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   "source": [
    "# Copyright 2025 Keysight Technologies Inc."
   ]
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    "Absolute_phase\n",
    "==============\n",
    "\n",
    "Each microwave output channel in the QCS can track phase\n",
    "in one of two ways: consistent phase or coherent phase.\n",
    "This is configured when adding virtual channels in a channel\n",
    "mapper by addressing the argument of ``absolute_phase=True``\n",
    "or ``absolute_phase=False``.\n",
    "\n",
    "Consistent phase (Absolute_phase=True)\n",
    "--------------------------------------\n",
    "\n",
    "If the channel is configured with ``absolute_phase=True`` then the\n",
    "IF parameters (phase, frequency and amplitude) are encoded into the\n",
    "waveform memory. Consequently, if the signal is downconverted and acquired\n",
    "on a digitizer it will have the same absolute phase (phase of the demodulated\n",
    "signal in the I/Q plane) in every shot. Because of this, ``absolute_phase=True``\n",
    "is typically used for readout channels where consistent phase is critical.\n",
    "\n",
    "Note that subsequent pulses played on a channel with ``absolute_phase=True``\n",
    "will have the same absolute phase and therefore are **not** guaranteed to be\n",
    "phase coherent with one another.\n",
    "\n",
    "Multiple signals with different frequencies can be multiplexed on channels with\n",
    "``absolute_phase=True``. There is no explicit limit on the number of tones\n",
    "that can be multiplexed, but keep in mind that the combined amplitude of the\n",
    "output signal must still fit in the output range of the AWG. As more tones are\n",
    "combined the maximum amplitude of each tone is divided down.\n",
    "\n",
    "Because all parameters of the pulse are encoded in the waveform memory for this\n",
    "channel type, hardware-accelerated scans are not possible for any parameter\n",
    "other than delay.\n",
    "\n",
    "Coherent Phase (Absolute_phase=False)\n",
    "-------------------------------------\n",
    "\n",
    "If the channel is configured with ``absolute_phase=False`` then the IF parameters\n",
    "(phase, frequency and amplitude) are explicitly stored along with each waveform\n",
    "and only the envelope is encoded in waveform memory. In this configuration, the\n",
    "waveform is built in real time and the phase is tracked by a digital upconverter\n",
    "(DUC) on the module’s FPGA.\n",
    "\n",
    "In this configuration, subsequent pulses will be phase coherent with each other,\n",
    "making this the ideal configuration for qubit control channels. Because the DUC\n",
    "is free-running, acquiring the downconverted waveform on a digitizer will give\n",
    "a different phase each shot. This means that if the time trace is averaged over\n",
    "many shots it will generally tend toward zero.\n",
    "\n",
    "A physical channel with ``absolute_phase=False`` can support up to 16 different\n",
    "frequencies. Sequences can switch between different frequencies on this channel\n",
    "without sacrificing phase coherence. In this mode, multiple frequencies cannot\n",
    "be multiplexed to play back at the same time on a single physical channel.\n",
    "\n",
    "Hardware sweeps of amplitude, phase, and frequency are only available for\n",
    "``absolute_phase=False`` channels.\n",
    "\n",
    "Finally, note that for both ``absolute_phase=True`` and ``absolute_phase=False``,\n",
    "the IF waveform is upconverted by a microwave Numerically Controlled Oscillator\n",
    "(NCO). This NCO has its phase reset at the start of an experiment but is\n",
    "free-running from that point on. Because of this, if the microwave signal is\n",
    "viewed on a high-frequency scope, it will show a different absolute phase\n",
    "shot-to-shot. Consistent absolute phase is only observed when the microwave\n",
    "signal passes through a QCS downconverter at the same frequency as the microwave\n",
    "NCO. For this reason we recommend using the same Local Oscillator (LO)\n",
    "frequency for downconverters and AWGs used for readout."
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