Transcript Single Photon Source for Quantum Communication

Single Photon Source for
Quantum Communication
Sarah Walters, Meng-Chun Hsu, Hubert Zal, Pierce Morgan
Single photon source- all photons are separated from
each other (antibunching)
single photon source
attenuated laser pulses
(never have antibunching)
How to create single photons?
Focus the laser beam on
a single emitter
Photon
Single emitter emits
single photon at a time
because of fluorescence
lifetime
Fluorescence Lifetime
•While the electron is in a higher energy level,
no more electrons can be excited
•The photon must be emitted before the
electron can be excited again
•Time electron is in a higher energy level is
fluorescence lifetime
Application of single photon sources is absolutely
secure quantum communication
Encode
information
using different
polarization
states of
photons
The problems with creating
such technology is due to
the difficulties in
developing robust sources
of antibunched photons on
demand.
In contrast to
classical
communication,
where an
eavesdropper
(Dr. Lukishova) is
able to
measure the
transmitted
signals without
arousing Pierce’s
or Meng-Chun’s
attention, in
quantum
cryptography
eavesdropping
can be detected
by Meng-Chun or
Pierce.
How do we prove that we have single photons?
We need to measure the time interval between two consecutive photons
and prove that no photons have zero time intervals between them (this is
called antibunching)
Measure flourescent antibunching
using Hanbury Brown and Twiss
inteferometer
Beam splitter directs about half of the
incident photons toward the
first APD and half toward the second APD
One is used to provide a ‘start’
signal, and the other, which is on a delay,
is used to provide a ‘stop’
signal. By measuring the time between
‘start’ and ‘stop’ signals, one
can form a histogram of time delay
between two photons and the
coincidence count
Histogram
two single-photon counting avalanche
photodiodes APD1(T) and APD2(R)
Experimental Setup
APD 1
Single emitter
APD 2
Filter
Microscope cover
slips
Nonpolarizing
beam
splitter
Microscope objective
532nm
laser
Confocal Fluorescent Microscope
sample is placed here
laser beam
enters here
filters diminish
intensity of laser
beam
Preparing to put the sample on
the confocal microscope
Two types of emitters were used – single color centers in
nanodiamonds and single colloidal semiconductor
Cadmium Selinium Tellurium quantum dots
The primary
problems with
using
fluorescent
dyes and
colloidal
semiconductor
nanocrystals in
cavities are the
emitters’
bleaching.
Liquid diamond
monocrystaline- same
diamond as found in
jewelry
Both are only
Several
nanometers
Quantum dots –
very small
molecules made to
act as a single atom
Samples we created ourselves
using nanodiamonds in liquid
crystal
Samples are later placed onto the
microscope using magnets
47.0
99.0
105
47.0
217
200
99.0
83
200
328
300
175
250
200
175
180
160
150
125
120
100
Go to a
specific
position
50
25
X min
and
X max
0
Y min
and
Y max
25
50
47.0
75
99.0
100
125
150
175
200
200
175
180
160
150
140
125
120
100
100
300.0
250.0
200.0
150.0
50
0.0
25
75
25
0
0
25
100
125
50
75
100
125
150
175
200
150
175
200
Intensity of
photons per
emitter
time
APD1
APD2
100.0
50.0
50
50
Area
of
scan
350.0
75
25
75
83
217
0
41
Specific
position
focus on top right
10/28/2009
200
0
100
100
100
75
0
150
140
125
200
150
0.0
Intensity
over time
100000.0
200000.0
300000.0
400000.0
t im e (m s )
500000.0
600000.0
700000.0
5 by 5 micron scan
800000.0
Sample: Nanodiamonds
3
0.0
99.0
60
574
200
500
175
Sample moves as laser scans it line by line.
400
150
300
200
125
100
100
21
75
50
25
0
Scan of single line
Forw. or APD1
Backw.or APD2
300.0
0
25
50
75
100
125
150
175
200
25 by 25 micron scan
275.0
250.0
225.0
200.0
175.0
150.0
125.0
100.0
75.0
50.0
25.0
0.0
2500.0
5000.0
7500.0
10000.0 12500.0 15000.0 17500.0 20000.0 22500.0 25000.0
posit ion (nm )
Photons detected of one line
Sample: Nanodiamonds
No
antibunching
Sample: Nanodiamonds
Some
antibunching –
minimum at 0
time interval
Sample: Nanodiamonds—Index
Matching Fluid
APD1
APD2
220.0
200.0
180.0
5 by 5 micron scan
160.0
140.0
120.0
100.0
80.0
37.0
65.0
60
0.0
5000.0
10000.0 15000.0 20000.0 25000.0 30000.0 35000.0 40000.0 45000.0 50000.0
t im e (m s)
intensity over time
100
321
88
250
200
75
150
100
62
50
50
Fluorescence of color
centers in nanodiamonds
4
38
25
Confocal microscope focuses on emitter
12
0
0
12
25
38
50
62
75
88
100
Sample: Nanodiamonds—Index
Matching Fluid
14.0
Confocal microscope
focuses on different
emitter
29.0
62
100
321
88
250
200
75
150
3
62
100
50
50
4
38
25
12
0
APD1
0
APD2
200.0
180.0
160.0
140.0
120.0
100.0
80.0
60.0
0.0
50000.0
100000.0
150000.0
t im e (m s)
200000.0
250000.0
300000.0
12
25
38
50
62
75
88
100
Sample: Nanodiamonds—Index
Matching Fluid
32.0
55.0
27
100
321
88
250
Confocal microscope
focuses on different
emitter
200
75
150
3
62
100
50
50
4
38
25
12
0
0
12
25
38
50
62
75
88
APD1
100
APD2
160.0
140.0
120.0
100.0
80.0
60.0
0.0
50000.0
100000.0
150000.0
t im e (m s)
200000.0
250000.0
300000.0
Sample: Nanodiamonds in Cholesteric
Liquid Crystal
165.0
81.0
80
430
200
350
175
300
250
150
200
125
150
100
100
58
75
50
25
0
0
25
50
75
100
125
150
175
200
Forw. or APD1
Backw.or APD2
300.0
275.0
250.0
225.0
200.0
25 by 25 micron scan
175.0
150.0
125.0
100.0
75.0
50.0
0.0
2500.0
5000.0
7500.0
10000.0 12500.0 15000.0 17500.0 20000.0 22500.0 25000.0
posit ion (nm )
Sample: Quantum Dots
APD1
APD2
11.2 by 11.2 micron
scan
700.0
600.0
500.0
400.0
300.0
200.0
100.0
0.0
0.0
100000.0
200000.0
300000.0 400000.0
t im e (m s)
500000.0
600000.0
700000.0
160.0
800000.0
33.0
58
305
200
250
175
200
150
150
100
125
Laser focused on single
quantum dot
50
100
0
75
50
25
0
0
25
50
75
100
125
150
175
200
Sample: Quantum Dots
121.0
137.0
368
200
2000
175
1500
150
1000
125
500
100
0
75
50
25
0
Blinking of quantum dots
0
25
50
75
100
125
150
175
APD1
200
APD2
700.0
600.0
500.0
400.0
300.0
200.0
100.0
0.0
0.0
250000.0
500000.0
t im e (m s)
750000.0
Sample: Quantum Dots
Antibunching –
minimum at 0
time interval
Research done….
Thanks to Dr. Lukishova