Single Photon Source for Quantum Communication Sarah Walters, Meng-Chun Hsu, Hubert Zal, Pierce...
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Transcript of Single Photon Source for Quantum Communication Sarah Walters, Meng-Chun Hsu, Hubert Zal, Pierce...
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
Single emitter emits single photon at a time because of fluorescence lifetimePhoton
•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
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 toclassical communication, where an eavesdropper (Dr. Lukishova) is able tomeasure the transmitted signals without arousing Pierce’s or Meng-Chun’sattention, in quantum cryptography eavesdropping can be detectedby 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
two single-photon counting avalanche photodiodes APD1(T) and APD2(R)
Beam splitter directs about half of the incident photons toward thefirst 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, onecan form a histogram of time delay between two photons and thecoincidence count
Histogram
Experimental Setup
APD 2
AP
D 1
Non-polarizing beam splitter
Dichro
ic mirr
or
Filter
532nm laser
Microscope objective
Microscope cover slips
Single emitter
Confocal Fluorescent Microscope
Preparing to put the sample on the confocal microscope
laser beam enters here
filters diminish intensity of laser beam
sample is placed here
Two types of emitters were used – single color centers in nanodiamonds and single colloidal semiconductor Cadmium Selinium Tellurium quantum dots
Both are only Several nanometers
Quantum dots – very small molecules made to act as a single atom
Liquid diamond monocrystaline- same diamond as found in jewelry
The primary problems with using fluorescentdyes and colloidal semiconductor nanocrystals in cavities are theemitters’ bleaching.
Samples we created ourselves using nanodiamonds in liquid crystal
Samples are later placed onto the microscope using magnets
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47.0 99.0 105
5 by 5 micron scan
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time (ms)800000.00.0 100000.0 200000.0 300000.0 400000.0 500000.0 600000.0 700000.0
APD1
APD2
focus on top right emitter 10/28/2009
X min and
X max
Y min and
Y max
Go to a specific position
Specific position
Area of
scan
Intensity over time
Intensity of photons per
time
Sample: NanodiamondsSample: Nanodiamonds
300.0
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position (nm)25000.00.0 2500.0 5000.0 7500.0 10000.0 12500.0 15000.0 17500.0 20000.0 22500.0
Forw. or APD1
Backw.or APD2
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3 0.0 99.0 60
25 by 25 micron scanScan of single line
Sample moves as laser scans it line by line.
Photons detected of one line
Sample: Nanodiamonds—Index Matching Fluid
Sample: Nanodiamonds—Index Matching Fluid
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time (ms)50000.00.0 5000.0 10000.0 15000.0 20000.0 25000.0 30000.0 35000.0 40000.0 45000.0
APD1
APD2
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37.0 65.0 60
5 by 5 micron scan
Confocal microscope focuses on emitter
Fluorescence of color centers in nanodiamonds
intensity over time
Sample: Nanodiamonds—Index Matching Fluid
Sample: Nanodiamonds—Index Matching Fluid
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time (ms)300000.00.0 50000.0 100000.0 150000.0 200000.0 250000.0
APD1
APD2
Confocal microscope focuses on different emitter
160.0
60.0
80.0
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time (ms)300000.00.0 50000.0 100000.0 150000.0 200000.0 250000.0
APD1
APD2
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Sample: Nanodiamonds—Index Matching Fluid
Sample: Nanodiamonds—Index Matching Fluid
Confocal microscope focuses on different emitter
Sample: Nanodiamonds in Cholesteric Liquid Crystal
Sample: Nanodiamonds in Cholesteric Liquid Crystal
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position (nm)25000.00.0 2500.0 5000.0 7500.0 10000.0 12500.0 15000.0 17500.0 20000.0 22500.0
Forw. or APD1
Backw.or APD2
25 by 25 micron scan
Sample: Quantum DotsSample: Quantum Dots
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160.0 33.0 58
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time (ms)800000.00.0 100000.0 200000.0 300000.0 400000.0 500000.0 600000.0 700000.0
APD1
APD2
Laser focused on single quantum dot
11.2 by 11.2 micron scan
Sample: Quantum DotsSample: Quantum Dots
700.0
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time (ms)750000.00.0 250000.0 500000.0
APD1
APD2
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121.0 137.0 368
Blinking of quantum dots