1. Ultrafast 2D Quantum Switching of p‑Electron Rotations
in a Nonplanar Chiral Molecule by Using Linearly Polarized UV Laser Pulses
Mineo, Hirobumi (峯尾　浩文)
Institute of Atomic and Molecular Sciences, Academia Sinica 
(中央研究院原子分子科學研究所)
J. Am. Chem. Soc. 134, (2012)
J. Chem. Phys. 138, (2013)
各位大家好, 我叫峰尾浩文.
我來台灣11年, 但是第一次來中興大學演講, 我想幾乎大家都不認識我,
所以我想先簡單地自我介紹一下.
其實我原本在台灣出生, 因為我母親是台灣人, 後來到日本, 一直待在那裡
長大. 11年前又回來台灣當博士後.
剛回來台灣的時候我作的研究領域是原子核物理的理論計算.
就是把電子和質子scatter之後, 得到質子結構的資訊.
所以跟我現在做的研究有差別.
後來7年前轉到原子分子, 光學方面, 研究對象變成原子分子, 就變大.
用強雷射來引起分子的游離化, 或離子的解離的數值計算.
在今天的演講我所用到的都是獨立的分子, 但是研究的方向還是往更大的scale.
固態的分子nano particle, 大小也是從angstrom到幾十或幾百nm的scale.
我的演講是照這個流程進行.
先介紹背景跟目的.
因為透過演講我要討論aromatic ring, 環狀的分子上的pi electron current的控制.
所以用一個aromatic molecule來解釋引起pi electron current的mechanism.
這個時候同時產生角動量angular momentum.
接下來, 用兩個環狀的分子連結起來做的分子來示範2維的quantum switching.
在任何2維的方向, 產生pi electron current跟angular momentum.
swithcing的時間是100fs之內的,超快的短時間.
最後總結演講.
Introduction of purpose and background
Mechanism of p electron ring current
2D ultrafast quantum switching
Numerical simulations
Summary and conclusion

2. Introduction Quantum control of electronic and molecular dynamics?
Chemistry
Ionization, and electronic states in molecules
Dissociations of molecules and ions
Selection of chiral molecules
Industry, Electronics
LCD, Organic electroluminescence display
Molecular transistor (potential possibility)
HDD (~ ps) =
:Laser field
L.Y. Hsu, H. Rabitz, PRL 109,
(2012)
Possibility of Ultrafast switching (~fs)?
Organic molecule is more ecology
We will demonstrate 2D Ultrafast switching in a non-planar chiral molecule
Applicability depends on development of technology

3. Quantum control is important in
chemistry, electronics, physics and industry
(We focus on) Laser control of electron (p-electron) ring current
UV laser pulse
=angular momentum ~ magnetic field
p-electron rotations in a chiral aromatic molecule
UV laser pulse
2D switching of p-electron rotations in a non-planar chiral molecule

4. Important role of p electrons in aromatic molecules
High reactivity due to delocalization of p electrons
Kekulé structure (1865) and delocalized p electrons in benzene
p-orbital=pz-orbital
Resonant
delocalized
Question:
p-electrons rotate ?
Which direction?
Clockwise or anti-clockwise ?
How to control rotation by using laser?

5. Fundamental studies on laser-induced p electron rotations
Ex. Simulations electron rotations in aromatic molecules
( I. Barth et al., J. Am. Chem. Soc., 128 , 7043 (2006)
Generation of p- electron currents by a circularly polarized laser pulse;
The rotational direction is determined by circularly polarized pulse.

6. Ex. : p electron rotations in Chiral aromatic molecules driven by
a linearly polarized (LP) laser pulse S R
M. Kanno, et al., Angew. Chem. Int. Ed. 45, 7995 (2006)
2,5-dichloro[n](3,6)pyrazinophane (DCP)
(CH2)n Cl N N Cl
Cl:氯
N:氮
Planar chirality
Molpro structure optimization: MP2 / 6-31G* : CASSCF(10,8) / 6-31G*

7. Can LP laser pulses rotate p electrons?
Because
i) LP pulse has no photon angular momentum
ii) Chiral aromatic molecule has no angular momentum states.
What is the mechanism of p electron rotation?
Use a DCP chiral molecule to understand the mechanism and principles
Under fixed-nuclei condition, “no” vibrational states

8. Mechanism of p electron ring current

9. The principle of p-electron rotations
Coherent excitation of a coupled quasi-degenerate electronic states using linearly polarized laser pulses
benzene（D6h)
Chiral molecule DCP (C2h) S0
G (1Ag)
1E1u
L (1Bu)
H (1Bu)
Symmetry breaking
e+ (e-)
|𝑐 𝐻 | 2 =
|𝑐 𝐿 | 2
UV pulse laser
Chirality
Generation of an electronic coherent state

10.  electron rotational direction and laser polarization vectors
Approx. angular momentum states
Anti-clockwise
Clockwise
|+
|
Electron
rotation
Resonant excitation of LP pulse
in-phase |L |H
out-of- phase　|L |H
e+ excitation +
e excitation
Temporal behavior of superposition of 　　　　　　　　　　　 + +

11. Time evolution of p-electron driven
polarization vector e+
:one cycle of electronic transition
Time
T/4
T/2
3T/4
State
|L + |H
|L - i |H
|L - |H
|L + i |H +i −i +1 +i −i +1 +i −i +1
Phase
Factor +i −i +1 −1
Rotational
direction
of electron
(no rotation)
(Clockwise rot.)
(no rotation)
(Anti-clockwise rot.)
The initial rotational direction is determined by the direction of polarization vector:
e+: clockwise rotation; e− : Anti-clockwise rotation

12. Results of p-electron dynamics in the fixed-nuclei approximation
E(t)
T/2
|0>
|->
|+>
|->
|+>
1.0
clockwise
rotation
counterclockwise
rotation
Oscillations between
clockwise and counterclockwise
rotations
-1.0 10 20 30 40 50 fs
9-cycle clockwise
Rotation of electron

13. Summary of first half
p-electron rotation in Chiral molecule is induced by LP laser
Initially,
direction of rotation Angular momentum
e in phase clockwise negative
e- out of phase Anti-clockwise positive
Design of multi-dimensional ultrafast switching devices?
<- Non-planar Chiral molecule
Later alternatively oscillate by a period

14. 2D ultrafast quantum switching

15. Ultrafast 2D quantum switching of p-electron rotations in a
Non-planar chiral molecule
(P)-2,2’- biphenol
C2 point group OH
A, B OH X
Geometry optimization: DFT 6-31+g(d,p)
Excitation states: TDDFT 6-31+g(d,p)

16. b1 b2 a b1 C: clockwise A: anti-clockwise p-Electron rotation
Angular momentum

17. pump-dump laser pulse Coherent control Fix directions of
p-electron rotations
Angular momentum
6.84 eV
b2(B)
b1(B)
6.78 eV
6.67 eV
a (A)
dump
dump
pump
pump
0 eV 17 g

18. Theory, formalism Density matrix method
Liouville equation:
diagonal: population, off-diagonal: coherence
:interaction with laser field
: the transition dipole moment operator
: angular frequency difference between states a and b 18

19. :single electron operator
Expectation value
:single electron operator
Excited states: 19

20. is a unit vector which is perpendicular to a ring K
Angular momentum
is a unit vector which is perpendicular to a ring K
Current
S is a surface perpendicular to a current

21. m: electronic excited states
i: atomic cite
m: electronic excited states
a: a a’
b: b b’ = or
H. Mineo et al., J. Chem. Phys. 138, (2013) 21

22. Numerical simulations

23. (a)
H. Mineo et al.,
J. Am. Chem. Soc. 134, (2012)
0.1
0.0
-0.1
300
0.1
200
0.0
-0.1
100
t/fs
(b)
100
200
300
0.0
-0.5
-1.0
0.5
1.0
(b)
E(t)/GVm-1
t/fs
0.2
0.0
EX(t)
-0.2

24. Maximum values of magnetic field and current
b1b2 excitation case:
H. Mineo et al., JCP 138, (2013)
Intensity of laser field used for pump:
Comparative!
Mg-porphyrin
Ex.,
Benzene
CP laser
I. Barth et al.,
JACS,128, 7043 (2006)

25. Summary and conclusion
We proposed a method for control of a
2D ultrafast switching of p-electron rotations for nonplanar chiral aromatic molecule, (P)-2,2’-biphenol by using LP laser pulses.
Direction of p-electron rotations is determined by
polarization direction and central wavelength
We designed a sequence of overlapped pump-dump laser pulse
The key point for 2D rotations is to select
a set of three quasi-degenerate excited states involving both
A and B irreducible representations in the C2 point group.
Angular
momentum
Excited states
pump-dump
Component of
A B
B B
wc, (pump pulse)

26. Application
Ultrafast multi-dimenstional quantum switching device
2-qubit quantum computer
Perspective
In this work we only treat isolated molecule (gas phase)
to demonstrate 2D ultrafast switching
NOT enough treatment
Extend to more complicated system,
Solid state

27. Appendix

31. a R
I: ring current
m0 =4px10-7 H/m=(Wb/A/m) :magnetic permeability If
Use
If , the laser field induced magnetic field is
Magnetic flux:

32. ii) Photocurrent induced magnetic flux for a selective control of single spin
Current I and magnetic flux density B

33. iii) New method for identification of molecular chirality
R- enantiomer or S-enantiomer can be identified by observing photo-current
induced magnetic moments.

34. Relations of p-electrons rotation and direction of angular momentum
ab1 excitation
b1b2 excitation
Ex polarization
Ex polarization Y Z x X L R Y Z x X L R X Z
Rotations in the same direction
Rotations in the opposite direction Z X

35. The UV spectrum of the optically-allowed p-electronic excited states with transition energies.
The excited state 27 has A symmetry, and the other excited states 28, 32 have B symmetry,
which are defined to be called as a, b1, b2 respectively.
The excited energies are given as follows, a (Ea=6.67 eV), b1 (Eb1=6.78 eV), b2 (Eb2=6.84 eV)

37. Porphyrin
Scaffold (chirality)
Electrode (Au)

39. S1 R1

40. S1 R1
Average asymmetry factor
=−0.005± S1 , ±0.002 (R1)