The Creation of Single Photon Sources
By: Joseph Cosentino, Matthew Farkas,
David Kim, Yuntao Ma, and Chris
Miller.
Lab Instructor: Luke Bissell
Quantum B Team
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Single photon sources have already been
created and somewhat utilized but they are not
very efficient.
Luke Bissell’s Phd research goals are to create
more efficient single photon sources and to
find sources that emit polarized photons.
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The first method of obtaining single photon
sources was to attenuate a laser to one photon.
This does not work, because in actuality, the
laser is emitting an AVERAGE of one photon.
Sometimes the laser will emit two, or none at
all. This method is not efficient.
Luke Bissell (our lab instructor) is searching for
an efficient emitter of single photons and
polarized single photons.
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There are number of other theoretical methods
that can be used to create single photons:
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Quantum Dots, Single Atoms, Single Molecules, or
Color centers in a diamond (nitrogen vacancy).
We used quantum dots, they are nanocrystals
that are not difficult to create and manipulate.
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They are simply the most efficient method of going
about the research.
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“Individual color centers in diamond are promising for near-term quantum
technologies including quantum key distribution and metrology. Here we show
fabrication of an as-yet uncharacterized nickel-related complex in diamond which
has photophysical properties surpassing the two main-stay centers for singlephoton applications, namely, the nitrogen-vacancy and the nickel-nitrogen
complex (NE8) center. This center was fabricated using focused ion-beam
implantation of nickel into isolated chemical vapor-deposited diamond crystals. A
possible correlation of the center to a Ni/Si complex is substantiated by a
coimplantation of Ni and Si into a pure bulk diamond. Room-temperature
photoluminescence studies reveal a narrow emission in the near infrared region
centered at 768 nm with a lifetime as short as 2 ns.”
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Courtesy of:
http://prb.aps.org/abstract/PRB/v79/i23/e235316
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Quantum Dot’s are small crystalline structures
(nanocrystals) that have the properties of single
atoms of two energy levels.
Since they act as single atoms, they will emit a
single photon when excited.
Isolating these nano-crystals is difficult.
NeV
Single Photon
coincidence counts
0
interphoton times
76 MHz repetition rate,
CW excitation
~6 ps pulsed-laser
at 532 nm
excitation at 532 nm
Non-Antibunching
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Semiconductor nanocrystals that behave as 2
level atoms with size-dependent properties.
Electrons require a specific amount of energy to
jump the bandgap.
Electrons emit a photon when they fall to lower
energy levels.
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Why can’t we attenuate a laser down to the
single photon level?
The average number of photons emitted is 1.
The actual number is greater than 1 or is 0.
Do not get 1 photon at a time as in Quantum
Dots.
L. J. Bissell, S. G. Lukishova, A. W. Schmid, et al., Chiral Photonic
Bandgap Microcavities with Single Colloidal Semiconductor Quantum Dots,"
Proceedings of SPIE, Submitted.
The laser is a diode-pumped solid-state with 532nm wavelength, 6 ps pulse duration and 76 MHz pulse repetition rate.
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There are three major types of information that
we gathered in this lab:
•
•
•
The intensity of an area of Quantum Dot solution
The emitted photon counts of particular Quantum
Dots
And in the case of the CLC solutions the wavelength
spectrum of the emitted photons
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We used a Labview application built by a
former UR grad student
Creates images of what the two APDs detect on their
imaging area using the images’ intensity data
 Also used shows the intensity data of a particular
point within the image over time. (histogram)
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Used to determine the location of potential
sites of individual Quantum Dots
99.0
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November 12th, 705nm Quantum Dots on glass, 20nM
concentration (Histogram and Intensity Images)
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We used proprietary software called TimeHarp
which is made specifically for counting
individual photons
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The software essentially takes the same information
that is displayed in Labview and plots the number of
counts based on the delay in time between the
counts
Used to determine whether a given Quantum
Dot is anti-bunched or not.
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November 12th, 705nm Quantum Dots on glass, 20nM concentration (Count
Plot)
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We used some proprietary software called
Andor Solis for Imaging:
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Gathered and displayed data collected by the EMCCD camera about a chosen quantum dot’s emission
spectrum
Used in conjunction with a rotating polarizer to
determine if the CLC containing the QD is
polarizing the QD’s emissions (as is desired)
A sample with a linear polarizer
rotated at 43 degrees in the imaging
path
Same sample with a linear polarizer
rotated at 135 degrees in the
imaging path
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Polarizer at 43 degrees
Polarizer at 135 degrees
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That the spot in the sample tested is a quantum
dot
That this particular quantum dot is a single,
anti-bunched dot
And that the CLC is polarizing the light
Quantum Cryptography
=1
=1
=0
=0
+
Alice
or
x
Eve
Bob
N. Gisin, et al., Rev. Mod. Phys. 74, 145-195 (2002)