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激光光谱实验室
Single molecules quantum
dynamics and quantum optics
肖连团
量子光学与光量子器件国家重点实验室
山西大学激光光谱实验室
Dalian 6, Aug, 2010
激光光谱实验室
1
光缔合制备超冷分子及其在量子信息中的应用
2
超冷里德堡原子的实验研究
3
单分子量子光学
超冷分子
光缔合超冷铯分子与超
冷铷铯分子的制备、测
量与调控。
超冷里德堡原子
Dye laser
Cs+
Cs2+
时序控制示意图
探测装置示意图
0.24
0.20
0.16
0.8
Relative Intensity(arb.u.)
Ti:Sa laser
Intensity of Rydberg atoms(arb.u.)
0.28
0.12
0.08
0.04
0.6
0.4
0.2
0.0
-80
-60
-40
-20
0
20
40
60
80
Frequency(MHz)
0
10
20
30
40
Relative Intensity of green laser(mW)
50
Outline
• Introduction
- Why single-molecule optics detection?
- How to detect single molecules?
• Single molecules probe
- Long memory time effect in soft matter
- Probing surface dynamics
• Single molecules fluorescence manipulation
- Electric-current modulation
- Enhancement and suppression of singlemolecule fluorescence
• Single molecules quantum optics
- Interaction between single molecule and
single photons
- Quantum states
• Discussion and Outlook
• Single molecules probe
1.1 Single molecule optics
 In molecular physics texts, single molecule
detection has proven to be a unique method to
investigate the behavior of complex condensed
systems.
 In chemistry texts, molecular interactions and
chemical reactions are generally described on a
single-molecule basis.
 The single molecule approach has changed the way
problems are addressed in biophysics or even
biochemistry.
Single molecule observation
• In 1952, Schrodinger said that “ We would never
experiment with just one electron, one atom or one
molecule ”.
• In 1960, Feynman anticipated the future and then said
“ There are no physical limitations to arranging atoms
the way we want ”.
• By 1980s, Scanning Tunneling Microscopy and
observations of fluorescence from a single molecule
allowed us manipulate single molecules, atoms and bonds.
Scanning Tunneling Microscopy
Can we really catch hold of a single
molecule?
 Single molecule studies do not mean taking one
molecule and analyzing it.
 Its only that we are detecting one molecule at a time.
 Detection volume is 1  m3.
 When a fluorophore traverses the laser excitation
volume, a fluorescence photon burst is generated.
 The bursts are analyzed in terms of number of
photons emitted.
 It doesn’t mean only one experiment on one molecule
but millions of experiments on one molecule.
 Histograms are made out of these large number of
experimental results.
Single-Molecule Optics
Prof. Dr. Michel Orrit
1. Single molecules
spectroscopy
2. Organic field effect
transistors
3. Rheology
• " Single pentacene molecules detected
by fluorescence excitation "
Phys. Rev. Lett., 65 (1990) 2716-19.
•"Molecular entanglements"
Science 297 (2002) 1160-1163
•"Photothermal imaging of nano- metal
particles among scatterers"
Science 298 (2002) 369-370
•"The motions of an enzyme soloist"
Science 302 (2003) 239-240
•"Single-Molecule Optics"
Annu. Rev. Phys. Chem. 55 (2004) 585
•"Single-photon sources"
Rep. Prog. Phys. 68 (2005)
•"Quantum light switch"
Nature. Phys 3 (2007) 755-756
Organic field effect transistors
The conducting layer
of an organic crystal
is doped with a very
small concentration
of DBT dye
molecules.
Figure 1: (a) Source-drain current versus gate voltage for different
source-drain voltages of an Ac-crystal in a FET structure.
(b) Stack of fluorescence-excitation spectra.
单分子纠缠
1.2 Single molecule fluorescence detection
Molecules randomly dispersed inside a matrix host :
Transparent liquid or polymer thin film ,
"spin-coated" on a glass cover-plate
100 nm
Surface density
~ 1 molecule / 10 m2
Glass cover-plate
Photobleaching
Intensité (kHz)
60
50
40
30
20
10
0
0
10
20
30
40
Temps (s)
50
60
Time behavior of the fluorescence signal
Set up – Gaussian Beam
Sample
Focal Volume
Lens
Dichroic
Mirror
laser : λ1
Fluorescence
λ1
λ2
Fluorescence
light : λ2
Molecules are
Fluorescent
Confocal Microscopy
O.M Resolution limit ~ 200nm
But we want to see single
molecule!
-> Confocal Microscopy
• Single molecules probe
2.1 Motivation
• In the particular case of glass-forming
systems, rotational diffusion will probe the
relaxation of the host because the
rotation of the dopant molecules is subject
to this relaxation.
• Since the single-molecule approach not
only yields the average but also the
distribution of rotation times, it directly
probes the extent of spatially
inhomogeneous dynamics in the host.
Characteristic timescales
 Absorption
10-15s
 Vibrational relaxation 10-12s
 Lifetime of S1
10-10 – 10-7s
 Intersystem crossing
10-10 – 10-8s
 Internal conversion
10-11 – 10-9s
 Lifetime of T1
10-6 – 1s
 Diffusion
10-2s - minutes
Molecular Fluorescence by Bernard Valeur, Wiley-VCH
Fluorescence Correlation Spectroscopy
Probing viscosity with fluorescence
• Fluorescence Anisotropy (during emission)
• Polarization fluctuations (small ensembles)
Our Method:
Single-molecule orientation
Rotational diffusion time:
V (T )

k BT
V is the hydrodynamic molecular volume of the fluorophore,
η is the viscosity of glycerol.
Supercooled liquid
supercooled
liquid
As a supercooled
liquid is cooled
to lower
temperatures, its
viscosity
increases and the
molecules which
comprise it move
more and more
slowly.
• Liquids at temperatures below their melting points
are called supercooled liquids.
Polarized single-molecule fluorescence
单分子荧光光子计数
光子总计数
1000
800
800
600
600
Photon counts /10 ms
400
200
400
0
800
水平偏振光子数
200
600
6000
400
200
0
600
垂直偏振光子数
400
400
200
200
0
0
0
5
10
15
Time (s)
20
25
30
4.0
4.5
5.0
5.5
6.0
6.5
7.0
Time (s)
两个偏振方向的光子计数是跳跃改变的，当一个方向的光子计数
减少时，另一个方向的光子计数就会相应的增大 。
7.5
Single-molecule tumbling at variable T
T-dep. of tumbling rates for 69 molecules
Long memory time of local tumbling rate
2.2 The dynamics of polymer
glasses surface
Obj
Pulse Laser
DM
H
F
SPCM
PBS
Computer
S
SR dye molecules
SPCM
P
实验装置图
Orientation imaging of single SR
molecules on polymer glasses surface
•分子a：偶极取向对应水平方向，
•分子b：偶极取向对应垂直方向，
分子c：表现出了三重态的影响，
荧光出现中断
•分子d：在探测过程中被光漂白了
•分子e：偶极取向在两个方向之间
跳动
区域面积10×10 m2 ，成像像素为
150×150，采样积分时间为10 ms
Single molecule orientational states
30000
25000
2(a)
20000
15000
10000
5000
21000
14000
7000
25000
20000
15000
10000
5000
0
0
0
0
2
Time (s)
4
6
6
3(a)
30000
Intensity (cps)
28000
Intensity (cps)
Intensity (cps)
35000
35000
1(a)
8
4
10
5
6
Time (s)
2(b)
1(b)
150
7
Time (s)
50
3(b)
90
60
40
Occurrence
120
Occurrence
Occurrence
200
150
100
50
30
-0.9
-0.6
-0.3
0.0
D (a.u.)
0.3
0.6
0.9
20
10
0
0
30
0
-0.9
-0.6
-0.3
0.0
D (a.u.)
0.3
0.6
0.9
-0.9
-0.6
-0.3
0.0
D (a.u.)
Three typical jumping patterns of orientation are obtained
statistically from reorientational molecules on PMMA surface.
0.3
0.6
0.9
•
Our experiments yield the characteristic
timescale of the SM's rotational diffusion
and thereby probe the relaxation dynamics.
•
Our results indicate the presence of
extremely long-lived spatial inhomogeneities
in supercooled glycerol probably related to
very slow, larger-scale dynamics.
• The rotational correlation time quantified
the time scales for the dynamics of the
polymer glasses surface.
Outlook: SM’s and nano-probing for soft matter studies
SM probe
Solid-solid interaction
-Friction: local
pressure and
temperature, third
body,...
-Adhesion: role of a
soft layer in between
two solids, probed with
different dyes
3. Single molecules
fluorescence manipulations
3.1 Preparation of samples
1、The single SR dyes
molecules are prepared by
spin-coating onto the a silica
glass substrate.
2、ITO films are spin-coated
onto dyes molecules.
3、PMMA polymer are spincoated onto ITO film.
Results
10000
Electric-current
modulation of
singlemolecule
emission
intensity.
Intensity/cps
8000
6000
4000
2000
I/mA
0
0.2
0.0
0
20
40
60
80
100
Time/s
6000
Intensity/cps
5000
4000
3000
2000
1000
I/mA
0
0.27
0.00
0
20
40
60
Time/s
80
100
120
Results
Suppression of single-molecule fluorescence by different
electric-current.
0.092mA
0.191mA
0.260mA
0.429mA
6000
Intensity/cps
5000
4000
3000
2000
1000
0
0
10
20
30
Time/s
40
50
60
Results
Enhancement of single-molecule fluorescence by some electriccurrent, sporadically.
4000
Intensity/cps
3000
2000
1000
I/mA
0
0.191
0.000
0
10
20
30
Time/s
40
50
Results
Enhancement and suppression of single-molecule fluorescence by different
electric-current.
Results
Results
Possible mechanism
Polymer chain
Photoexcitation
Radiative or nonradiative decay
to the ground state
Singlet excited
Relax
state
Formation of long living triplet state
Charge separation
SR + acceptor
kf
kB
SR
++
acceptor-
e
Electron
acceptor
4. Single molecules quantum optics
单分子与单光子强耦合：
• By focusing the excitation light near to the extinction crosssection of a molecule, it is possible to explore resonance
fluorescence over nine orders of magnitude of excitation
intensity and to separate its coherent and incoherent parts.
• Under weak excitation, the detection of a single molecule with
an incident power as faint as 600aW, paving the way for
studying nonlinear effects with only a few photons.
Introduction
• In view of quantum optical operations with
photons and emitters, it would be highly
desirable for as many of the incident photons
as possible to interact with a single emitter.
• Such a regime would open the door to a
wealth of nonlinear interactions between
single emitters and single or few photons,
which have been so far only achieved using
sophisticated high-finesse microcavities.
• Coherent preparation of a single molecule
electronic state.
4.1 EFFICIENT DETECTION OF A
SINGLE EMITTER IN TRANSMISSION
• In the weak excitation regime, the effect of
a molecule on an incident plane wave can
be formulated as
•
is the extinction crosssection of the transition between two
levels.
• A key technological hurdle in resonant
spectroscopy of single molecules in the
condensed phase is to achieve a tight
focus.
单分子能级与吸收
T =1.4 K
a, The energy-level scheme of a molecule with ground state and excited state.
Manifold 3 shows the vibrational levels of the electronic ground state.
b, The arrangement of the lenses in the cryostat.
c, Schematic diagrams of the optical set-up.
d, A laser scan image of a single molecule, showing a FWHM spot of 370 nm.
单分子与光子强耦合
Here, solid-immersion lens technology is used to reduce
the focus area F close to the diffraction limit, enabling us
to achieve an efficient coupling between a single
molecule and a freely propagating laser beam in a
single-pass encounter.
单分子透射谱
An example of a raw transmission spectrum, revealing a
11.5% dip determined by the lorentzian fit. The integration
time per pixel was 160 ms and the noise amounts to 0.7%.
• The excitation spectrum registered on PD1 has
to take into account the interference between the
excitation field Ee and the field Em scattered by
the molecule according to
The first term is simply the part of the incident
intensity that arrives at the detector.
The second term proportional to A represents the
molecular emission and is always positive.
The third term in this equation, also called extinction,
is proportional to B and denotes the interference
between Ee and the coherent part of Em.
Two examples of the
recorded spectra.
The blue and the green
lines show the
contributions of the
molecular fluorescence
intensity and extinction
components respectively.
SINGLE-MOLECULE DETECTION
WITH ULTRAFAINT LIGHT SOURCES
Figure5 Few photons exciting a molecule. An extinction
spectrum recorded from a single molecule under an
ultrafaint detected power of 550 photons per second,
equivalent to an incident power of 600aW.
Raw Stokes-shifted
fluorescence of a single
molecule red curve and a
theoretical fit black curve.
a) Maximum Rabi frequency of
Ω=370 MHz and a pulse
area of A=5.7π .
b) displays the result of an
experiment with fixed the
pulse duration to 4 ns and
increased the laser intensity.
Outlook
• Triggered Single Photon Sources
1. Quantum Cryptography
2. Quantum computing
3. Single photons interact with single
molecule
• Coherent state preparation based on
low temperature single molecules
Thank you for your attention!