Bragg cavity spectroscopy

docs/source/api/potentials.rst

@@ -110,3 +110,4 @@ Time dependent variables
     ~linear_ramp
     ~s_ramp
     ~quench
+    ~probe_pulse

docs/source/stubs/torchgpe.utils.potentials.probe_pulse.rst

@@ -0,0 +1,6 @@
+torchgpe.utils.potentials.probe\_pulse
+======================================
+
+.. currentmodule:: torchgpe.utils.potentials
+
+.. autofunction:: probe_pulse

docs/source/user_guide/fundamentals.potentials.rst

@@ -173,11 +173,14 @@ DispersiveCavity
 - :py:attr:`cavity_angle` (the angle of the cavity with respect to the horizontal),
 - :py:attr:`pump_angle` (the angle of the pump with respect to the horizontal),
 - :py:attr:`waist` (the waist of the gaussian pump beam).
+- :py:attr:`cavity_probe` (the on-axis probe field. Supports time-dependent parameters).
 
 Note that the lattice depth is expressed in units of the recoil energy :math:`E_r = \hbar^2 k^2 / 2m`, where the wave number :math:`k` is computed from the :math:`d_2` pulse of the atomic species the gas is made of, and the specified atomic detuning.
 Additionally, observe that :py:attr:`atomic_detuning`, :py:attr:`cavity_detuning` and :py:attr:`cavity_decay` have to be considered frequencies. The corresponding rates are obtained by the potential itself, by multiplying them by :math:`2 \pi`.
 
-Finally, :py:attr:`waist` is the waist of the gaussian pump beam. It defaults to infinity, which corresponds to a plane wave. Note that differently from the :class:`~torchgpe.bec2D.potentials.Lattice` potential, the :class:`~torchgpe.bec2D.potentials.DispersiveCavity` potential does not account for the wavefront curvature and the Gouy phase. 
+:py:attr:`waist` is the waist of the gaussian pump beam. It defaults to infinity, which corresponds to a plane wave. Note that differently from the :class:`~torchgpe.bec2D.potentials.Lattice` potential, the :class:`~torchgpe.bec2D.potentials.DispersiveCavity` potential does not account for the wavefront curvature and the Gouy phase. 
+
+Finally, an additional on-axis probe field can be added to the potential via the :py:attr:`cavity_probe`. This is useful to study the response of the system to a perturbation. A pre-defined probe field is defined in :py:meth:`~torchgpe.utils.potentials.probe_pulse`
 
 .. image:: ../_static/fundamentals_cavity_angles.svg
     :align: center

torchgpe/bec2D/potentials.py

@@ -181,9 +181,10 @@ class DispersiveCavity(NonLinearPotential):
         cavity_angle (float, optional): The angle in the 2D plane of the cavity. Defaults to :math:`0`
         pump_angle (float, optional): The angle in the 2D plane of the transversal pump. Defaults to :math:`\\pi/3`
         waist (float, optional): the waist of the gaussian beam. Defaults to infinity
+        cavity_probe (Union[float, Callable], optional): The on-axis cavity probe. It can be set to be either a constant or a function of time. Defaults to :math:`0`
     """
 
-    def __init__(self, lattice_depth: Union[float, Callable], atomic_detuning: float, cavity_detuning: Union[float, Callable], cavity_decay: float, cavity_coupling: float, cavity_angle: float = 0, pump_angle: float = np.pi/3, waist: float = np.inf):
+    def __init__(self, lattice_depth: Union[float, Callable], atomic_detuning: float, cavity_detuning: Union[float, Callable], cavity_decay: float, cavity_coupling: float, cavity_angle: float = 0, pump_angle: float = np.pi/3, waist: float = np.inf, cavity_probe: Union[float, Callable] = 0):
 
         super().__init__()
 
@@ -195,13 +196,15 @@ def __init__(self, lattice_depth: Union[float, Callable], atomic_detuning: float
         self.cavity_angle = cavity_angle
         self.pump_angle = pump_angle
         self.waist = waist
+        self.cavity_probe = cavity_probe
 
     def on_propagation_begin(self):
         self.is_time_dependent = any_time_dependent_variable(
-            self.cavity_detuning, self.lattice_depth)
+            self.cavity_detuning, self.lattice_depth, self.cavity_probe)
 
         self._cavity_detuning = time_dependent_variable(self.cavity_detuning)
         self._lattice_depth = time_dependent_variable(self.lattice_depth)
+        self._cavity_probe = time_dependent_variable(self.cavity_probe)
 
         self.g0 = 2*np.pi*self.cavity_coupling
         self._atomic_detuning = 2*np.pi*self.atomic_detuning
@@ -253,7 +256,7 @@ def get_alpha(self, psi: torch.tensor, time: float = None):
 
         self.eta = np.sqrt(self._lattice_depth(time))*self.eta_prefactor
 
-        alpha = self.c1*self.eta*order/self.c6
+        alpha = (self.c1*self.eta*order + self._cavity_probe(time)*(self.Er/spconsts.hbar))/self.c6
 
         return alpha
 

torchgpe/utils/potentials.py

@@ -80,6 +80,23 @@ def quench(v0=1, v1=0, quench_time=1):
         """
     return lambda t: v0 if t < quench_time else v1
 
+
+def probe_pulse(amplitude, detuning, t0 = 0, phase = 0):
+    """Implements a probe pulse with a givem amplitude, detuning, and phase.
+
+    Args:
+        amplitude (float): The amplitude of the pulse.
+        detuning (float): The detuning between the cavity's transverse pump frequency and the probe frequency.
+        t0 (float, optional): The time at which the pulse starts. Defaults to :math:`0`.
+        phase (float, optional): The phase of the pulse. Defaults to :math:`0`.
+
+    Returns:
+        float: The value of the pulse at time :math:`t`
+        """
+    omega = 2*torch.pi*detuning
+    return lambda t: 0 if t<t0 else amplitude * torch.exp(1j*(omega*t + phase))
+
+
 # --- Potential base classes ---