Merge pull request #99 from frosati1/lib

New propagation library created by moving code 
related only with propagation from tf.utils to 
propagation.py in c3/libraries

c3/experiment.py

@@ -23,13 +23,16 @@
 from c3.signal.gates import Instruction
 from c3.model import Model
 from c3.utils.tf_utils import (
-    tf_batch_propagate,
-    tf_propagation_lind,
     tf_matmul_left,
     tf_state_to_dm,
     tf_super,
     tf_vec_to_dm,
 )
+
+from c3.libraries.propagation import (
+    tf_batch_propagate,
+    tf_propagation_lind,
+)
 from c3.utils.qt_utils import perfect_single_q_parametric_gate
 
 
@@ -309,7 +312,7 @@ def process(self, populations, labels=None):
         populations_final = []
         populations_no_rescale = []
         for pops in populations:
-            # TODO: Loop over all tasks in a general fashion
+            # TODO: Loop over all model.tasks in a general fashion
             # TODO: Selecting states by label in the case of computational space
             if "conf_matrix" in model.tasks:
                 pops = model.tasks["conf_matrix"].confuse(pops)

c3/libraries/fidelities.py

@@ -19,8 +19,12 @@
     tf_average_fidelity,
     tf_superoper_average_fidelity,
     tf_state_to_dm,
+)
+
+from c3.libraries.propagation import (
     evaluate_sequences,
 )
+
 from c3.utils.qt_utils import (
     basis,
     perfect_cliffords,

c3/libraries/propagation.py

@@ -0,0 +1,325 @@
+"A library for propagators and closely related functions"
+
+import tensorflow as tf
+from c3.utils.tf_utils import (
+    tf_kron_batch,
+    tf_matmul_left,
+    tf_spre,
+    tf_spost,
+)
+
+
+@tf.function
+def tf_dU_of_t(h0, hks, cflds_t, dt):
+    """
+    Compute H(t) = H_0 + sum_k c_k H_k and matrix exponential exp(i H(t) dt).
+
+    Parameters
+    ----------
+    h0 : tf.tensor
+        Drift Hamiltonian.
+    hks : list of tf.tensor
+        List of control Hamiltonians.
+    cflds_t : array of tf.float
+        Vector of control field values at time t.
+    dt : float
+        Length of one time slice.
+
+    Returns
+    -------
+    tf.tensor
+        dU = exp(-i H(t) dt)
+
+    """
+    h = h0
+    ii = 0
+    while ii < len(hks):
+        h += cflds_t[ii] * hks[ii]
+        ii += 1
+    # terms = int(1e12 * dt) + 2
+    # dU = tf_expm(-1j * h * dt, terms)
+    # TODO Make an option for the exponentation method
+    dU = tf.linalg.expm(-1j * h * dt)
+    return dU
+
+
+# @tf.function
+def tf_dU_of_t_lind(h0, hks, col_ops, cflds_t, dt):
+    """
+    Compute the Lindbladian and it's matrix exponential exp(L(t) dt).
+
+    Parameters
+    ----------
+    h0 : tf.tensor
+        Drift Hamiltonian.
+    hks : list of tf.tensor
+        List of control Hamiltonians.
+    col_ops : list of tf.tensor
+        List of collapse operators.
+    cflds_t : array of tf.float
+        Vector of control field values at time t.
+    dt : float
+        Length of one time slice.
+
+    Returns
+    -------
+    tf.tensor
+        dU = exp(L(t) dt)
+
+    """
+    h = h0
+    for ii in range(len(hks)):
+        h += cflds_t[ii] * hks[ii]
+    lind_op = -1j * (tf_spre(h) - tf_spost(h))
+    for col_op in col_ops:
+        super_clp = tf.matmul(tf_spre(col_op), tf_spost(tf.linalg.adjoint(col_op)))
+        anticomm_L_clp = 0.5 * tf.matmul(
+            tf_spre(tf.linalg.adjoint(col_op)), tf_spre(col_op)
+        )
+        anticomm_R_clp = 0.5 * tf.matmul(
+            tf_spost(col_op), tf_spost(tf.linalg.adjoint(col_op))
+        )
+        lind_op = lind_op + super_clp - anticomm_L_clp - anticomm_R_clp
+    # terms = int(1e12 * dt) # Eyeball number of terms in expm
+    #     print('terms in exponential: ', terms)
+    # dU = tf_expm(lind_op * dt, terms)
+    # Built-in tensorflow exponential below
+    dU = tf.linalg.expm(lind_op * dt)
+    return dU
+
+
+@tf.function
+def tf_propagation_vectorized(h0, hks, cflds_t, dt):
+    dt = tf.cast(dt, dtype=tf.complex128)
+    if hks is not None and cflds_t is not None:
+        cflds_t = tf.cast(cflds_t, dtype=tf.complex128)
+        hks = tf.cast(hks, dtype=tf.complex128)
+        cflds = tf.expand_dims(tf.expand_dims(cflds_t, 2), 3)
+        hks = tf.expand_dims(hks, 1)
+        if len(h0.shape) < 3:
+            h0 = tf.expand_dims(h0, 0)
+        prod = cflds * hks
+        h = h0 + tf.reduce_sum(prod, axis=0)
+    else:
+        h = tf.cast(h0, tf.complex128)
+    dh = -1.0j * h * dt
+    return tf.linalg.expm(dh)
+
+
+def tf_batch_propagate(hamiltonian, hks, signals, dt, batch_size):
+    """
+    Propagate signal in batches
+    Parameters
+    ----------
+    hamiltonian: tf.tensor
+        Drift Hamiltonian
+    hks: Union[tf.tensor, List[tf.tensor]]
+        List of control hamiltonians
+    signals: Union[tf.tensor, List[tf.tensor]]
+        List of control signals, one per control hamiltonian
+    dt: float
+        Length of one time slice
+    batch_size: int
+        Number of elements in one batch
+
+    Returns
+    -------
+
+    """
+    if signals is not None:
+        batches = int(tf.math.ceil(signals.shape[0] / batch_size))
+        batch_array = tf.TensorArray(
+            signals.dtype, size=batches, dynamic_size=False, infer_shape=False
+        )
+        for i in range(batches):
+            batch_array = batch_array.write(
+                i, signals[i * batch_size : i * batch_size + batch_size]
+            )
+    else:
+        batches = int(tf.math.ceil(hamiltonian.shape[0] / batch_size))
+        batch_array = tf.TensorArray(
+            hamiltonian.dtype, size=batches, dynamic_size=False, infer_shape=False
+        )
+        for i in range(batches):
+            batch_array = batch_array.write(
+                i, hamiltonian[i * batch_size : i * batch_size + batch_size]
+            )
+
+    dUs_array = tf.TensorArray(tf.complex128, size=batches, infer_shape=False)
+    for i in range(batches):
+        x = batch_array.read(i)
+        if signals is not None:
+            result = tf_propagation_vectorized(hamiltonian, hks, x, dt)
+        else:
+            result = tf_propagation_vectorized(x, None, None, dt)
+        dUs_array = dUs_array.write(i, result)
+    return dUs_array.concat()
+
+
+def tf_propagation(h0, hks, cflds, dt):
+    """
+    Calculate the unitary time evolution of a system controlled by time-dependent
+    fields.
+
+    Parameters
+    ----------
+    h0 : tf.tensor
+        Drift Hamiltonian.
+    hks : list of tf.tensor
+        List of control Hamiltonians.
+    cflds : list
+        List of control fields, one per control Hamiltonian.
+    dt : float
+        Length of one time slice.
+
+    Returns
+    -------
+    list
+        List of incremental propagators dU.
+
+    """
+    dUs = []
+
+    for ii in range(cflds[0].shape[0]):
+        cf_t = []
+        for fields in cflds:
+            cf_t.append(tf.cast(fields[ii], tf.complex128))
+        dUs.append(tf_dU_of_t(h0, hks, cf_t, dt))
+    return dUs
+
+
+@tf.function
+def tf_propagation_lind(h0, hks, col_ops, cflds_t, dt, history=False):
+    col_ops = tf.cast(col_ops, dtype=tf.complex128)
+    dt = tf.cast(dt, dtype=tf.complex128)
+    if hks is not None and cflds_t is not None:
+        cflds_t = tf.cast(cflds_t, dtype=tf.complex128)
+        hks = tf.cast(hks, dtype=tf.complex128)
+        cflds = tf.expand_dims(tf.expand_dims(cflds_t, 2), 3)
+        hks = tf.expand_dims(hks, 1)
+        h0 = tf.expand_dims(h0, 0)
+        prod = cflds * hks
+        h = h0 + tf.reduce_sum(prod, axis=0)
+    else:
+        h = h0
+
+    h_id = tf.eye(h.shape[-1], batch_shape=[h.shape[0]], dtype=tf.complex128)
+    l_s = tf_kron_batch(h, h_id)
+    r_s = tf_kron_batch(h_id, tf.linalg.matrix_transpose(h))
+    lind_op = -1j * (l_s - r_s)
+
+    col_ops_id = tf.eye(
+        col_ops.shape[-1], batch_shape=[col_ops.shape[0]], dtype=tf.complex128
+    )
+    l_col_ops = tf_kron_batch(col_ops, col_ops_id)
+    r_col_ops = tf_kron_batch(col_ops_id, tf.linalg.matrix_transpose(col_ops))
+
+    super_clp = tf.matmul(l_col_ops, r_col_ops, adjoint_b=True)
+    anticom_L_clp = 0.5 * tf.matmul(l_col_ops, l_col_ops, adjoint_a=True)
+    anticom_R_clp = 0.5 * tf.matmul(r_col_ops, r_col_ops, adjoint_b=True)
+    clp = tf.expand_dims(
+        tf.reduce_sum(super_clp - anticom_L_clp - anticom_R_clp, axis=0), 0
+    )
+    lind_op += clp
+
+    dU = tf.linalg.expm(lind_op * dt)
+    return dU
+
+
+def evaluate_sequences(propagators: dict, sequences: list):
+    """
+    Compute the total propagator of a sequence of gates.
+
+    Parameters
+    ----------
+    propagators : dict
+        Dictionary of unitary representation of gates.
+
+    sequences : list
+        List of keys from propagators specifying a gate sequence.
+        The sequence is multiplied from the left, i.e.
+            sequence = [U0, U1, U2, ...]
+        is applied as
+            ... U2 * U1 * U0
+
+    Returns
+    -------
+    tf.tensor
+        Propagator of the sequence.
+
+    """
+    gates = propagators
+    # get dims to deal with the case where a sequence is empty
+    dim = list(gates.values())[0].shape[0]
+    dtype = list(gates.values())[0].dtype
+    # TODO deal with the case where you only evaluate one sequence
+    U = []
+    for sequence in sequences:
+        if len(sequence) == 0:
+            U.append(tf.linalg.eye(dim, dtype=dtype))
+        else:
+            Us = []
+            for gate in sequence:
+                Us.append(gates[gate])
+
+            Us = tf.cast(Us, tf.complex128)
+            U.append(tf_matmul_left(Us))
+            # ### WARNING WARNING ^^ look there, it says left WARNING
+    return U
+
+
+def tf_expm(A, terms):
+    """
+    Matrix exponential by the series method.
+
+    Parameters
+    ----------
+    A : tf.tensor
+        Matrix to be exponentiated.
+    terms : int
+        Number of terms in the series.
+
+    Returns
+    -------
+    tf.tensor
+        expm(A)
+
+    """
+    r = tf.eye(int(A.shape[-1]), batch_shape=A.shape[:-2], dtype=A.dtype)
+    A_powers = A
+    r += A
+
+    for ii in range(2, terms):
+        A_powers = tf.matmul(A_powers, A) / tf.cast(ii, tf.complex128)
+        ii += 1
+        r += A_powers
+    return r
+
+
+def tf_expm_dynamic(A, acc=1e-5):
+    """
+    Matrix exponential by the series method with specified accuracy.
+
+    Parameters
+    ----------
+    A : tf.tensor
+        Matrix to be exponentiated.
+    acc : float
+        Accuracy. Stop when the maximum matrix entry reaches
+
+    Returns
+    -------
+    tf.tensor
+        expm(A)
+
+    """
+    r = tf.eye(int(A.shape[0]), dtype=A.dtype)
+    A_powers = A
+    r += A
+
+    ii = tf.constant(2, dtype=tf.complex128)
+    while tf.reduce_max(tf.abs(A_powers)) > acc:
+        A_powers = tf.matmul(A_powers, A) / ii
+        ii += 1
+        r += A_powers
+    return r