Remake (#9)

Remake of horqrux in the style of pyqtorch, i.e., geared towards Qadence.

Author: dominikandreasseitz

docs/index.md

@@ -18,92 +18,172 @@ pip install horqrux
 Let's have a look at primitive gates first.
 
 ```python exec="on" source="material-block"
-from horqrux.gates import X
-from horqrux.utils import prepare_state
-from horqrux.ops import apply_gate
+from horqrux import X, random_state, apply_gate
 
-state = prepare_state(2)
+state = random_state(2)
 new_state = apply_gate(state, X(0))
 ```
 
 We can also make any gate controlled, in the case of X, we have to pass the target qubit first!
 
 ```python exec="on" source="material-block"
 import jax.numpy as jnp
-from horqrux.gates import X
-from horqrux.utils import prepare_state, equivalent_state
-from horqrux.ops import apply_gate
+from horqrux import X, product_state, equivalent_state, apply_gate
 
 n_qubits = 2
-state = prepare_state(n_qubits, '11')
+state = product_state('11')
 control = 0
 target = 1
 # This is equivalent to performing CNOT(0,1)
 new_state= apply_gate(state, X(target,control))
-assert jnp.allclose(new_state, prepare_state(n_qubits, '10'))
+assert jnp.allclose(new_state, product_state('10'))
 ```
 
-When applying parametric gates, we pass the numeric value for the parameter first
+When applying parametric gates, we can either pass a numeric value or a parameter name for the parameter as the first argument.
 
 ```python exec="on" source="material-block"
 import jax.numpy as jnp
-from horqrux.gates import Rx
-from horqrux.utils import prepare_state
-from horqrux.ops import apply_gate
+from horqrux import RX, random_state, apply_gate
 
 target_qubit = 1
-state = prepare_state(target_qubit+1)
+state = random_state(target_qubit+1)
 param_value = 1 / 4 * jnp.pi
-new_state = apply_gate(state, Rx(param_value, target_qubit))
+new_state = apply_gate(state, RX(param_value, target_qubit))
+# Parametric horqrux gates also accept parameter names in the form of strings.
+# Simply pass a dictionary of parameter names and values to the 'apply_gate' function
+new_state = apply_gate(state, RX('theta', target_qubit), {'theta': jnp.pi})
 ```
 
 We can also make any parametric gate controlled simply by passing a control qubit.
 
 ```python exec="on" source="material-block"
 import jax.numpy as jnp
-from horqrux.gates import Rx
-from horqrux.utils import prepare_state
-from horqrux.ops import apply_gate
+from horqrux import RX, product_state, apply_gate
 
 n_qubits = 2
 target_qubit = 1
 control_qubit = 0
-state = prepare_state(2, '11')
+state = product_state('11')
 param_value = 1 / 4 * jnp.pi
-new_state = apply_gate(state, Rx(param_value, target_qubit, control_qubit))
+new_state = apply_gate(state, RX(param_value, target_qubit, control_qubit))
 ```
 
-A fully differentiable variational circuit is simply a sequence of gates which are applied to a state.
+We can now build a fully differentiable variational circuit by simply defining a sequence of gates
+and a set of initial parameter values we want to optimize.
+Lets fit a function using a simple circuit class wrapper.
+
+```python exec="on" source="material-block" html="1"
+from __future__ import annotations
 
-```python exec="on" source="material-block"
 import jax
+from jax import grad, jit, Array, value_and_grad, vmap
+from dataclasses import dataclass
 import jax.numpy as jnp
-from horqrux import gates
-from horqrux.utils import prepare_state, overlap
-from horqrux.ops import apply_gate
+import optax
+from functools import reduce, partial
+from operator import add
+from typing import Any, Callable
+from uuid import uuid4
+
+from horqrux.abstract import Operator
+from horqrux import Z, RX, RY, NOT, zero_state, apply_gate, overlap
+
+
+n_qubits = 5
+n_params = 3
+n_layers = 3
 
-n_qubits = 2
-state = prepare_state(2, '00')
 # Lets define a sequence of rotations
-ops = [gates.Rx, gates.Ry, gates.Rx]
+def ansatz_w_params(n_qubits: int, n_layers: int) -> tuple[list, list]:
+    all_ops = []
+    param_names = []
+    rots_fns = [RX ,RY, RX]
+    for _ in range(n_layers):
+        for i in range(n_qubits):
+            ops = [fn(str(uuid4()), qubit) for fn, qubit in zip(rots_fns, [i for _ in range(len(rots_fns))])]
+            param_names += [op.param for op in ops]
+            ops += [NOT((i+1) % n_qubits, i % n_qubits) for i in range(n_qubits)]
+            all_ops += ops
+
+    return all_ops, param_names
+
+#  We need a function to fit and use it to produce training data
+fn = lambda x, degree: .05 * reduce(add, (jnp.cos(i*x) + jnp.sin(i*x) for i in range(degree)), 0)
+x = jnp.linspace(0, 10, 100)
+y = fn(x, 5)
+
+@dataclass
+class Circuit:
+    n_qubits: int
+    n_layers: int
+
+    def __post_init__(self) -> None:
+        # We will use a featuremap of RX rotations to encode some classical data
+        self.feature_map: list[Operator] = [RX('phi', i) for i in range(n_qubits)]
+        self.ansatz, self.param_names = ansatz_w_params(self.n_qubits, self.n_layers)
+        self.observable: list[Operator] = [Z(0)]
+
+    @partial(vmap, in_axes=(None, None, 0))
+    def forward(self, param_values: Array, x: Array) -> Array:
+        state = zero_state(self.n_qubits)
+        param_dict = {name: val for name, val in zip(self.param_names, param_values)}
+        state = apply_gate(state, self.feature_map + self.ansatz, {**param_dict, **{'phi': x}})
+        return overlap(state, apply_gate(state, self.observable))
+
+    def __call__(self, param_values: Array, x: Array) -> Array:
+        return self.forward(param_values, x)
+
+    @property
+    def n_vparams(self) -> int:
+        return len(self.param_names)
+
+circ = Circuit(n_qubits, n_layers)
 # Create random initial values for the parameters
-key = jax.random.PRNGKey(0)
-params = jax.random.uniform(key, shape=(n_qubits * len(ops),))
-
-def circ(state) -> jax.Array:
-    for qubit in range(n_qubits):
-        for gate,param in zip(ops, params):
-            state = apply_gate(state, gate(param, qubit))
-    state = apply_gate(state,gates.NOT(1, 0))
-    projection = apply_gate(state, gates.Z(0))
-    return overlap(state, projection)
-
-# Let's compute both values and gradients for a set of parameters and compile the circuit.
-circ = jax.jit(jax.value_and_grad(circ))
-# Run it on a state.
-expval_and_grads = circ(state)
-expval = expval_and_grads[0]
-grads = expval_and_grads[1:]
-print(f'Expval: {expval};'
-       f'Grads: {grads}')
+key = jax.random.PRNGKey(42)
+param_vals = jax.random.uniform(key, shape=(circ.n_vparams,))
+# Check the initial predictions using randomly initialized parameters
+y_init = circ(param_vals, x)
+
+optimizer = optax.adam(learning_rate=0.01)
+opt_state = optimizer.init(param_vals)
+
+# Define a loss function
+def loss_fn(param_vals: Array, x: Array, y: Array) -> Array:
+    y_pred = circ(param_vals, x)
+    return jnp.mean(optax.l2_loss(y_pred, y))
+
+
+def optimize_step(params: dict[str, Array], opt_state: Array, grads: dict[str, Array]) -> tuple:
+    updates, opt_state = optimizer.update(grads, opt_state)
+    params = optax.apply_updates(params, updates)
+    return params, opt_state
+
+@jit
+def train_step(i: int, inputs: tuple
+) -> tuple:
+    param_vals, opt_state = inputs
+    loss, grads = value_and_grad(loss_fn)(param_vals, x, y)
+    param_vals, opt_state = optimize_step(param_vals, opt_state, grads)
+    return param_vals, opt_state
+
+
+n_epochs = 200
+param_vals, opt_state = jax.lax.fori_loop(0, n_epochs, train_step, (param_vals, opt_state))
+y_final = circ(param_vals, x)
+
+# Lets plot the results
+import matplotlib.pyplot as plt
+plt.plot(x, y, label="truth")
+plt.plot(x, y_init, label="initial")
+plt.plot(x, y_final, "--", label="final", linewidth=3)
+plt.legend()
+
+from io import StringIO  # markdown-exec: hide
+from matplotlib.figure import Figure  # markdown-exec: hide
+def fig_to_html(fig: Figure) -> str:  # markdown-exec: hide
+    buffer = StringIO()  # markdown-exec: hide
+    fig.savefig(buffer, format="svg")  # markdown-exec: hide
+    return buffer.getvalue()  # markdown-exec: hide
+# from docs import docutils # markdown-exec: hide
+print(fig_to_html(plt.gcf())) # markdown-exec: hide
 ```

horqrux/__init__.py

@@ -1,5 +1,14 @@
 from __future__ import annotations
 
-from jax import config
-
-config.update("jax_enable_x64", True)  # you should really really do this
+from .apply import apply_gate, apply_operator
+from .parametric import PHASE, RX, RY, RZ
+from .primitive import NOT, SWAP, H, I, S, T, X, Y, Z
+from .utils import (
+    equivalent_state,
+    hilbert_reshape,
+    overlap,
+    product_state,
+    random_state,
+    uniform_state,
+    zero_state,
+)

horqrux/abstract.py

@@ -0,0 +1,125 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any, Iterable, Tuple
+
+import numpy as np
+from jax import Array
+from jax.tree_util import register_pytree_node_class
+
+from .matrices import OPERATIONS_DICT
+from .utils import (
+    ControlQubits,
+    QubitSupport,
+    TargetQubits,
+    _dagger,
+    _jacobian,
+    _unitary,
+    is_controlled,
+    none_like,
+)
+
+
+@register_pytree_node_class
+@dataclass
+class Operator:
+    """Abstract class which stores information about generators target and control qubits
+    of a particular quantum operator."""
+
+    generator_name: str
+    target: QubitSupport
+    control: QubitSupport
+
+    @staticmethod
+    def parse_idx(
+        idx: Tuple,
+    ) -> Tuple:
+        if isinstance(idx, (int, np.int64)):
+            return ((idx,),)
+        elif isinstance(idx, tuple):
+            return (idx,)
+        else:
+            return (idx.astype(int),)
+
+    def __post_init__(self) -> None:
+        self.target = Operator.parse_idx(self.target)
+        if self.control is None:
+            self.control = none_like(self.target)
+        else:
+            self.control = Operator.parse_idx(self.control)
+
+    def __iter__(self) -> Iterable:
+        return iter((self.generator_name, self.target, self.control))
+
+    def tree_flatten(self) -> Tuple[Tuple, Tuple[str, TargetQubits, ControlQubits]]:
+        children = ()
+        aux_data = (self.generator_name, self.target, self.control)
+        return (children, aux_data)
+
+    @classmethod
+    def tree_unflatten(cls, aux_data: Any, children: Any) -> Any:
+        return cls(*children, *aux_data)
+
+    def unitary(self, values: dict[str, float] = dict()) -> Array:
+        return OPERATIONS_DICT[self.generator_name]
+
+    def dagger(self, values: dict[str, float] = dict()) -> Array:
+        return _dagger(self.unitary(values))
+
+    @property
+    def name(self) -> str:
+        return "C" + self.generator_name if is_controlled(self.control) else self.generator_name
+
+    def __repr__(self) -> str:
+        return self.name + f"(target={self.target[0]}, control={self.control[0]})"
+
+
+Primitive = Operator
+
+
+@register_pytree_node_class
+@dataclass
+class Parametric(Primitive):
+    """Extension of the Primitive class adding the option to pass a parameter."""
+
+    generator_name: str
+    target: QubitSupport
+    control: QubitSupport
+    param: str | float = ""
+
+    def __post_init__(self) -> None:
+        super().__post_init__()
+
+        def parse_dict(values: dict[str, float] = dict()) -> float:
+            return values[self.param]  # type: ignore[index]
+
+        def parse_val(values: dict[str, float] = dict()) -> float:
+            return self.param  # type: ignore[return-value]
+
+        self.parse_values = parse_dict if isinstance(self.param, str) else parse_val
+
+    def tree_flatten(self) -> Tuple[Tuple, Tuple[str, Tuple, Tuple, str | float]]:  # type: ignore[override]
+        children = ()
+        aux_data = (
+            self.name,
+            self.target,
+            self.control,
+            self.param,
+        )
+        return (children, aux_data)
+
+    def unitary(self, values: dict[str, float] = dict()) -> Array:
+        return _unitary(OPERATIONS_DICT[self.generator_name], self.parse_values(values))
+
+    def jacobian(self, values: dict[str, float] = dict()) -> Array:
+        return _jacobian(OPERATIONS_DICT[self.generator_name], self.parse_values(values))
+
+    @property
+    def name(self) -> str:
+        base_name = "R" + self.generator_name
+        return "C" + base_name if is_controlled(self.control) else base_name
+
+    def __repr__(self) -> str:
+        return (
+            self.name + f"(target={self.target[0]}, control={self.control[0]}, param={self.param})"
+        )