PDF (double-sided) - Physics Department, UCSB - University of ...
PDF (double-sided) - Physics Department, UCSB - University of ... PDF (double-sided) - Physics Department, UCSB - University of ...
one microwave line for X/Y-rotations, and one readout line to detect the switching of the squid. These lines get driven by several GHz DAC boards and one microwave source. The GHz DAC boards connect to a computer via ethernet and the microwave source uses a GPIB connection. Furthermore, the squid readout pre-amplifier gets configured via a serial link. These three hardware interfaces – GPIB, ethernet, and RS-232 – are exposed to the LabRAD system via one dedicated Server Module each – the GPIB Server, the Direct Ethernet Server, and the Serial Server. Above these sits a set of device Servers that each implement the communication protocol of one device type to provide higher level functions like “Set the output of the microwave source to 7 GHz at 2.7dBm”. The next level in the stack – the Qubit and DAC Calibration Servers – abstract the exact hardware configuration by allowing the user to, for example, load a sequence of voltages into the “Squid Bias” channel on “Qubit 2” (rather than “FO 1” on “GHz DAC 17”). This data is then corrected for imperfections in the analog electronics chain and automatically sent to the right GHz DAC board. Up to this level the software does not impose any limits on the hardware control beyond preventing erroneous configurations. Until here, starting from the hardware/software interface, the first layers in the software abstraction stack closely mimic the first layers in the hardware stack. 154
The next layers correspond to the “applications” (i.e. the experiments) that are to be run on the quantum computer. For now, at the base of this stack is a collection of Experiment Servers that provide functions to take one data point of a specific experiment (Rabi, T1, Bell Violation, etc.). These Servers are called by the “Sweep Server” which varies one or more of the experimental parameters to generate n-D datasets. At the highest level in the stack sit several Client Modules that allow the user to edit parameters, run sweeps, and view the resulting data sets. Let’s go over the different Modules in detail starting from the Client end. 7.5.2 DC Rack Controller Starting with the right-most branch of the diagram in Figure 7.1, the DC Rack Controller consists of a LabVIEW VI that provides an interface to the user to set up the DC bias rack, which houses the FastBias and PreAmp cards. Apart from configuring diagnostic outputs, the most important feature is the ability to control the cutoff voltage that the PreAmp uses to detect the squid’s switch to the voltage state. The only function of the DC Rack Controller is to translate user interactions with switches and dials on the front panel to calls to the DC Rack Server that performs the actual updates. 155
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The next layers correspond to the “applications” (i.e. the experiments) that<br />
are to be run on the quantum computer. For now, at the base <strong>of</strong> this stack is a<br />
collection <strong>of</strong> Experiment Servers that provide functions to take one data point <strong>of</strong><br />
a specific experiment (Rabi, T1, Bell Violation, etc.). These Servers are called by<br />
the “Sweep Server” which varies one or more <strong>of</strong> the experimental parameters to<br />
generate n-D datasets. At the highest level in the stack sit several Client Modules<br />
that allow the user to edit parameters, run sweeps, and view the resulting data<br />
sets. Let’s go over the different Modules in detail starting from the Client end.<br />
7.5.2 DC Rack Controller<br />
Starting with the right-most branch <strong>of</strong> the diagram in Figure 7.1, the DC<br />
Rack Controller consists <strong>of</strong> a LabVIEW VI that provides an interface to the user<br />
to set up the DC bias rack, which houses the FastBias and PreAmp cards. Apart<br />
from configuring diagnostic outputs, the most important feature is the ability to<br />
control the cut<strong>of</strong>f voltage that the PreAmp uses to detect the squid’s switch to<br />
the voltage state. The only function <strong>of</strong> the DC Rack Controller is to translate<br />
user interactions with switches and dials on the front panel to calls to the DC<br />
Rack Server that performs the actual updates.<br />
155
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