Atlas driver Operation¶

The information on this page guides users through the features of the WebSQ driver software running on a Single Quantum system.

Switch On the Driver¶

To switch on the driver:

• Push the button on the front panel.

Driver Connection¶

The WebSQ driver connects over Ethernet, either directly to a computer or through a router.

Default configuration:

• IP address: 192.168.1.1 or sq.local

• DHCP address range: 192.168.1.5 to 192.168.1.200

• Username: user

• Password: websq

The driver interface follows the HTML5 standard and can be accessed using an HTML5-compatible browser. A recent version of Google Chrome or Mozilla Firefox is recommended.

Note: If you are locked out because of incorrect network settings or forgotten login credentials, reset the driver by holding the front-panel button for more than 8 seconds.

Direct Connection¶

To connect the driver directly to your computer:

• Enter 192.168.1.1 in your browser.

• Alternatively, enter sq.local/.

If you configured a hostname in the Networking settings, you can access the system at hostname.local/.

Wi-Fi or Network Connection¶

Connect the driver to a router with Wi-Fi access to use it from any computer or mobile device connected to the same network.

Disable the driver’s DHCP server in the Networking settings because the router typically acts as the DHCP server.

For more information about the network configuration, see #software-configuration.

WebSQ Interface¶

Login¶

After connecting to the WebSQ driver, the login screen appears.

Default credentials:

• Username: user

• Password: websq

Important: The WebSQ driver runs a DHCP server by default. Do not connect it to an existing network before disabling its DHCP server. Use the supplied USB-to-Ethernet adapter to configure the network settings first.

After logging in, you can change the username and password under Configuration > Access Control.

Available navigation options:

Home Window¶

The Home window provides the main controls and monitoring tools for operating the superconducting nanowire single-photon detectors.

It is divided into three sections:

• Real-Time Monitor

• Control

• Alignment Helper

Real-Time Monitor¶

The Real-Time Monitor displays a time trace of the detected photons for each detector.

Available functions:

• Right-click the graph to select automatic or manual Y-axis scaling.

• Enable the detector bias currents.

• Set the photon-counting integration time.

• Record measurement data.

• Clear old data from the plot to improve automatic scaling.

Recording controls allow you to:

• Start recording, with a limit of 100,000 lines.

• Stop recording and delete the stored file.

• Name the file and add comments.

• Download the recorded file.

Control¶

The Control section displays photon counts and allows you to adjust the detector bias currents and trigger levels.

Available controls:

• Counts: Displays photon counts in a large format for alignment.

• Visible: Shows or hides individual graph traces.

• Bias Current: Opens a dialog for selecting the adjustment increment. The polarity of the bias current and trigger level can also be changed for all detectors simultaneously.

• Trigger Level: Opens a dialog for selecting the trigger-level adjustment increment.

Keyboard Shortcuts¶

Alignment Helper¶

Activate the Alignment Helper to generate a sound with a frequency proportional to the photon count rate of the selected detector channel.

Available settings include:

• Rollover threshold, with a default value of 1 MCnt

• Square sound

• Sine sound

• Sawtooth sound

• Triangle sound

These settings are available under Configuration > Sound/LED.

The brightness of the front-panel LED can also be adjusted to minimize interference with sensitive measurements.

Detector Operation¶

An SNSPD must have a properly configured bias current to operate at peak performance. The highest detector efficiency is achieved when the detector is biased close to its critical current.

Below the critical current, the detector voltage remains at 0 V. When the bias current exceeds the critical current, the detector voltage rises sharply.

The Tune window helps determine a suitable detector operating point.

Auto Search¶

The Auto Search function identifies a bias current corresponding to a selected dark count rate.

To use Auto Search:

1. Ensure that no light reaches the detector.

2. Open Auto Search using the magnifying-glass icon.

3. Select a target dark count rate.

4. Start the search.

Note: A minus sign indicates that Auto Search could not find a suitable bias current. Select a different dark count rate and repeat the search.

Higher count rates may be achieved by lowering the bias current. However, this can reduce detection efficiency. Make fine adjustments to determine the optimal operating point.

Detector Temperature¶

The Temperature window displays the detector temperature history during cooldown and warm-up.

• Download the temperature history using the download icon.

• The history covers the period since the last driver startup.

• Switching off the driver deletes the stored temperature history.

• The maximum storage capacity is 100,000 entries.

• When this limit is reached, new entries replace the oldest entries on a first-in, first-out basis.

Configuration¶

The Configuration menu contains the following settings:

• Data Presentation

• Networking

• Trigger Level

• Sound/LED

• Time

• Access Control

• Update

Data Presentation¶

The Data Presentation settings apply to all graphs and allow you to configure:

• X-axis font size

• Y-axis font size

• Graph line width

• Normalization of detected photons to photons per second

Networking¶

The Networking settings allow you to configure access to the WebSQ driver.

For detailed instructions, see #software-configuration.

Trigger Level¶

The WebSQ driver converts analog pulses from the SNSPDs into digital signals that can be read by the internal counter.

Digital pulses are generated when the rising edge of the analog detection signal crosses the trigger level. A suitable trigger level is generally half the pulse peak value.

Use an oscilloscope to determine the trigger level. If an oscilloscope is unavailable:

1. Increase the trigger level until photon counts are no longer registered.

2. Record this value as the peak level.

3. Set the trigger level to half the peak level.

4. Repeat the procedure for every detector channel.

Example:

• Peak level: 630 mV

• Trigger level: 315 mV

Sound and LED¶

The Sound/LED settings allow you to configure:

• Sound type

• Rollover frequency

• Front-panel LED brightness, if supported by the hardware

The available sound types are:

• Square

• Sine

• Sawtooth

• Triangle

Note: These settings do not affect recorded photon-count data.

The internal counters can count up to 2 GHz and have a dead time of 500 ps.

Time¶

Use the Time settings to configure the system time and time zone.

The configured time is used to timestamp generated files and their entries.

Access Control¶

Use the Access Control settings to change the username and password.

Update¶

Use the Update settings to upload and install an update ZIP package. Installing an update may take several minutes.

Warning: Never switch off the driver during an update. Doing so may damage the system.

Help¶

The Help menu allows you to:

• View or download the manual.

• Download sample code for communicating with the WebSQ driver.

• Review the installed software licences.

Advanced Settings¶

The Advanced Settings menu contains system settings that normally only require calibration at the factory.

Changing these settings is strongly discouraged. Their functionality is documented to keep the system open and configurable.

For detailed information, see #advanced-settings.