operations (1), (2), and (3) in the fourth embodiment._ab(Ω_p; Ω_cFigure showing
FIG. 21 shows ΔI read after information recording operations (1), (2), and (3) in the fourth embodiment._abDiagram showing (Δω)
FIG. 22 shows ΔI before recording information in the fifth embodiment._abDiagram showing (Δω)
FIG. 23 shows ΔI after recording information in the fifth embodiment._abDiagram showing (Δω)
FIG. 24 is a diagram showing energy levels of a YAG crystal containing 0.1 mol% of Eu as a recording medium of the sixth embodiment.
FIG. 25 shows the result of reading information recorded on the recording medium of the sixth embodiment (ω_p, Ω_c)Plane
FIG. 26 is another (ω_p, Ω_c)Plane
FIG. 27 is a diagram schematically showing a recording / reproducing apparatus according to a seventh embodiment.
[Explanation of symbols]
｜ 1 ＞ ・ ・ ・ First level
| 2> ... Second level
| 3> ... the third level
ω_p... Frequency of probe light (first coherent light)
ω_c... Frequency of coupling light (second coherent light)
Ωp: Rabi frequency of probe light
Ωc: Rabi frequency of coupling light
11, 12 ... Ring dye laser
13. Recording medium
14 ... Photomultiplier
15 ... AD converter
16 ... Personal computer
17 ... Beam splitter
18 ... Photomultiplier
19 ... AD converter
20, 21 ... Personal computer
22 ... External storage device
23 ... Display
24. Ring dye laser
25 ... Excimer laser
26 ... Dye amplifier
27 ... BBO crystal
28 ... Personal computer
29, 30 ... Beam splitter
31, 32 ... Photomultiplier
33, 34 AD converter
35-40 ... mirror

Claims (9)

As a recording medium, a solid having a physical structure having an energy level structure composed of energy levels of 3 levels or more is used.
The number of physical structures contained in the solid is N,
The predetermined three levels of the i-th physical structure are the first, second, and third levels,
With h being the Planck constant, the energy of the first level is hω _i1 / 2π, the energy of the second level is hω _i2 / 2π, the energy of the third level is hω _i3 / 2π,
When | ω _i3 −ω _i1 | is ω _i31 , | ω _i3 −ω _i2 | is ω _i32 , and | ω _i2 −ω _i1 | is ω _i21 ,
By irradiating the recording medium with light or an electron beam, applying an electric or magnetic field to the recording medium, or applying pressure to the recording medium, (ω _i31 , ω _i32 ) in N physical structures Information is recorded on the recording medium, and the distribution of (ω _i31 , ω _i32 ) or the distribution of ω _i21 is detected based on the change in the optical spectrum of the physical structure. A recording / reproducing method, wherein the information is reproduced. The N maximum value of omega _{i 31} in the physical structure max (ω _i31), the minimum value min (ω _i31),
The N maximum values of omega _i32 in the physical structure max (ω _i32), the minimum value min (ω _i32),
When the angular frequency of the first coherent light is ω _p and the angular frequency of the second coherent light is ω _c ,
The recording medium is irradiated with the first and second coherent light that satisfy the conditions of min (ω _i31 ) <ω _p <max (ω _i31 ), min (ω _i32 ) <ω _c <max (ω _i32 ). , Measuring at least one of the absorption of the first coherent light in the recording medium and the fluorescence of the recording medium generated through the absorption of the first coherent light for a plurality of (ω _p , ω _c ) pairs The recording / reproducing method according to claim 1, wherein information recorded on the recording medium is reproduced. The N maximum value of omega _{i 31} in the physical structure max (ω _i31), the minimum value min (ω _i31),
The N maximum values of omega _i32 in the physical structure max (ω _i32), the minimum value min (ω _i32),
The angular frequency of the first coherent light is ω _p , the angular frequency of the second coherent light is ω _c , and ω _p −ω _c is Δω,
The first and second coherent lights satisfying the condition that Δω is constant and min (ω _i31 ) <ω _p <max (ω _i31 ), min (ω _i32 ) <ω _c <max (ω _i32 ) The absorption of the first coherent light in the recording medium when irradiated to the recording medium is I _ab (ω _p ; ω _c ), and the fluorescence of the recording medium generated through the absorption of the first coherent light is I _{When lu} (ω _p ; ω _c ),
I _ab (Δω) = ∫I _ab (ω _p ; ω _p −Δω) dω _p
And I _lu (Δω) = ∫I _lu (ω _p ; ω _p −Δω) dω _p
2. The recording / reproducing method according to claim 1, wherein information recorded on the recording medium is reproduced by obtaining at least one of a plurality of different Δω. The solid has a fourth level that causes a structural change when electrons are excited to that level;
The energy of this fourth level is hω _i4 / 2π,
| Ω _i4 −ω _i1 | to ω _i41 , | ω _i4 −ω _i2 | to ω _i42 , | ω _i4 −ω _i3 | to ω _i43 ,
The N maximum values of omega _i41 in the physical structure max (ω _i41), the minimum value min (ω _i41),
The N maximum values of omega _i42 in the physical structure max (ω _i42), the minimum value min (ω _i42),
The N maximum values of omega _i43 in the physical structure max (ω _i43), the minimum value min (ω _i43),
When the rabbi frequency of the first coherent light is Ω _p and the rabbi frequency of the second coherent light is Ω _c ,
If Ω _p <Ω _c ,
The recording medium includes the first and second coherent light beams and an angular frequency larger than min (ω _i41 ) and smaller than max (ω _i41 ), or larger than min (ω _i43 ) and larger than max (ω _i43 ). Irradiating a third coherent light having a small angular frequency;
If Ω _p > Ω _c ,
On the recording medium, said first, said second coherent light, and min (ω _i42) larger max (ω _i42) smaller angular frequency than than or min (ω _i43) larger than max (ω _i43), 2. The recording / reproducing method according to claim 1, wherein information is recorded on the recording medium by irradiating a third coherent light having a smaller angular frequency. As a recording medium, a solid having an energy level structure composed of three or more energy levels,
An optical system for irradiating the recording medium with first and second coherent light,
The optical system includes N as the number of physical structures included in the solid,
The predetermined three levels of the i-th physical structure are the first, second, and third levels,
The h as Planck's constant, the first level of the energy hω _i1 / 2π, wherein the second level of energy hω _i2 / 2π, wherein the 3 Etchiomega energy level of the _i3 / 2 [pi,
| Ω _i3 −ω _i1 | to ω _i31 , | ω _i3 −ω _i2 | to ω _i32 ,
The maximum value of omega _{i 31} in the N physical structures max (ω _i31),
The minimum value of omega _i32 in the N physical structures min (ω _i32),
The minimum value of omega _{i 31} in the N physical structures min (ω _i31),
The maximum value of omega _i32 among the N physical structure max (ω _i32),
When the angular frequency of the first coherent light is ω _p and the angular frequency of the first coherent light is ω _c ,
The angular frequency of the first and second coherent lights is within a range satisfying the conditions of min (ω _i31 ) <ω _p <max (ω _i31 ) and min (ω _i32 ) <ω _c <max (ω _i32 ). A recording / reproducing apparatus comprising means for changing. 6. The optical system according to claim 5, wherein when ω _p −ω _c is Δω, the optical system includes means for changing the angular frequency of the first and second coherent light under a condition where Δω is constant. Recording / playback device. The solid has a fourth level that causes a structural change when electrons are excited to that level;
The optical system is
The energy of the fourth level is hω _i4 / 2π,
| Ω _i4 −ω _i1 | to ω _i41 , | ω _i4 −ω _i2 | to ω _i42 , | ω _i4 −ω _i3 | to ω _i43 ,
The N maximum values of omega _i41 in the physical structure max (ω _i41), the minimum value min (ω _i41),
The N maximum values of omega _i42 in the physical structure max (ω _i42), the minimum value min (ω _i42),
The N maximum values of omega _i43 in the physical structure max (ω _i43), the minimum value min (ω _i43),
When the rabbi frequency of the first coherent light is Ω _p and the rabbi frequency of the second coherent light is Ω _c ,
If Ω _p <Ω _c ,
The recording medium includes the first and second coherent light beams and an angular frequency larger than min (ω _i41 ) and smaller than max (ω _i41 ), or larger than min (ω _i43 ) and larger than max (ω _i43 ). Irradiating a third coherent light having a small angular frequency;
If Ω _p > Ω _c ,
On the recording medium, said first, said second coherent light, and min smaller angular frequency than larger max (ω _i42) than (omega _{i4 2)} or min (omega _i43) larger than max, (omega _i43 6. The recording / reproducing method according to claim 5, further comprising means for irradiating a third coherent light having an angular frequency smaller than (2). The optical system has means for measuring at least one of absorption of the first coherent light in the recording medium and fluorescence of the recording medium generated through absorption of the first coherent light. The recording / reproducing apparatus for recording according to any one of claims 5, 6, and 7. When | ω _i2 −ω _i1 | is ω _i21 ,
Information is recorded on the recording medium by changing the distribution of (ω _i31 , ω _i32 ) in the N physical structures, and the distribution of (ω _i31 , ω _i32 ) or the distribution of ω _i21 is detected to detect the information. The recording / reproducing apparatus for recording according to claim 5, wherein the recording / reproducing apparatus is a recording / reproducing apparatus.

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