Add base classes for baths.

qutip/baths/base.py

@@ -0,0 +1,151 @@
+""" Base classes for environmental baths. """
+
+from enum import StrEnum
+
+
+class BathStatistics(StrEnum):
+    """
+    An enumeration of bath statistics.
+    """
+
+    BOSONIC = "bosonic"
+    FERMIONIC = "fermionic"
+
+
+class Bath:
+    """
+    Base class for representing environment baths.
+
+    Parameters
+    ----------
+    T : float
+        The temperature of the bath.
+
+    Attributes
+    ----------
+    T : float
+        The temperature of the bath.
+    statistics: BathStatistics
+        The statistics of the bath. Either `BOSONIC` or `FERMIONIC`.
+    """
+
+    def __init__(self, T):
+        self.T = T
+
+    @property
+    def statistics(self):
+        raise NotImplementedError(
+            "Sub-classes of Bath should provide a .statistics property."
+        )
+
+    def spectral_density(self, w):
+        """
+        Return the spectral density of the bath.
+
+        Parameters
+        ----------
+        w : array-like or float
+            The angular frequencies at which to evaluate the specral density.
+
+        Returns
+        -------
+        spectral_density: array-like or float
+            The spectral density values for each ``w``.
+
+        Notes
+        -----
+        Note that various conventions for the definition of the spectral
+        density exist. We follow the convention:
+
+        XXX: We want to give the integral form here, or perhaps both the
+             discrete and integral forms, but definitely not just a
+             discrete for in terms of Dirac deltas which makes a bit no
+             sense.
+
+        $$
+            J(\omega) = \pi \sum_k \left| g_k \right|2 \delta \left( \omega − \omega_k \right).
+        $$
+        """
+        raise NotImplementedError(
+            "Sub-classes of Bath should implement .spectral_density()."
+        )
+
+    def correlation_function(self, t):
+        """
+        Return the single-time correlation function of the bath.
+
+        Parameters
+        ----------
+        t : array-like or float
+            The times at which to evaluate the correlation function.
+
+        Returns
+        -------
+        correlations: array-like or float
+            The correlation function values for each ``t``.
+        """
+        raise NotImplementedError(
+            "Sub-classes of Bath should implement .correlation_function()."
+        )
+
+    def power_spectrum(self, w):
+        """
+        Return the power spectrum of the bath.
+
+        Parameters
+        ----------
+        w : array-like or float
+            The energy of each mode for which to evaluate the power spectrum.
+
+        Returns
+        -------
+        spectrum: array-like or float
+            The power spectrum for each mode ``w``.
+        """
+        raise NotImplementedError(
+            "Sub-classes of Bath should implement .power_spectrum()."
+        )
+
+
+class BosonicBath:
+    """
+    Base class for representing bosonic environments.
+
+    Parameters
+    ----------
+    T : float
+        The temperature of the bath.
+
+    Attributes
+    ----------
+    T : float
+        The temperature of the bath.
+    statistics: BathStatistics
+        The statistics of the bath, i.e. `BOSONIC`.
+    """
+
+    @property
+    def statistics(self):
+        return BathStatistics.BOSONIC
+
+
+class FermionicBath:
+    """
+    Base class for representing fermionic environments.
+
+    Parameters
+    ----------
+    T : float
+        The temperature of the bath.
+
+    Attributes
+    ----------
+    T : float
+        The temperature of the bath.
+    statistics: BathStatistics
+        The statistics of the bath, i.e. `FERMIONIC`.
+    """
+
+    @property
+    def statistics(self):
+        return BathStatistics.FERMIONIC