qutools quED User manual

.
quCR Manual Version 3.2 (October 16, 2019)
www.qutools.com quCR Manual Version 3.2 Page 1

Contents
Contents
1 Introduction 2
1.1 General Warnings ................................ 3
1.2 Installation ................................... 3
1.3 Power ...................................... 3
2 Front Panel 3
3 Back Panel 5
4 Twin APD Module 6
5 Touch Panel 8
5.1 Touch Panel Software Overview ........................ 8
5.2 The quLD Module ............................... 9
5.3 The quCNT Module .............................. 11
5.4 The quMotor Module .............................. 18
5.5 The quInfo Module ............................... 19
6 Controlling the quCR via Ethernet 25
6.1 Open a VNC connection ............................ 25
6.2 HTTP Interface ................................. 25
1 Introduction
This manual describes the controller of qutools' quED - entanglement demonstrator. It
features a laser diode controller, a coincidence counter and a twin APD
1
photon counting
module. The laser diode controller regulates the temperature of the laser diode and the
current owing through it. The counter module displays the single and coincidence count
rates of the signals coming from the APD module.
1
APD: Avalanche Photo Diode. When working in the so-called Geiger mode, these devices can be used
to register single photons with a rather high eciency.
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1.1 General Warnings
1.1 General Warnings
Before starting to use the controller, please read the instruc-
tion manual carefully. Make sure that you are familiar with
and have obeyed all necessary safety precautions, especially
with respect to laser safety and electrostatic discharges (ESD).
Please consult the document quED User's and Operation
Manual for this purpose.
 Do not connect this controller to anything but the optics
part of the quED system.
 Do not open the case of the controller and do not un-
necessarily remove the APD module.
 Never remove or install the APD module while the con-
troller is running.
 Always turn the laser diode current down before switch-
ing it o.
 Always switch o the laser diode before turning o the
controller.
1.2 Installation
For the installation and connection of the quED controller, please refer to the quED User's
and Operation Manual delivered with the system.
1.3 Power
To switch on the system, please make sure that a suitable power cord is plugged into the
socket (see gure 2(11)) and supplied with 100..230 V, 50..60 Hz AC. Then, switch on
the key switch (see gure 1(1)). Please note that even when the key switch is in the o
position, the controller may still consume some power. To ensure that the controller is
switched of completely, please unplug the power cord from the controller socket.
2 Front Panel
The front panel (see Fig. 1) consists of only a few elements:
 P ower switch (1): The power key switch in the left lower corner turns the main
power of the controller on or o. Make sure you always switch o the laser (see
below) before you switch o the main power.
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Figure 1: The front panel of the quED controller. Power key switch (1), touch
panel (2), rotary encoder (3), laser on/o switch (4).
 T ouch panel (2): Most of the functionality is accessible through the touch panel.
See section 5for more information.
 R otary encoder (3) (middle, right): Use the rotary encoder to increase or decrease
values shown on the touch panel. Note that a press on the rotary encoder while
manipulating a data eld brings you back to the default value.
 L aser on/o switch (4): The laser switch in the right lower corner switches the laser
on and o. When it is switched on, it glows red.
Warning: Before switching on the laser, make sure that you
are familiar with laser safety regulations and that it is safe to
switch on the laser.
Always turn o the laser using this button before switching o the controller com-
pletely! Before switching of the laser, turn down the current.
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3 Back Panel
Figure 2: The back panel of the quED controller. Additional APD signal outputs
(5), LAN socket (6), USB host socket (7), Serial port connector (8),
Laser/TEC connector (9), Stepper motor connectors (10), Mains power
connector (11)
The back panel (see Fig. 2) consists of the following connectors (from left to right, top to
bottom):
 A dditional APD signal outputs (optional) (5): These BNC connectors output the
TTL signals from the APDs. Since they are passing through an FPGA, their timing
can be slightly altered.
 L AN (6): Not used in user mode.
 U SB (7): Type A USB host connector. Can be used to connect a USB memory
stick or e.g. the external stepper motor driver (optional).
 S erial (8): Serial connector. Not used in user mode.
 L aser/TEC (9): Connect the cable here that is plugged to the laser head at the
other end. Be careful with electrostatic discharges (see quED manual). The pinout
is as follows:
# Name Potential
1 Fan - N.C.
2 Peltier +
3 Peltier -
4 N.C.
5 Thermistor 1 GND
6 Fan + N.C.
7 Laserdiode - GND
8 Laserdiode + var.
9 Thermistor 2
 M otor 1 to 3 (10): Stepper motor driver connectors (optional). Connect the stepper
motors (optional) here. Only use this with suitable stepper motors from qutools.
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 M ains Power Connector (11): Use a certied cattle plug to connect the quED
controller to a power socket. The input voltage has to be in the range between 100
and 230 V AC, 50 to 60 Hz and can draw up to 180 W.
4 Twin APD Module
On the right-hand side of the controller there is the twin APD module. It works as a
two-channel single photon counter. It is a vital part of the quED system and should be
handled carefully. When no optical bers are attached to the inputs the protective caps
should always be used to cover them. Please be careful not to expose the APD inputs to
very bright light. Normal room light intensities should be no problem, however.
Warning: Never remove or install the APD module while
the controller is running. It will get damaged.
Status LEDs The two LEDs display the internal status of the APD module:
Power LED Temp LED Meaning
on ashing
Internal temperature (i.e. the temperature
of the APDs themselves) out of bounds (e.g.
during start-up), trying to reach desired
value.
constantly on or o constantly on or o Everything is O.K.
ashing o Module is booting
ashing Module has registered a problem. See trou-
bleshooting.
Tip: High Background Count Rate It sometimes happens that there is a high back-
ground count rate in one or both APDs. Often this results from stray light coming
in through the ber connection at the front panel. If you encounter this problem,
please try to cover the ber connections e.g. with some black tissue and/or switch
o unnecessary light sources.
Troubleshooting When the two LEDs of the APD module are ashing, it has encoun-
tered a problem. There may be dierent reasons for that, e.g. the desired temper-
ature was not reached after 10 minutes. We suggest to do the following:
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1. Leave the controller switched on (if the APDs are overheated, they can cool
down sooner, because the fan stays on).
2. Have a look at the ambient temperature in the room. Is it very warm? If so,
try to get it cooler.
3. Is something blocking the ventilation of the controller? Make sure that is not
the case.
4. Wait at least 30 minutes to let the APD module cool down.
5. Restart the system, observing how the LEDs of the APD module are behaving.
6. If they still report a problem, call qutools support.
The most probable cause for this behavior is that the APD module is overheated.
This can happen when the ambient temperature is too high ( >25 ◦ C) or when
the ventilation slots are blocked. Please make sure that the ventilation openings
beneath, at the back and at the front of the controller are kept clear.
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5 Touch Panel
The quED controller features an integrated embedded computer with a touch panel. You
can control the laser diode driver, the integrated counting module and the stepper motors
(optional) with it.
5.1 Touch Panel Software Overview
The touch panel software is composed of four dierent modules
1. quLD: The laser diode driver module
2. quCNT: The counter module
3. quMotor: The stepper motor module (optional)
4. quInfo: The information and administration module.
Every module consists of dierent tabs, which provide information and accomplish dier-
ent tasks.
Each of those four modules can be selected via the sidebar . The sidebar is always visible
on the right most side of the touch panel. You can cycle through the dierent tabs of
each module by repeatedly touching its module button. Alternatively you can cycle back
and forth with a horizontal swipe gesture on the main display.
However, you may not see all those buttons if your version of the controller doesn't contain
all the hardware modules (e.g. the stepper motor driver).
The larger, left part of the screen is the module screen, where the contents of the dierent
modules are displayed. Also some tabs of the modules are only available if the software
is running in the expert mode (see section 5.5.1).
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5.2 The quLD Module
5.2 The quLD Module
The quLD module has two dierent tabs:
1. User Parameters
2. Settings
1
5.2.1 User Parameters
Figure 3: The rst tab of the quLD module: User Parameters.
This tab informs you about the current running through, and the temperature of the laser
diode.
After selecting the Set Current line edit via the touch screen you can change the value
of the parameter using the rotary encoder on the front panel. The LASER button, on
the top right side, indicates whether the laser emission is turned on or o (see gure 3).
The data elds Actual Current and Actual Temperature display the respective values
measured by the controller. They should be close to the corresponding Set values.
Please note the red warning triangle which might appear in the sidebar. This warning
indicates that at least one of the parameters doesn't t the desired value. This can also
be the case when the laser is switched o, but the value Set Current is non-zero.
Additionally one can enable a Picture in Picture (PiP) mode by clicking on the PiP
button. This mode comes in very handy if you want to monitor or change the laser diode
1
only available in expert mode
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5.2 The quLD Module
current while you are working in another module (see gure 4). By clicking the PiP
button once more you can disable this mode again.
Figure 4: The rst tab of the quLD module with enabled picture in picture mode.
5.2.2 Settings
The settings tab is shown in gure 5. Here you can set various options which should not
be changed by an unauthorized user, such as maximum and minimum of the laser diode
set values. Additionaly you can change the rate of the proportional and integral part of
the temperature feedback loop.
After setting those values you can either save them to the EEProm of the quLD hardware
or discard them by loading the saved values from there.
Warning: Do not change the preset maximum and minimum
values unless you are absolutely sure this is necessary and safe
to do. Wrong parameters can lead to a complete failure of the
quED.
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5.3 The quCNT Module
Figure 5: The second tab of the quLD module.
5.3 The quCNT Module
The second button on the sidebar belongs to the quCNT counter module. The rst two
tabs of this module are displaying the current rates of the dierent avalanche photo diode
(APD) channels and their coincidences. The rst one shows them as plain numbers and
the second one as a time dependent plot. The third tab provides dierent display setting
for those tabs. Subsequent tabs are only displayed depending on the installed hardware
options. Among them are taps to help you perform a measurement of the bell inequality,
to register a Hong-Ou-Mandel dip or to generate random numbers.
The rst three tabs are named
1. Rates
2. Graph
3. Multipliers and Settings
5.3.1 Rates
The Rates tab displays the dierent count rates and the integration time of each APD
channel and their coincidences (see gure 6). The bar at the bottom can be used to select
the rates that are shown. There is the possibility to restrict the selectable channels using
the quInfo module in expert mode (see sections 5.5.1 and 5.5.4).
A single shot of the rates can be triggered by pressing the SiS button. The Go button
will be deactivated and become grey. For the free-running mode activate the Go button
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5.3 The quCNT Module
Figure 6: The rst tab of the quCNT module with the dierent rates displayed.
again. The user button refers to the integration time set in the multipliers and settings
tab.
5.3.2 Graph
This tab of the quCNT module visualizes the count rates of the APD channels as a plot
against time (gure 7). The values on the y-axis always indicate detections per second,
regardless of the selected integration time.
Besides the bar at the bottom, with same functionality as described in section 5.3.1, the
Graph tab includes four new buttons. The Go button is used to start and stop the plot.
The Clear (Clr) button is used to erase the data in the plot. The autorange button
toggles autoranging of the y-axis and, nally, The button with the USB symbol ( ) is
used for saving the plot data to a usb ash drive.
Because coincidence rates are usually much lower than single event rates, each of the rates
can be multiplied by an integer as described in section 5.3.3. This factor is also shown in
the plot as can be seen in gure 7(in this example a green x 2 close to the y axis).
5.3.3 Multipliers and Settings
As shown in gure 8the Multipliers and Settings tab consists of various line edits which
can be used to change the multiplier of a rate. This factor is then applied to the count
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5.3 The quCNT Module
Figure 7: The second tab of the quCNT module with the dierent rates depicted
in a graph.
Figure 8: The third tab of the quCNT module with the various multipliers and
settings
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5.3 The quCNT Module
rates before plotting them in the Graph tab. In the lowest line of this tab you can set the
number of data points in the Graph tab (display range) and the user integration time,
which will eect both, the Rates and the Graph tab.
5.3.4 RNG
Figure 9: The RNG tab of the quCNT module.
This tab of the quCNT module can be used as a random number generator if at least
three dierent APDs (channels 0, 1, and 2) are installed in your hardware. You can toggle
the RNG mode by pressing the respective button as seen in gure 9. A coincidence event
between APD 0 and APD 1 is then interpreted as a zero bit and a coincidence event
between APD 0 and 2 as a one bit.
Warning: For the time the RNG mode of the quCNT module
is enabled, there will be no new count rates displayed in the
rst or second tab of this module.
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5.3 The quCNT Module
The other buttons shown in gure 9are used for saving the random data either as an
ASCII string or as binary data to a USB ash drive. The Clear button is used to delete
the gathered random bits.
The section above the buttons shows the number of registered ones and zeros in the
random string as well as their bias (proportion of ones with respect to all events). The
most recently fetched bits are displayed on the left hand side of the screen.
5.3.5 Entanglement Visibility
Figure 10: Tab for measurement of the two-photon correlation visibility
The Entanglement of the quED two-photon output state can be analyzed by a measure-
ment of the visibility of the two-photon correlations in mutually unbiased bases. If the
polarizers in front of the detectors are mounted in motorized stages and attached to the
quMotor driver, this tab can do the visibility measurement completely automatically.
Alternatively, without motorized stages, the user can trigger a single correlation measure-
ment by a click on the according box after setting the polarizers manually. The Visibility
will be displayed once all measurements in a row are done. Note that the laser has to be
enabled manually prior to this measurement.
5.3.6 Correlation Curves
This tab enables measurements of the correlation of the two output photon polarizations.
For the given integration time, angular interval and number of steps, the number of
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5.3 The quCNT Module
Figure 11: Tab for measurement of correlation curves
coincidences is registered with the rst polarizer in the orientation 'H', '+45', 'V' and
'-45' automatically. The data can subsequently be stored on an attached USB drive.
5.3.7 CHSH Measurement
In order to evaluate the CHSH inequality, the coincidence rates for 16 polarizer settings
have to be measured. Again, if the polarizers are mounted in motorized stages this can be
done completely automatically in this tab. Without motorized stages the tab assists the
user in the CHSH measurement: Simply adjust the polarizers for each of the 16 settings
and click the according tab do trigger the coincidence measurement.
Once all measurements are completed, the CHSH inequality is evaluated and the result
is displayed together with an error information. Note that the laser has to be enabled
manually prior to this measurement.
5.3.8 Houng-Ou-Mandel eect
This tab shows up if a motor controller is present when starting the quCR. It enables
an automatic measurement of Houg-Ou-Mandel eect with an optional motoized qu2PI
setup.
Please note that the qu2PI motor has to be connected to the third channel of the motor-
driver and that only coincidences of APD channel 0 and 1 are registered.
Four input elds control the measurement:
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5.3 The quCNT Module
Figure 12: Tab for measurement of the CHSH inequality
Figure 13: Tab for measurement of the Houg-Ou-Mandel eect.
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5.4 The quMotor Module
Position: This eld displays the actual position of the linear actuator. You can also
manipulate the value. Please understand that this simply shifts the scale. It is
usually best to manuall set the position of the actuator to a dened position (perhaps
a marking) and then set the position eld to zero.
Target: This eld indicates the target position of a measurement scan. Once started, the
actuator will move in steps of Stepsize towards this target position.
Stepsize: The measurement scan will be done in steps of the size indicated here. This
parameter can only be manipulated in multiples of the stepper motor stepsize which
is 1/3200 mm. The display changes accordingly when the stepsize eld has focus.
Integration Time: This sets the integration time per measurement point.
The measurement scan is started with the Start button. Once the scan is completed,
the state of the arrow button determines how the target position is updated:
The position where the last scan started from becomes the new target position.
Useful to scan across the HOM-dip back and forth.
The target is incremented by the length of the last scan. Useful to search for the
HOM-dip by scanning 1 mm, then the next and so on.
The data acquired can be stored on an attached ash drive with the USB ( ) button.
5.4 The quMotor Module
The quMotor module is controlled with this tab which is only displayed when the motor
driver option is installed: the Motor Positions tab is shown in gure 14.
5.4.1 Motor Positions
In the Motor Positions tab you can change the absolute position of the motors in the
range from -400
◦
to 400
◦
. This is done by selecting the position eld and adjusting the
value using the rotary encoder.
The angular positions are relative to the magnetic hardware references of the motors
2
. In
case these angles are not valid anymore  i.e. after the motors had been blocked or moved
by hand  valid positions can be obtained using the Go to Zero button.
To account for the angle between the magnetic reference of the motor and the installed
optical element, an oset value can be stored. For this purpose a button make Zero
is displayed in expert mode. When pressed, the motor measures the angle between its
current position and the magnetic reference and stores this value as a the new oset. In
this way, even a manually set position can be stored as the new zero position. A second
2
The hardware reference is realized with a hall sensor and a small magnet on the circumference of the
large wheel.
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5.5 The quInfo Module
Figure 14: The only tab of the quMotor module.
button nd Ref displayed in expert mode can be used to test the calibration routine
of the motor driver. However, the angular position values then do not respect the stored
oset value anymore.
To facilitate measurements one of three PIP windows can be enabled:
Measurement PIP: allows to change the angular position of the motors to arbitrary
values
Visibility PIP: oers hotkeys for the eight angular combinations necessary to measure
the visibility of an output state
CHSH PIP: oers hotkeys for the 16 angular combinations necessary to measure the
violation of a CHSH inequality
5.5 The quInfo Module
The quInfo module is used for dierent administrative tasks. However most of the tabs
in this module are only available in the expert mode:
1. Change Mode
2. Info and USB Update
1
3. Change Expert Pass phrase
1
4. Rates Conguration
1
.
1
only available in expert mode
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5.5 The quInfo Module
5.5.1 Change Mode
Figure 15: The tab used for switching to the expert mode.
Warning: The expert mode should only be used when ab-
solutely necessary. While in this mode, the user has approach
to parameters which might cause permanent damage to the
laser diode.
This tab, shown in gure 15, is used to change to the expert mode. Here all circles
on the right hand side can be clicked once to compose the proper pass phrase. If you
pressed a wrong circle, you can retry by pressing the Reset button on the left. After you
successfully entered the pass phrase, the quInfo Module immediately switches to the Info
and USB Update tab described in section 5.5.2. The Change Mode tab itself, will change
like displayed in gure 16 and is then used for switching back to the standard mode.
5.5.2 Info and USB Update
This tab provides you with some additional information such as the current software
revision and the startup time. It also shows the current IP address(es) of the device (see
gure 17). Please use the refresh button to update the IP display when necessary.
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